Frequency Sensitivity and Equal Loudness Characteristics

The ear is most sensitive in the range of frequencies between 500 and 4000 Hz, less sensitive at higher frequencies and much less sensitive at low frequencies. This range of greatest sensitivity coincides with the range for voice communication.

Through listening tests, this variation in sensitivity has been evaluated. The curves in Figure 6.4.1 present these data. These curves are commonly called equal loudness curves, but equal sensation curves describes them more accurately. They describe several of the ear's characteristics. The lowest curve represents the threshold of hearing for the healthy young ear. The dotted portions of the curves (not a part of the ISO recommendation from which these data come) indicate the change in hearing which occurs with increasing age; they show not noise-induced presby-cusis but sociocusis. These dotted curves describe a loss in hearing acuity within the intelligibility range of frequencies.

The curves also show that as the amount of energy increases, the difference in sensitivity almost disappears. The thresholds of discomfort and pain (not part of this figure) actually fall quite close to the 120 and 140 dB levels respectively.

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