When it comes to encouraging congregational singing, a room with a long RT60 is desirable. Loud and long reverberation helps people to not be self conscious, and to sing out loudly. However, when the congregation wants to understand the sermon, a room with a short RT-60 is desirable. The traditional problem with church acoustic projects is that you can’t have it both ways. It’s either a win-lose situation, too reverberant for speech or too dry for singing. And so, an effort is made to strike a compromise. The result is a lose-lose situation, where nobody’s happy.
We studied the situation to find a low cost, win-win solution and we found one. It has to do with the fact that the sound paths involved with speech are quite different from those involved in congregational singing. We discovered that we can quiet down the speech sound path while leaving the singing sound path untouched, bright and reverberant. It’s not an RT60 adjustment, it’s a signal-to-noise adjustment we call “voicing the room.”
Revoicing a church is a powerful process and the results are simply amazing. Church sanctuaries are big rooms where many different activities take turns taking place. The Minister needs a room that has high intelligibility. The music director needs a room that is reverberant to support congregational singing. The choir needs a small reverberant space around them to stay in tune and powerful. The praise band needs a very dry sounding space around them, like a recording studio. All these and possibly more have to coexist within the envelope of the sanctuary acoustics.
Our approach when voicing the church is performance oriented. The church wants to be bright yet clear sounding. This means we add as little acoustic material as possible and carefully position it so as to best control only the problem reflections.
In a large hall, there are 3 areas of problem reflections: Front to back; side to side; and floor to ceiling. In many cases, the floor to ceiling sound is already being treated by a carpeted floor and suspended ceiling, Tectum and batt, or other acoustic tile. However, the bare walls allow unchecked circulation side to side and front to back sounds. It is on these areas that our work comes to focus. We do not apply general purpose, mild mannered acoustics over all surfaces, but instead apply strong acoustics located in special areas that particularly relate to the sound emitted from the loudspeakers.
Our first concern is the rear wall. Here we apply a tight pattern of broad band acoustics blended with diffusion on the upper part of the wall. This acts to simultaneously absorb and side scatter sound reflections off the upper rear wall. Reflections off the lower rear wall of course are returned, listened to, and absorbed by the congregation. By this, we strongly reduce the return off the back wall of the church that doesn't speak to the congregation but does feed the buildup of the reverberant noise floor.
The next area of concern is the front side walls. Sound up through the middle octave of the piano keyboard expand away from the loudspeaker equally in all directions. The resulting side to side echo and multiple reflection problems must be treated. The back half of the side walls need no treatment because the sound from the speakers reflects off of them right into the absorptive rear wall. The lower half of the side walls need no absorption because the downward wave is driven into the floor and congregation. Only the upper front quarter of the side walls need treatment.
The congregation prefers this voicing of the room because the speakers no longer sound muddy, blurred and difficult to understand. The strength of confusing echoes as well as the buildup of the reverb field has been reduced. However, the room still sounds bright and lively because sounds from the congregation are reflected back to them, returned off the remaining bare sections of the walls.
The material we use for absorption is very efficient throughout the vocal sound range. After all, it is the sound of the voice that needs to be clearly transmitted from the speaker to the congregation. Our approach to sound control for churches is to reduce the strength of those early reflections that do not contribute directly to the understanding of speech from the loud speakers. In so doing, we reduce the built up strength of the reverb field but not so much its decay rate, RT-60.
Reverb time is the measure of how fast energy is removed from a room. We do increase the reverb rate because we have added absorption into the room.
However, our work is designed carefully to reduce the strength, the loudness of the reverb field, and incidentally, the rate of the reverb decay. This is the "signal-to-noise" approach to noise control and it is consistent with intelligibility requirements. As a result, we achieve clear sounding rooms that still retain their reverberant signature. Both the Pastor's need for intelligibility and the music director's need for a reverberant room can be satisfied at the same time in the same space.