Weighting networks
Loudness of a sound (that is, the subjective response of the ear) varies with frequency as
well as with sound pressure and that the variation of loudness with frequency also depends
to some extent on the sound pressure. Sound-measuring instruments are designed to make
allowances for this behavior of the ear by the use of electronic “weighting” networks. The
various standards organizations recommend the use of three weighting networks, as well
as a linear (unweighted) network for use in sound level meters. The A-weighting circuit
was originally designed to approximate the response of the human ear at low sound
levels. Similarly, B and C networks were intended to approximate the response of the
ear at levels of 55-85 dB and above 85 dB, respectively. The characteristics of these
networks are shown in Figure 2.3. A fourth network, the D-weighting, has been proposed
specifically for aircraft noise measurements. However, it has not gained acceptance and
the trend appears to be towards the exclusive use of the A-weighting network. Figure
2.3 shows the correction which must be added to a linear reading to obtain the weighted
reading for a particular frequency. When even a weighting network proves desirable,
in industrial locations, the A-weighting network was taken to measure noise. Table 2.2
represents the A- weighting corrections for different frequency bands