Development of a new standard laboratory protocol for estimation of the field attenuation of hearing protection devices: sample size necessary to provide acceptable reproducibility.
The mandate of ASA Working Group S12/WG11 has been to develop "laboratory and/or field procedure(s) that yield useful estimates of field performance" of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested for one earmuff and three earplugs via an interlaboratory study involving five laboratories and 147 subjects, and incorporated into a new standard that was approved in 1997 [Royster et al., "Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S 12, Noise," J. Acoust. Soc. Am. 99, 1506-1526; ANSI, S12.6-1997, "American National Standard method for measuring real-ear attenuation of hearing protectors" (American National Standards Institute, New York, 1997)]. The subject-fit methodology of ANSI S12.6-1997 relies upon listeners who are audiometrically proficient, but inexperienced in the use of HPDs. Whenever a new method is adopted, it is important to know the effects of variability on the power of the measurements. In evaluation of protector noise reduction determined by experimenter-fit, informed-user-fit, and subject-fit methods, interlaboratory reproducibility was found to be best for the subject-fit method. Formulas were derived for determining the minimum detectable difference between attenuation measurements and for determining the number of subjects necessary to achieve a selected level of precision. For a precision of 6 dB, the study found that the minimum number of subjects was 4 for the Bilsom UF-1 earmuff, 10 for the E.A.R Classic earplug, 31 for the Willson EP100 earplug, and 22 for the PlasMed V-51R earplug.
Murphy
William J
WJ
Hearing Loss Prevention Section, National Institute for Occupational Safety and Health, 4676 Columbia Parkway MS C-27, Cincinnati, Ohio 45226, USA. wmurphy@cdc.gov
Franks
John R
JR
Berger
Elliott H
EH
Behar
Alberto
A
Casali
John G
JG
Dixon-Ernst
Christine
C
Krieg
Edward F
EF
Mozo
Ben T
BT
Royster
Julia D
JD
Royster
Larry H
LH
Simon
Stephen D
SD
Stephenson
Carol
C
D001309:Auditory Threshold; D004430:Ear Protective Devices / Q000706:statistics & numerical data*; D004867:Equipment Design; D006801:Humans; D008144:Loudness Perception; D009622:Noise; D012015:Reference Standards; D015203:Reproducibility of Results; D018401:Sample Size; D013018:Sound Spectrography