Fletcher-Munson curve

The Fletcher-Munson curves, now more accurately referred to as equal-loudness contours, illustrate how the human ear perceives loudness at different frequencies. These curves, developed by Harvey Fletcher and W.A. Munson, show that our hearing sensitivity varies with frequency.1

Key points include:
* The ear is most sensitive to frequencies around 1,000 to 4,000 hertz.2
* At lower and higher frequencies, a sound must be more intense to be perceived at the same loudness.21
* The threshold of hearing is lowest around 4,000 hertz, partly due to the resonance of the ear canal.1
* The curves are based on subjective judgments and are defined by loudness levels in phons, which relate to sound intensity in decibels at 1,000 hertz.1
* The threshold of pain is also indicated on these diagrams.1

The ear functions as a spectrum analyzer, converting sound waves into electrical impulses that represent sound intensity as a function of frequency. This nonlinear response is necessary to perceive both very quiet and very loud sounds.31