Sound
Level Meters
General Information
Sound
level meters are frequently used in industry today. Applications vary from
doing environmental noise level surveys in the field and laboratories, to
quality control inspections of parts on finished products. One company
uses a Sper Scientific sound meter to measure the noise in the bearing of
a motor. If the dB or decibel level is too high, the bearing is rejected.
Sound
level meters measure sound pressure (waves) by taking sound in through a
microphone and processing it with a filter. This filter gives a
"weighting" to the frequencies which make up the sound. The
weightings normally found on sound survey meters are "A" and
"C." The "A" weighting is used by most regulatory
agencies as the standard filter through which all the frequencies that can
make up sound are filtered. The "weighted" intensity of the
sound is then expressed in decibels (dB) by the meter. For the frequency
weightings for the "A" and "C" filters on Sper
Scientific sound meters, see the chart below:
Nominal
Frequency
HZ |
A
Weighting
dB |
C
Weighting
dB |
| 10 |
-70.4 |
-14.3 |
| 12.5 |
-63.4 |
-11.2 |
| 16 |
-56.7 |
-8.5 |
| 20 |
-50.5 |
-6.2 |
| 25 |
-44.7 |
-4.4 |
| 31.5 |
-39.4 |
-3.0 |
| 40 |
-34.6 |
-2.0 |
| 50 |
-30.2 |
-1.3 |
| 63 |
-26.2 |
-0.8 |
| 80 |
-22.5 |
-0.5 |
| 100 |
-19.1 |
-0.3 |
| 125 |
-16.1 |
-0.2 |
| 160 |
-13.4 |
-0.1 |
| 200 |
-10.9 |
0 |
| 250 |
-8.6 |
0 |
| 315 |
-6.6 |
0 |
| 400 |
-4.8 |
0 |
| 500 |
-3.2 |
0 |
| 630 |
-1.9 |
0 |
| 800 |
-0.8 |
0 |
| 1000 |
-0 |
0 |
| 1250 |
+0.6 |
0 |
| 1600 |
+1.0 |
-0.1 |
| 2000 |
+1.2 |
-0.2 |
| 2500 |
+1.3 |
-0.3 |
| 3150 |
+1.2 |
-0.5 |
| 4000 |
+1.0 |
-0.8 |
| 5000 |
+0.5 |
-1.3 |
| 6300 |
-0.1 |
-2.0 |
| 8000 |
-1.1 |
-3.0 |
| 10000 |
-2.5 |
-4.4 |
| 12500 |
-4.3 |
-6.2 |
| 16000 |
-6.6 |
-8.5 |
| 20000 |
-9.3 |
-11.2 |
