Page 64 - The Master Handbook Of Acoustics

39
SOUND LEVELS AND THE DECIBEL

1/2
f 2 = (2,500) (2 )
f 2 = (2,500) (1.4142)
f 2 = 3,535.5 Hz

Measuring Sound-Pressure Level

A sound level meter is designed to give readings of sound-pressure
level; sound pressure in decibels referred to the standard reference
level, 20 µPa. Sound level meters usually offer a selection of weighting
networks designated A, B, and C having frequency responses shown in
Fig. 2-3. Network selection is based on the general level of sounds to
be measured (background noise? jet engines?), such as:

• For sound-pressure levels of 20–55 dB...use network A.
• For sound-pressure levels of 55–85 dB...use network B.
• For sound-pressure levels of 85–140 dB...use network C.
These network response shapes are designed to bring the sound level
meter readings into closer conformance to the relative loudness of
sounds.

10

0 C
Relative response - dB 10 B A

20

30

40
20 100 1 kHz 10 kHz

Frequency - Hz
FIGURE 2-3

A, B, and C weighting response characteristics for sound level meters. (ANSI S1 .4-1971.)