Biophysics of the ensiferan ear - III. The cricket ear as a four-input system

1. The small (anterior) tympanal membrane in the ear of the cricket Gryllus campestris L. is non-functional in hearing (Fig. 4). 2. The large (posterior) tympanum vibrates in its basic mode in the entire frequency range investigated (1-30 kHz). 3. The velocity and the phase angle (sound pressure to vibration velocity) of the large tympanum are very much influenced by whether the ipsilateral spiracle is open or closed (Fig. 5). 4. The velocity and the phase angle of the large tympanum are less influenced by the state of the contralateral spiracle. The experiments demonstrate, however, that sound waves in the frequency range from 1 to 22 kHz travel from the contralateral spiracle through the connecting tracheal tube to the back (internal) surface of the tympanum. The internal sound pressure (p_b) thus provided amounts to about 35% of the sound pressure (p_f) acting on the front (external) surface of the tympanum. This part of p_b is rather independent of frequency (Figs. 6 and 7). 5. The velocity and the phase angle of the large tympanum are little influenced by sound transmitted through the contralateral (large) tympanum. The p_b thus provided amounts to 10-20% of p_f (Fig. 8).