A curve plotted as a function of frequency defining the sound pressure level required to give equal loudness is?

equal loudness curve

Explanation:

The curves of equal loudness, first established by Munson and Fletcher in 1930 and subsequently recalculated by Robinson and Dadson, show the relationship that must exist between the frequencies and intensities (or sound pressure) of two sine sounds to be perceived equally loudly., that is, with the same loudness.

The sinusoidal sounds contained along each curve have the same loudness. This frequency dependence would be mainly due to the transfer characteristics of the external and middle ear. It should also be noted that as the sound pressure level increases, the curves become flatter, that is, the frequency dependence is smaller as the sound pressure level increases.

The loudness level of any sound (complex) is determined by comparing its loudness with that of a sinusoidal sound.