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Measurements of three-wave mixing amplitudes on solids whose third order elastic constants have also been measured by means of the elasto-acoustic effect are reported. Because attenuation and diffraction are important aspects of the measurement technique results are analyzed using a frequency domain version of the KZK equation, modified to accommodate an arbitrary frequency dependence to the attenuation. It is found that the value of β so deduced for poly(methylmethacrylate) (PMMA) agrees quite well with that predicted from the stress-dependent sound speed measurements, establishing that PMMA may be considered a hyperelastic solid, in this context. The β values of sedimentary rocks, though they are typically two orders of magnitude larger than, e.g., PMMA’s, are still a factor of 3–10 less than those predicted from the elasto-acoustic effect. Moreover, these samples exhibit significant heterogeneity on a centimeter scale, which heterogeneity is not apparent from a measurement of the position dependent sound speed. [ABSTRACT FROM AUTHOR]

General Radio and Metrosonics brand portable noise dosimeters were used to record daily average 24-h log equivalent sound levels [Leq(24)] in 127 children and youths aged 7.0 to 20.0 years (?±S.D. = 14.2±3.5 years). These children were a subset of those participating in a long-term serial study of hearing in children at the Fels Research Institute. Seventy-five children had multiple 24-h recordings; 234 measurements were made in all. The mean Leq(24) was substantial, between 76.7 and 83.8 dB and several children had levels dangerously high, above 90 dB. There were no significant age trends or racial differences for Leq(24) and no significant differences in Leq(24) occurred between tests recorded during the school year (September-May) and those recorded during the summer (June-August). There were, however, small, but significant sex differences; boys had a mean Leq(24) about 2 dB higher than girls. Hearing threshold levels were positively correlated with Leq(24) in girls, but a similar trend was not present in boys. The mean Leq(24) (±1 S.D.) for data collected with Metrosonics dosimeters was 76.7±5.7 dB (n = 58) and 83.8±5.1 (n = 109) for data collected with the General Radio dosimeters. These significantly different means may be explained by the properties of the two dosimeter types arising from differences in the design philosophy of the instruments. These design differences result in systematic measurement errors in the two dosimeter types; the GR dosimeters systematically overestimate actual noise in certain situations while Metrosonics dosimeters underestimate it in different situations. While there are differences between the instruments as to how noise is measured, the data from either instrument provide a reasonable estimate of noise exposure in children, data that are not otherwise available. Furthermore, they provide strong evidence that the noise exposure in children is substantial. [ABSTRACT FROM AUTHOR]

Serial auditory thresholds are being recorded at six-month intervals from 224 children and youths aged 4-18 years. The data from the first year show girls have lower threshold levels than boys, especially from 12-17 years, and, in both sexes, those aged 12-17 years have lower thresholds than those aged 6-11 years. Median total noise exposure scores tend to be higher in boys than girls, especially after 10 years of age, but these scores are not significantly correlated with auditory threshold levels. The incidence of exposure to events associated with noise increases markedly in teenage boys and is related to auditory threshold levels. There are no significant associations between auditory threshold levels and responses to general health questions or attained stature, but there are associations with meatal abnormalities. There is suggestive evidence, particularly in girls, that rapid maturation is associated with lower threshold levels, especially at lower frequencies. [ABSTRACT FROM AUTHOR]

The effects on human hearing of 24 and 48 hour continuous and 48 hour intermittent exposures to pink noise at an Leq of 85 dB were measured by pure tone audiometry to address two questions. First, previous studies have demonstrated an asymptotic temporary threshold shift (ATTS), i.e., growth of TTS ceases, after 8-16 hours of exposure to sound. On the assumption that these effects on hearing are the same once asymptote is reached, there should be no difference between the growth of TTS, level of ATTS and recovery from the two exposure durations. Second, if the equal energy concept is appropriate to exposure durations of 48 hours then the effects found for the interrupted conditions should also demonstrate some similarity with the effects from continuous noise exposures. For instance, results of earlier work has shown similar recovery times between 24 hour interrupted and continuous noise exposures. Present results demonstrate that (1) for the 24-48 hour continuous exposures, TTS growth patterns and ATTS levels are similar. However, recovery from the 48 hour exposure was significantly longer than for the 24 hour condition, and (2) for the 48 hour interrupted exposures, growth and recovery patterns are similar to those of continuous exposures, although the magnitude of the TTS was less and the recovery to pre-exposure hearing more rapid than for continuous exposures. [ABSTRACT FROM AUTHOR]

Measurements of sound exposure (n = 151) were recorded in children aged 6 to 18 years with Metrosonics dB 301 Metrologgers. For each child, a log equivalent sound level (Leq) and corresponding sound source were recorded for 480 separate 3-min intervals during a 24-h period. Data for each individual were summarized into 20 activity (sound source) categories, and an Leq (8) and Leq (t) computed for each, where t is the total time spent engaged in a specific activity. Analysis of variance reveals highly significant differences in Leqs among activities, and Duncan's multiple range test suggests four groupings. Lawnmowers/combustion engines, live music, school bus, and school assembly/recess are major sound sources for children; each sound source has an Leq(t) > 80 dB in boys and girls and average exposure duration of 0.5 to 2.1 h per day for those exposed. There is a significant sex difference in total sound exposure; Leq(24) = 77.8 ± 6.1 and 75.2 ± 5.3 in boys and girls, respectively. Boys appear to place themselves in a noisier environment than girls, since girls have a lower mean Leq than boys for virtually every activity. [Work supported by EPA and USAF.] [ABSTRACT FROM AUTHOR]

Noise exposure over a 24-h period has been measured with portable dosimeters for 32 males and 30 females between 8 and 20 years of age. The mean Leq(24) was 80.9 dB, with a standard deviation of 6.04 dB. The regression of Leq(24) on age was 0.21 dB/year, although this is not statistically significant. The correlation between Leq(24), and the auditory thresholds at 1000, 2000, 4000, and 6000 Hz, while tending to be positive, were not statistically significant in either sex. However, in females a correlation of 0.32 (p = 0.09) was observed between thresholds at 4000 Hz and Leq(24), in males the corresponding correlation was -0.19 (p = 0.33). The group tested with the General Radio model 1954-9780 dosimeter had a mean (83.3 dB) significantly different from the groups tested with the Bruel and Kjaer model 4424 and the Loomis Laboratories model 3573 (78.6 and 76.9 dB, respectively) dosimeters. [Work supported by EPA and USAF.] [ABSTRACT FROM AUTHOR]

JASMA,63,S65,1978 [ABSTRACT FROM AUTHOR]

Six-monthly serial data from 224 children aged 4-18 years include puretone auditory thresholds, noise exposure, otological histories, and data relating to body size and maturity. Otological abnormalities in these 'normal' children may be associated with higher auditory thresholds. Also auditory thresholds are related negatively to stature and levels of sexual and skeletal maturity. The girls have slightly lower thresholds than the boys; this sex difference is larger in the older children and the median total noise exposure scores are considerably higher for boys than girls in the older groups indicating noise exposure may adversely affect hearing ability. Furthermore, in the older groups, especially boys, the six-monthly increments are larger, in the direction of hearing loss. The noise exposure data indicate specific important sources of noise. [Work supported by U.S. Environmental Protection Agency and the Aerospace Medical Research Laboratory.] [ABSTRACT FROM AUTHOR]

The nonlinear characteristics of an acoustic tube wave propagating along the axis of a fluid-filled circular borehole in an elastic solid which is locally isotropic but whose properties may vary radially are considered. The analysis is carried out in the quasistatic limit. All terms are considered through quadratic in the amplitude of the wave and the amplitude of 2nd-harmonic generation is expressed as well as the pressure dependence of the tube wave speed, dVT/dp, in terms of the fluid and formation of nonlinear parameters. The results show that if there is no radial variation of the shear modulus of the solid then both the amplitude of 2nd-harmonic generation and dVT/dp are independent of the third-order elastic constants of the solid and nearly equal to those of the fluid alone. If there is a radial variation of the shear modulus then our numerical calculations indicate that both the amplitude of 2nd-harmonic generation and dVT/dp can be completely dominated by the nonlinear parameters of the solid. A perturbation theory is derived that is valid for the case in which the shear modulus is nearly constant, which demonstrates that the nonlinear response is scaled by the value of the third-order parameters of the solid, leveraged by the degree and depth of alteration of the shear modulus. [ABSTRACT FROM AUTHOR]

Results are reported on a two-dosimeter system for the measurement of the daily personal exposure to noise. This system is supposed to estimate the true noise dose without the influence of the voice of the wearer. Two identical dosimeters were used with their microphones located on a helmet, in the front and back positions, respectively. The dosimeters simultaneously measured the Leq and the n-percentile-exceeded levels. These data were then used to eliminate the voice contribution to the noise dose. Provided certain constraints are fulfilled, preliminary results obtained in various environmental conditions have shown good performance of this system, especially at low noise levels. Main constraints are: (1) the daily measurement should be divided in homogeneous periods with respect to noise, and (2) if the wearer speaks for a certain period fraction, his or her voice level should be consistent with the Lombard effect. Examples are given. [ABSTRACT FROM AUTHOR]

Twelve volunteers experienced 24-h continuous exposures to a 13-oct band of noise centered at 1000 Hz. Exposure effects at levels of 75, 80, and 85 dBA were investigated in separate sessions occurring several days apart. Hearing thresholds were measured at twelve frequencies between 125 and 12 000 Hz prior to, during, and following exposure. TTS acquisition and recovery are discussed relative to (1) asymptote, (2) exposure interruption for hearing threshold measurement, and (3) other studies of long duration exposure. [ABSTRACT FROM AUTHOR]

The databases and models for the prediction of noise-induced permanent threshold shift (NIPTS) from industrial noise exposures are reviewed. Models available in 1973, compared with later models and data, are shown still to be reasonable. The effect of hearing conservation procedures on the acquisition of new data is discussed. Because of the impact of hearing conservation, new research focus is recommended in three areas: sex differences, newly hired individuals exposed for the first time in occupational noise, and the contribution of nonoccupational noise through the use of questionnaires and dosimetry.

A dosimeter based on the equal energy rule with range from 55 to 110 dB was used to monitor continuously the noise exposure of one subject. The subject, who is the second author of this report, works in a relatively quiet laboratory area. The daily A-weighted average sound level was measured for each 24-h period [L(eq(24))] beginning at approximately 8:00 a.m. During the day the noise exposure associated with specific activities was noted. The 31-day average sound level was 76 dB while the daily L(eq)(24)) values varied from a low of 59 dB to a high of 83 dB. The type of activity that contributed most of the subject's total sound dose was night-time parties at private homes or nightclubs. Five such parties accounted for 42% of his total sound dose. One exposure at an automobile hobby shop and three outings at a bowling alley contributed another 27% to the total sound dose. If these outside recreational activities had been avoided, the 31-day average sound level would have been reduced to 71 dB. The problems involved in monitoring a 24-h noise exposure as well as future plans for more elaborate studies are discussed.

Using the information available from Inter-Industry Noise Study, the hearing levels of 68 pairs of workers, matched for sex, age, and exposure level, were evaluated. For each pair, one of the participants had indicated exposure to nonoccupational gunfire during the previous year. Differences in mean hearing levels between the male participants exposed to gunfire and those not exposed were clearly apparent and varied between 9 to 16 dB for the frequencies at 3000, 4000, and 6000 Hz. There were no significant differences in female hearing threshold levels. These changes in male hearing are equivalent to the effect of an occupational exposure of 89 dB for 20 years. However the results do not indicate that there are any synergistic effects between gun exposures during a participants recreational time and noise exposure during his working hours.

An exact measurement of the effectiveness of a hearing protector requires the determination of how well it works in the specific noise in which it is to be worn. As a practical matter, though, people do not generally remain in a single noise spectrum throughout a working career or even throughout a working day, so it does not matter so much that most measurers are not likely to be equipped to perform spectrum analyses. Other techniques for judging earplugs and earmuffs are obviously necessary. Previous research has tried to find the average attenuation given by a particular device in several (or many) noises, or it has tried to deal with the attenuation given in noises given with particular C-minus-A values. In this paper, a procedure is developed for compressing these multiple-spectra calculations into a single-spectrum computation that proves to be at least as accurate as the more complex methods.