The physiology of the locust ear

III. Acoustical properties of the intact ear

Summary

The sensitivity of three different preparations of the tympanal organ (“isolated”, “operated”, and “intact”, see Fig. 7a–c) has been measured over a wide range of frequencies (Figs. 3 and 6). The sensitivity of the intact ear to low frequency sound depends on the fat content of the animal (Figs. 4 and 5). The effect of diffraction (Fig. 8), the sound absorption in internal tissues (Fig. 10), and the sound transmission through the animal (Fig. 9) have been measured in order to explain the observed sensitivities in the three preparations. The internal tissues seem to act as an acoustic low-pass filter. Therefore, at high frequencies the intact and operated ears are acting almost as pressure receivers (Fig. 2a). The isolated ear is acting as an unbaffled pressure gradient receiver (Fig. 2b) with an “effective distance” of 0.8 mm. A mathematical model for asymmetric sound receivers is presented and used to calculate the force acting to move the tympanum in the operated ear at low frequencies. The driving forces in intact and operated ears are of the same order of magnitude as in a similar pressure receiver (table). The membrane vibrations at high frequencies are heavily damped both by the radiation resistance and by friction in the internal tissues behind the ear. The implications of these results for the understanding of directivity are discussed. Some common methods for determination of threshold are compared.

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Michelsen, A. The physiology of the locust ear. Z. Vergl. Physiol. 71, 102–128 (1971). https://doi.org/10.1007/BF01245156

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Keywords

  • Pressure Gradient
  • Common Method
  • Driving Force
  • Radiation Resistance
  • Sound Absorption