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Goal: To limit noise-related distractions and properly use absorption that works in conjunction with the sound system.
- Related Codes & Standards
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- Tips/Considerations
- Recommended reverberation time: 0.8-1.2 seconds.
- Background noise levels should be kept to a minimum. Three primary potential noise sources are mechanical equipment (HVAC), noise from adjacent theaters and lobby, and outdoor noise.
- HVAC noise, which is often overlooked, can negatively impact the usability of a space. To help protect your design, the NC level should not exceed 30 to 35. When specifying NC, specify an actual rating, such as NC 30, rather than a range, such as NC 30-35. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an NC level.
- Noise from the lobby area can be disruptive. Be sure openings such as doorways are properly sealed. Consider a vestibule door system.
- Excessive room length should be avoided.
- Beware of potential outdoor noise impacting your space. For example, is your location near a flight path, a railroad or freeway? If so, you might have to pay critical attention to blocking this noise. To do so effectively, you must address not only the STC or isolation quality of the exterior wall, but also for the possibly weaker building elements, such as the windows, doors and HVAC systems.
- A common, and often ineffective, practice is to use absorptive materials only on the back wall of a cinema. This is meant to reduce slap back; but slap back impacts the performers, which, in this case, are actors on a movie screen. Primary concern should be given to the audience. Although absorption on the back wall might be necessary, the critical areas are the side walls. Walls, except possibly those closest to the screen, should be absorptive.
- It is vital to control the noise transfer between theaters. Nobody wants to hear the booming of cannons from the movie next door during the pivotal love scene in the movie you paid to see. The STC rating should be at least 60-65, but keep in mind that STC ratings only address noise isolation from 125 Hz to 4000 Hz. This range is fine when considering speech frequencies, but gives no information for sounds that register at lower frequencies, such as the base notes of the music or explosion sound effects, which often register below 125 Hz. In such cases, be aware that the STC rating might not accurately describe how well that particular wall will work at that noise level.
- There are various certifications and programs (such as THX®) that have their own acoustic related criteria for cinemas (for example, NC level, STC rating and reverberation time).
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