SiE33-003
Appendix
General Information
93
7.1.2
Faint Noises and Correcting Operating Noise with Respect to Faint Noises
Faint noises are defined as peripheral sounds existing while the unit is not running, which are picked up
when measuring operating noise. If these faint noises are 10 dB or more than the noise produced by the
unit, the measured value can be taken as the operating noise of the unit. But, the difference must be
corrected if less than 10 dB, because of the effect these noises have on the actual measured value. Also,
when the sound meter remains unchanged even while the unit is stopped, we can determine the
operational noise to be at least 10 dB less than the faint noises, but we cannot pinpoint the operating noise
exactly.
For example, if the faint noises are some 65 dB and the noise produced by the unit in operation is 70 dB,
the indicated difference comes to 5 dB. Using Table 3, we recommend you correct the operating noise by
about 2 dB to 68 dB.
7.1.3
Calculating Operating Noise
When two or more units are running at the same time, the amount of operating noise they produce rises.
The total amount of noise produced can be obtained ahead of time with Chart 4.
Sample calculation 1
L
1
and L
2
are given as compounded sounds of 50 and 49 dB respectively. Since L
1
– L
2
= 50 – 49 = 1, the
corrective value is 2.5, therefore 50 + 2.5 = 52.5 dB.
Sample calculation 2
When sounds of 40 dB, 38 dB, 37 dB and 40 dB are placed in order of magnitude, we obtain the following:
40 dB, 40 dB, 38 dB, 37 dB
To start, the difference between 40 dB and 40 dB is 0, therefore we take a corrective value of 3dB and
obtain 40 + 3 = 43 dB. The compounded sound of 43 dB and 38 dB has a 5.0 dB difference, thus a
corrective value of 1.2 dB, which gives us 44.2 dB from 43 + 1.2. In the same manner, the corrective value
for 44.2 dB and 37 dB is approximately 0.7 dB, or in other words, 44.2 + 0.7 = 44.9 dB.
Table 3 Correcting the effect of faint noises
Unit: dB
Difference between when noise
is produced and when not
1
2
3
4
5
6
7
8
9
10
Corrective Value
–6.9
–4.4
–3.0
–2.3
–1.7
–1.25
–0.95
–0.75
–0.60
–0.45
Si33-003.book Page 93 Monday, June 25, 2001 9:06 AM
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