Methods of measuring the attenuation of hearing protection devices

Abstract

The published literature describing three real-ear-attenuation-at-threshold (REAT), nine above-threshold, and four objective methods of measuring hearing protector attenuation is reviewed and analyzed with regard to the accuracy, practicality, and applicability of the various techniques. The analysis indicates that the REAT method is one of the most accurate available techniques since it assesses all of the sound paths to the occluded ear and, depending upon the experimenter's intention, can reflect actual in-use attenuation as well. An artifact in the REAT paradigm is that masking in the occluded ear due to physiological noise can spuriously increase low-frequency (less than or equal to 500 Hz) attenuation, although the error never exceeds approximately 5 dB, regardless of the device, except below 125 Hz. Since the preponderance of available data indicates that attenuation is independent of sound level for intentionally linear protectors, the use of above-threshold procedures to evaluate attenuation is not a necessity. An exception exists in the case of impulsive noises, for which the existing data are not unequivocal with regard to hearing protector response characteristics. Two of the objective methods (acoustical test fixture and microphone in real ear) are considerable time savers. All objective procedures are lacking in their ability to accurately determine the importance of the flanking bone-conduction paths, although some authors have incorporated this feature as a post-measurement correction. The microphone in real-ear approach is suggested to be one of the most promising for future standardization efforts and research purposes, and the acoustical test fixture technique is recommended (with certain reservations) for quality control and buyer acceptance testing.

Impulse noise and hand-arm vibration in relation to sensory neural hearing loss.

“…At present, the earmuff usage time is estimated to be 79 070 for forest workers and 93 % for shipyard workers. The attenuation of earmuffs under work conditions is not well known (2,6,10,15). In this study it was measured with a miniature microphone method with an estimated error of only ± 2 dB in frequency response, due to the positioning of the microphone close to the ear canal entrance (4, 6, 7).…”

“…Our aim was to evaluate the noise level at the external ear in accordance with Robinson's immission level. The sound pressure at the eardrum could be calculated from the noise reduction by the open ear transfer function (6). • ," :…”

“…Outside the earmuff a microphone of the same type was attached to the headband of the earmuff (37). The attenuation of the earmuffs was calculated as the difference between the signals, which is also kno wn as noise reduction (6). These data, and the results from previous studies in a shipyard (36) and in forest work (40), were used to predict individual hearing loss according to a model developed by Robinson (44).…”

Comparison of subjective and objective methods for the measurements of hearing protector devices attenuation and occlusion effect

“…Comprehensive reviews of measurement methods commonly used to evaluate the attenuation performance of hearing protection devices (HPD) can be found in the literature [1]- [5]. These methods are usually divided into two categories: subjective and objective methods.…”

An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs

“…Music is characterized by complex spectral characteristics, most of which are concentrated in the low frequencies (i.e., <100 Hz). Research has shown that the REAT procedure has known limitations for accurately assessing occluded perception of frequencies below 500 Hz, due to masking by physiological noise [15].…”