Think of Acoustics First, Not Last
By: Nick Colleran
Before presenting the new sanctuary design to the committee or congregation, determine that what you hear will be as good as what you see. Making a decision with only the eyes can hurt the ears (and attendance). Once the audience falls in love with a design, there is a higher hurdle to corrective changes. Doing it over is both costly and stressful.
The sound system cannot fight the room. The room is “alive.” Acoustics may be passive electronically, but an untreated, poorly shaped room is active acoustically. The distance between walls determines what frequencies will be emphasized and which will be cancelled. Complete cancellation will occur when a wall is one-half wavelength away from its source. The reflected peak, or forward motion (push) of the sound wave, travels back from the wall and meets the incoming trough (pull) of the cycle and sums to zero.
Boosting the “missing” sound’s frequency electronically with an equalizer will simultaneously boost its reflected out-of-phase component, retaining a net sum of zero. Hence, it is a zero sum game. Absorption, diffusion, and trapping can remove or redirect sound to overcome the basic room geometry and dimensions.
Why Trap Bass?
In a sealed room, with no acoustical treatment, bass may be inaudible due to internal wave cancellations, but, if the walls and windows are acoustically thin, the lows will travel throughout the neighborhood. This combination of the effects of physics will exacerbate the problem as the sound man compensates for what is heard (or not heard) inside the room, while being unaware of the sound outside.
For Bass: Size and Shape Matter
Now You Hear It
(As a side note, excessive automotive bass has a common contributing cause. The sealed passenger chamber reduces audible bass inside the vehicle, while the thin car walls and windows allow the neighbors to feel the experience.)
One Size Does Not Fit All
While a proper acoustical environment can reduce the need for extra sound equipment, or several replacements to get the system right, knowing the intended use of the room can similarly reduce the need for acoustical materials to be purchased more than once. As with sound gear, adding enhancements is more rewarding than fixing a bad initial solution.
To prevent sound from traveling through walls requires two components: heavy sound blocking mass and light sound absorbing porous materials. Absorption won’t stop sound penetration but inside a wall, but fiberglass insulation will trap the air to prevent the cavity from behaving like a drum, with one wall vibrating when sound hits the other side.
Any commercial building insulation will provide the necessary sound absorption. Multiple drywall layers can supply the necessary mass. For retrofits, a layer of mass loaded vinyl (one-eight-inch thickness) and a layer of acoustical wall covering (one-quarter-inch thickness) will usually solve the problem. The elimination of sound (as vibration) traveling throughout the building can be accomplished with isolation pads.
One of the lowest cost methods is to float the praise band’s stage. This is something to do during construction and, for dollars spent, has a high return in both room-to-room isolation and lower on-stage feedback. A stage floated in several sections will keep the bass from traveling up the stand to the singer’s microphone, as well as prevent the entire band’s performance from rocking the nursery.
Dealing with acoustics first, including defining the intended performance in the space, will cost less and allow the sound system to perform “as advertised.” If systems are up and running but underperforming, it is usually not the equipment, unless the system is improperly designed.
Today, there is very little bad equipment. Unfortunately, there are many bad rooms, especially if “bad” is defined as those not meant for their intended current purpose. If you get the room right, the sound system may heal itself.
Nick Colleran is past president of SPARS (Society of Professional Audio Recording Services), past president of the VPSA (Virginia Productions Services Association), a former recording artist, and recording engineer. He is a principal of Acoustics First Corporation, which designs, manufactures, and distributes products to control sound and eliminate noise for commercial, residential, and industrial uses, www.acousticsfirst.com.