By Nick Colleran
The cancellation or reinforcement in various sound frequency ranges is a function of the distance from the sound source to the room walls. If sound hits a wall halfway through its cycle, the positive peak of the wave reflects back and combines with the negative “trough” of the wave and cancels to zero. This is an acoustical “zero sum” game.
Similarly, if the wall first encountered is a full wavelength from the source, the reflected wave will combine with the next and boost the sound in that range. Variations in these extremes will partially combine or cancel to influence what the listener hears — some good, but generally bad. A cut-only equalizer can help reduce the excess reinforcement, but early on manufacturers realized that the room would effectively devour any attempts to boost absent frequencies.
All this said, once the room is treated and tamed not to fight back, the investment in quality sound equipment can reach its full potential. Considering the acoustics first allows everything to work at its best.
First, the question of what makes up the performance should be addressed. While everyone might sound great singing in a tiled shower, most folks won’t sing out in an acoustically dead, or “dry,” room without reverberation. There’s no echo to disguise individual voices and average pitch by blending.
The ideal room will achieve clarity by reducing the excess reverberation with acoustical absorption. The common choice is fabric-covered wall panels. The calculation of necessary material is computed without the need for a computer, using century-old arithmetic: the Sabine equation. First, the room’s existing sound absorption is calculated; then, its desired absorption. The difference is what must be added.
Preserving the room’s life for singing or music while clearly understanding the minister’s message can be achieved with diffusion. Much like peanut butter — easier to swallow when spread over bread — diffusion removes the acoustical “lumps,” preserving sound but making it easier to digest. For a demo, visit.
Nick Colleran is a principal at Acoustics First Corporation in Richmond, VA. He is past president of Society of Professional Audio Recording Services (SPARS) and of the Virginia Productions Services Association (VPSA), and a former recording artist and recording engineer.