ASA 124th Meeting New Orleans 1992 October

4pPPa20. Effects of standing waves on high-frequency thresholds.

Bin Zhou

David M. Green

Psychoacoust. Lab., Psychol. Dept., Univ. of Florida, Gainesville, FL 32611

The effects of standing waves in the ear canal on high-frequency pure-tone thresholds were investigated. Sound was transmitted from a transducer to a high-impedance source by a long plastic tube 0.64 cm in diameter. The high-impedance source was coupled to the ear canal by a shorter plastic tube 7 cm in length. Thus a standing wave field was created between the high-impedance source and the eardrum. Using a broadband stimulus, standing wave patterns were recorded by a small microphone placed near the high-impedance source. Several maxima and minima of the standing wave pattern were located in the frequency range from 6000--12 500 Hz. Thresholds were measured at two successive minima, the maximum between them and two intermediate values. Thresholds were also obtained with the high-impedance source removed from the system, resulting in a source impedance approximately equal to the characteristic impedance of air. Thresholds with and without the high-impedance source were compared and standing wave ratios (the difference between thresholds at the standing wave maximum and minimum) of 5--10 dB were observed. [Research supported by NIH.]