Trane TRG-TRC007-EN manual period two, Loudness Contours, Sound Perception and Rating Methods

period two

Sound Perception and

Rating Methods

notes

Loudness Contours
	120
mPa	100
ref 20
	80
dB
pressure,	60
sound	40
	20
	0							10,000
	20	50	100	200	500	1,000 2,000	5,000
					frequency, Hz			Figure 20

The sensation of loudness is principally a function of sound pressure, however, it also depends upon frequency. As a selective sensory organ, the human ear is more sensitive to high frequencies than to low frequencies. Also, the ear’s sensitivity at a particular frequency changes with sound-pressure level. Figure 20 illustrates these traits using a set of contours. Each contour approximates an equal loudness level across the frequency range shown.

For example, a 60 dB sound at a frequency of 100 Hz is perceived by the human ear to have loudness equal to a 50 dB sound at a frequency of 1,000 Hz. Also, notice that the contours slant downward as the frequency increases from 20 to 200 Hz, indicating that our ears are less sensitive to low-frequency sounds. The contours are flatter at higher decibels (> 90 dB), indicating a more uniform response to “loud” sounds across this range of frequencies.

As you can see, the human ear does not respond in a linear manner to pressure and frequency.

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