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Nov 1982

Volume 72, Issue S1, pp. S1-S108

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back to top Session FF. Noise V: Measurement and Human Effects of Impulse Noise in the Workplace
Invited Papers
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Impulse noise measurement: The physiological basis (A)

G. Richard Price

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S52-S52 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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In designing a system to measure noise there are many interacting considerations, among them the electrical/acoustical state‐of‐the‐art, regulatory requirements, administrative concerns, and economic issues. In contrast to these fluctuant elements, the structure of the auditory system is for all practical purposes fixed and establishes limits to many technical issues. Although theoretical work in the noise effects area is in its infancy, this paper will discuss the developing information with respect to the issues inherent in the measurement of noise, such as high‐ and low‐frequency cutoffs, temporal factors, “trading ratios,” and limits on the dynamic range.
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Intermittence and the total‐energy hypothesis (A)

W. D. Ward, C. W. Turner, and D. A. Fabry

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S52-S52 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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The theory that auditory damage is proportional to the total A‐weighted acoustic energy that has entered the ear has been shown to hold for single uninterrupted exposures to steady 700–2800‐Hz noise in the chinchilla, provided that a critical level of 110–115 dBA is not exceeded. The theory is not correct, however, if any appreciable interruptions in exposure occur. Earlier research [W. D. Ward, T. Kiester, and C. W. Turner, J. Acoust. Soc. Am. Suppl. 1 66, S61 (1975)] had established that breaking up a 220‐min exposure at 114 dB SPL into 22 10‐min exposures, two per week, reduced both permanent threshold shift (PTS) and cochlear damage (missing outer hair cells, MOHC) by an amount equivalent to a reduction of at least 7 dB in level. Present results primarily compare the damage produced by a 15‐day continuous exposure at 92 dB SPL to that generated by nine weeks of “work‐week” exposure (8 h/day Monday through Friday). The average PTS at 1, 2, 4, and 8 kHz was 11 dB for the continuous exposure, 4 dB for the work‐week exposure, and the MOHC count dropped from 640 to 340. The work‐week values were similar to those observed in a group exposed continuously for 15 days to 85 dB SPL, indicating again a “saving” equivalent to a 7‐dB reduction, though this value is surely coincidental. Implications for exposure criteria will be discussed. [Work supported by NIH grant NS 12125.]
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Industrial impact noise: Description and definition (A)

John Erdreich, Thomas Doyle, and Steve Spaeth

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S52-S52 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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In order to define the practical requirements of instrumentation for the measurement of industrial impact noise and to determine common parameters of industrial impact noise which should be considered in the study of the biological effects of such noise, survey measurements were made in industries which produce impulse noise. The measurements were made to include a bandwidth from 10 Hz to 40 kHz and a dynamic range of either 42 or 72 dB, for analog and direct digital recording, respectively. From the impact noise samples, we calculated true rms sound pressure level for the burst, peak‐level, crest factor based on burst duration, and 1‐s equivalent continuous level. Dose based on 3‐dB/doubling and 5‐dB/doubling A‐weighted slow response and A‐weighted fast response was calculated also. We will discuss the descriptors of impuse noise and also present preliminary data which address the variability of impulse noise signatures from the same process and the same machine.
Contributed Papers
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The influence of continuous background noise on impact noise‐induced TTS (A)

Raymond Hétu and Réjean Lazure

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S52-S53 (1982); (2 pages)

Online Publication Date: 12 Aug 2005

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The present study assessed the influence of a continuous background noise on the effect of the peak level and the number of impacts producing a 15 dB TTS3 at 4, 6, and 8 kHz. A group of 15 normal‐hearing adults were exposed to different conditions of noise. The critical peak level (CL) of an impact noise was first determined. The CL defined as the level producing the criterion amount of TTS3 when the impacts were presented in series of 60 at a rate of one every 2 s. This CL was not altered by the introduction of a continuous broadband noise at 85 dBA. But it was lowered by 3 to 6 dB among one‐third of the subjects when the background noise was at 105 dBA. Referring to the latter condition, both the peak and the continuous level were lowered by 4 dB and the number of impacts increased by a factor of 6: no increase in the amount of TTS3 resulted. However, for a tenfold increase in the number of impacts, a 13‐dB decrease in the peak and the continuous level did produce a slightly but significantly higher amount of TTS3. Implications of these results are discussed in term of exposure limits to industrial noise. [Work supported by INRS grant # N/D 25‐80‐25.]
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Measurement of short duration high level impact noises (A)

Per V. Brüel

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S53-S53 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Over the past few years there has been a growing suspicion that in shipyards, and in metal working industries with punch presses and forging processes, etc., the acoustic environment contains very short duration high level impulses. Since impulsive sounds as a rule are of very short duration, the human ear, and the standardized sound level meter can far from measure correctly the maximum sound pressures of impulses, simply because the integration time of the human ear and of the sound level meter is considerably longer than the impulse duration. Furthermore, the relatively long time intervals between short impulses, make the use of a sound level meter with “peak” holding capacity difficult in practice. In this article it is shown how the peak pressures can be measured three times a second and Leq every minute with the aid of two sound level meters (one with 30‐μs rise time and the other an integrating sound level meter) and a two channel level recorder. The instrumentation setup is battery driven and can operate without attention for seven days. The acoustic environments of a number of different industries have been measured with this set of instruments. The results show that in metal industries the levels of the short duration impulses are considerably higher than those found in wood industries.
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Characterization and calibration of microphone systems for measurement of impulselike sounds (A)

Victor Nedzelnitsky

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S53-S53 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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Measuring the peak value of impulse noise is required by damage‐risk criteria for hearing, material design standards, and for characterization of exposure to hazardous sound levels in industrial workplaces and the military. Other areas of application include building design and land‐use planning. However, use of current proposed ANSI and IEC standards provides only highly accurate magnitude calibration of microphone cartridges and systems in response to sinusoids, and does not ensure accuracy in measuring the peak values of impulse noise. Convenient approximate methods for audio‐frequency measurement include calibration of small, wideband transducers of ultrasonic resonance frequency by means of electrostatic actuators (for phase response and relative magnitude response) and by reciprocity‐based methods (for absolute magnitude response at selected frequencies). Such transducer systems can have a fairly flat magnitude response and an approximately linear phase response throughout most of the audio range. Precision sources of transient or impulselike sound are also very useful. Several methods for realizing such sources are discussed; one particularly simple and robust device utilizes aerodynamic impact sound from colliding spheres. For in situ measurements of personal sound exposure, additional consideration must be given to the influences of microphone position and diffraction produced by the torso, head, and external ear.
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