SMPTE RP 141-1995

This practice provides measurement methods and recommended maximum levels for indoor background sound pressure levels in theaters and review rooms. The practice is limited to the noise of heating, ventilating, and air conditioning systems, intrusive noise from the projectors associated with the theater, and noise from any other mechanical or electrical equipment in the theater building. The practice is intended for application when the background noise is essentially a solid-state sound, without strong time-varying components.
The practice does not cover intrusive noise from other sources outside the theater, such as airplanes, highway traffic, adjacent theaters, or the like.
The practice does not cover noise resulting from the operation of the sound system in the theater.
The practice does not cover vibration of the theater; i.e., movement of the building below 20 Hz.