Home Engineering Building Acoustics
Projection, Sound, and Lighting Booths
In the olden days, a theatre would feature a projection booth. Should there still be one in your project, cf. Section 220.127.116.11.
The lighting booth is used to control all the lighting fixtures of the theatre. There usually is some purring noise from the fans of the equipment. More to the point, as the booth might be operated open to the theatre, it is necessary to apply an absorptive treatment in this booth.
The sound booth is usually located next to it. Usually, the sound engineer will want to hear the natural sound of the theatre, so during operation it will often be opened to the theatre. An absorptive treatment will be needed in this booth to prevent the undue emission of noise from the cooling fans of the equipment (there definitely is some, though most of the amplifiers will usually be housed in a cooled soundproof enclosure, which may even be located farther away in the basement).
There are quite a few trends with theatres. A theatre may be fan shaped or horseshoe shaped, and depending on the size, it may feature balconies. Most of the time the back wall is absorptively treated in order to prevent an echo; if it is not, then it will probably be diffusive. Next, the lateral walls are absorptively treated too (for good intelligibility, one avoids lateral reflections). The proscenium walls are often reflective.
A usual rule of thumb is to make sure that the volume does not exceed 4000 m3, with a maximum seating capacity between 800 and 1000, while limiting the volume per seat to 6 m3 .
The ceiling usually is reflective (e.g., plaster). Ideally, the shape of the ceiling is designed so as to help propagate the sound energy to the middle and the rear of the theatre. However, that shape often depends on the architectural wishes, as there will normally be a lighting bridge over the front of the stage that the architect may want to hide.
Seats are of the normal performance hall type. This means that the variation of acoustic absorption between the occupied or nonoccupied situation is no greater than 15%. The floor covering often is carpet.
In order to avoid a grazing incidence on the audience, which would be damageable for direct sound, an 8 cm clearance is required between rows. This usually is increased to 12 cm for visual purposes .
The walls of the theatre can be made of thick (at least 30 cm) reinforced concrete, but they can also be made of thick (at least 45 cm) plasterboard partitions. In both cases, access and exit are performed through air locks, for both acoustic and lighting purposes.
Balconies of a theatre should feature a height that is at least equal to its depth  or even greater than two times its depth .
Do beware of operators stating that they will never use amplified music! This is quite usual nowadays, and the sound insulation of the premises must be designed accordingly.
The stage tower usually houses quite a lot of machinery. It usually is absorptively treated (but nevertheless, remember that the reverberation time target is 1.5 s), bearing in mind that this treatment must be shock resistant to bear with the frequent handling of back scenes. Due to the amount of fire hazard material in this space, there usually are a few smoke exhaust trapdoors. They must be acoustically designed both to prevent the intrusion of external noise inside the stage tower and to prevent the radiation of noise from the show in the environment. A 45 dB trapdoor clearly is a minimum.
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