Paul L. Michael

Reference threshold sound pressure levels for the Welch Allyn AudioScopeTM

The Welch Allyn AudioScope has been evaluated as an audiometer screening instrument using a threshold, loudness balancing technique. Two sets of eartips have been compared to determine which eartip configuration would yield the most reliable audiometric data. The AudioScope has also been evaluated by the American National Standard Method for Coupler Calibration of Earphones using both sets of eartips, and reference threshold sound pressure levels for the AudioScope were developed by combining the coupler and loudness balance data. The most reliable eartip configuration for audiometric purposes is identified and guidelines for use of the audiometric screening instrument are proposed.

Real-ear threshold level comparisons between the telephonics TDH-39 earphone with a metal outer shell and the TDH-39, TDH-49, and TDH-50 earphones with plastic outer shells.

There has been a recent expression of concern that the metal shells of most audiometric earphones could consitute a safety hazard because they can conduct electricity and are often used near electrical‐power supplies. In response to this potential safety hazard, Telephonics has constructed new TDH‐49, and TDH‐50 earphones with nonconducting outer shells. Real‐ear threshold comparisons were used to determine if the samples of plastic‐cased earphones could be substituted directly for the standard, metal‐cased earphones. The ten, trained‐listener subjects showed normal audiometric thresholds with good reliability. The real‐ear performance of the plastic‐cased earphones did not differ significantly from the of the metal‐cased earphones and it was concluded that these earphones could be used interchangeably in audiometric testing.

Loudness Discrimination Index (LDI): a test for the early detection of noise susceptible individuals

Work has been completed at the Environmental Acoustics Laboratory during the past year on developing an industrially feasible Loudness Discrimination Index (LDI) Test. Data obtained on experimental subjects who had been exposed to brief, high-level sound showed that the maximum Loudness Discrimination Index Shift (LDIS-Max.) is a valid and reliable indicator of temporary, noise-induced, hearing change. This test is better suited to industrial usage than the traditional TTS test. Suggestions for the implementation of LDI testing in the industrial setting are discussed.

The effect of high level sound exposure on the loudness difference limen.

Currently used threshold audiograms fail to detect the early stages of noise-induced hearing impairment. Threshold shifts may reach 10 to 15 dB before the impairment is detected. Loudness difference limen and critical band phenomena may provide an earlier and more sensitive test for such hearing impairment. Data is reported which shows that the difference limen shift (DLS) due to noise persists longer than temporary threshold shift (TTS). These findings suggest that DLS may be a more feasible tool for industrial use than either TTS or monitoring audiometry.

Noise attenuation characteristics for supra‐aural audiometric headsets using the models MX–41/AR and 51 earphone cushions

Continuing problems with the consistency of the MX–41/AR earphone cushion’s physical and acoustical characteristics have led to the development of a one‐piece cushion (model 51) by the Telephonics Corporation. The attenuation characteristics of this one‐piece cushion have been measured according to ASA Standard 1–1975 (ANSI S3.19–1974) and are reported herein. The attenuation characteristics provided for the wearer by the model 51 cushions tend to be slightly greater than those of the MX–41/AR cushion but the differences are not generally significant, with α = 0.05.

A comparison of acoustical performance between a new one‐piece earphone cushion and the conventional two‐piece MX‐41/AR cushion

A new one‐piece earphone cushion, model 51, that should afford more reliable hearing measurement data than the conventional two‐piece MX‐41/AR earphone cushion, has been developed by Telephonics Corporation. In particular, the material used for the one‐piece cushion should be more stable over a long period of time than the sponge material used in the two‐piece MX‐41/AR cushion. In addition, the single material of the one‐piece cushion is more easily compounded and thus easier to control than those materials used in the two‐piece cushion, and the cementing operation required for the two‐piece cushion is avoided. The acoustical performances of the one‐ and two‐piece cushions mounted on a TDH‐39 earphone were compared by threshold‐loudness‐balance and coupler measurements. The comparison with threshold‐loudness‐balance measurements on ten subjects showed no significant differences with a confidence of 95% and coupler measurements showed differences less than 0.8 standard deviations in all cases (i.e., no sig...

Calibration data for a circumaural headset designed for hearing testing

Standard reference threshold levels for the new Telephonics circumaural headset using TDH−39 and TDH−50 earphones have been measured. Because the circumaural headset cannot be mounted meaningfully in the same suspension with a conventional supra‐aural assembly, it was necessary to perform loudness balancing at threshold. The circumaural headset, furthermore, cannot be calibrated on the standard, NBS‐9A coupler. Thus, it was necessary to develop a new coupler and to refine a new coupler measurement procedure. Data on the comparative attenuation and the subjective voltage and power sensitivities of the two headset designs are reported. Objective data from coupler measurements are also reported. Implications of these findings are discussed and reference‐threshold sound‐pressure levels for the two headset types using both the TDH−39 and the TDH−50 earphones are reported. In general, it was observed that the clincial use of the new Telephonics circumaural headset affords significantly greater attenuation of ba...

A procedure for the early detection of noise-susceptible individuals.

Currently used threshold audiograms fail to detect the early stages of noise-induced hearing impairment. Threshold shifts may reach 10 to 15 dB before the impairment is detected. Loudness difference limen and critical band phenomena should provide an earlier and more sensitive test for such hearing impairment.

Hearing protector performance—an update

A single-number descriptor, the A-weighted sound pressure level, has been used widely during the last 10 years for the assessment of noise exposure levels. Prior to that time octave band levels were the common means for describing noise exposures. Hearing protector noise reduction data have been presented in various ways to facilitate the calculation of exposure levels while wearing hearing protectors. This paper describes both single-number and octave band procedures for presenting hearing protector noise attenuation data and discusses advantages and disadvantages of each.

Calibration data for the Telex 1470‐A audiometric earphones

Standard reference threshold levels for the Telex 1470‐A audiometric earphones have been determined. The psychoacoustic evaluation of these earphones was completed by loudness balancing at threshold. The earphones were balanced to comparison standard earphones calibrated at the National Bureau of Standards. Coupler calibration was accomplished using the American National Standard Method. Objective (coupler) and subjective (psychoacoustic) data were combined and the resulting reference threshold sound pressure level data are reported herein. These data were compared to previous data for the 1470‐type earphone. While good agreement with previous data was noted for low and mid frequencies, sizeable differences did occur at high frequencies. Possible sources of these discrepancies are discussed.