Dynaudio AIR 6 - Introduction

Appendix: Acoustics
Dynaudio Professional AIR reference manual – 2014-09-28 107
Introduction
When we talk about making a room “sound right”, we
are usually dealing with room acoustics. As a science,
acoustics has been around for about a hundred years.
Until then, good acoustics happened by experiment, by
experience, or simply by accident. Today, we know a lot
more about the parameters that inuence the “sound”
of a room.
A control room should basically act as neutral as possi-
ble. But this is not always the case. Let’s take a look on
some of the issues that we need to 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 (utter) echo
Now let us go through these issues one by one.
Reverberation time
The reverberation time is dened as the time un-
til a sound is attenuated by 60 dB after the source is
stopped.
In real life, we can experience reverb times from ap-
proximately 0 seconds (outdoors or in anechoic cham-
bers) to around 10 to 12 seconds. In special reverb
chambers, the time may exceed 20 seconds.
Control rooms should normally have a reverb time
around 0.2 to 0.3 seconds.
Why do we have reverberation?
The speed of the propagating sound wave is very slow
– at least compared to light, which travels at approxi-
mately 1130 feet or 340 meters per second.
If there are no reecting surfaces between the sound
source and our ears, only the direct sound is heard, and
there is no reverberation.
If there is a single reecting surface, we may hear the
reected sound in one way or another – but there is still
no reverberation.
If the sound is generated in a typical room, there are
many reections. Each of these reections travels dif-
ferent paths, with varying distances to the listener. Each
time the sound hits an (absorbing) surface, it will lose
some energy.
Fig. 57: One sound source, one receiver and no room.
Only the direct sound is received.
Fig. 58: One sound source, one receiver, and one
reecting surface. The sound is received twice. In the
control room, this is normally experienced as comb
ltering – see later.
Fig. 59: One sound source and one receiver in a
typical room. The sound impulse is reected on
many surfaces. The reections are perceived as
reverberation.