An ambient noise sensing system is a system designed to monitor continuously the changing ambient noise levels to electronically adjust the audio level of a sound reinforcement or system. The ambient noise is monitored with a sensing microphone (usually an elecret mic). This microphone must be placed properly to catch a good average sound level of all ambient noises in the room or the area. It should not be positioned too close to indvidual noise or sound sources. With the properly set system page announcements and music are clearly audible even during periods of high noise levels but are not too loud during quiet periods. Several sensing microphones can be used to get an average ambient noise signal of any larger area.
The main unit ot an ambient sensing system normally includes controls for activity threshold, maximum level boost, maximum level attenuation, attack time and ramp speed during level changes, ambient mic input threshold.
With an ambient noise sensing system the minimum signal to noise ratio for sound reinforcement / paging / voice alarm can be assured. This ratio is usually 10 to 15 dBA (speech signal is 10 to 15 dBA higher than the ambience noise signal).
|ambient noise sensing with more than one measurement microphone|
Attack times are usually 0,2 to 30 seconds per changed dB of the output speech signal. The decay time is the slope of gain decrease after the (measured) ambience noise is decreased. The usual range is also 0,2 to 30 seconds per dB.