Basic Power Management for DJs

How much power does your rig take? What about various components of lighting? Do you know the average and peak amp draws?

If you don’t, it’s time you learn! Every room has a different electrical layout. Some have independent outlets and some have a “quadrant” system. Some are 15amp, some 20amp, and some just plain suck and trip everytime someone sneezes.

Knowing your amperage draw also saves your client money; Let’s say that you are doing a prom and the hotel charges for power drops. You ask for 4 20amp circuits but you only needed two. The school winds up paying TWICE as much for power that you don’t need. Anything you can do to save the client money will make you look that much better.

So how do you calculate amperage? Some lights tell you the power draw on the back (not to be confused with fuse rating), but even then it can get pretty darn inaccurate. A quick calculation also yields a rough explanation of what the amperage is (the AMount of power being used):

W/V = A. Basically, you take the wattage draw, divide by voltage available, and you get amperage! Sounds easy, right? The problem lies that a 600W amp pulls MORE than 600W of power, and a 250W light has motors, fans and other power-sucking doo-dads. You also need to realize that not every venue has the same voltage coming out of the outlets; you’ll find various voltages from 110V to 120V. This affects your math greatly!

But wait, there’s more! If you use a long extension cord, the voltage drops depending on the length and gauge of the run.

ARGH! If only there was some easy way! Well, of course there is. Head over to Lowe’s and pickup Kill-A-Watt. The device is simple to use: plug your load into it and it will tell you the amperage draw. This device is SUPER easy to use and EVERY DJ/production company should own one (or two).

This will put you in full control of your power draw, alongside a circuit sniffer (more on that later). Here are some tips when it comes to power draw:

*Remember that you don’t want to maximize your load; give yourself 10-20% headroom, so you have 16-18amp draw on a 20 amp circuit.

Several power conditioners, surge protectors, etc only handle a 15AMP load.

*Most ballrooms and venues *should* use 20AMP breakers, but unless you see those IN PERSON, assume they’re 15!

*Buy a circuit sniffer! This handy tool allows you to match paired outlets. Never take anyone’s word about what circuits are separate UNLESS they’re an electrician.

*Thin gauges of cable can cause weird effects (as can load-heavy devices). For example, if you run subs and black lights in the same circuit, you’ll notice that the black lights flicker to the beat.

I can proudly say that by practicing these techniques, and taking careful notes on each venue, I’ve yet to trip a breaker. After all, nothing is more embarrassing! So go pick up a KIll-A-Watt and arm yourself with the best tool ever!

How to (Properly) Wrap Cables

How to (Properly) Wrap Cables

By: Allan Reiss, product manager for Chauvet

When new cables are purchased, they are sometimes folded (yes, folded) end to end, which makes properly wrapping them a challenge. Not only is this unproductive, but re-training cables can be frustrating.

Earning a degree in recording engineering will undoubtedly drill this concept into your head, but you can take a free crash course here at Mobile Beat DJ University and spend that unused cash on new lights for your rig. This cable practice is not only great for the mobile disc jockey, but it’s also very useful for home theater installations, bands, mobile musicians or a garden hose.

Here are seven steps for a right-handed person using the over-under technique:

1)Make sure the cable is tangle and knot-free by laying the entire cable out on the floor.

2)Hold one end of the cable in your left hand, with the connector facing to your left, and use your right hand to make a 12-inch loop. (See pic 1) This is the “over” part.

3)Let go of the cable with your right hand and you should now have one complete loop in your left hand.

4)Grab the cable with your right hand about two feet away from your left hand.

5)Move your right hand closer to your left hand. (See pic 2) While moving your hand, rotate your right hand clockwise and make the second loop. (See pic 3) Your left hand should now be holding two loops. This is the “under” part.

6)Grab the cable with your right hand again and make a 12-inch loop into your left hand, but this time don’t rotate your right hand clockwise. Your left hand should now be holding three complete loops. This is the “over” part.

7)Repeat steps five and six until the cable is off the floor.

When your cables are properly wrapped and handled with care, they will last a few years longer. This will save you from having to buy more cables. Another benefit to good cable management is the amount of time you’ll save while setting up your gigs. When the cables unwrap quickly and easily, they can be taped down with little manipulation and enable you to move on to the next task.

There are different ways to wrap lengthy cables so don’t think this is the “end-all-be-all” of cable management. You might be taught a different method that works better for you so feel free to experiment for a while. Whichever method you choose, your cables will love you forever.

A Simple Guide to Speakers

A SIMPLE GUIDE TO SPEAKERSWe get numerous calls from customers asking how to compare one company’s speakers to another. You can find two nearly identical speaker cabinets with nearly identical components that have drastically different specifications and prices. There are many logical explanations for this. Before we go any further, let me make it clear that the following guide to speakers is “our opinion” based on 25 years in the business dealing with almost every major and minor brand of speakers.

1. SPEAKER CABLES AND 1/4 INCH PLUGS
Here’s the most important note about speakers I can pass on to you. NEVER use 1/4 inch phone plugs for speaker connections. That would be best compared to having a 2 inch water pipe coming from your street to your house, having a 1 inch water pipe running to all the faucets in your house and connecting the two by reducing each of them to a half inch connector. When you use a 1/4 inch plug and jack for speaker connections, you have less connection area than you would have if you touched the tip of one fingernail with another. This translates into a loss of power. We have tested two identical speaker cabinets powered by two channels of the same amp using a speaker cord with 1/4 inch plugs on both ends for the left speaker and on the right speaker we used a cord without any plugs so we connected the wires directly to the red and black binding posts on the amp and the speaker. Everyone in the room could hear the difference in volume between the two speakers.

2. IMPEDANCE: 2 OHM, 4 OHM, 8 OHM, 16 OHM
All speakers have an impedance measurement just as they have a diameter measurement. Not all speakers are 15 inches in diameter and not all speakers are 8 ohms. The most common 12, 15 and 18 inch woofer used in speaker cabinets by clubs and DJ’s is an 8 ohm woofer. If you have two of them in one cabinet you can wire the two woofers in parallel to create a 4 ohm cabinet, or you can wire them in series to create a 16 ohm cabinet. The parallel wired 4 ohm cabinet will produce much more volume, (6dB to be exact), and would be considered much more efficient. The series wired 16 ohm cabinet will need much more power, (4 times as much), to produce the same volume as the 4 ohm cabinet, so it would not be a good choice for economic reasons. Since the 16 ohm cabinet will need more power to produce volume, many lower end companies mass produce these cabinets and heavily advertise the high power that they can handle, as if that makes it a better speaker than the more efficient and lower power speaker. This is the most misleading specification we see in advertising. One club audio company that advertises as much or more than anyone else makes a dual 15 cabinet with two 16 ohm woofers wired parallel to create an 8 ohm cabinet. They advertise it as having a huge power handling capability, but in reality it is much less efficient when used with the same amps that would easily power other cabinets loaded with two 8 ohm woofers wired in parallel. Another mass advertised speaker has two 4 ohm woofers wired in series to create an 8 ohm cabinet. This is still not as efficient as the two 8 ohm woofers wired parallel. This is where you must make a choice. Do you want a good sounding, efficient speaker cabinet that you can power with a small affordable amp, or do you want a speaker that produces much less volume and you have to buy a larger amp, but you have a little less chance of blowing.

While we are talking about speaker impedance we need to mention something about amplifier impedance. Most amps tell you the power output at 8 ohms, 4 ohms and 2 ohms (if the amp is capable of handling 2 ohms). An amp is most comfortable driving an 8 ohm load. That’s why the 8 ohm rated power output is the lowest and the distortion level at 8 ohms is also the lowest. When you connect a 4 ohm speaker to the amp, it’s a harder load for the amp to power, just like pulling a 5,000 pound trailer is harder on your car than pulling a 2,000 pound trailer. The power output rating is higher than at 8 ohms, but the distortion level is also greater. Many of the popular low price amps today are not capable of powering a 2 ohm load. It would simply heat up the power transistors too much. For amps that can handle a 2 ohm load, it is the hardest load for the amp to handle and causes the most heat build up which leads to a higher level of distortion.

If you have ever installed your own car audio system, you may have noticed that 4 ohm and 2 ohm loads on the amps are common. That’s because there is so much road noise when driving your car that the higher distortion level of the amp usually goes unnoticed.

3. MAGNET WEIGHT
This is another very misleading specification. Most people think that a woofer with a 90 ounce magnet has to be better than a woofer with a 50 ounce magnet. Simple logic tells you that this should be true, but it is not. We have seen many woofers with larger magnets not perform as well as woofers with smaller magnets and we have also seen many companies rate their magnet weights wrong. This would be like thinking that all cars with larger engines out-perform cars with smaller engines. There are too many other factors involved for that statement to be true. Voice coil diameter, number of windings, size and type of winding wire and cone material are all just as important, but you almost never see these items listed in advertising.

4. POWER: RMS, CONTINUOUS, PEAK
I have a good friend that has tested speakers in the U.S.A. for over 30 years and he gave me the best definitions for these 3 power ratings. He sends a sweeping signal of all frequencies to the speaker and slowly increases the power. When he feels like he is getting near the maximum power that the speaker can handle, he extends the time before raising the level again. When he hears the slightest distortion or smells the coil getting hot, he backs it off 5 watts and lets it run for a few hours. If it endures that test, it gets a “Continuous Power Rating” of the power it handled for those hours.

RMS is the product of a math formula and it would rarely ever be the same as the continuous power level measured manually. In our industry the two terms are often mistakenly used to describe the same thing. I would rather have an honest manual measurement than a math formula.

Peak power usually means the highest amount of power that the speaker can handle for less than a second at a time. Although you can test a speaker for this measurement using the same method above, it is more common today to see speaker manufacturers double the continuous power measurement and call that the peak power even though it may not be technically accurate.

Just like the other measurements of speakers we mentioned above, power handling is very misleading. We tested a pair of speakers from one of the biggest advertising club audio companies that were rated at 320 watts. When they arrived, they had a spec sheet that showed the PEAK power handling at 320 watts but the continuous power handling capability was rated at 160 watts. During the test, the horn driver began distorting at around 100 watts when the music had heavy bass playing. You might wonder how a speaker that starts distorting at 100 watts can be advertised as a 320 watt speaker.

There is no standardized method of measuring these speaker specifications. Everybody does it however they please. Some companies choose to rate conservatively which is better for you but doesn’t look so good on paper, while other companies grossly exaggerate their specifications to look great in advertising but it’s not so good for the customer. The best way to measure the power handling capabilities of a speaker is to play the same music through it that the customer will be playing through it. Since that is not usually possible, most companies send computer generated signals to the speaker and see how many watts it can handle before it distorts. (That would be the point at which the voice coil has been thrown past the edge of the upper magnet plate). If that signal is full range and not just one frequency, and played for 4 hours, you will get a close idea of how much power the speaker can really handle.

Unfortunately, many budget speaker companies will send a signal that is just one frequency and crank up the power for 30 seconds to get a high power handling reading that is not an accurate representation of what the speaker will do with full range music playing through it. This type of reading may be legally “correct”, but not what you and I would consider “true”. Another method we have seen used by many budget speaker companies is to take the power handling capabilities of each individual component in the cabinet and add them up. If they were each measured conservatively and you made a great crossover to protect each one, this would be a better method than the single frequency signal method, but still not as accurate as a full range signal played for 4 hours.

5. CROSSOVERS: ELECTRONIC AND PASSIVE
A crossover limits the frequency range that reaches a speaker. Almost everyone will say too much power blows speakers. It would be more accurate to say that too much of the wrong frequency blows speakers. First and most important note; I have never found anyone that disputes the opinion that an electronic crossover is better than a passive crossover. Here’s why: an electronic crossover selects the frequencies to be passed to the speakers at a low line level before the amplifier. At this low level, there is no distortion and absolutely no loss of signal. A passive crossover is usually mounted inside the speaker cabinet and selects the frequencies to be passed to the speakers at a very high level after the amplifier. The main problem we have seen with these passive crossovers in budget speakers is the design of the crossover itself. To save money, they usually scrimp on this component a little too much. We have seen many crossovers that were designed to handle only 50 watts installed in a cabinet that was rated at 120 watts. This is the main reason we see so many budget speakers distort earlier than their more expensive counterparts.

There are 4 types of passive crossovers:
LOW PASS, HIGH PASS, BAND PASS, NARROW BAND PASS.

LOW PASS crossovers allow low frequencies to pass through to the speaker while gradually reducing the power of the higher frequencies and cutting them off. Coils are used in low pass crossovers because they cut out the higher frequencies.

HIGH PASS crossovers allow the high frequencies to pass through to the speaker while gradually reducing the power of the lower frequencies and cutting them off. The power reduction increases as the frequencies become lower. Capacitors are used in high pass crossovers because they cut out low frequencies.

BAND PASS crossovers are a combination of the two above. They only allow a certain band, or range of frequencies to pass through to the speaker. This type of crossover is most often used on mid range speakers where the extreme highs and lows are cut off so they do not reach the speaker and cause it to distort.

NARROW BAND PASS crossover must be used when the band of frequencies chosen to reach the speaker is less than a decade apart, that is, if the high crossover frequency is less than 10 times the low crossover frequency. A narrow band pass crossover has the same function as the normal band pass, however, it is wired very differently.

Crossover points or frequencies are achieved by using different values of coils and capacitors. There are different rates for the reduction of power, called SLOPES. The most common are 6dB, 12dB and 18dB slopes. A 6dB slope will reduce the power at a rate of 6dB per octave starting at the chosen crossover frequency, creating a gradual slope of power reduction. The 12dB and 18dB per octave slopes work the same way except that a 12dB slope has twice as much reduction per octave as the 6dB slope and an 18dB slope has 3 times the amount of reduction, thus cutting off those frequencies 3 times as fast.

If you are making your own crossovers, here are a few starting tips:
Air core coils are best for higher frequencies. Iron core coils are best for lower frequencies. Solid iron core coils are best for low frequencies at high power (over 300 watts). Polypropylene are the best capacitors. Mylar capacitors are next best. Non-polarized electrolytic are the most commonly used.

6. SPL 1w/1m
This stands for Sound Pressure Level measured at 1 watt of power and at a distance of 1 meter from the speaker. This should be a great way to gauge the efficiency of all speakers and although there is a standard method of performing the test, many of the budget speakers we have tested don’t come close to the manufacturers spec’s.. From what I have seen in speaker catalogs, I think most measurements have been copied from the spec’s of the individual horn or midrange components instead of an actual reading from all components operating together in the speaker cabinet.

7. HORN DRIVERS: COMPRESSION AND PIEZO
The least expensive of the two is the Piezo driver. Most people think of a small round tweeter when you say Piezo, but there are also larger, threaded horn drivers that have a piezo element instead of a voice coil. Piezo drivers have a vibrating ceramic disk that is usually capable of producing only 2 or 3 frequencies

Because there is no voice coil in a Piezo driver, it is usually harder to blow than a compression driver with a voice coil. Most people don’t even use a crossover with a Piezo driver. Right now most people would be wondering why anyone should use a compression driver if they cost more and can be blown easier. The answer is simple, they sound better. The Piezo is most commonly referred to as being harsh sounding because of its 3 frequency limit. Yes, it can produce high’s and a lot of volume, but it has never produced high’s as smoothly as a good compression driver.

There are two types of compression drivers used in our industry. The less expensive of the two has a Phenolic diaphragm and the more expensive unit has a Titanium diaphragm. The Titanium diaphragm is much better for reproducing the extreme high’s heard when a drummer crashes his cymbals. Both units have a heavy magnet and a voice coil with wire windings just like any woofer. Both units need a good crossover to protect them from harmful low frequencies.

8. STEREO OR MONO
While every club and mobile DJ has their own opinion about running their system in stereo or mono mode, the most common method is to run the sub-woofers mono and the rest in stereo. Most people agree that sub-woofers running in a stereo mode tend to muddy up the low bass where a mono mode has all sub-woofers producing the same thump at the same time for a much more pronounced bass sound.

9. SUB-WOOFERS: FRONT LOADED, HORN LOADED, BAND PASS
FRONT LOADED sub-woofers are cabinets that have the woofer facing the front just like a common full range DJ speaker cabinet. These units usually produce more bass within the first 30 feet of the cabinet, but lose volume as you step farther away.

HORN LOADED sub-woofers have the woofer mounted inside a large cabinet where you can’t see it. The most well known horn loaded sub cabinet is the Cerwin-Vega Earthquake. This cabinet is designed so the sound created by the woofer travels a precise distance through a precise opening before it is released from the cabinet. The distance and opening size are calculated by math formulas based on the woofers specifications. These units usually produce less bass within the first 30 feet of the cabinet than a front loaded cabinet would, but the sound travels much farther.

BAND PASS sub woofers are designed with the woofer mounted inside and have two chambers of precise size with one chamber having one or more ports to release only a certain band of low frequencies. The size of the two chambers as well as the size and number of ports are the result of math formulas based on the woofers specifications.

10. LOCATION OF SPEAKERS
The best location for speakers in a night club is the same for mobile DJ’s. You want the sub-woofers on the floor near the dance area and you want the mid’s and high’s about one foot above the crowds head. This is because the mid’s and high’s are directional and if they are aimed at the dancers body, the person behind them would hear less volume. Bass is not directional and therefore does not need to be raised. Sub-woofers usually do best on the floor and near a corner to help resonate the bass.

www.cheaplights.com

Sound Reinforcement Terms Explained for DJs

What I will provide here is the technical terms and their technical definitions. Following that will be my attempt to place the information in a context than almost anyone can understand. I will be as basic as I can, and will site examples if necessary. The explanations will be from a DJ’s point of view and I hope useful in that light.I understand that most DJs do not have a degree in electronic engineering. But the more we understand about the sound systems we run, the better we can make them sound in the different venues in which mobile DJs play. Playing in different buildings and even at outdoor shows, we need a basic understanding of sound terms to help us understand how it all works.

I have copied the terms and their technical definitions from the Peavey Electronics’ web site. I have only used the terms that I thought would be the most useful for us, as DJs.

Thank you Peavey. J
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AUDIO RANGE

20 Hz to 20,000 Hz. (Twenty cycles per second to twenty thousand cycles per second). The frequency response spectrum of human auditory perception.

Explanation:

This is the AVERAGE range of hearing in humans; age and sex of the person determine the true hearing range. Most people do not hear the full range of 20 Hz to 20,000 Hz. DJ sound systems do not cover the full range of the sound we hear. Our sound systems cut out the low end of the spectrum anywhere from 63Hz (with two and three way enclosures) to 40Hz with good subwoofers. The very low sounds are very hard to reproduce with a “portable” sound system.
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BIAMP

Separating the audio spectrum into two bands, i.e., high frequencies (high pass) and low frequencies (low pass) by means of an electronic crossover and using two separate amplifiers or channels of an amplifier. One amp or channel is used to amplify and project the high pass signals (high frequencies) from the high frequency component or horn of the speaker system. The other amp or channel amplifies the low pass signals (low frequencies) and projects them from the woofer or low frequency component of the speaker system, resulting in increased headroom and dynamic range.

Explanation:

Bi-Amping your system can and will make your system “cleaner” sounding by increasing the headroom of the system. More power = more headroom. Your gear does not work so hard to make the same volume or sound pressure.
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BRIDGE MODE (Mono)

Operating a stereo amplifier in mono via the bridge mode switch, which then makes Channel A output the positive power rail and Channel B output the negative power rail. Since the signal swings between A and B Channels, the output of the amplifier is twice that of single channel operation.

BRIDGING

Connecting one electrical circuit in parallel with another. Example: Paralleling power amplifier inputs.

Explanation:

Depending on your Amp/Speaker combination, bridging your Sub woofer amp (or amps) may increase your headroom and dynamic range. Even if your tops in a bi-amp system are in stereo, the subs, being in mono, will have little to no effect in the stereo image. The human ear cannot tell the direction of sub woofer frequencies. Bridging the amp is also called Parallel Mono because of the A and B sides (or right and left channels) of a stereo amp being in parallel with each other when bridged.

How much of an advantage is bridging your Subwoofer amplifier in a BI-amp system?

For this example I will use two 8-ohm subwoofers and a Peavey CS-800S stereo Amplifier. Connected in stereo, the subs would be receiving 240 watts per channel @8 ohms per channel. (480 watts total both channels.)

The same Amplifier Bridged into the same two 8 ohm Speakers (making a 4 ohm load now) would be making 1200 watts!

Also very important is the “Low Cut” feature found on some power amplifiers, electronic crossovers and EQs. The cut is normally at 40Hz. If you have this feature you should have it to the “ON” Position. This is because MOST sound enclosures (speakers) can not reproduce sub frequencies below 40Hz. This has your amp wasting power making frequencies that the speaker can not reproduce. The result of this is both a waste of your power and your headroom.
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CLIPPING

Amplifier overload causing a squaring off or undesirable change in the wave form resulting in distortion or perceptible mutilation of audio signals.

Explanation:

Music and other audio are in a wave form that is rounded at the top and bottom. When and amplifier is turned up beyond it’s capability to reproduce the wave form correctly it will chop off the top and bottom of the wave form. This is called a “clip”.

Clipping can cause damage to the amplifier and the speakers. The power amplifier is not the only amplifier capable of clipping. The mixer board pre-amp can be “clipped” as well by trying to boost the signal too much.

If a clip is sent from the mixer pre-amp to the amplifier, the amplifier will reproduce the clip just like any other source and can still damage the power amplifier and speakers without the clip lights on the amplifier ever lighting up!
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CONTINUOUS POWER

This power rating represents the most conservative statement of the capability of an amplifier. It is also called “RMS” power. It denotes the amount of power an amplifier can deliver when amplifying a constant steady tone. It is usually measured at a signal frequency of 1000 Hz for a specific distortion. Continuous power in watts: W = V2/R Power in watts equals the voltage squared divided by the resistance of the load.

Explanation:

This is the only power output measurement of an amp to look at when buying an amp. It is the true reading of the power output of the amp. This is the power reading with a single tone just before the amp starts to “clip”. This works the amp harder than we will with music as a source.
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CROSSOVER (X-OVER)

An electronic device that is used to separate an audio signal into two or more bands of frequencies or component signals above and below a certain frequency, said to be the crossover frequency or crossover point. Crossovers can be active or passive.

CROSSOVER PASSIVE

A passive crossover is built into most speaker cabinets in order to separate bands of frequencies from the full range speaker level signal produced by the power amplifier, and routing those bands of frequencies to the proper speaker or driver. Most commonly found speaker crossovers also use iron in the inductors to decrease their size. This can be a source of distortion due to the nonlinearities in the coil from core saturation. The power going to the high frequency drivers must be attenuated due to the increase in efficiency of a high frequency driver as compared to a bass driver. This power has to go somewhere and it’s usually converted into heat through the use of resistors.

Explanation:

The last two sentences are the important ones here. The passive crossover wastes power from the amp by dumping part of the power to a resistor, converting the power to heat inside the speaker cabinet. Too much amp power can burn up the resistor and ruin the crossover.

CROSSOVER ACTIVE

Electronic or active crossovers don’t have the problem of excess power because only the power needed by the driver must be generated by the amplifier. An active crossover is employed when bi-amping a system. The active crossover separates the audio spectrum (full range) into bands of frequencies above (high pass) and below (low pass) a certain frequency (x-over point). The low pass is rolled off (attenuated) so many dB per octave above the crossover frequency. The high pass is rolled off (attenuated) below a certain crossover frequency at a rate of so many dB per octave. The high pass and low pass outputs of the electronic (active) crossover are connected to the inputs of two separate power amplifiers whose respective outputs are used to drive the high end (horns) or low end (woofers) of a sound system.

Explanation:

A much more efficient way of sending the correct frequency to the correct drivers (speakers inside the cabinet). The active crossover will not waste power from the amp by the use of resistors. All the power made by the amplifier (or amplifiers) is used to make sound. The electronic crossover is used inline before the amplifier in a bi- or tri-amp system. Some brands of amps have them built right in the amp!
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CYCLE OR HERTZ

A unit of motion referenced to a time period of one second. The frequency of a vibration or oscillation in units per second. 100 Hertz or 100 c.p.s. (cycles per second) refers to the number of times a second (100) a string is vibrated or an amplifier is swinging between its positive and negative supply voltage.

Explanation:

The easiest way to compare this is with common 115-volt house voltage. (North American) The AC current swings from positive to negative 60 times a second, or 60 Hz (Hertz). With voltages, the term only refers to AC (alternating current).

DC (direct current) does not change frequency or polarity.
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THE DECIBEL

Originally the “bel” in honor of Alexander Graham Bell, was the logarithmic term called the “transmission unit.” This was used to express the transmission losses of long telephone lines. The “bel”, being too large for practical use, was later changed to “decibel”. The decibel has no actual numerical value, but is used only to express a ratio between two voltages, currents, powers, or impedance’s. BASIS OF THE DECIBEL SYSTEM MATHEMATICS – The logarithm: The exponent of that power to which a fixed number (called the base) must be raised in order to produce a given number (called the antilogarithm). The decibel uses logarithms to the base of 10 called LOG. This is not to be confused with the so-called natural logarithm to the base “e” called LN used in many electronic formulas. Below are mathematical manipulations of antilogarithms and logarithms. Voltage, current, SPL, distance: 20 Log X1/X2 Power = 10 Log P1/P2.

dB (decibel)-

A unit for describing the ratio of two voltages, currents, or powers. The decibel is based on a logarithmic scale when measuring differences in sound pressure level (SPL). The amount of change in sound pressure level perceivable is directly proportional to the amount of stimulus (the more sound present, the greater the change must be, to be perceived).

O dB

In the measurement of SPL or Sound Pressure Level, 0 dB is referenced to the threshold of hearing or auditory perception of a tone of 1000 cycles (hertz) per second (1 kHz). 0 dB must always be referenced to some base of measurement. In gain functions 0 dB is unity gain (1).

3 dB

The amount of SPL gained by doubling the power to a speaker. The amount gained by doubling the number of speakers.

+/- 3 dB

Plus or minus 3 dB is a measurement of frequency response that exhibits no more than +3 dB and no less than -3 dB below a given reference. It is actually a 6-dB window. The Response of 60 Hz to 14 kHz +/-3 dB means that within the bandwidth of sixty cycles per second to fourteen thousand cycles per second, no frequency is +3 dB more nor -3 dB less than a specified reference frequency.

3 dB DOWN (-3 dB)

The point at which a measured power level is 3 dB below the specified level. In an electronic crossover, the point (frequency) at which the high pass signal is -3 dB down in response or power level is considered the crossover point (frequency).

-6 dB

The amount of loss in SPL as you double the distance away from a sound source.

dBm

A decibel scale referenced to 0 dBm = 1 milliwatt of power into 600 Ohms or .7746 volts RMS across 600 ohms.

dBu

Primarily a British term for gain referenced to 0 dBu = .7746 volts RMS.

dBV

A decibel scale referenced to 1 volt RMS; 0 dBV = 1 volt.

dBW

A term for power gain referenced to 0 dBW = 1 Watt.

Explanation:

The most confusing term I know of, the decibel is the most misunderstood term in the sound reinforcement world. Even with careful reading above, most people don’t understand.

The decibel is not a fixed number or value. It is used to tell the difference between two values. The way it is figured depends on what you’re working on. Sound pressure is figured differently than electrical values. Voltage, current, SPL (sound pressure level), and distance are all different values.

And all use the term decibel to state their different values. That’s why it’s so confusing!

A decibel is a logarithm formula, if you remember that fact you will be much less confused in the future.
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EFFICIENCY

The ratio, usually expressed as a percentage, of the useful power output to the power input of a device. EFFICIENCY RATING OF A TRANSDUCER/ENCLOSURE…is the SPL the unit produces at a 1 W RMS input power level measured 1 meter from the unit. Doubling the input power raises the SPL 3 dB. Doubling the number of enclosures raises the SPL 3 dB. Doubling the input power and the number of enclosures raises the SPL 6 dB. Doubling the distance (near field) lowers the SPL 6 dB.

Explanation:

This is the 1 watt/1meter SPL (sound pressure level) printed on the back of your pro speaker cabinet. The Higher the number the better the speaker enclosure uses the amp power you give it. Or another way to put it is the higher the 1W/1M number; the louder the speaker cabinet is with the same power (watts) given to it. By today’s

standards, a rating of at least 98db 1W/1M should be common for Pro DJ use.
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HEADROOM

The difference between the average operating power level of an amplifier circuit and the point at which clipping or severe distortion occurs.

Explanation:

Headroom is the volume left in your system between your normal volume level and the maximum output of the system. If you have to run your system wide open all the time to do your shows you have no headroom in the system, and you should consider upgrading your system (amplifier/s and/or speakers). Headroom is good to have because the system will sound better if it is not being strained to its limits. Imagine driving your car everywhere you go with your foot on the floor all the time.

HEARING

The human hearing system is very well designed. It has a dynamic range of over 120 dB. Contemporary digital recording techniques can only achieve a dynamic range of about 90 dB. The typical threshold of pain is around 140 dB, with discomfort starting around a sound level of 118 dB.

THE NORMAL AUDIBLE FREQUENCY RANGE is considered to be 15 Hz to 20 kHz. The typical hi-fi specification range is 20 Hz to 20 kHz. One has to question the validity of this range since 20 Hz is more “feeling” than “listening”, and most people can’t hear 20 kHz (only the young). Sound reinforcement specifications reflect 50 Hz to 15 kHz (sometimes 40 Hz). Interestingly enough, this just happens to be the FCC limits on FM radio. The typical telephone has a frequency response of 400 Hz to 4 kHz. The human ear does not hear all frequencies at the same

CHANGE IN SOUND LEVEL

(60 dB, 1 kHz); about 50% of people can hear a 2 dB change; everyone can hear a 3 dB change. Therefore . . . 1 dB frequency response specs are good; 3 dB specs are fair. TWICE AS LOUD TESTING: 50% of people say about 7.5 dB change is twice as loud, some as low as 5 dB, and some as high as 10 dB. This test is very level and frequency sensitive. Higher sound levels produce lower numbers . . . frequencies below 1 kHz and above 5 kHz yield higher numbers. Therefore, since a doubling of power is only 3 dB more, how much more is really required to produce the “twice as loud”; see your power chart! “A CS 800® plays twice as loud as a CS 400®”…”wrong”, only 3 dB louder. With a complex signal, such as program music, a 10-dB change is approximately twice as loud.

Explanation:

I put these in here just for your information. We need to understand basic human hearing as well as Sound Equipment to do the best job possible in my opinion.
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IMPEDANCE

The total opposition to alternating current flow presented by a circuit. The resistance to the flow of alternating current in an electrical circuit, generally categorized as either “high” or “low”, but always expressed in ohms. Commonly used to rate electrical input and output characteristics of components so that proper “match” can be made when interconnecting two or more devices, such as a microphone, loudspeaker or amplifier.

Explanation:

For DJ use this term is common for microphones. For microphones it’s very easy for us to tell the differences, as the connectors are different for high or low impedance microphones (1/4 inch for high and XLR plugs for low).

For speakers and amp matches we use the term “ohms” more than impedance. I will address that explanation in the ohms heading, even though impedance is also a proper term.
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MODE

Another word for room resonance. When sound energy is restricted by boundaries (such as walls, floor, and ceiling), waves are developed at certain frequencies or wavelengths that are integers of the distance between the room boundaries. Room modes or resonance cause standing waves because once the wave is generated it stands there, i.e., the positive pressure peaks (anti-nodes) and negative pressure troughs (nodes) stay stationary within the boundaries.

Explanation:

After setting up in a Hall and walking around and listing carefully, you sometimes can hear the standing waves in the room at certain points (dead spots in the room as far as hearing the sound system evenly everywhere.) The best way to correct this is not with the EQ, but by changing your speaker placement in the room. Changing the angle from the stage to the center of the dance floor or the space from the back of the speaker to the wall can effect the sound greatly. You also can use standing waves to your advantage by making it easier to talk in the table area and louder on the dance floor
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OHM

The unit of electrical resistance, equal to the resistance through which a current of one ampere will flow when there is a potential difference of one volt across it. Ohm is the unit of measure used to express opposition to current flow. Every wire or part through which electricity passes has some resistance to that passage.

Explanation:

This is commonly used to match speaker/amplifier loads. The main thing to remember about ohm numbers and speakers is that the lower the number, the harder the amplifier has to work and the lower the ohm load on the amplifier, the more power the amplifier will make.

Amplifier load maximums are printed on the amplifier or are in the manual (sure you still have the manual! J

An example of common speaker loads for a stereo amplifier per channel and available amplifier power are, (our example amplifier is a Peavey CS-800S and can use a 2-ohm load per channel Max):

One 8-ohm cabinet per side (240 watts per channel @8 ohms)

Or

Two 8-ohm cabinets per side giving us a 4-ohm load per channel. Speaker cabinets are connected by using the in and out on the back of your Pro speaker cabinets; out from the amp to the first cabinet and out of the first cabinet to the second (400 watts per channel @4 ohms).

Or

Three 8-ohm cabinets per side giving us a 2-ohm load per channel. These are connected the same as the two cabinets per side example except that the out on the second cabinet goes to the third speaker cabinet (600 watts per channel @2 ohms).

Or

One 4-ohm speaker cabinet per side. The advantage to using one 4-ohm cabinet over one 8-ohm cabinet is that the 4-ohm cabinet is 3Db louder. The amp makes more power into the 4-ohm load than the 8-ohm load and you get more volume

(400 watts per channel @4 ohms).

Or

Two 4-ohm Speaker cabinets per side, still using the ÿÿÿ

Troubleshooting Equipment Problems

Remain Calm!!! This is one of the best pieces of advice that I can give you. Let me explain what the “Big Eye” is. This phenomenon occurs, when something such as a major equipment problem arises five minutes prior to having to introduce a wedding party. Your two eyes will instantly mold together into one, creating tunnel vision. This is known as the Big Eye, and you should avoid this at all costs! Losing your cool when an equipment problem arises will drastically reduce your chances of correcting the problem. Remaining calm, cool and collective will help you find the problem much quicker.
Do not tell anyone about the problem unless it is absolutely necessary!! This will limit the amount of bad publicity you get from an equipment problem.
Use the process of elimination to find the problem. Simply put, switch things that work with things that do not work in order to trace the problem down to the point of origin.
Keep in mind, if you are using professional grade equipment, the chance of a speaker or the amp “blowing” are very minimal!!! In our experience, the most likely causes of most equipment problems, are faulty interconnect cables, and human error. If you keep this in mind when a problem occurs, you will be able to relax, and diagnose the problem with less difficulty.
The use of quality interconnect cables, speaker cables and extension cords cannot be emphasized enough. If you have good quality cables that are brand new, you have a baseline with which to work. Typically, once you have tested a new cable of sufficient quality as being in good working condition, it doesn’t just “break” overnight. When something doesn’t work, and you KNOW that your cables are in good condition, it will reduce the possibility of the problem coming from your cables.
Use a standard system to identify a faulty connector cable or cord. I recommend that you tie a knot in both ends of the cord you have identified as being bad, so that it does not get confused as being a spare in the future.
Always keep all of your connections in line, keeping the left channel output from your music sources connected to the left “in” and “outputs” of every components, all the way down to your speaker. The same goes with the right side. This way, if the left speaker isn’t working, you will be able to trace the source of the problem much easier.
Scenario # 1
No Electrical Power To All Components When Initially Turning Power OnYou’ve set your system up completely, switched on your power distributor and your equipment is not turning on – none of it. Your first step should be to check your power strip light to see if the power strip is on. If not, then check the outlet that you are plugged into.

Before unplugging, make sure your entire system is turned off. Unplug your extension cord and examine the prongs. If it appears OK, plug it back in and turn your system back on. Make sure the levels on your mixer and amp are all at minimum! Unplug again and try plugging in an extra power strip. Flip the switch on and see if it lights up. If not, you probably have a dead outlet or a circuit breaker has tripped. Before assuming that the outlet itself is dead, plug an appliance directly into the outlet, such as a CD player.

If you still have no power, it’s a good idea to approach someone at the hall about your problem. Some outlets are controlled by switches. Some outlets have a tripped circuit breaker, which they can often access and flip back on. Believe it or not, some banquet halls turn the power off to all of the wall outlets because they believe that they are conserving energy! In this case, all you need to do is turn the breaker on at the panel.

Of course, the outlet may simply be dead and you’ll need to find the closest working outlet. If you suspect the circuit breaker, find a gray metal box mounted in the wall. You will see a number of switches. Most will be in the “on” position. If you see one in the “tripped” position (in the middle), flip it first to the “off’ position, and then to the on position. This may be your circuit! Go check with the power strip!

Now let’s assume your outlet is working. Your extension cord may be at fault. Try another cord. Hopefully, you have a backup. If not, ask if you can borrow one. You should always have at least two extension cords in case one is faulty. Make sure the cord is plugged in properly at the wall and where it connects at your equipment.

I once followed all these procedures and still couldn’t get power to my equipment. I started to panic, but then I went back and followed the current trail back to my power strip. I had forgotten to switch it on! Usually these problems are very simple. Learn to laugh at yourself when you do something this dumb. It helps your smile when the show starts.

Scenario # 2
Power Failure To All Components While Playing Music

The dance floor is rockin’, you’re taking a request and all of a sudden…. WHAT???!!! There is no sound and no juice to your equipment. Your first glance should be at the wall outlet that you are plugged into. Make sure it hasn’t been pulled out. Whenever possible, plug in your system where no one else can reach it. This happened to me at an Elementary school once. The outlet was only about 2 inches from the floor. It was also beside the table where I had my request pad. When I announced I was taking requests, a crowd developed and my extension cord was knocked out. This happened three times before I finally had to place my hand truck where the kids couldn’t touch the cord.

Also, make sure the other end of the extension cord is plugged in. You may have just tripped on it. The next thing that you should check, is the power light on the power strip. Is the light lit, indicating that you have power up to that point? If those two are fine, you have probably tripped a circuit breaker.

If you are running two amplifiers or some power hungry lights, you may have to back something off. The important point to emphasize here is that you can’t go back to what you were doing because you will most likely trip the breaker again.

In a typical electrical system, there are usually six to eight outlets on a circuit, which is tied to one circuit breaker in the electrical panel. Ideally, you should be plugging your sound equipment into one circuit, and your lighting equipment into another circuit. The problem is figuring out which outlets go to which circuit breakers. Most DJs that use a modest lighting system (a few par cans and a beam style light) do not go to the trouble of locating a separate circuit. If this is the case, and a circuit breaker trips, the lighting is most likely the source of the problem. Lighting draws a tremendous amount of electrical power and you should try to run the extension cord to an outlet as far away from the original outlet that you started with. You should try to plug into an outlet that is on a different circuit. One possible solution is to take the extension cord that is servicing your lights, and start plugging it into other outlets PRIOR to turning the breaker back on. Once you find a “live” outlet, leave the lights plugged to that, and turn the breaker back on to the sound equipment. This may not be possible, if the event requires you to turn the power back on IMMEDIATELY (I.E., a wedding). In this event, you will need to disconnect the lights. Obviously, your lights are not a priority if you continue to trip the breaker.

Check to see if there are halogen lights, coffeemakers, or other electric cooking appliances plugged into the same circuit. I once played a homecoming dance where 5 halogen work lamps were shined on the walls. I was running a bi-amped system, and used a Vertigo II, and a halogen spot on my mirror ball. Did I mention my fog machine as well? The halogen work lamps were pulling about 1.5 amps each. I tripped the breaker three times before suggesting to my contact to turn off the work lamps. That did the trick, and we were rockin’ the rest of the night!

On yet another occasion, a caterer had a lot of heating appliances plugged into the same circuit that I was operating on. My sound equipment drew just enough electricity to trip the breaker. You may have to plug into a different circuit, or suggest other items be plugged in elsewhere.

Before going to the circuit breaker box, TURN YOUR ENTIRE SYSTEM OFF! You do not want to suddenly turn power back on when your system is cranked. You could blow you amp, speakers, or at least some fuses. Find your breaker box and proceed as in scenario #1.

Scenario # 3
One Component Only Is Not Receiving Power

You have power to all of your components except one. Make sure the power switch on that component is on. I amaze myself at how many times I forget to do this. If that doesn’t work, check the plug and make sure it is properly plugged into you power strip. Check the prongs to make sure they are not bent. Try another “outlet” in the strip if possible. Believe it or not, I have actually had one outlet on a power strip go bad!

Check the fuse to the appliance, if it has one. Most amp’s and some mixers and CD players have fuses, and this is one potential source for a component to not operate..

Most professional amplifiers have two features that other components do not. The amplifier may have an automatic internal “shut-down” device (similar to a circuit breaker) built inside that will shut the amp down if it is driven too hard. When this happens, the power light will not be lit, and it will appear that the amplifier has no electrical power. This very same symptom can occur if the fuse to the amp has blown. The only way to tell the difference is to check the fuse to the amp. If the fuse is fine, you can assume that the shutdown device has activated. The only way to fix the problem when the shutdown device has activated is to cool the amp as quickly as possible. Once the amp turns back on, you must lower the volume on the mixer, since the main reason that the shut-down device activates is that you played distortion!! This typically happens when a newer DJ is using a smaller amplifier for a large event, and tries to get more out of the system than it is capable of delivering.

The amplifier may also have an external breaker button that may activate. In some brands, this breaker has taken the place of the fuse. If your amp has this feature, you should become familiar with its location and normal operating position. This way, you will be able to easily identify as to whether it has tripped. As with the internal shut down device described above, if the external breaker button trips, you cannot go back to playing at the same levels you were prior to it’s activation! Remember, it activated for a reason! This leads me to my next subject, playing distortion.

Most DJ’s assume that the possibility of blowing a speaker comes from playing too loud. This is definitely not the case. Professional equipment will tolerate loud volumes of music for hours on end. The thing that blows speakers is called distortion. This occurs when increase the levels on the mixer from a crystal clear sound to a slightly distorted sound. It is easy to blow a speaker rated at 500 watts with an amp rated at just 50 watts if you pump a distorted sound into the amplifier and speakers.

The key is, keep the sound crystal clear at all times. Good indicators on when you are playing distortion are your VU meters on the mixing board. If you are constantly in the red, you will probably be playing distortion. If you are unsure, walk around to the front of the speakers and check the sound. When in doubt, lower the level on the mixer. Playing distortion will most likely blow the horns/tweeters on the speaker first.

If this all fails, you may have a bad power cord or power supply in your component. This is a great reason for having backups with you, especially if the component is a mixer or amp.

Scenario # 4
One Speaker Does Not Work/One Channel Is Out

The two most likely causes of this problem are:

Faulty interconnect cables
A short on a terminal output post on the mixer, EQ, CD player, etc.
I have already described the importance of having quality interconnect cables that are in new condition. Let me elaborate on the problem with a terminal on a player, signal processor or mixer shorting out. Plugging and unplugging interconnect cables takes its toll on your mixer, signal processor and CD/Tape players. Each time you plug and unplug, it places wear and tear on the unit. Each terminal that you see on the outside of a component has a wire soldered to it on the inside. Eventually, this solder joint gives way, and you begin to have a short in that terminal. At first, you can gently wiggle the terminal, and get the sound to “pop” back in, however eventually the connection inside will be totally lost and you will have to repair the unit. Placing your equipment in a case and leaving everything pre-connected can easily avert this problem.

Your initial actions for sound to one speaker only

While the music is playing, observe your VU meters. Make sure your mixer is in stereo mode. If only one channel is registering a signal, then the problem is occurring before or inside the mixer. If both channels are registering, then the problem is occurring somewhere between the inside of your mixer and your speakers (it is possible to have the VU meters show a stereo output, and the solder joint at the output terminal be bad).

The first thing you should do in this situation is to play a different CD player. This will help you determine if you have a problem with the entire system, or just one part of it. Does your other CD player or tape deck produce sound to both channels, or is one channel also dead? Lets break down the symptoms so you can follow the sequence of events easier;

One component produces sound to one speaker only, all others work fine in both channels.
If you have one particular CD player that is only producing sound output to one channel, but all others are working properly, you may safely assume that the problem is located in one of these three places: 1) in the source component itself (i.e., bad playback head on a cassette deck, or defective stylus on a turntable); 2) in the connection from the source component to the mixer; or 3) in the mixer input itself.

Check your cable connections from the music source (CD player, turntable, mini-disc, etc). Re-connect both ends of the audio cable, gently wiggling the effected terminal (left or right channel) on the mixer and the CD player or other playback device. The problem could simply be a short on one of the terminals. If the problem persists, try switching the right and left cables at the mixer. If the problem persists, you have a faulty RCA cable or audio source component. Replace the cable first, before assuming the worst. Cable failure is the most common problem encountered by sound engineers.

Try plugging the CD player that is only producing one channel to another input on the mixer. This will tell you if the player itself is bad, or the problem is located inside that one input on the mixer. Mixer inputs do, occasionally go bad, and you shouldn’t assume that just because you have changed the connector cable without success, that the player itself has a short inside the unit.

Sound From ALL Playback Devices Going To One Speaker Only
The mixer VU Meters may be showing a stereo output, but do not assume that the mixer is actually sending sound out of its output connections! One easy way to rule out your speaker, or speaker cable, is to plug the speaker cable that isn’t working, to the side of the amp that you know is working. If by doing this, that speaker starts working, you have ruled out the possibility of the speaker and speaker cable as being bad. This means that the problem is somewhere between your mixer and amp.

However, if you switch the speaker cable to the other channel on the amp, and it still does NOT work, this means that the problem is in the speaker cable or the speaker itself. Go to your speakers and check that connection. Try replacing the speaker cable. If not, perhaps the speaker is blown.

If you have ruled out the possibility of the problem being the speaker or the speaker cable, work your way back to where they connect to the amplifier. Check that connection carefully, especially if you are using banana plugs. Check your amplifier settings. Are both channels turned up? Check the inputs to your amp. Again, a loose connection could be the culprit. Follow your connections all the way back to your mixer. If you are still encountering a bad channel, try reversing the connections ONE AT A TIME. When the bad channel changes sides, you have found your bad connection. Replace that cable immediately.

Occasionally, a mixer can be the culprit, sometimes even when the VU meters show a stereo output to both channels. If you have traced the problem to the inside of the mixer, try plugging to one of the other outputs on the mixer, such as a “tape out”. If this doesn’t work, if your mixer has a mono mode, activate the mono mode and ride it out that way for the evening. One word of caution! It is not preferable to plug both speakers to one channel on the amp, when the mixer is only producing one channel. This makes your amp work much harder. If your mixer doesn’t have a mono mode, carry spare “Y” adapters so that you can take the one channel output and drive both channels of your amp.

It is possible, but rare, that your amp could lose one channel. In this case, plug both speaker cables to the one channel on the amp that is working. Note: You should only plug both speakers to one channel on the amp after you have correctly diagnosed that one channel on the amp is bad! In my experience, when a DJ tells me that they plugged both speakers to one channel on the amp, they incorrectly diagnosed the problem, and put the “quick fix” on the problem.

Scenario #5
No Sound Coming From One Component In Either Channel, All Others Have Sound To Both Channels.

This is probably a very simple problem. For example- my CD player is plugged into the “line” input on Channel 1. Is my selector switch set to receive signals from the phono input or the line input? OOOPS! Boy did I feel stupid! But that sure was easier than replacing my cable.

Rats- that didn’t work! It is highly unlikely that the connector cable is bad on both channels, but try replacing the cable. If that still doesn’t work, you have either a defective source component or one input on your mixer is defective. If you have a spare input on your mixer, try it. This may solve that problem. Otherwise, you will need to replace or repair your source component.

Scenario # 6
The System Doesn’t Sound Good

Scratchy sound can have several sources. If you are playing records, your stylus may be extra dirty or even damaged. Your record may be damaged as well. If you are playing cassette tapes, the heads may be dirty. Clean them with a professional head cleaner using soft tip cotton swabs. The heads may also need to be demagnetized with a head demagnetizer. CDs generally do not sound any worse unless there is a serious problem with the digital converter.

The most common problem encountered with CDs is skipping. This may occur if people are bumping your equipment or the floor. Try using isolation pads under your case to minimize this problem. CDs may also skip if they are dirty or scratched. Check the CD and clean if necessary. A third reason for a CD player skipping is a dirty laser lens. Keep a CD lens cleaner handy. If you start to have skipping problems, this may help eliminate them. Make sure your CDs are free from moisture as well as dust.

Another frequent source of substandard sound system occurs when the equalizer is accidentally deactivated. I have had this happen more than once!

If you’re getting a really distorted sound, make sure that your CD player isn’t accidentally plugged into a phono input. You would be amazed at the number of people that have made that mistake, and you only make that mistake once!

If your mixer has a stereo/mono button, it will not sound quite right, if the button is placed in the mono mode. This isn’t to say that playing in the mono mode is a bad thing, as a stereo sound can only be appreciated within approximately 25 to 35 feet of the speakers. After that, people really can’t tell the difference. However, if you are used to playing in the stereo mode, and the system doesn’t sound the way you are accustomed to hearing, this could be the problem.

My number one cause of “bad sound” comes from inadvertently flipping my microphone switch in the “talkover” position. This causes your sound level to drop dramatically. The reflex is to turn up your source fader and then your master volume to compensate. If this happens to you, TURN YOUR FADERS DOWN BEFORE FLIPPING THE SWITCH BACK!

Mixers are the single most common source of noise in the DJ system. They collect a lot of dust that settles into the fader slots. The dust both interrupts the electrical contact and generates static interference in your signal. It is best to clean your mixer with a slightly damp towel and then dry thoroughly. You can purchase cans of “blast air” at computer stores for cleaning your fader slots. The scratchy sound generated by a bad or dirty fader is the best argument for keeping your mixer in a sealed case when not in use.

If you suspect a particular fader is the source of your noise, try using another channel if possible until the fader can be replaced or fixed.

Quality power amplifiers usually do not generate a lot of noise unless they are being fed an excessive or dirty signal. Static is a frequent noise related problem. This occurs when something isn’t grounded properly, or when a “ground loop” occurs. The ground loop can be avoided by using insulators with your rack screws on everything that you rack mount, from your mixer, to your EQ or signal processor, down to your amp. If the insulators do not fix the problem, perhaps a signal processor or EQ is too close to your mixer or amp. Try isolating all of your components, one at a time to see where the problem is coming from. I know more than one DJ who has had to reconfigure their case system to reduce static.

For other types of noise or bad sound, check your mixer settings and your VU meter. If you are going into the red too often, your source component fader is set too high. Also, beware of setting your master volume too high or too low. If you are using banana plug outputs, make sure there are no stray strands of wire touching the opposite channel or polarity (I.E., black wire touching red).

If your noise is intermittent, it may be a connection. Check your cables, inputs, and outputs. Cable shorts are the single most common source of signal dropout. If your inputs/outputs appear dirty, clean them with a professional electrical contact cleaner.

The noise source we all dread are defective speakers. The problem may be with your input, and can often be fixed with simple tools. If the problem is the speaker itself, you would be best advised to have it repaired by a professional. Replacing speaker coils, foam rounds, and cones are tedious work. If you’re looking for a challenge, this is it. If only one speaker is damaged, you may simply disconnect the bad one, turn down your amp’s output on the bad one, and switch your mixer to “mono” instead of stereo. You will have to push your remaining speaker twice as hard to maintain volume, but it’s better than shutting down completely.

Scenario # 7
The System Doesn’t Play As Loud As Normal

First of all, check your fader settings. Make sure you have turned up the proper fader. Second, check your master fader. Look at your VU meters. Are you getting a signal on both channels? If not, check your signal source and cables. If so, check your microphone talkover switch. The talkover switch is the second most frequent cause of lack of volume, with the master control being improperly set as being the primary source. If the talkover switch is on, make sure your fader levels are in the normal range before flipping it back.

I hate to admit this, but I have seen DJ’s who have plugged the connector cable from the mixer to an OUTPUT on the amp. This sometimes leads to a slight sound coming out of the speakers. Closely related, would be to have the speaker cables plugged into the INPUTS of the amp!!!!!! Can you believe that someone would do this?? I have personally witnessed this!

Volume deficiency may also occur when the equalizer is deactivated accidentally. The sound will be fairly loud, but it won’t have quite the punch that it normally does. This happens on a fairly regular basis, and is one of the primary reasons that I strongly recommend that your sound check BEGINS with a check of all mixer and signal processing controls to ensure that they are properly set.

Check your amp output settings. Is the sound coming from one speaker only? If so, this will prevent your system from playing as loud as you are used to. See the section above for troubleshooting sound to one speaker only.

Scenario # 8
Feedback From The Microphone

A howling or high-pitched squeaking sound is created when your microphone is receiving music or your voice coming from the speakers. Never stand directly in front of a speaker with your microphone turned on. Try to stand off to the side and even behind the sound field whenever possible. There are several ways to immediately reduce feedback. The first is to turn down the fader controlling the volume to the microphone. The second is to turn down the master volume, only if it somehow was placed higher than normal. The third is to adjust your equalization. Howling feedback can be tweaked by reducing frequencies in the 250-1000 Hz range. This is why it is advantageous to have separate bass and treble controls for your microphone. You can make the adjustments to the mic, without effecting the sound to the music. Simply reducing the treble will eliminate much of the feedback. Squealing is usually indicative of being too close to the speaker.

When you give up the microphone to someone else, be sure to tell them to hold it no further than four inches from their mouth and stress the importance that they stand clear of the speakers. If they speak clearly and in a normal tone of voice, you should be able to provide sufficient volume without feedback. If you have a wireless mic, remember to keep the receiver level at a reasonable level. If it is too low, your signal will be weak, which will force you to turn up the other volumes. If it is too high, you will encounter howling.

Speaker placement is crucial in avoiding feedback. If you can turn the sound field slightly away from the microphone, you can reduce feedback without lowering your volume settings. Experiment with your speaker placement to minimize feedback. Try it before your show. You’ll feel more comfortable during announcements.

Always use a quality microphone with a cardoid or hyper cardoid pattern. These microphones pick up speaking voices very well, and tend to reject sound not directed into them. Make sure it is a low impedance model (with XLR connectors). I highly recommend the industry standard, the Shure SM-58. This microphone has been around a long time, and is perfect for announcements.

Introduction To Equipment Components

I. Basic FactorsChoosing equipment may well be one of the most excruciating decisions for the new mobile DJ. You wonder if it will last, whether you might be missing something better, or if you’ll end up spending more than you can actually afford. Chill your anxiety with a little planning before purchasing. Just because a deal looks good doesn’t mean it is good. There are four basic factors you should consider before purchasing. The first determining factor is not money, but rather your customer market.

A. Customer Market

Before jumping into the sometimes perilous surf of mobile DJing, you should test them. First of all, are there successful DJs in your geographic area? If not, determine why. Many small towns simply do not generate enough parties to support a mobile DJ. If you just want to start part time, this may deal with that problem. Be aware that most DJs have other jobs in addition to their weekend work. That does not mean you can’t make a living at it, it just means you have to be successful and in a market sufficient to generate the business that will be required to generate a sufficient income.

Most DJs work a wide variety of parties. Some specialize in weddings, but they usually will do a private party or school dance if they have a last minute call for a date that was not booked. All this to say- don’t expect to play only the music you like. You must be willing to play a wide variety of music to get a wide variety of customers. You will need a lot of customers to generate the income required to pay for the equipment you need and/or want.

For the mobile DJ, there are several basic markets. In regard to size of your system, there are basically three. These include small parties (under 100 people), medium size parties (100 – 300 people), and large parties (generally 300-1200 people). Most mobile DJs will commonly handle small and medium size parties, with the occasional large show. Your equipment should be able to handle the medium size party with little problem. You can often rent extra equipment to handle larger parties.

B. Budget

Your budget will also limit how much you spend on your equipment. You may have to forego that 1200.00 dual CD player with seamless looping. Many DJs start with home CD players a basic mixer, a pro amplifier and some decent pro speakers. The term “pro” refers to equipment normally intended for heavy-duty use including bands, large public address systems, and dance clubs. Home stereo amplifiers and speakers do not generate enough power to drive large speaker systems to high volume levels in a large room. They are also not durable enough to handle these volumes for 3-5 hours at a time. Durability is also an important factor when you are carrying home stereo amplifiers and speakers over the road. Home stereo equipment is simply not designed for this application, and will eventually fail due to the punishment that they will receive when used in this manner.

Because of this, it is best to place the highest priority of your budget on speakers and an amplifier. Cheap speakers and a poor amplifier will only cause heartache in a very short time. Pushing a cheap amplifier excessively will damage the best speakers, and the cheaper speakers will fry even faster. Realistically (and no, I’m not referring to brand names here!), you can expect to pay anywhere between 500.00 and 1200.00 for a quality pro amp, and 600.00-1200.00 for a pair of quality speakers. That does not include stands, cases, and cables! Concentrate first on what will help you sound great, then you may want to go after the bells and whistles.

C. Transportation Options

A local band is breaking up and is selling their system at pennies on the dollar. Your techie friend tells you the stuff is in great shape and is a steal. Should you jump on it? Maybe – if you can get it home. Keep in mind that you will be moving your equipment to and from every show. Do you really want speakers that weigh 95 lbs. each? Even more important is what vehicle will you use to get to and from shows? It won’t be easy to fit a lot of bulky equipment in a hatchback. If you already have a mini-van, sport utility vehicle, or a cargo van, you have a little more flexibility.

Do your back a big favor- buy a heavy-duty hand truck. You may be able to get by with a 30.00 convertible truck at first. These are not ideal, but they’re much better than carrying each item in by hand. Many DJs use the “Rock and Roller” carts. I use the largest model, the RR-10. It has saved me a lot of time and backaches, and has been well worth the 170.00 I paid for it. It holds my entire basic system plus CDs and mini-discs! It expands from 2′ to 4′ and has a 500 lb. Capacity. Whatever cart you choose, make sure it can handle the load without tipping!

D. Personal Preferences

While the first three factors require logical consideration, your preferences don’t. We often buy things because they look cool, or they have a more “quality feel”. There is nothing wrong with these preferences. They often lead to a “best decision”- but often after the three preceding factors have been considered. Make sure you try out your purchase before buying if that is possible. If you don’t like it, don’t hesitate to return it if your dealer allows returns. Be comfortable with your equipment- it will either help you or hinder you.

II. Sound Equipment Selection

Your DJ system must have A) MEDIA B) MEDIA Player C) Mixer D) Amplifier E) Speakers F) Connections. A quality DJ system will also have microphones and processors. This section is designed to show how these components work independently and as part of a total system. We will also present some examples of differing designs of each chain of the DJ system.

A. Media

Simply put, media is the format of the music you will be presenting. The most common media used by DJs are compact discs, vinyl records, mini-discs, and cassette tapes. Computer generated media is growing in usage, but is currently not practical for most beginning DJs. Superior CD recorders and mini-disc recorders are quickly replacing cassette tapes. Vinyl is still a strong niche market for DJs, but the styles of music available are primarily limited to rap and club music. Compact discs are still the overwhelming media of choice for the mobile DJ. The largest variety of new music is readily available on compact disc. Mini-discs offer the DJ the option of producing pre-mixed music, special “style discs” (like current ballads, line dance country, party classics, etc.) and vocal drops or pre-recorded announcements. CD recorders offer the same convenience with the exception of some editing features and ease of use. You should understand that it is illegal to make recordings for DJ applications! Whichever media you choose, make sure it allows you to easily please your customers.

B. Media Players

Media players do more than simply play music. They help you present it with your style. Mobile DJs should look for players with a quality feel as well as performance. Some CD players have features that make this much easier. First of all, a dual CD player offers the convenience of having the controls close to your mixer. Instead of bending over to look at your controls, you simply glance down at your angled mixer rack. Some players offer exceptionally fast cueing (setting the song to the beginning before starting) and start-up (how fast the music comes on when you press “play”). Some newer models have “skip chips”, that is, circuit boards that prevents your music from skipping when someone stomps near your player. For the perfectionist, there are players with “seamless looping” that allow you to mix from one song into another without missing a beat. Finally, there are players that remember specific songs and will cue them automatically to “hot buttons”. There are other advanced features available on CD players as well as mini-disc players, but these are the ones most preferred by DJs. They are also the features most DJs ask for when new media players are presented to them

The number of media players that you carry is also an issue. Quite routinely, newer DJ’s will carry only two CD players to each event that they perform. If one of them malfunctions, and you are left with only one operational CD player, you have a major problem on your hands. Carrying only two CD players (or just one dual CD player) is a disservice to your client, and to your reputation. Generally, you should have at least three CD players if that is your main format.

C. Mixers

Mixers do just that. They take a variety of media, mix them together, and send that signal to your amplifier. They receive signals through inputs and send them out through outputs. A typical mixer can handle two turntables, two CD players, a microphone, and a mini-disc player or extra CD player. Most DJ style mixers have output “channels”. The most common are 2, 3, and 4 channel models. Each channel typically has two possible source inputs to it that are controlled by a selector switch. A mixer with four channels may cost more than a three-channel unit, but it will also give you greater performance flexibility.

Determine your needs with the idea that you may add on later. Make sure you are comfortable with the fader action. Assignable crossfaders may make mixing easier, but they can become a source of mistakes also. Sound effects may be fun, but how often will you really use them? Samplers are another toy in this category. You need to be serious about using them if you want to truly justify your purchase. Equalizers can be helpful, especially when starting out. Use them wisely and sparingly. I highly recommend models with two microphone inputs. You don’t need to worry about switching cables if one mic goes out and you have a back up plugged in.

Another good feature to look for on your mixer, is a separate bass and treble control for the microphone. This allows you greater flexibility in adjusting the proper sound for the mic as well as the music.

An audio mixer consists of five parts:

· A mixer

· A pre-amplifier

· A cueing system

· An equalizer system (optional on some mixers)

· A meter system

The mixer section is the mechanism that allows you to gradually fade from one song to another. There are individual volume controls that allow you to increase or decrease the volume to each component, such as a CD or tape player, the microphone, etc. There is a main “Master” volume control that control all of the components hooked to the mixer. It does not matter how high an individual volume control to a CD player is set, if the Master control is at the lowest position, you will not get any sound out of the mixer! The Master volume control should be set at approximately 1/2 volume at to start.

The pre-amplifier system is the portion of the mixer that is used for turntables or phono inputs. This is necessary because the raw sound produced by a turntable is very low compared to CD players or tape decks. By comparison, the signal produced by a CD player or tape deck is much higher. The pre-amplifier system boosts, or amplifies the very low signal from the phono cartridge so that it matches the higher output signal of a CD player or tape deck. Most mobile DJ’s do not use turntables. The one thing you need to remember is that you cannot plug a CD player or tape deck into a “phono input”. If you do, you will get a very distorted sound.

The Cueing system on a mixer is designed to allow you to listen to a song through a headset from one CD player, while a song is playing from a different CD player through the speakers. Typically, while people are dancing to one song, you get your next song ready, and preview the song through the headset. There is a separate volume control for the headset.

The equalizer on the mixing board is designed to allow you to adjust the bass, treble and midrange sounds of the system.

The meter system of the mixer is important to the disc jockey. The “VU” meters on the mixer tell the disc jockey if he is overloading the amplifier. Specifically, the level on the VU meter tells you how “clean” the signal is going into the amplifier. When the VU meter is constantly in the red, this indicates a distorted signal, and will eventually result in a blown speaker, overheated amplifier or both. These meters can also be used as a troubleshooting tool when determining if there is a problem with one of the components or the mixer itself. There are two sides of the meter, one left channel, and one right channel. In the event that the meter is only displaying output from one channel, you will most certainly have sound from only one speaker (assuming you are using the stereo mode). In this situation, it usually means that the mixer is receiving sound from only one channel of the CD player/tape deck.

A good mixer will often last longer than most of your system. My first mixer was five years old when I bought it, and I enjoyed it thoroughly for three more years. Make sure you try before you buy. This is the one piece of equipment you will touch a lot. Be comfortable- and keep it clean!

D. Amplifiers

Amplifiers are the “muscle” of your system. They take the signals delivered from your mixer and convert them into electrical power sufficient enough to drive your speakers at volumes exceeding 120 decibels! This is one of the two most important items in your system. A great amplifier will let you deliver more-than-sufficient volume with very little strain. For the medium-sized parties mentioned earlier, you will need at least 200 watts per channel at 8 ohms with a distortion rating below 1%. Keep in mind that the more you run your amp at full output, the greater the wear and tear due to heat. Many DJs start with 300+ watts per channel.

Most amplifiers have at least two inputs – one for each channel or speaker (left and right channels). They also have two to four outputs that go to the speakers. Typically, you will find two different types of outputs on most amplifiers. The first type, is the “banana plug”. You can find this on the back of your amp by finding the red and black posts that stick out of the amp. There should be at least one pair of “banana plug” speaker outputs per channel. The other type of speaker output is the ¼” female output. You can easily locate the speaker outputs by locating the black and red banana plug terminals. The ¼” speaker output is generally located adjacent to the banana plug outputs.

In the event that the amp gets overheated, the possibility of the amp blowing a fuse or tripping a built in “shut-down” circuit breaker may occur. Most amplifiers have a built-in shut down breaker that shuts down the amp because it has overheated. The amp can be used after it has cooled down (usually 15 minutes). If the amp shuts down, before continuing, you should find out why it overheated to begin with. The usual cause of an amp overheating and shutting down is due to trying to play too loud to the point that you play a distorted signal. While it is important to know about the possibility of the amplifier shutting down due to being overheated, you should know that there is an extremely small chance of this actually happening, provided that you are using brand name, professional amplifiers.

You can expect to pay between 500.00 to 1200.00 for an amp rated 300-400 wpc. This may seem like a “budget buster” at first, but a quality amp can last 10 years or more, if you take care of it. Check the warranty when you buy – some are better than others. The best warranties are typically 3-5 years and are “no fault”. That means that repairs will be covered for anything short of obvious abuse (I.E., mangled casing, soda stains on circuit board, etc). Make sure your amp can be serviced locally. Next Day Air shipping can be expensive on a heavy amplifier. Buy quality and minimize repair hassles.

E. Speakers

Quite simply, speakers are the most important link in your sound system. Amplifiers, CD players, and mixers do not produce sound. Speakers produce sound when signals of sufficient amplitude are fed to them. Much can be said about electronic measurements of speakers, but these measurements rarely tell you what your ears hear. Speakers are the one component that you should strongly consider purchasing from a local dealer. The only way to truly judge a speaker is to listen to it. Be sure to listen to a wide variety of music at a variety of volume levels. Walk around the room and notice any changes, especially in high-end instruments and voice. Keep in mind that while a speaker may seem to have a stronger high end, it may cause “listener’s fatigue” at loud levels over several hours. Also note the “throw” of the system- that is, how far the sound will carry and cover an area. Some systems have a great throw, but may sound harsh at close range. Others may have a very smooth high end and weak room coverage. A good balance between these two will make announcements more pleasing to your client’s ears.

Efficiency is another crucial consideration when selecting speakers. Some speakers require substantially more power to reach a 101 dB sound pressure level at I meter. Most speaker systems have this rating in their literature. Compare these numbers. The speaker that requires fewer watts to reach 101db is the most efficient. Speakers of greater efficiency require less power from your amplifier, allowing it to run cooler and avoid clipping. This can be a deciding issue between two speakers of similar sound quality.

Power ratings show the maximum power over a sustained period of time a speaker can handle. One common misconception is “you should never hook up a speaker to an amplifier with a higher power output than the speaker’s power rating”. Speakers typically can absorb short-term (several seconds) power surges as high as two to four times their power rating. Speakers with higher ratings may often produce higher volume levels and lower distortion than those of lower power ratings. Higher power ratings can also mean that a speaker requires more power to reach a high volume. Be sure to look at both efficiency and power ratings when comparing speakers.

Size and weight should not be overlooked. Many mobile DJs use 12″, 2-way speakers on stands as opposed to larger systems placed on the floor. Placing speakers on stands positioned above the heads of your audience allows greater room coverage. Moving speakers away from the floor and other hard surfaces reduces total bass output, however.

Your back may decide this one. Typical 12″, 2-way systems weigh about 35-45 lbs. 15″, 2-way and 3-way systems generally weigh between 50-85 lbs. You will need to decide which way you want to go to obtain the sound you will need.

One option you may want to explore, is to start out with a nice quality pair of 12″, 2-way speakers that you use on speaker stands, with the idea that you can add another set of larger speakers that sit on the floor for better sounding bass. With two 8 ohm speakers (one speaker per channel), you place an 8 ohm load on each channel of your amp. By simply adding another pair of 8-ohm speakers, you will then place a 4-ohm load on your amp, giving you more power output per channel. The concept of using one small and one larger pair of speakers is a convenient alternative that will add a deep, rich sound to your system without the hassle of going to a bi-amped system.

F. Processors

Processors make changes to the music signal. Generally, they are connected between the mixer and the amplifier. There are four basic types commonly used by DJs- equalizers, compressor/limiters, time alignment devices, and crossovers.

Equalizers are essentially a group of volume controls that adjust volume at specific frequency ranges. They are often built into mixers, and can be very useful for “cleaning up” a “muddy” or “bright” mix. Many sound engineers approach equalization as a “balancing act” rather than “add more bass” or “add more treble”. A mix that sounds muddy may simply have insufficient treble output, or it may be both insufficient treble output and too much bass. At the extreme end, it may simply be too much bass. The objective is balance and smooth sound. Because mobile DJs work in a large variety of rooms, an equalizer is generally a necessity. Most DJ mixers have equalizers built in for good reason. In the words of Toy Story’s Woody- “If you don’t have one – get one!”

Compressor/limiters selectively take a signal and reduce its dynamic range. The louder passages are no longer so loud, and the softer passages are easier to hear. They also limit the possibility of amplifier clipping and subsequent distortion if set properly along with a proper signal level. This can be very helpful when you’re trying to squeeze every decibel you can out of that best man who’s afraid of the microphone during his toast. These are more helpful in larger shows that typically cover a large area.

Time-alignment devices generally divide the signal into bass and treble content. The bass signal is released to the amplifier milliseconds before the high-end signal. This change often produces very noticeable results. Bass often seems fuller with more punch and clarity of high-end content; vocals seem to increase as well. The two most common units on the market are the BBE Sonic Maximizer and the Aphex Aural Exciter. If you are leaning toward smaller speakers, but are worried about their bass output, test drive one of these. I have a 12″ system that sounds dramatically fuller thanks to my time aligner.

Crossovers divide the signal from the mixer to the amp into two or three parts. This allows for the use of separate amplifiers and multi-speaker systems. Typically, crossovers are used to send lower frequencies (below 150 Hz) to a subwoofer and the upper frequencies to a full range speaker. This allows the full range speaker to produce those higher frequencies more efficiently, and the subwoofer to produce substantially greater bass output than the full range system. Crossovers have controls that allow you to adjust the “turnover” frequency- that is the frequency at which the signal does not pass through. They also allow you to control the signal output of each half of the total signal.

Subwoofer systems are more commonly used in high schools, colleges, and clubs where music content is often bass heavy.

G. Microphones

The mobile DJ will use his microphone often, and often at very critical moments. A high quality vocal microphone is relatively inexpensive compared to much other DJ equipment. The Shure SM-58, which is beyond question the microphone most commonly used by mobile DJs and professional announcers, generally can be purchased at just over 100.00 at many music stores. There are other great basic microphones in this price range also. You should avoid microphones that do NOT have an XLR connector. Some cheaper microphones will have a ¼” connector. This is very undesirable, and the trademark of a poor sounding mic. A cabled microphone is a must even if you decide on a wireless microphone; you should always have a backup.

Wireless microphones allow the mobile DJ to get away from his console and get out on the dance floor to teach, motivate, and PARTY with his guests. A wireless headset allows hands-free operation, but is impractical to hand to the best man for a toast. A hand-held wireless allows you to get out on the dance floor, but limits what you can say and do at the same time. Many DJs have both headset and handheld wireless microphones in their system. This allows them the flexibility to talk with hands free and allow others to talk without hassling with a wire or the location of the DJ area.

If you decide to go wireless, true diversity systems are the least expensive quality system available. UHF systems offer far greater range (ability to speak further from the receiver) than true diversity systems, but are more expensive. In the last year, however, UHF prices have dropped dramatically. Shop around on these. Also, be sure you can rack mount your receiver. A damaged receiver means a dead microphone.

H. Connections

Putting a group of components together in a rack means nothing if they are not properly connected. When budgeting a system, it is imperative that you price all the cables you will need as well. A typical DJ system will require at least 2 sets of speaker cables, one set of quality RCA cable pairs for every media player, a set of cables to connect mixer to amp, and any other cables required for microphones and processors. Heavy-duty power strips and extension cords are also a major necessity. Occasionally you may have to run an extension up to 100′ long. This cord should be no lighter than 14 gauge and 12 gauge if possible. Consider also rack-mountable power strips like the Rack Rider. The more cables you can keep inside your mixer case, the cleaner your setup will appear, and you will save time and wear by making fewer connections during setup. I highly recommend keeping a spare of each cable and connector in your system. Also keep fuses for mixer, amp, and speakers handy.

If you have media players (such as CD player or mini-disc) in a case other than your mixer case, you can decrease wear on your mixer inputs by running a second RCA pair to a pair of female-to-female RCA plugs attached to the mixer case just inside near the back. This is one of the many brilliant ideas I have stolen from posters at ProDJ.com. I would love to thank and credit that poster if I could remember who it was!

III. Casing

A. Transport

Transport casing refers to the carriers of cables, extension cords, microphones, and other miscellaneous items. For bulky items that are not especially fragile, there are many large cases available at very reasonable prices. For all my cables (and a few light chaser/controllers), I use a large plastic Contico trunk that cost just 19.99 at a department store. It is lightweight, has a strap handle in the front, and molded-in handles on each end. It has two latches and is stackable. I use a second for props. These hold a lot of maracas, inflatable guitars, and YMCA hats as well!

B. Equipment

The most common indicator of a “newbie” DJ is the lack of proper casing for their equipment. Newbies often stack a mixer on top of two home CD players and place their amp right beside them. I know, because I did this at one time too. Yes I damaged one CD player. Yes I tripped over hanging power cords several times. Yes my setup looked like a mess- a tangle of wires for all to see. When I became serious, I watched (and helped) some more experienced DJs. I soon discovered the two major benefits of equipment casing- saving your equipment from damage and saving a lot of time for setup/tear down. One other advantage of casing is that it offers a professional appearance to your system.

The most common equipment case for the mobile DJ is the mixer case. It includes slanted or pop-up rails to accommodate a mixer, wireless microphone receiver, and a dual CD controller. The bottom typically holds items like a power distributor, CD player. mini-disc player, equalizer, amplifier, etc. These cases have racks that are measured in “spaces”. A rack mount “space” is 1.75″ high x 19″ wide. A typical size for a mixer case is “8/6″, that is, 8 rack spaces on the slanted top, and 6 rack spaces on the vertical bottom. Be sure to measure carefully the requirements of your equipment before buying. Also keep in mind the TOTAL WEIGHT of the case once you have filled it. A large case may be more convenient, until you have to lift it.

Another common case is the SKB roto-molded cases. These are lightweight (compared to plywood & carpet cases), heavy duty, shock resistant, and close with a tight seal. Most of their cases are only vertical style, however. I have recently seen an ad for an SKB mixer case (a 10/6 pop-up model, but I have yet to see these in any stores or catalogs. A “workstation” version with a pullout drawer for the mixer is also available.

If you start out using consumer CD players that are not rack mountable, you can still protect these units in a case. This can be done by purchasing a regular rack mount case, and getting a rack mount adapter tray. One DJ I know uses velcro to secure the CD player to the tray, and in turn, velcros another CD player right on top of the first one. This protects your CD players, and also provides you with a more professional looking system.

IV. Sources of Information

The starting place for equipment information would have to include the Gear Board on ProDJ.com as well as Mobile Beat magazine. Talk to other DJs and see if you can help them. Many will be glad to feed you a lot of information in exchange for your “roadie” dues. Yamaha has an excellent manual on sound reinforcement that covers everything from beginner to intermediate and beyond. Salesmen at music stores may often have a lot of product knowledge, but you must keep in mind that they are paid to SELL and MAKE MONEY. They may not always have your best interests at heart. Check out catalogs from some of the major advertisers at ProDJ.com (click on Mall) and Mobile Beat magazine. Compare pricing when you shop and don’t be afraid to ask for a better deal- after all- you work hard for the money!

Equipment Setup and Sound Checks

When setting up your Equipment, there are certain things you must consider. We will try to address the basics; remember everyone’s needs and expectations will vary. First of all, if this is to be a “mobile” set-up then you will want to consider what type of console will work best for you. There are many different sizes and styles available already built or you can build your own to suit your needs.Section One

Cases – It cannot be emphasized enough…you need to protect your equipment in cases. There are two main advantages of cases. First, the life span of your equipment will be doubled when it is protected by a case. Second, the appearance of your system will be much more professional if everything is housed inside a case covered with black or gray carpet. (See the article on Equipment Components for more information on creative casing ideas.)

Basic System Design – The Coffin System

The advantage to having your equipment in a console (or coffin) is that almost everything stays wired up, the individual pieces of equipment are protected during transport and your set looks more professional. The important things to consider when choosing or designing a console are:

Accessibility of controls
Layout of equipment
Portability
Looks
Accessibility of Controls:

It is very important that you can not only reach all the controls of your system, but that you are able to easily SEE all the controls as well. If you are tall, a console that slants the equipment upward will make it easier to see the displays and controls, if you are short, your console should probably be one designed to sit on a table or stand of some sort. This way you can adjust the height by selecting something suitable to set it on. Your console should only be as wide as your reach; you shouldn’t have to step around to reach your equipment.

Layout of Equipment:

Equipment should be laid out in a logical manner. In discussing layout designs we learned that we both prefer to have our components arranged side to side and top to bottom. We break it down like this:

Source Equipment:

CD, MD, Cassette, Turntable, Microphone, etc., should be in the top or upper area of your console. These are the types of equipment that get used the most often and should be easiest to access.

Control Equipment:

Mixer, Controllers, etc., should be mounted in the upper area of the console but at waist height, so your hands will naturally rest on the controls

Processing and Output Equipment:

Equalizers, Effects Processors, Amplifiers, don’t normally get adjusted after they are set properly, so they can be mounted in the lower areas of a console or even a separate rack.

Portability:

Generally speaking, you want to be able to move your equipment all at once, including your music, to reduce the opportunities for thieves to access your gear. This can make your console very heavy.

If you have the convenience of a helping hand (Assistant DJ, Roadie, etc.), it’s easily possible for you to move everything at once. If, however, you need to accomplish this yourself, you may very well be stuck.

Some thought must be given to how this console will be moved and carried. Having wheels on your console is a big help, or at least having a wheeled device that your console can set upon for transport.

Looks:

A console will help you to project a Professional look. Most cases are covered in a short, dense Grey or Black carpeting-type material that is very easy to care for and will maintain it’s good looks for many years. If your console has an open back, (which is good for repair access, and ventilation), you can use a drape or curtain to cover this area during gigs. Plus, this gives you the added benefit of hiding your feet and whatever else you put under your console.

Basic System Design – Side To Side Component System

The side to side system allows you to reduce the size and weight of your components into two or three smaller and lighter cases. If you typically do not have help, or routinely have to carry your equipment up large flights of stairs, this system may be more desirable than the coffin system.

As stated before, your equipment shouldn’t be any further apart than your reach. Usually the sources are divided into 1 & 2 or R & L, so they correspond to the basic location of the sliders on your mixer. This aids in the quick acquisition of control functions while working once you get used to your layout.

With your Equipment mounted in a console, your Set-Up/Tear-Down time is greatly reduced. You can roll everything in, lay out and hook up your speaker cables, run your power cord to your source, and be into your sound checks in a very short time.

Section Two

Wiring Basics:

Wiring will be the next section we cover. Knowing how to wire your own system is very important and can help you diagnose and sometimes fix problems that can occur at a gig. We will cover these basic areas:

Electrical
Line/Phono/Mic Level Signals
Amp Output/Speaker Level Signal
Electrical:

Your Electrical Power Source is extremely important. If there is not enough power you risk at least blowing the breaker and at worst, frying your amplifier. Your power requirements can be figured using this formula:

Watts divided by Volts = Amps

A standard commercial 120V, 20A wall outlet will supply 2400 w of power. (Volts x Amps = Watts)

Note: Residential electric outlets are typically rated at 15 amps.

Now look on the back of all your equipment and there should be a rating of how much power (in watts) each particular piece uses, (not Output Power…as in an Amplifier, but Power Consumption). Add all these numbers together and use the formula outlined above. This will tell you how many 20Amp circuits you need to safely run your show.

A Power Conditioner is a very good idea. Units such as those made by Furhman and many other companies will keep nasty peaks and dips from damaging your system. Even though an outlet is rated at 120V, 20A, that doesn’t mean that it is a steady and constant source. The actual power available can fluctuate enough to cause some problems, and a Power Conditioner helps to level out the power being fed to your system.

Line/Phono/Mic Level Signals:

Line Level Signal:

These are the High Level signals that your amplifier will turn into Speaker Level Signal in the next section. Line Level signal is approximately 245mV (millivolts), and is produced by your source components, such as CD, MD, Cassette, CD+G, VCR, etc. Line Level is the actual sound that you will eventually hear. The Line Level signal is usually routed through your Mixer. The Mixer is an infinitely variable Pre-Amplification device that allows you to control the amount of each source component signal that will ultimately be fed to your amplifier.

Line Level signals are very sensitive to RFI (Radio Frequency Interference), and must be routed through shielded cables to avoid this interference.

Phono Level Signal:

These are the Low Level signals produced by your Turntable and are approximately 10microwatts. These signals are extremely sensitive to RFI so you must use shielded cables. The shielded cables must be fed into special inputs on your Mixer. This will allow the turntable to be pre-amplified enough to match the Line Level signal at the outputs of your mixer and be fed down the chain to your amplifier.

Microphone Level Signal:

This is the signal that is your voice. These signals are Low Level, approximately 10 millionth of a watt and very sensitive to all sorts of electrical noises. Shielded and Balanced cables are recommended. Balanced cables for Mics usually use the common XLR (3-pin) type connector. They are considered to be “balanced” due to having 2 conductors for the signal and also a shield of interwoven wire that is connected to pin 1, thereby making a solid shield no matter how many cables you link together. Standard shielded cables have 1 conductor for the “hot” signal and utilize the shielding weave as the “common” conductor.

Amplifier Output Signal or Speaker Level:

This is the signal that is sent from your Power Amp to your Speakers. Mostly it is expressed as Watts Per Channel, but that can be misleading. Your Amplifier spends far more of its working time functioning at way below it’s rated maximum output power.

Depending on the signal level voltage your pre-amp or mixer is sending out at any given moment, your Power Amplifier may only be producing a fraction of it’s rated maximum output. This is only the first half of the story, you must also consider the Load Impedance placed on the Power Amp outputs…your Speakers. To break this down to it’s simplest terms, Speakers are rated as a 2ohm, 4ohm, 8ohm or 16ohm load. You’ll notice this load rating doubles as it increases. This will make a BIG difference to your Power Amp’s Health and Happiness. Most Power Amps will operate safely with a 4 to 8 ohm load per channel, although the smaller the load impedance, the higher the Maximum Power Output in Watts and the more heat generated by your Power Amp.

A simple way to think of this is in terms of liquid flow: The lower the Load Impedance, the more output wattage is allowed to flow from the Power Amp. The higher the Load Impedance, the more that flow is restricted. You can go too high as well as too low for the safe operation of your Power Amp. NEVER run your Power Amp without a load. Anytime it is powered up, you MUST have a load of some sort attached (Speakers have to be plugged in).

Follow up:

Wiring your System together is like building with blocks. Everything must go in a certain order for it to work properly. Follow the Music through the system and you’ll know how everything should be put together. First you have the Source Components (CD, MD, LP, Cassette, etc.) the output from these is directed into separate input channels of your Pre-Amp/Mixer for level control processing. The output signal from your Mixer is then directed through either your Signal Processing equipment, (Equalizer, Aural Exciter, Reverb/Special Effects, Electronic Crossover, etc.), or directly to your Power Amp., and then ultimately to your Speakers.

When plugging it all in, remember…Outputs go to Inputs and Inputs go to Outputs. Sometimes the identifying markings on the hookups can be confusing. Thinking about it this way can help reduce the confusion.

Section Three

The Real Work:

In this section we will cover how to get your system set-up, working, and sound checked at the gig.

Safety and Security
Load-In
Set-Up
Sound Check
Load out
Precautions for Playing Outdoors
Condensation Problems
Tear-Down/Clean-Up
Safety and Security:

The Safety of everyone involved is something to be considered. Do not lift more than you can safely carry. Get help, use a cart or a hand-truck. Do not stack things so high or wide that moving them presents a danger to yourself or others.

The Security of your equipment is the security of your livelihood. NEVER leave sight of your vehicle without locking it. Never leave your equipment and supplies unsecured in hallways, loading docks, or lobbies…ESPECIALLY YOUR MUSIC! Everybody wants a CD/MD/LP collection just like yours! But, nobody wants to pay the price you did. Why should you give somebody a great music library for free? If you are worried about the Load-in/Load-out, request that on site Security Personnel be available to watch you unload and load your equipment, especially late at night in unfamiliar areas. We carry Thousands of Dollars worth of equipment that looks very inviting to crooks, BUT CAN ALL BE REPLACED. If you are injured or killed while being robbed, you are irreplaceable.

Load-In:

First and Foremost, Arrive On Time!!

It seems like a trivial thing to emphasize, but our experience has shown that a high percentage of the time that equipment problems arise, the disc jockey was late in arriving at the event and had to rush setting up. Arriving at least one hour prior to the event is a quality control measure. You should arrive far enough in advance of the contracted time to allow you to be completely set up and have a thorough sound check completed a minimum of 30 to 40 minutes prior to the contracted time. This, of course, will depend on the size of your sound system, access to the area you are to set up and the number of helpers you have available.

The Load-In should be done early enough to allow ample time for all phases to be accomplished prior to the Guests arrival. If you are unfamiliar with the venue you are playing, always allow enough time for unforeseen difficulties, such as stairs, limited access, locating electrical sources, etc.

Once you have all your equipment and supplies moved into the proper area, it’s time for Set-Up.

For new Disc Jockeys, it is suggested that you arrive even earlier than this. The extra time will allow you to review the music lists provided by the customer as well as time to mentally prepare yourself to do a good job!

Set-Up:

Place your equipment in the locations where it will be for that event, keeping in mind traffic patterns of the room and your access/egress in case of emergency. We usually try to center our console’s on the edge of the Dancefloor, unless something else is there, (like the Head Table at a Wedding).

If your equipment is in more than one console/rack, wire these sections together first. Next, lay out your speaker cables, keeping in mind traffic patterns, and plug them into your speakers.

Speaker stands are used for most mobile DJ applications, since they elevate the sound, and evenly disperse the sound throughout the room. Make sure that your speaker stands are located to minimize the tripping hazard from the legs.

Tidy Up!

Your finished set-up reflects on your image and the perception that everyone will have about you as a professional disc jockey and entertainer. It is imperative that you make every effort to conceal all wires, cables and electrical cords. This means that you should never have speaker wires or extension cords hanging from the front side of the table (if you use a table). The “guts” of the system should never be seen by the guests.

Duct Tape: Check with the management BEFORE you tape anything down, some places do not allow tape on their carpets and floors, others will only allow certain types of tape. Always ask first.

After you have permission, tape down your cables so as to keep anyone from tripping over them. Things should be done in this order; electrical cords = from the wall to the console with the extra coiled up at the console. Speaker Cables = from the console to the speaker with the extra coiled up at the speaker. The reason for leaving the extra at the point of termination is for adjustment. If you have to move a speaker later in the event, you will have some cable available to do so and won’t have to re-apply the tape for safety.

When using duct tape for speaker cables and other wires, tape it crossways, rather than with the length of the cable. You should tape the cable every 8 to 10 inches. Taping with the length of the cable can make it next to impossible to remove the tape after the show (especially if the tape sticks together!

Sound Check

Your Sound Check is an integral part of your set-up process. This is where you make sure everything is functional and ready to go. Before you jump right in to your Sound Check, you should check with the management and let them know you are going to perform this test, because it can get loud. Assure them that this is only to check for problems and won’t last long.

Before turning components on, make sure that the volume controls on the amp are turned down. The main electrical connections should be done last to avoid anything getting powered before it should be. Run your electrical cable(s) to your source(s) and connect.

When Powering Up your individual equipment, you should start at the beginning of the sound chain and work your way forward; Source equipment first, then the Mixer, the Processing equipment and finally, (with the speakers connected) the Power Amplifier. Powering-Down is exactly the opposite, shut down the Power Amp first, then the other gear. This will help you avoid undue stress on your components from “turn-on thumps”, that loud “Whump!” sound you get if you do things out of order.

After this, make sure that all switches and controls on the mixer are in the appropriate position:

• Equalizer switch is activated

• Master volume is up in the appropriate position

• Equalizer tone controls are in the appropriate position

• All input switches are set to accept the signal from the CD players and other playback devices you use, as well as the switch for the microphone

• Make sure that the “talkover” switch for the microphone is turned off

• Any “Assign” knobs should be in the appropriate position (off, if you don’t use crossfaders)

• The headset control is set to the “cue” position

• The stereo/mono switch is in the stereo position

• The bass and treble controls for the mic are both set at approximately.

The first thing that you should check is the microphone. The microphone has a mono output, and a signal will be automatically delivered to both the left and right channels of the mixer. It is desirable to start your equipment check with the mic first because you can firmly establish if you have a good signal from the mixer to the amp, and from the amp to the speakers. If one speaker does not work in the initial mic check, then you know that the problem is somewhere between the mixer and the speakers. If you started the equipment check with a CD Player, then your CD player or the connector cord between the player and mixer can add to the possibilities of where your problem is located. Starting your sound check with the mic reduces the number of places to check for a problem.

Your sound check should start by checking each channel on the amplifier separately. Turn channel A up, and channel B down. Do a sound test with the mic, then switch and check channel B on the amp. Once you have confirmed a complete sound check in both channels, you can be sure that everything from the mixer to the speakers works fine.

Your main objective at this point is to make sure that all cassette decks, mini-disk players and CD players work in both the left and right speakers. The time to find any problems with the equipment is prior to the contracted starting time. This means you need to play all of the components to ensure a good, clear sound is coming from both speakers.

Choose music for your test that you know well and preferably consists of some acoustic instrumentation, (Piano, Drums and Upright Bass are good, try the song “Kissing a Fool” by George Michael) and also some music that is representative of what you’ll be playing at that event. Play this test music at a higher level than normal and walk around the room. Listen for any echoes, harshness or “dead spots”, try replacing the speakers to a slightly different location, and walk it again.

You need to play something from and through each piece of gear you’ve got, even if you don’t think you’ll use it at this event. Speak into your Microphone(s), turn on the lights, etc. Do you have extra batteries for your wireless?

If no guests have arrived yet, you should make a thorough check of all components through the speakers. A more discreet approach is in order if the guests are already present, especially at banquets where people are already eating, or where there are awards or presentations going on. Point the speakers toward the DJ table (not toward the guests) and tap the mic, first through the right channel, then through the left channel. This tells you that your mixer and amp are working properly. Now, play all components through the headset, to ensure that all of the components are at least sending a signal to the mixer. Once you start playing, you should double check each of the components by checking to be sure you have sound to both speakers. The object is to make sure that everything is working properly, without disrupting the guests when you check the equipment out.

It is important that you have a full equipment check of all components complete at least thirty minutes prior to the contracted time!

Precautions for Playing at Outdoor Locations

If playing outside, make sure that sun, rain, etc do not affect you and all your equipment. Your company contract should clearly state that the customer is responsible for providing shelter from the sun and the rain. Do not set up in an unsheltered area when the heat and sun can damage your equipment!! If you are playing at someone’s home and there is no place to set up under cover, then consider setting up inside the house, and place the speakers outside. This is undesirable from an interactive standpoint, but merely an option, depending on the type of event.

Keep in mind the type of materials used for constructing the “equipment”. Plastic is used in much of the equipment we use. Do not make the mistake of underestimating the effects of sunlight on your CD Library. CD’s will melt if left in direct sunlight for long periods of time. This has proven to be the case on more than one occasion where the DJ brought back CD’s that the tops of the disc had melted.

Most importantly, communicate with your client in advance, and explain what your needs are. In most cases, some accommodations can be made to protect your equipment from the elements.

In those unusual cases where there are no options to keep your equipment out of direct sunlight, consider purchasing a canopy for your equipment and charging an additional fee to the client!

Condensation Problems

While playing outside on hot, humid days, you will probably encounter severe condensation on the equipment. Be certain to allow extra time when you are playing outside during these weather conditions. Condensation is caused by a sudden, drastic temperature change, such as when you take a component out of an air-conditioned car and place it outside on a hot, humid day (usually a 20 to 30 degree difference). It is important to note that condensation is not just formed on the outside of the components……it has also formed on the inside!!! This presents a problem in operating the CD players. CD players will simply not operate until the moisture formed on the inside of the unit evaporates. This is due to condensation forming on the laser pick-up device. More than one DJ has had the occasion to set up their equipment on a hot, humid day, only to find that the CD players would not work for an hour until the unit dried out.

The best way to avoid condensation is to avoid a sudden, drastic temperature change. This means that you cannot let your equipment get cold when it is hot and humid outside!!! We suggest that you gradually cut back on the air conditioning temperature in your vehicle until you eventually turn the air conditioning off, just prior to arriving to the event location. Your vehicle will then gradually warm up to the same outside air temperature. This may not be very comfortable, but it is much better than not being able to start the music on time!! It is important to monitor the temperature with the equipment inside the car. Do not melt the equipment!!!

Tear-Down/Clean-Up

Tear-Down goes just the opposite of Set-Up. First you Power-Down your equipment starting from the Power Amp and working your way through to the Sources. Then Un-tape your cables, paying careful attention to get all the tape goo off your cables and the floor. Unplug the Power cable(s), unplug the speaker cables; put them all away properly. Pack up your music and you’re ready to look around the area checking to make sure nothing has been left behind. (I once found the B&G’s Wedding Certificate left on a table after everyone was gone; they were very happy when I returned it!-Ken). Once you are certain that everything is together and your area is clean, then proceed to getting your equipment moved out to your vehicle.

Load-Out:

Remembering your safety and security measures. Get your equipment back to your vehicle and load up for the trip home. Once you are loaded and ready, lock your vehicle, go back inside and thank the manager and his staff. You may be the first DJ/Entertainer to ever do this at that facility and how good does that make YOU look?

In Closing, remember to always be safe and thorough. Following a set pattern will ensure that you, your staff and your equipment will be around for many shows to come.

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