Wye Cables….Why not?

July 26, 2017 by Ben Stowe, CTS

A DJ recently posed the following question on an industry chat board, “If it’s such a bad idea why do so many Djs do it?” I think the simplest answer to the question would be that there are a lot of things people don’t understand, and in the absence of good information they do things that shouldn’t be done. This isn’t exclusive to DJs, not even by a long shot. If it were, we wouldn’t have the Darwin Awards or those great shows on TruTV documenting poor decision making at it’s finest.

 

The topic that prompted him to post that question was whether or not you could/should sum the outputs of a mixer using a wye cable so that Left and Right would now be a summed Mono. While it’s a really bad idea, I’m not sure it rates up there with trying to break into a building and getting stuck in an air vent as far as entertainment value goes. I guess the producers of those TV shows are looking for something a little more exciting than potentially damaging some sound equipment.

There are lots of reasons we might want to sum stereo outputs into mono. Often subwoofers are used in a mono configuration, for lots of good reasons. Also, many DJs offer remote, satellite speakers for multi-room applications. With a single speaker in a remote room we don’t want to lose half of our musical information or have stereo imaging. We just want the sound, all of it, in there.

One might think we can just take a wye cable (2 in to 1 out) and sum the signal. Not so. Wye? (excuse me) Why, you ask? It’s a question of impedance. The outputs on our audio devices have a low impedance, typically 100 to 600 Ohms, where inputs have a much higher impedance, typically 10,000 to 20,000 Ohms. Low always drives high. As a sidebar, when we parallel inputs we decrease the impedance, just as when we parallel speakers. This is ok to do with a wye cable when splitting a single output into more than one input, as long as we keep a ratio of at least 10:1. For example, if we drive a 100 Ohm output into a 10,000 Ohm input we have a ratio of 100:1. If we drove that same 100 Ohm output into a parallel of 10,000 Ohm inputs we have a ratio of 50:1, and so on. The reason this doesn’t work in reverse is that we have two low impedance outputs that will try to drive each other. They will still drive the high impedance input, but with potentially significant loss, and potentially serious damage to each of the outputs.

Ben Stowe, CTS Ben Stowe, CTS (18 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