Page 102 - The Master Handbook Of Acoustics

77
THE EAR AND THE PERCEPTION OF SOUND

20

10
Echo
Reflection level (redirect) - dB 10 0 Spaciousness Image broadening C

20

Reflection B
30 inaudible

A
40
0 20 40 60 80
Reflection delay - ms

FIGURE 3-20
The effects of lateral reflections on the perception of the direct sound in a simulated
stereo arrangement. These measurements were made in anechoic conditions, lateral
angles 45–90 degrees, with speech as the signal. (A) Absolute threshold of audibility
of the reflection. (B) Image shift/broadening threshold (A & B After Olive and Toole, 22
23
and Toole. ) (C) Lateral reflection perceived as a discrete echo (After Meyer and Schod-
24
25
der, and Lochner and Burger ).
Researchers are trying to determine what noise exposure workers are
subjected to in different plants. This is not easy as noise levels fluctu-
ate and workers move about, but wearable dosimeters are often used to
integrate the exposure over the work day. Industries are hard pressed
to keep up with changes in regulations, let alone the installation of
noise shields around offending equipment and keeping ear plugs in or
ear muffs on the workers. Nerve deafness resulting from occupational
noise is recognized as a distinct health hazard.