2.5 Equal loudness counter and weighting networks
2.5.1 Equal loudness counter
The ear is less sensitive to low frequencies than to high frequencies. For example, a
20-Hz tone at 70 dB sounds as loud as a 1000 Hz tone at 40 dB. Equal loudness contours
(Figure 2.2) show that as sound levels increase, the ear becomes more uniformly sensitive
to all frequencies. In general, an equal-loudness contour is a measure of sound pressure
(dB SPL), over the frequency spectrum, for which a listener perceives a constant loudness
when presented with pure steady tones. The unit of measurement for loudness levels is the