How to choose your sound alarm
Selection assistance
Sound frequency is expressed in Hertz. An increase of 3 dB corresponds to a doubling of the sound power.
Law of sound propagation
The law of sound attenuation or gain as a function of distance is as follows: X dB at Y meters = (X – 6) dB at (2 x Y) meters.
So when the distance doubles, the sound power drops by 6 dB.
Ear filter
The ear acts as a filter. The sound power, after the ear filter, is expressed in dB(A). As shown in the table below, a sound, depending on its frequency, will be more or less reduced:
Frequency :
- Up to 500 Hz >> Reduction of: 0dB (A)
- from 500 to 1 K Hz >> – 3 dB (A)
- from 1 K to 2 K Hz >> – 5 dB (A)
- from 2 K to 4 K Hz >> – 9 dB (A)
French evacuation sound
The NFS 32001 standard requires a modulated sound between the frequencies of 440 and 554 Hz.