Integrating Sound Level Meter / EN
39
08/15/16 Version No. 01
20. APPENDIX C INFLUENCE OF BACKGROUND NOISE
When measuring a certain sound in a certain location, all other sounds present at that
location except the measurement target sound are background noise (also called
ambient noise or dark noise). Since the sound level meter will display the combination
of target sound and background noise, the amount of background noise must be taken
into consideration when determining the level of the target sound.
If the difference between the instrument reading in absence of the target sound and the
reading with the target sound is more than 10dB, the influence of background noise is
small and may be disregarded. If the difference is less than 10dB, the values shown in the
table below may be used for compensation, to estimate the level of the target sound.
Background noise compensation
Display reading difference with
and without target sound (dB)
4
5
6
7
8
9
Compensation value (dB)
-2
-1
If for example the measured sound level when operating a machine is 70dB, and the
background noise level when the machine is not operating is 63dB, the compensation
value for the difference of 7dB is -1dB. Therefore the sound level of the machine can be
taken to be 70dB + (-1dB) = 69dB.
The above principle for compensating the influence of the background noise assumes
that both the background noise and the target sound are approximately constant. If the
background noise fluctuates, or contains very different spectral content and especially
if it is close in level to the target sound, compensation is difficult and will often be
meaningless.
