Page 40 - Winter 2011

PROFESSIONAL STUDIOS:
HERE’S ANOTHER FINE MESS YOU HAVE GOT ME INTO
Marshall Long
Marshall Long Acoustics 13636 Riverside Drive Sherman Oaks, California 91423
Professional studios
Professional studio work is a subset
of architectural acoustics that
combines both art and science in
the design of working rooms for music
and film (video) production. These stu-
dios are not an end in themselves, nor even a place where the ultimate listener will hear music, but a step in the process of crafting an audio product. As such they may have design requirements that exceed those found in the ultimate listening environment, which may range from a living room, to a movie theater, or even to an automobile.
Sound studios are generally constructed as two or more rooms: (1) a studio where the music is performed, and (2) a control room where music is recorded and processed. In addition there can be ancillary rooms for voice over, sound effects (Foley), and isolation booths for individual or small groups of instruments. Where video or film is a component there are screens that may be incorporated into a studio (for film scoring) or a control room (for dubbing or editing).
Each of these specialized rooms has specific acoustical requirements (Long, 2006). A short summary list is given below;
1. Quiet-ontheorderofNC10to15.
2. Isolation from adjacent spaces.
3. Freedom from acoustical defects such as flutter.
4. Adequate absorption (often variable).
5. Reasonable diffusion.
6. Visual communication between the control room
and the studios.
7. Control of bass reverberation and modal buildup.
There may also be specific design requirements depend- ing on the work habits of an individual user or accommoda- tion of technical equipment.
In this article I would like to address a portion of the first two items on the list, i.e., quiet and noise isolation from adja- cent areas using three examples from real studio projects I have encountered. The most common noise problems are mechanical equipment, external factors such as transporta- tion related sources (including footfall), and adjacency to other theaters or sensitive receivers. In all these cases the noise control begins with vibration isolation of the noise source or the receiving room itself.
Vibration isolation
Vibration isolation is a phenomenon associated with a driven spring-mass system as shown in Fig. 1. At low driving frequencies the motion of the mass exactly follows the motion of the driver. As the driving frequency increases, the
“Needless to say, the atmosphere was highly charged.”
mass amplitude reaches a maximum, at the spring-mass resonant frequency. As the driving frequency increases further, the mass amplitude decreases sharply until it falls below the driving amplitude at a frequency above 1.4 times the driv-
ing frequency. This is the basis for the phenomenon known as vibration isolation.
The natural or resonant frequency of a simple spring- mass system can be written in terms of the static deflection of the vibration isolator under the weight of the supported object.
where δi is the deflection of the isolator in inches.
As the isolator deflection increases, the natural frequen- cy decreases, and the amount of isolation increases for a given excitation frequency. Isolator deflection can be con- trolled by; (1) using softer isolators (e.g. springs rather than neoprene) and (2) increasing the load on each isolator (by
using a heavier mass or fewer isolators).
Figure 1 also shows the effect of damping on the amount
of isolation. Damping has its greatest influence around reso- nance and is most useful in limiting excursion in this region. Damping actually decreases the amount if vibration isolation which can be achieved. The figure also shows two driving point locations, one directly on the supported mass and the second on the support structure. In the case of studio floors
Fig. 1. Transmissibility curves for vibration isolation (Ruzicka, 1971).
36 Acoustics Today, January 2011