Sanctuary Acoustics FAQsAudio/Visual, TECHNOLOGY Monday, February 3rd, 2014
Just about every worship space has “acoustical culprits” — under-the-radar elements which rob this critical venue of its sound
clarity. We asked Nick Colleran, vice president of Acoustics First Corporation in Richmond, VA, to navigate some of them for us.
What kind of havoc can a particularly noisy HVAC system wreak on a worship space?
Nick Colleran: An intermittent HVAC system can be worse than a constant drone — not unlike a truck or a train rumbling by outside the church.
There are several ways to abate the noise, most of which are less costly to do during the initial construction. The lowest frequencies (bass) will travel through the structure to appear elsewhere in the building.
To prevent this, the machinery should be floated on vibration mounts to decouple from the structure. Ducts should have flexible joints to decouple them from the machinery, and they should be lined with sound-absorbing material. There should be several bends to prevent sound passing in a straight line, and ducts should be oversized — compared to “normal” — to slow the air and reduce noise.
How much of an effect can flooring and upholstery have on acoustical quality?
Colleran: Flooring can reduce or enhance (exacerbate) reverberation time, either improving or reducing speech intelligibility.
Thick carpet will absorb significant sound, while thin industrial carpet does little to reduce sound, except in the high-frequency range.
Hardwood bounces more sound around the room, and polished granite can make the room impossible for speech — although a traditional choir might sound more “heavenly.”
A reflective floor, combined with hard-surfaced walls (drywall, plaster, finished wood), isn’t a match made in heaven, except for the choir.
In some sanctuaries, speech is clear, but music is dull and lifeless. Is there an acoustical basis for this?
Colleran: Most often, reverberation time (RT60) — how long the sound “rings out” after its initial impact — is
The timing of the reverb can be estimated by popping a fully inflated balloon and clocking the pop’s duration until it’s no longer audible (60dB down). In general, a reverb time of .9 to 1.0 seconds is good for speech, allowing clarity without sounding “dry” or “dead” and making the speaker feel the need to shout.
At the other extreme, traditional music likes to hear a reverb time of 1.5 to 1.6 seconds in most traditional spaces. A compromise in between these numbers can usually work for all involved.
With modern music, there are examples of reverb times as low as .6 seconds being great for the pastor, while the high-energy praise and worship performers
are free to have their sound man “dial in” the echo, delays and reverberation appropriate to studio-produced music and vocals.
What structural elements affect acoustics most?
Colleran: Round or hexagonal structures focus sound.
Rooms that are wider than they are deep won’t allow the sound to develop, or to stretch out. Flat rear walls will cause sound to reflect back to the source (“slap back”), often out of time with the music, causing the audience to be annoyed and the musicians to be confused trying to find the beat. Flat, parallel surfaces will create flutter echoes which garble the spoken word and influence the room’s musical response. Flat ceilings and hard floors are another source of this problem. A vaulted ceiling might reflect, but it usually won’t cause flutter.
A sanctuary might have a flat, drop-tile ceiling in a lay-in grid. This is often seen in mall venues repurposed for worship. If it’s a reasonably high ceiling and the tiles are acoustical fiberglass, the sound can be very good and might not need more than some strategically placed wall panels to control the direct reflections. If a few tiles are replaced with an open grid (covered with a thin sheet of plastic to avoid debris passing through), the entire ceiling might be used as a bass trap, and thereby remove boom from the room for little cost.
Any other insights?
Colleran: As an overall rule, don’t take what’s seen on TV as the room you’re actually hearing. By that, I mean sound — particularly music — is often recorded elsewhere. If you observe closely, you can often see a performer singing into the wrong side of a microphone, and the horn section might be a synthesizer with actors dancing and holding real instruments on camera.
A second rule is that it’s always cheaper to fix the acoustics first, before going through a series of sound systems that can never overcome the physics of bad room geometry.
— Reporting by RaeAnn Slaybaugh