Patent
1975-09-15
1977-04-26
Stewart, David L.
179 1N, H04R 2900
Patent
active
040202984
ABSTRACT:
A portable device primarily for use in determining the effectiveness of various personal hearing protectors in attenuating hazardous noise. The device comprises an electronic circuit for generating audio test signals at varying amplitude levels, and a display for providing numerical indications usable to measure accurately the difference in amplitudes between the respective audio signals. The test signal increases or decreases in loudness in response to a subject-operated hand switch which also triggers display of the appropriate numerical indication at amplitude levels determined subjectively by the individual being tested. The electronic circuit of the device preferably is capable of producing such test signals in complex, multifrequency form with preweighting of the power spectrum of the signal so as to emphasize the most potentially hazardous frequencies. Specially designed earcups having audio transducers resiliently mounted within are provided for the testing of earplug effectiveness in an environment of ambient noise. The device is capable of testing attenuation utilizing amplitude levels either at the threshold of hearing perception or at supra-threshold levels wherein the test ear signal is compared with a reference signal in the contralateral ear to allow for testing in a high or fluctuating ambient noise level. For purposes of the latter test, the device produces a reference signal which is audibly distinguishable from the test signal, other than with respect to amplitude. Numerical indications are produced by a digital display responsive to a digital counter which also controls the attenuation level of the test signal.
REFERENCES:
patent: 3729598 (1973-04-01), Tegt
patent: 3784745 (1974-01-01), Stearns
patent: 3890470 (1975-06-01), Allen
patent: 3906158 (1975-09-01), Lake
patent: 3922506 (1975-11-01), Frye
Acoustical Society of America Standard 1-1975; Published by American Institute of Physics; Adopted 8-14-74.
Epley John M.
Frisch Arnold
Leach Austin F.
Hearing Evaluation & Acoustic Research, Inc.
Stewart David L.
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