Equal-loudness contour

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 phon, and is arrived at by reference to equal-loudness contours. By definition, two sine waves of differing frequencies are said to have equal-loudness level measured in phons if they are perceived as equally loud by the average young person without significant hearing impairment.

Etymology

The term "equal-loudness contour" is derived from the concept of equal perceived loudness across different frequencies. The term "phon" is derived from the Greek word for sound or voice, "phone".

History

Equal-loudness contours were first measured by Fletcher and Munson at Bell Labs in 1933 using headphones, and the data they collected are called Fletcher-Munson curves. Robinson and Dadson refined the process in 1956 to obtain a new set of curves, in a format that has become the standard in the study of psychoacoustics.

Measurement

Equal-loudness contours are derived from the sound pressure level (SPL) required for a pure tone to be perceived as equally loud as a reference tone at 1 kHz. The contours are often measured using headphones, but can also be measured using loudspeakers in rooms treated to have a flat frequency response.

Related Terms

• Sound pressure: The force of sound on a surface area perpendicular to the direction of sound.
• Phon: A unit of loudness level for pure tones.
• Psychoacoustics: The study of the perception of sound.
• Fletcher-Munson curves: The first equal-loudness contours, measured by Fletcher and Munson.
• Robinson-Dadson curves: A set of equal-loudness contours measured by Robinson and Dadson.

See Also

• Audiogram
• Decibel
• Hearing (sense)
• Loudness

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