Larry H. Royster

Representative hearing levels by race and sex in North Carolina industry

An extensive sample of North Carolina industrial audiometric test data has been compiled. The sample includes data from several different types of industrial environments, with the size of the industries represented ranging from less than fifty to over eight thousand employees. The total population considered is in excess of 14000 employees. The data are examined using analytical techniques developed over the past six years while investigating the effectiveness of industrial hearing conservation programs. One of the findings is significant differences in the initial hearing threshold levels by race and sex. A second observation is differences by race and sex in the change in haring levels with time It is concluded that the hearing levels of industrial employees differ significantly by race and sex. The differences are of such magnitude that meaningful evaluations of industrial audiometric data bases are not possible unless the race and sex compositions of the population are considered.

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 S12, Noise

This paper describes research conducted by Working Group 11 of Accredited Standards Committee S12, Noise, to develop procedures to estimate the field performance of hearing protection devices (HPDs). Current standardized test methods overestimate the attenuation achieved by workers in everyday use on the job. The goal was to approximate the amount of attenuation that can be achieved by noise‐exposed populations in well‐managed real‐world hearing conservation programs, while maintaining acceptable interlaboratory measurement variability. S12/WG11 designed two new laboratory‐based protocols for measuring real‐ear attenuation at threshold, with explicit procedures for subject selection, training, supervision, and HPD fitting. After pilot‐testing, S12/WG11 conducted a full‐scale study of three types of earplugs and one earmuff tested by four independent laboratories using both protocols. The protocol designated as ‘‘subject‐fit’’ assessed the attenuation achieved by subjects who were experienced in threshold ...

Age effect hearing levels for a white nonindustrial noise exposed population (ninep) and their use in evaluating industrial hearing conservation programs

A nonindustrial noise exposed population (NINEP) describing age effects for white males and females has been established that can be used as a reference in evaluating an industrial noise exposed population (INEP) data base. In making this comparison, it is desirable to match the two populations properly with respect to sex, race and age characteristics. Since there presently does not exist an equivalent black NINEP, it is necessary to first isolate the data representing the black population from the industrial sample. A definite learning curve exists in industrial audiometric data bases, with the degree of learning dependent upon the effectiveness of the hearing conservation program. Therefore, this variation must be considered when attempting to compare the industrial audiometric test data with the white NINEP data base presented herein.

The flextensional concept: A new approach to the design of underwater acoustic transducers

Abstract The general design concept of the Flextensional Underwater Acoustic Transducer is presented. In addition, the five different possible shell designs are discussed and classified in one of five different classes.

Presumed noise‐induced permanent threshold shift resulting from exposure to an A‐weighted Leq of 89 dB

The noise-induced permanent threshold shift (NIPTS) resultings form up to ten years of exposure to an average A-weighted sound level Leq of 89 dB was investigated. Prior occupational noise exposure was controlled for by eliminating subjects with previous high-noise-level jobs or uncertain exposure histories. The final population consisted of 42 males and 58 females working a steady-state broadband noise environments. No attempt was made to screen subjects for any auditory pathology. A 222-subject control group from the same geographic area as the exposed subjects was selected such that none of its constituents had any effective industrial noise exposure. Presumed NIPTS was calculated by correcting each individual audiogram of the exposed subjects according to the aging curves developed from the control population hearing levels. The results indicated a considerable male-female difference in NIPTS, even though both groups were exposed to the same Leq. Averaging the results for all 100 subjects, in order to make comparisons to other available data, yielded results in close agreement to predictions based upon the work of Burns and Robinson, Baughn. NIOSH, and Passchier--Vermeer, indicating that 10 years of exposure to a daily Leq of 89 dB causes measurable hearing loss at 4 kHz.

Age effect hearing levels for a black nonindustrial noise exposed population (NINEP).

A nonindustrial noise exposed population (NINEP) that describes the age effects for a black male and female population has been established. The mean hearing threshold levels for the black NINEP are significantly lower (better hearing) than the previously established mean HTLs for a white NINEP when compared by sex. The availability of the black NINEP now makes it possible to more accurately evaluate a typical industrial noise exposed population (INEP).

Using audiometric data base analysis.

Audiometric data base analysis (ADBA) offers the most direct means of judging the effectiveness of a hearing conservation program (HCP) in preventing occupational hearing loss. However, numerous factors need to be accounted for if the findings are to be meaningful. This paper discusses several parameters known to influence the interpretation of group data statistics in assessing HCP effectiveness. Testing factors that affect the stability of the data base include audiometric techniques, calibration procedures, testing environment, and the motivation and prior experience of the subject. Pertinent population parameters include age, sex, race, current and prior noise exposures, learning effects, and the types of hearing protectors in use. Two case histories are presented to illustrate the application of ADBA techniques. Specific analysis procedures reviewed include comparisons of mean thresholds for selected industrial and nonindustrial populations, rates of change in mean hearing levels over a period of time, baseline and sequential test-retest comparisons, and different threshold shift criteria. The preliminary results of ADBA research being done by the American National Standards Institute (ANSI) S12.12 Working Group are summarized, including desirable criterion ranges for several statistics established by applying them to control data sets.

The Contribution of Personal Radios to the Noise Exposure of Employees at One Industrial Facility

An investigation of the contribution made to an employees noise dose from the output of personal radios was performed at a North Carolina textile manufacturing facility where the daily time-weighted average sound level (TWA) was approximately 87 dB, A-weighted sound pressure level [dB(A)]. The measured mean equivalent diffuse field output level of the personal radios was determined to be 83 dB(A) with a range from 70 to 98 dB(A). The daily TWA of a typical employee who did not use a personal radio was determined to be 86.6 dB(A), whereas the exposure of personal radio users was 88.5 dB(A)--an increase of 1.9 dB(A). This increase in exposure was estimated to result in 4 dB of additional permanent noise-induced hearing loss at 4 kHz for the 5th percentile (most sensitive portion) of the population after 20 years of exposure beginning at age 20. The study concluded that the additional contribution of the personal radios to the employees daily TWA did not pose a significant additional threat to their hearing. Specific hearing conservation criteria, however, were recommended for continuation of personal radio use at the facility.

Development of a Mathematical Model for the Class V Flextensional Underwater Acoustic Transducer

The purpose of this paper is to present development of a mathematical model for the Class V flextensional underwater acoustic transducer. The transducer is approximated through the consideration of three distinct problems. A thin piezoelectric disk with an arbitrary impedance on its edge is solved in terms of Bessel functions. The shell vibration problem is solved using a finite‐difference model to approximate the shell. The acoustic radiation problem is solved by obtaining the source density distribution for a system of quadrilaterals representing the transducer. With the source density of each quadrilateral, the near‐ and farfield pressures and velocities can be found. Utilizing these three components, a model is then constructed for the transducer. A comparison of the results from the mathematical model is made with those obtained from experiments in order to validate the model.

Comparisons Between the Median Hearing Threshold Levels for an Unscreened Black Nonindustrial Noise Exposed Population (NINEP) and Four Presbycusis Data Bases

The median hearing threshold level (HTL) data representing an unscreened black nonindustrial noise exposed population (NINEP) are compared to the median HTL data of three previously established presbycusis data bases by Hinchcliffe, Corso, and Rosen, and the data base developed by Robinson and Sutton. The data bases are all normalized relative to age 18. Comparisons are made between the black NINEP and the presbycusis data base HTLs for different sex and age groupings. The unscreened black NINEP exhibits median HTLs similar to those of the presbycusis data bases for ages less than approximately 35-45 years. However, for age groupings greater than 35-45 years, the median HTLs of the black NINEP are generally lower (better hearing) than those of the referenced presbycusis data bases even though this data base exhibited significant nonindustrial noise exposures, and medical and pathological problems which were not screened out of the population.