About the EPA document collection held by the Noise Pollution Clearinghouse.
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Most useful EPA documents.
The Ability of Mildly Hearing-Impaired Individuals to Discriminate Speech in Noise
Alice H. Suter
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The investigation explores the relationship between hearing level at various audiometric frequencies and speech discrimination in different noise backgrounds. The study was designed specifically to test the American Academy of Opthamology and Otolaryngology's (AAOO) selection of a 26-decibel average of 500, 1000, and 2000 Hz as the point above which hearing handicap occurs. The AAOO method for computing hearing handicap has lately been brought into question for two primary reasons: the 26-dB fence is too high, and for the exclusion of frequencies above 2000 Hz. The present study, therefore, attempted to see if there were differences among individuals whose hearing was at or better than the low fence, and if so, what factors caused or affected the differences. Forty-eight subjects were tested with two types of speech materials: the University of Maryland Test #1 which employs simple, "everyday" sentences, and the Modified Rhyme Test, a closed-set test of rhyming monosyllables. Speech stimuli were presented at 60 dBA measured at the listener's ear. The noise stimulus, a babble of twelve voices, was presented at levels of 60 to 65 dBA. Subjects were divided into three groups according to their hearing levels at 500, 1000, and 2000 Hz. One group had normal hearing at all tested audiometric frequencies and the other two had mild hearing losses in the mid-frequencies and considerable amounts of loss in the high frequencies, which is typical of noise-hearing loss. Subjects listened to both speech materials in a quiet condition and in three levels of background noise. Group scores were compared in a three-factor analysis of variance and correlations between audiometric frequencies and individual discrimination scores were performed. Conclusions are drawn about the differences between the three groups, the effect of increasing noise on the discrimination of speech by hearing-impaired individuals, the equivalence of two kinds of speech materials, and the importance of certain audiometric frequencies to the discrimination of speech. Recommendations are made for computing hearing handicap in terms of the height of the fence and the inclusion of frequencies above 2000 Hz.
Annoyance, Loudness, and Measurement of Repetitive Type Impulsive Noise Sources
L.C. Sutherland, R.E. Burke
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This study was undertaken to evaluate subjective and objective aspects of moderate levels of noise from impulsive sources. The study excluded evaluation of hearing damage risk or annoyance from building vibration by high level impulsive noise, which were covered by recent recommendations of the National Research Council, Committee on Hearing Bioacoustics and Bomechanics, Working Group 69. While the study included original investigations into some of the objective aspects of impulsive noise, a detailed review of the literature on the subjective aspects was emphasized. Based on this available literature, the annoyance and loudness from a wide variety of repetitive impulse noises were evaluated. These results were applied to the evaluation of impulsive noise from a number of specific noise sources. Based on the most pertinent literature, it is tentatively concluded that a subjective impulse correction factor of +7 dB applied to the A-weighted equivalent sound levels of these types of repetitive impulsive noise sources would better define their effective level in terms of annoyance reactions. No additional correction is identified at this time for crest level or repetition rate. Research on subjective correction factors for helicopter blade slap is also reviewed and potential reasons for the smaller subjective correction factors (i.e. 0 to 6 dB) for annoyance response to this type of sound are discussed. It is recommended that refinements to this subjective correction factor be based on the use of standard loudness calculation methods (Stevens Mark VII or Zwicker) modified to include provision for a shorter time constant to reflect subjective response to short duration impulsive sounds. The study also included a brief experimental evaluation of the measurement of a wide variety of simulated repetitive impulsive-type signals varying in duty cycle, repetition rate, pulse frequency, and ratio of peak impulse signal level to continuous background noise level. When repetitive impulses are measured using maximum values of A-weighted (slow) readings on an Impulse Sound Level Meter, no objective correction is necessary in order to measure, with an accuracy of +/- 1.5 dB, the equivalent level (Leq) of the wide variety of impulsive signals investigated.
A Basis for Limiting Noise Exposure for Hearing Conservation
J.C. Guignard
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A compilation of data is provided, with references to published work, which represents the present state of knowledge concerning the effects of continuous and impulsive noise on hearing. The danger to the ear of both occupational and non-occupational human exposure to noise is considered. Data are included or cited which enable quantitative predictions to be made of the risk to hearing in the American population due to noise exposure in any working or living context. Recommendations are made concerning the need to obtain more definitive data. Relevant aspects of noise measurement, the physiology of hearing, and theories explaining the effects of noise on the ear are discussed in appendices to the main report. This report deals solely with the effects of noise on hearing; other physiological or psychological effects of noise are not considered in the present document.
Prediction of NIPTS Due to Continuous Noise Exposure
Daniel L. Johnson, Major, USAF
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In support of the main document, "A Basis for Limiting Noise Exposure for Hearing Conservation," this report compares the relationship of noise exposure to Noise Induced Permanent Threshold Shift (NIPTS) as predicted by the currently available works of Passchier-Vermeer, Robinson, Baughn and Kryter, and the yet unpublished work of the National Institute of Occupational Safety and Health. The works of Passchier-Vermeer, Robinson, and Baughn are selected since these are the only works that completely predict the relationship between NIPTS and noise exposure for various audiometric frequencies, sound pressure levels and population percentiles. The predictions of these three methodologies are averaged in order to provide one single relationship between continuous noise exposure and NIPTS. This relationship is presented in various ways so that the effect of noise exposure on hearing can be viewed in more than one way. Discussion concerning the type of frequency weighting, the equal energy rule, and long duration exposures is also provided.