Air_US_rev_111.qxd
ACOUSTICS - BACKGROUND INFO
Acoustics
When we talk about making a room "sound right", we are probably dealing with room acoustics as a science acoustics has been around for about hundred years. Until then good acoustics happened by experiment, by experience, or simply by accident.
Today we know a lot about the parameters that influence the "sound" of a room.
Talking about the control room we know that basically this room should act as neutral as possible. But this is not always the case. Lets just take a short look on some of the issues, than one must be aware of.
Good acoustics
Here is a list of important parameters concerning good acoustics.
•Proper reverberation time
•Good sound distribution
•Adequate sound pressure level
•Low background noise level
•No echo (flutter echo)
Now lets have a look on these headlines that will be adequate for the most purposes concerning sound production.
Reverberation time
The reverberation time is defined by the time it takes a sound to attenuate 60 dB after the source is stopped. In the real life we can experience reverb times from approximately 0 sec. (outdoors or in anechoic chambers) to something like
Control rooms normally should have a reverb time around 0.2 - 0.3 sec.
Why do we have reverberation? The speed of the propagating sound wave is very slow - at least compared to light: approx. 1130 ft. or 340 m per sec.
If there are no reflecting surfaces between the sound source and our ears, only the direct sound is heard and there is no reverberation.
If there is a single reflecting surface we may hear the reflected sound in one way or another, but there is still no reverberation.
If the sound is generated in a room, there are a whole lot of reflections. Each of these travels different paths with different distances on the way to the receiver. Each time the sound hits a surface it may loose some energy if the surface is absorbing.
•One sound source, one receiver and no room
•Only the direct sound is received.
•One sound source, one receiver, and one reflecting surface.
•The sound is received twice. (In the control room this is normally experienced as comb filtering, see later).
•One sound source and one receiver in a room.
•The sound impulse is reflected in many surfaces. All the reflections are melting together and heard as reverberation.
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