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The Art & Science of Audio & Video

Harvey Fletcher & Wilden Munson

HARVEY FLETCHER & WILDEN MUNSON, BELL LABS
FLETCHER-MUNSON LOUDNESS CURVES (1933)

Nearly 75 years ago, Harvey C. Fletcher and Wilden A. Munson—two Bell Labs engineers studying various aspects of subjective loudness—changed the way in which the world understands the hearing process. Their research asked a large number of subjects to compare the relative volume of two tones to a standard 1kHz tone at a set level. Averaging the results collected from the group, Fletcher and Munson defined of human hearing awareness at various frequencies.

In a landmark paper published in the October, 1933 edition of the Journal of the Acoustical Society of America, Fletcher and Munson showed that hearing is frequency selective, more specifically, hearing is most sensitive to pure tones in the 3,000 to 4,000 Hz range and less so above and below that. to perceive that a 100Hz signal is of equal loudness to a 3,000Hz tone, requires an actual SPL of the 100Hz tone that’s much higher than that of the 3kHz tone, particularly at low volumes.

The phenomenon was referred to as “Equal-Loudness Contours,” and although this original research was later updated and refined (most notably by D. W. Robinson and R. S. Dadson in 1956), Fletcher and Munson’s pioneering work laid the groundwork for creating industry-standard measurement curves, from the classic A/B/C/D-weighting filters to the current ISO 226:1987 standard.

Wilden Munson continued his acoustical research at Bell Labs until retiring in 1962. Harvey Fletcher worked on a number of projects at Bell Labs, including the development of a vacuum tube-based hearing aid and helped found the Acoustical Society of America, serving as its first president.

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March 8, 2008 - Posted by | Pioneers in Audio | , , , , , ,

1 Comment »

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