Heterodyne interferometer measurements of the frequency response of the manubrium tip in cat.

A heterodyne interferometer proved to be a very accurate tool to measure amplitude and phase of the malleus response during acoustical stimulation. It was shown that to obtain equal accuracy in the acoustical pressure measurements, pressure response must be remeasured at short time intervals. At frequencies above 4 kHz various gross resonances are apparent on the frequency response curves. The resonances are, depending on the animal, more or less pronounced. As a result of the improved accuracy changes of the malleus vibration response with time could clearly be discriminated. These changes can be related to shifts in frequency of the position of these resonances. Comparison of experimental frequency response and lumped parameter model predictions from literature shows that these resonances are not present in the model responses.