Room Acoustics 847carpeting adjacent corridors or offi ce fl oors can generally overcome the majority of such
problems. Wherever possible, corridors adjacent to studios should not be used at critical
times or their use should be strictly controlled. Main thoroughfares should not pass
through studio areas.
29.2.4 Sound Insulation
Having created a generally suitable environment for a studio, it is then up to the studio walls
themselves to provide the fi nal degree of insulation from the surrounding internal areas.
The degree of insulation required will very much depend on the following
- Uses of the studio, for example, music, speech, and drama.
- The internal noise level target, for example, NC20.
- Noise levels of the surrounding areas.
- The protection required to the surrounding area (e.g., in a pop music studio,
the insulation is just as much there to keep the noise in so that it will not affect
adjoining areas or studios as it is to stop noise getting into the studio itself).
Appropriate insulation or separation between the control room and studio is also
another very important aspect that must be considered here. The minimum value of
sound insulation required between control room and studio is probably about 55–60 dB.
Monitoring levels are generally considerably higher in studio control rooms than in the
home. For example, 85 dBA is quite typical for TV or radio sound monitoring, whereas
pop studio control rooms will operate in the high 90s and above.
Sound insulation can only be achieved with mass or with mass and separation. Sound-
absorbing materials are not sound insulators, although there is much folklore that would
have you believe otherwise. Table 29.2 sets out the fi gures, showing that only very high
values of sound absorption produce usable sound reductions.
To put the fi gures used in Table 29.2 in perspective, a single 4.5-in. (112-mm) brick wall
has a typical sound insulation value of 45 dB, and a typical domestic brick cavity wall
50–53 dB—and you know how much sound is transmitted between adjoining houses!
Furthermore, typical sound-absorbing materials have absorption coeffi cients in the region
of 0.7 to 0.9, which is equivalent to a noise reduction of only 5–10 dB.