Page 103 - The Master Handbook Of Acoustics

78 CHAPTER THREE

It is especially bad when one works all
Table 3-2. OSHA permissible noise exposure day in a high-noise environment, then
times.* engages in motorcycle or automobile rac-
Sound pressure level, Maximum daily ing, listens to a 400-watt stereo at high
dB, A-weighting, slow exposure level, or spends hours in a discotheque.
response hours The professional audio engineer operating
with high monitoring levels is risking
85 16
irreparable injury to the basic tools of the
90 8
92 6 trade—his ears. As high-frequency loss
95 4 creeps in, the volume control is turned up
97 3 to compensate, and the rate of deteriora-
100 2 tion is accelerated.
102 1.5 The key to conservation of hearing is
105 1 the audiogram. Comparing today’s audio-
110 0.5 gram with earlier ones establishes the

115 0.25 or less trend; if downward, steps can be taken to
check it. The audiogram of Fig. 3-21,
*Reference: OSHA 2206 (1978)
which looks something like the Big Dipper

0 Right

Hearing loss - dB (ISO) 20 ear

40

60
Left
ear
80
250 500 1,000 2,000 4,000 8,000
Frequency - Hz
FIGURE 3-21
Audiograms showing serious loss centered on 4 kHz, presumably resulting from years of
exposure to high-level sound in the control room of a recording studio.