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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 10-12 sec. In special reverb chambers the
time may exceed 20 sec.
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.