Compare: FLAT, NOISE CRITERION, NOISE RATING, PERCEIVED NOISE LEVEL. See also: LOUDNESS LEVEL, PRESENCE, SONE, VOLUME. The lowest curve repesents the THRESHOLD OF HEARING, the highest the THRESHOLD OF PAIN. Historically, the A, B, and C weighting networks on a SOUND LEVEL METER were derived as the inverse of the 40, 70 and 100 dB Fletcher-Munson curves and used to determine SOUND LEVEL. The PHON scale was devised to express this subjective impression of loudness, since the DECIBEL scale alone refers to actual sound pressure or sound intensity levels.
The intensity level of higher or lower tones must be raised substantially in order to create the same impression of LOUDNESS. The curves are lowest in the range from 1 to 5 kHz, with a dip at 4 kHz, indicating that the ear is most sensitive to frequencies in this range. Also called loudness level contours and the Fletcher-Munson curves. The curves are plotted for each 10 dB rise in level with the reference tone being at 1 kHz. The RESPONSE to frequencies over the entire AUDIO range has been charted, originally by Fletcher and Munson in 1933, with later revisions by other authors, as a set of curves showing the SOUND PRESSURE LEVEL s of PURE TONE s that are perceived as being equally loud.
The ear is not equally sensitive to all frequencies, particularly in the low and high FREQUENCY ranges. Equal_Loudness_Contours EQUAL LOUDNESS CONTOURS