Acoustic Characteristics of Insert-Earphone Versus External Earphone: Comparison through Sound Pressure Measurements in the Auditory Canal and Be'ke'sy Audiometry

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Abstract
The frequency response of an external earphone coupled to an ordinary earmould has been compared to a special insert-earphone, both through probe measurements of the sound pressure in the auditory meatus itself and through measurement of the threshold level with Békésy audiometry. The insert-earphone gave in both cases a greater effect, 10–13 dB at frequencies above 3000 Hz. This is imputed among other things, to the elimination of the lowpass filter action in the sound channel of the ordinary earmould. An increase in the sound pressure level which could be attributed to a reduction of the remaining volume in the auditory canal, was not noted. A radical reduction of this volume would, for practical reasons, be difficult to obtain with the material available. The significance of the insert-earphone's better high pitch response has been discussed and the practical difficulties involved in its use have been mentioned.