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The use of acoustic test fixtures to objectively measure earmuff attenuation.

NIOSH 1992 Apr; :37-40
The use of acoustic test fixtures (ATF) to objectively measure attenuation of noise by earmuff type protectors was evaluated. Diffuse field and free field measurements were performed in an anechoic room. The ATF was mounted on a microphone so that its center was 1.08 meters above the supporting surface. Protectors used were the Bilsom 2301, Optigard, Silenta Super and Sonogard. Influence of the mounting surface of the hearing protector on the ATF was measured. "Remount" and "Repeat" series were conducted. Results showed that in all cases, the remount series gave a variability of data that was greater than in the repeat series. For practical use of the objective method, the protector had to be taken off the ATF between measurements. Standard deviations for five replications of the diffuse and free fields were presented. In general, the deviation was almost the same, but at some frequencies (2 to 6 kiloHertz (kHz)) the deviation was higher in the free field situation. Mean insertion loss values were in general agreement in the frequency region 125 Hertz to 1kHz. Below and above this frequency range, deviations between results from the two fields were evident. Average standard deviation was slightly greater for the free field than for the diffuse field. The author concludes that the diffuse field is preferable for certification of hearing protectors, while the free field may be sufficient for the manufacturer's production tests.
Audiometry; Ear-protectors; Hearing-disorders; Industrial-exposures; Industrial-noise; Measurement-equipment; Noise-induced-hearing-loss; Occupational-exposure; Protective-equipment
Publication Date
Document Type
Conference/Symposia Proceedings
Fiscal Year
NTIS Accession No.
NTIS Price
Priority Area
Hearing Loss; Disease and Injury; Noise-induced-hearing-loss
Source Name
Proceedings, 1992 Hearing Conservation Conference, April 1-4, 1992, Lexington, Kentucky, Office of Engineering Services, University of Kentucky and NIOSH