Welch Allyn AM 232, Руководство по эксплуатации

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Elimination of ambient noise
Excessive noise in the test environment such as that produced by conversation,
typewriters, or other machines also reduces test validity because it tends to mask the
test signals particularly at the lower frequencies where earphone cushions provide
less effective attenuation. An acoustically tested room may be required if ambient
noise at the subject’s ears reaches objectionable levels - i.e., sufficient to cause
apparent hearing loss at the low frequencies. Also, Audiocups are available from
Welch Allyn as an optional accessory. If the test subject is in the same room as the
audiometer, it is recommended that the subject be seated about 1 meter (-3 ft) away
from the instrument.
Maximum permissible test environment sound-pressure levels are specified by
American National Standard Criteria for Permissible Background Noise during
Audiometric Testing, S3.1-1977 (revised). Table 2 shows the maximum background
levels that can be present inside the room while a valid hearing test is being con-
ducted. For more comprehensive information about hearing testing and hearing
conservation, refer to the
Bibliography .
Permissible noise levels
Test Tone Frequency (Hz) 125 250 500 750 1000 1500 2000 3000 4000 6000 8000
Test Room
*
34.0 22.5 19.5 21.5 26.5 26.5 28.0 33.5 34.5 38.0 43.5
Test Room
**
29.0 17.5 14.5 16.5 21.5 21.5 23.0 28.5 29.5 33.0 38.5
*
Ears covered maximum permissible octave band levels.
**
Ears covered maximum permissible one-third octave band levels.