A cancellation technique for the amplitude and phase calibration of hearing aids and nonconventional transducers.

A difficult problem in specifying the characteristics of electroacoustic transducers is the fact that the sound pressure level measured in a standard coupler or artificial ear is not the same as that at the eardrum. A related problem is encountered in specifying the overall gain of a hearing aid. This latter problem is especially difficult because of the complexity of the acoustic coupling between the hearing aid receiver and the eardrum. An additional complicating factor is the acoustic effect of mounting a microphone on the body (usually on the ear). The above problems are conipounded by the difficulty of nieasuring acoustic power (or energy) directly. Whereas sound pressure is relatively easy to measure, it is much more dificult to obtain measurements of volume velocity. In order lo deternline the power of a sound, however, it is necessary to know both the prercrrre and the volume velocity, as well as the relative phase of these two variables. Alternatively, the power of a signal can he derived fi-om measurements of sound pressure and acoustic impedance. The latter variable is, in general, a complex quantity with both real and imaginary conlponents and It is also not easily ~lieasured. In view of the above difficulties, it is common