Subwoofer Placement

June 28, 2017 by Ben Stowe, CTS

One of the great quandaries for a DJ is where to place their subs. Often there is no clear right answer as several factors must be considered. Often we must weigh aesthetics, architectural allowances, desired output and coverage and room acoustics. Acoustics and wave propagation can often confuse people, and maybe primarily because sound waves are invisible.

We’ll start very simple and make some of these things visible with the help of EV LAPS 3.37, which is an acoustic modeling program. It assumes a purely anechoic environment, that is to say that the room plays no role in the measurement. We are simply predicting the interaction between known speakers at given frequencies.

The stage size is 40 wide by 20 deep, and that is really just to illustrate spacing better. We are going to model 270 degrees of coverage from the downstage center point of the stage. We are measuring 3 frequencies represented by colored lines. 40Hz in blue, 60 Hz in red and 80 Hz in green

We are simply modeling the coverage in 2D from an overhead perspective to keep this very easy.

In our first example we can see two subwoofers (X12-128) placed on end, side by side. Immediately we note that there is nearly perfectly even coverage throughout the entire 270º we are measuring. We have complete summation between the subwoofers and they are acting as a single, very powerful unit. This configuration is best when possible due to the even coverage and complete summation.

In our second example we can see things change dramatically when we space the subwoofers 10 feet apart. 40Hz is still fairly even, but about 7dB down 90 degrees off stage left and right. 60Hz demonstrates some lobing with a power alley straight out from the subs with nulls about 45 degrees off the sides. 80Hz shows us three fairly even lobes with nulls between them. This means that as you walk in an arc around the speakers you would hear areas of loud, powerful bass, and others where it is reduced by as much as 24 dB, which is VERY substantial.

Our third example demonstrates the subs 20 feet apart and we see nulls and power alleys at all frequencies. Why do the frequencies react differently? Because sound travels in waves and the wavelength is determined by the frequency. A 40 Hz wave is approximately 28 feet long, 60 Hz is approximately 19 and 80 Hz is approximately 14. As the frequency increases, the wavelength decreases. Therefore the peaks and valleys of each wave will meet at different distances for different frequencies.

When we factor reflections from the room this can become very complex and that is more than we endeavor to cover in this article. The take-away here is that placement of multiple subwoofers has effects on the overall coverage. The desired coverage and output can then be weighed against the convenience of top-over-sub configuration and allowable placement.

Ben Stowe, CTS Ben Stowe, CTS (26 Posts)

Ben’s love of electronics and technology led to years of schooling in Electricity, Electronics, Robotics and Lasers. Ben supported himself through school by building and selling strobe lights and other electronic devices. He built his first DJ show largely from scratch and scrap, often repairing broken items others had thrown away because he could not afford to buy new equipment. He holds a Minnesota electrical license, and his AV installs have been featured in almost every major industry trade magazine. His relentless passion for education has led to a number of other certifications and accreditations, including the most widely recognized one in the AV industry, the InfoComm CTS. His love for education inspired him to begin the ProAcademy educational sessions, focused on increasing understanding of AV technologies within the industry. Ben has been involved in a number of technical writings, lectures, presentations, as well as research and development assistance with a number of manufacturers for products, industry wide. He is also a regular contributing author to industry magazines in the United States and Europe. Ben’s presentations have been featured across the world both as a part of industry leading trade shows, and as a presenter for various groups and functions. Some of these events include BPM in the United Kingdom, Mobile Beat, the ADJA National Convention, Wedding MBA, and a national tour as a headlining presenter for an industry magazine. The United States Armed Forces branches have also called upon Ben to provide engineering and training assistance. His highly informational, slightly nerdy and always funny presentation style have made him a favorite at events, while his sincere desire to help people with their application of technology have made him a favorite with them after the event. Ben serves the industry as the President of NLFX Professional, an industry leading supplier of sound, lighting and video systems, a role he has maintained since founding the company in 1993.

Filed Under: Sound Engineering for Mobile DJs