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Come back to decree 98-1143 about sound limitation and allowed measured levels.
It is clearly written that 105dB (A) is an average level computed by integration during 10 to 15 mn. The (A) refers to the analysis
bandwidth, called weighting. A weighting is close to the human ear.
The average level measurement with a sono meter is a LAeq measure : "L" for level, " A" for A weighting, " eq" for equivalent. This is
similar to the mean level of a varying signal, that will have the same energy than a fix signal at this level.
If you use a usual sound processor, like in FM broadcasting, on one side you will suddenly plane the level over 105dB loosing
dynamics, and on the other side you will get a very loud sound without clarity.
SNA 50-2 design is intend to respect the decree, without disturbing the audio signal.
SNA50-2 features a sound regulator,integrating smoothly the peak levels, according a soft curve, with settable rising and falling.
Proper installation, to get maximum efficiency, absolutely requires a sono emter with LAeq during 10 to 15mn. Once again it is
possible to visualize instantaneous level over 105 dB.
The following figure shows the acoustic pressure evolution with and without SNA 50-2.
A Without process the average level is around 115dB with peaks at 130 dB.
B With process SNA50-2 move everything with a105dB average level, without change on the curve shape. Dynamics is not
corrupted.
C In case of noise harm, this curve demonstrate that SNA 50-2 according to its settings, is able to keep the level under 105 dB.
Pressure
( dB
SPL )
130
110
105
100
90
80
AMIX
ANNEX 4 : SNA AND DECREE 98-1143
A
WITHOUT PROCESS
WITH PROCESS
(
average level 105 dB
- SNA50-2 EFFECT -
B
C
WITH PROCESS
)
(
average level
46
Time
90 dB)
SNA 50-2
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