Page 82 - Master Handbook of Acoustics

FIGURE 4-10 Bandwidth affects the loudness of sounds. (A) Three noises of different bandwidths,
but all having the same sound-pressure level of 60 dB. (B) The subjective loudness of the 100- and
160-Hz noise is the same, but the 200-Hz band sounds louder because it exceeds the 160-Hz critical
bandwidth of the ear at 1 kHz.

The reason is that 160 Hz is the width of the ear’s critical band at 1 kHz. This is demonstrated by
the fact that if a 1-kHz tone is presented to a listener along with random noise, only the noise in a
band 160-Hz wide is effective in masking the tone. In other words, the ear acts like an analyzer

composed of a set of bandpass filters stretching throughout the audible spectrum. This filter set is not
like that found in an electronics laboratory. The common 1/3-octave filter set may have 28 adjacent
filters fixed and overlapping at the −3 dB points. The ear’s critical band filters are continuous; no
matter what frequency we choose, there is a critical band centered on that frequency.

Research shows how the width of the critical bands varies with frequency. This bandwidth
function is shown in Fig. 4-11. In particular, critical bands become much wider at higher frequencies.
There are other methods for measuring critical bandwidth; they provide different estimates
particularly below 500 Hz. For example, the equivalent rectangular bandwidth (ERB) (that applies to
young listeners at moderate sound levels) is based on mathematical methods. The ERB offers the