Acoustically treating an auditorium can be a tricky thing to do. The large open rooms are often far too reverberant though, so – in most cases – incorporating acoustical treatment into auditorium design is a must.
Achieving great auditorium acoustics is difficult because it requires there be a happy medium between sounding “alive” and sounding “dead”.
When live performances (bands, orchestras, plays, speeches, etc.) are involved, words and notes need to ring throughout the space. This ring increases sound quality and allows for the entire audience to hear better.
The problem is that there is a fine line between a pleasant ring and an echoic mess. If sound rings too much it quickly – and quite dramatically – reduces sound quality and the audience’s ability to hear clearly.
So … what’s the solution? How is one to find the happy place between absent and disruptive ….. alive and dead ……. pleasant and painful ….. ?
The answer is to use a combination of absorption and diffusion.
The absorption reduces the amount of noise in the room so there is less reverberation. Diffusion breaks up and disperses the sound waves that aren’t absorbed. This reduces slap-back echo (reverberation between two parallel walls) and allows for the leftover sound to reverberate without being disruptive.
A perfect example of this type of treatment is in Virginia’s Woodberry Forrest School (read full case study). We treated the back wall of the school’s auditorium with absorptive wall panels, which absorb sound after it has passed the audience once. This reduces the amount of secondary waves (waves that have bounced off of an object) the audience hears.
The diffusion in this auditorium is applied to the side walls to eliminate the slap-back echo between the two side walls. They don’t absorb any of the noise though, so the sound remains in the room and rings.
To hear how well sound diffusers work to reduce slap-back echo watch this video we made: Sound Diffusion in an Auditorium
So … while sometimes tricky, creating great auditorium acoustics isn’t impossible. Just remember that too much absorption will eliminate the ring which is necessary in performance halls. Next, control the leftover sound with diffusers and your auditorium will be sounding great in no time.