Edgar A. G. Shaw

Earphones in audiometry

The advantages and disadvantages of three types of earphones for audiometric testing are discussed. Supraaural earphones continue to be recommended for this purpose, in preference to circumaural and insert types.

Limitations on the Use of Circumaural Earphones

Published material on the calibration of circumaural earphones is briefly reviewed. The present lack of knowledge about these earphones and about the earphone‐to‐ear coupling is indicated, and the resultant limitations on the routine use of circumaural earphones in clinical and industrial pure‐tone audiometry are presented.

Spatial perception, the acoustics of the external ear, and interactions with earphones

In free‐field listening, the perception of source elevation and discrimination between forward and rearward source positions appear to be largely dependent on the availability of high‐frequency spectral cues associated with the mode structure of the concha and diffraction by the pinna, respectively. The role of the concha is particularly clear between 5 and 10 kHz, while pinna‐diffraction effects are strongly developed between 2.5 and 6 kHz. When sounds are presented through earphones, the free‐field characteristics of the ear are replaced by very different characteristics that are dependent on complex and unreliable interactions between the individual earphone and the individual ear. Since these interactions are highly dependent on earphone design, it may be appropriate to focus attention on the special characteristics that may be desirable in earphones intended for use in the creation of virtual acoustical environments. These may include coupling that (i) allows the response at the eardrum to follow the...

Noise environments outdoors and the effects of community exposure

Man‐made noise, especially transportation noise, creates acoustical environments that are vastly different from those associated with pristine habitats. During the past 25 years, the day–night average sound level, Ldn, has gained substantial acceptance as a valid measure of the magnitude of any given pattern of community noise, taking into account its complex temporal and spectral characteristics. During the same period, the effects of various levels of noise exposure on human activities and well‐being have been widely studied. Data from many social surveys have been brought together and analyzed to clarify the relationship between noise level and the prevalence of annoyance which provides a broad indication of the impact of intrusive noise on human communities. Criteria based on such studies are now widely used in urban planning. In recent years, there have been impressive reductions in the noise emissions from commercial aircraft and notable improvements in the control of airport noise, while highway ba...

Occupational noise exposures with uneven temporal patterns

ISO 1999:1990 presents procedures for predicting noise‐induced permanent threshold shift as a function of noise exposure which is defined in terms of the equivalent continuous A‐weighted SPL, LAeq,T over an average working day (assumed to be of 8‐h duration) for a given number of years of exposure. Measurements are to be made with instruments capable of integrating high level impulses. These procedures are, of course, dependent on epidemiological data pertaining to the standard work week composed of approximately five 8‐h work days. Nevertheless, daily exposure durations greater than 8 h and exposures that vary substantially from day to day are included in ISO 1999:1990, though subject to minor limitations. From another point of view, studies of temporary threshold shift, during and following exposure to steady noise for prolonged periods, seem to indicate that caution is justifiable. So, perhaps prolonged exposure durations should receive special treatment as suggested in the report prepared for the Special Advisory Committee on the Ontario Noise Regulation. [Work supported by APS707/NRCC No. 25051, Ottawa 1985.]ISO 1999:1990 presents procedures for predicting noise‐induced permanent threshold shift as a function of noise exposure which is defined in terms of the equivalent continuous A‐weighted SPL, LAeq,T over an average working day (assumed to be of 8‐h duration) for a given number of years of exposure. Measurements are to be made with instruments capable of integrating high level impulses. These procedures are, of course, dependent on epidemiological data pertaining to the standard work week composed of approximately five 8‐h work days. Nevertheless, daily exposure durations greater than 8 h and exposures that vary substantially from day to day are included in ISO 1999:1990, though subject to minor limitations. From another point of view, studies of temporary threshold shift, during and following exposure to steady noise for prolonged periods, seem to indicate that caution is justifiable. So, perhaps prolonged exposure durations should receive special treatment as suggested in the report prepared for the Spec...

Analytical concepts and models for calculating hearing protector attenuation

In principle, the ideal hearing protector is a rigid airtight cover or plug that encloses a volume of air in contact with the eardrum and is sealed to an immovable object (the head or the external ear) by a resilient airtight cushion or interface. According to this simple view, the sound attenuation curve is solely dependent on a few lumped elements: the mass and area of the cover or plug, the acoustic impedance presented by the enclosed space, and the stiffness and mechanical resistance of the cushion or interface. In practice, the attenuation is also dependent on air leakage, body‐conducted sound, the lack of rigid support, wave effects, and mechanical imperfections. These factors and others have been measured, estimated, and modeled with considerable success though perfect agreement between theory and experiment remains elusive. So, perhaps there is still room for further work of a fundamental nature. In the meantime, despite their limitations, the classical analytical models continue to provide an inv...

Session W. Special Lecture on Ocean Acoustics

Ocean acoustics is a rich field of study embracing unique modes of sound propagation, specialized means of acoustic transduction, meteorological, biological, and man‐made noise, sophisticated signal processing, and exploration on a vast scale. This special lecture is intended to give all members of the Society a broad view of an important area of acoustics which is the primary field of interest for nearly one‐fifth of the membership.

Session J. Peter A. Franken Memorial Lecture on Environmental Noise

Noise increasingly degrades the quality of our living environment and therefore demands the attention of citizens and scientists alike. This lecture, for laymen as well as specialists, identifies the main sourcse of disturbing noise, describes the adverse impacts of noise on people, and illustrates many ways in which noise can be controlled. Toward achieving a quieter environment, scientists and engineers in recent years have made many technical advances, including important ones made by Dr. Franken (1930–1972), a distinguished member of the organizations sponsoring this lecture.