How do they design rooms with particular acoustics?



How do they design rooms with particular acoustics?

In: Engineering

I’m planning to do grad school for this in a few years, but the info I’ve been able to gather is that it’s a lot of trig. Because, y’know, waves.

Think about it like a pool table.

Soundwaves move, and when they hit a wall, they bounce off of that wall. And depending on what that wall is made out of, it affects the sound. Different materials do different things to that sound. So, a hard service like concrete will bounce a lot of the sound back, and soft material like foam will absorb a lot of that sound. The harder the material, the louder the sound will be when it bounces off of it. Just like with a pool table, if the sides were made out of hard material, the balls will bounce off of them harder than if they were made out of soft material. Note: different material also can affect other things about the sound, some making low pitched sound stronger, others making high pitched sound stronger, but I can’t explain that well.

Also, like a pool table, the angle of the walls affect how the sound bounces back. Depending on where you want the cue ball to go will determine what angle you bounce it off the wall. It’s the same with sound. In pool, you don’t really want a whole bunch of balls blocking a pocket, and in sound, you don’t really want a whole bunch of sound bouncing back into one particular spot.

If this is a concern at the design phase, there is software that could simulate acoustic behaviour. In the past, I imagine this was done with passed-down knowledge that was the result of trial and error, built over time to become trade knowledge.

If a room has already been built, the acoustic profile can be modified by using specific materials to absorb (much more often than reflect) (certain) sounds, in specific parts of the room.

If the room is going to be used for a concert or performance and have speakers, etc., one of the first things the audio engineer will do once the equipment is set up is to play some pink noise (kinda like white noise but more useful) and walk through the space with a frequency analyzer to figure out which frequencies are naturally amplified or reduced by the physics of the room, and this will be used to set up an initial EQ for the sound profile that will be tweaked as instruments etc. start making noise.

I was a small part of this process when Memphis, TN built the Cannon Center, which is a hall built for symphony and other concerts and has outstanding acoustics. The room was designed with acoustics in mind, but I was part of an ensemble that rehearsed in there for a few hours while technicians put up various sound absorbing / reflecting panels and moved them into the right positions. As for the specifics, I’m not sure, but I can tell you that hall is great for both the audience and the performers.

I also know that fine acoustic spaces avoid flat walls parallel to each other (or put baffles on said walls to stop echoes) because sound in that kind of environment will bounce back and forth, creating a very audible fast echo.