Acoustic basis of tuning fork tests.

OBJECTIVES

To obtain pilot data to determine the feasibility of supporting or refuting a theory regarding lateralization of sound in conductive hearing loss and to describe the application of this theory to other tuning fork tests.

DESIGN

Controlled audiometric testing with and without a conductive hearing loss.

SETTING

A tertiary medical centre.

METHODS

Sound pressure levels in external auditory canals were measured during presentation of 40- and 50-dB bone-conducted stimuli. Measurements were taken from five normal male subjects before and after inducing a conductive hearing loss.

OUTCOME MEASURES: If sound intensity in the ear canal was greater in the unobstructed ear canal than the obstructed ear canal, the hypothesis was supported. The number of subjects required to provide definitive proof was calculated from the measured intensity difference with and without the conductive loss and the intrasubject variability of sound intensity measurements. The applicability of the theory to other tuning fork tests and auditory phenomena was explored.

RESULTS AND

CONCLUSIONS

A total of 600 subjects would be required to provide evidence to support our theory using this method. The acoustic impedance mismatch-reflected sound theory could be applied to other tuning fork tests, but until further proof is available, it must be considered only a theory.