Page 12 - 2013 Spring

Fig. 4 Reverberation times for studos in the 500–1000 Hz. range (Doelle, 1972)
Fig. 5 Found space bass traps
layers of 5/8” drywall hung from springs to provide noise isolation through the ceiling- roof. Bass traps are built into the space above the equip- ment closet and into the video monitor enclosure. Windows are arranged so that there is visual contact between the control room and any point in the stu- dio, including the isolation booths.
Sound stages
Sound stages are large open rooms used for indoor movie production. Acoustically they are designed to be dead with all surfaces except the floors covered with 4 to 6 inch (100 to 150 mm) deep blankets of absorptive mate- rial. In the early 1950s many were built using recycled army mattresses hung on the walls. The floors are smooth and flat so that cameras can be dollied. The exposed wall surfaces can be faced with commercial quilted blankets covered with hardware cloth below an elevation of about 10 ft (3 m). The best rooms are built with isolated construction, floated floors, double-studded walls, and sepa- rately suspended drywall ceilings. Access is provided via sound rated doors, which can be quite large. Some facilities have control rooms adjacent to the stage for mixing and recording. Not infrequently, audio recording is done using directional microphones that transmit signals to wireless receivers located in racks in the same room but often 75-100 ft (23-30 m) away.
The most difficult aspect of sound stage design is noise control. Isolation from exterior noise is a challenge because many stages are built in con- verted warehouses with lightweight roofs and little thought to the isolation of traffic and aircraft noise. Large air conditioning units are required to cool the stage lighting fixtures and this equipment is often located on the roof, where it is difficult to control. It is preferable to separately support air handlers on grade or on an elevated steel platform dedicated to that pur- pose. Ductwork should be isolated from the structural framework either by resilient suspension or by a separate support system. Silencers located at a roof or wall penetration provide exteri- or as well as equipment noise control.
Scoring stages
Scoring stages are rooms in which the music for a film is recorded. The orchestra conductor, who is often the composer, faces both the musicians and a large screen on which the film is projected. As he conducts, he may lis- ten through a single headphone to a click track, which aids in synchro- nization of the film and the score. Visual cues are also projected onto the screen in the form of streamers that progress from left to right across the screen to mark the beginning of a transition or effect when they reach the right-hand side.
A scoring stage is large, almost the size of a concert hall. Like concert halls, the best ones are shoebox- shaped with high ceilings and irregu- larly shaped diffusers on the walls and ceiling. A very good one, Studio 1 at Abbey Road Studios in London, is shown in Fig. 6. Its dimensions are 92.6ft×59.7ft×39.4fthigh(28.2m × 16.1 m × 12.2 m) and its total vol- ume of 218,000 cu ft (6172 cu m) is about one-third that of Boston Symphony Hall. At one end there is a large (44 ft or 13.4 m wide) projection screen with the control room in an opposite corner.
Acoustics of Recording Studios 11