Sound System Engineering: It’s Not Guesswork

Depending on your needs, a line-array loudspeaker system may suit your worship space best, but in some cases, so too could a point-source speaker system.

Sound System Engineering: It’s Not Guesswork
As part of the PA system at Lakewood Church in Houston are these JBL VTX Series speakers, a three-way high directivity line array system.

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Designing a sound system is a daunting task for many people, and understandably so. There are many decisions to make, and a lot of them require a good amount of experience to get right.

Most importantly, you can’t just guess at a design, because it “looks about right.” In fact, that phrase is jokingly referred to as the “LAR approach,” among design professionals. That’s because so many systems are installed without any sort of scientific approach or real expert experience.

The results of an “LAR” system, as you may guess, are usually pretty terrible.  So, when in doubt, get the help of an acoustical consultant or trusted design-build firm, i.e., an integrator.

One of the most fundamental considerations in modern design is whether or not to use a “line array” speaker system.

Line arrays, the often J-shaped vertical sets of loudspeakers you see at large venues, came about as a way to solve the problem of getting even coverage from the front all the way to the back of a deep room. The operating principle of line arrays is that the acoustic output from adjacent boxes couples together to provide more energy to a destination further away.

You may be thinking that you could also just turn up a conventional loudspeaker loud enough to get enough energy to the back. There are some problems, though, with that approach. First, it would take an absurdly loud product to reach the distances needed in concert production. Second, people in the front of the room would be practically knocked over.

So how does a line array do it so well?

The interaction of the array’s individual boxes actually causes less energy to go where it doesn’t belong (vertically, anyway). The more boxes you have, the better control you have of where the energy goes and where it doesn’t. This interaction I’m talking about is known as constructive and destructive interference. All that means is that the boxes sum together in front, where you want them to. In addition, the acoustic outputs from the various boxes actually nullify each other in the areas (vertically) where you don’t want their sonic contribution.

Why are line arrays so often shaped like a “J”? Remember that we want more energy directed toward the back of the room. That’s because we have a longer distance to get there. Getting toward the front of the room, we need less energy because the array is closer to the people. Therefore, we start angling the boxes more aggressively to reduce the level going to those seats.


More About Brad Duryea
Brad Duryea is an audio engineer based in Houston, Texas, where he is the director of audio technology for Lakewood Church. He can be reached at [email protected] or via Twitter: @bradduryea.
Get in Touch: [email protected]    More by Brad Duryea
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Article Topics

Technology · Audio · Acoustical · Configurations · Engineered · JBL · LAR approach · Line Arrays · All Topics

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Comments

By Russ Alexander on April 21, 2017

Preach On!!! I just removed a system from my church that was most defiantly put up by a company who did not think about the sciences involved in acoustics. Not only was it improperly installed but the incorrect type of system was deployed for the space. Needless to say they now have a nice new line array hanging.

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