The larynx-melon-vestibular-lips (LMVL) model of the dolphin sonar. 1. The larynx pulse source

In spite of extensive investigations extending over the last ~35 years, the dolphin´s sound production mechanisms and their sites remain as unresolved and, indeed, controversial problems. The larynx-melon-vestibular-lips (LMVL) model, proposed here, identifies established acoustic mechanisms with specific anatomical parts, and appears to account for most (if not all) of the observed performance of the dolphin sonar. The LMVL model is based on the following system components: (1) the larynx, controlled by the palatopharyngeal sphincter and operating as a “saw tooth” relaxation oscillator, is identified as the source of the echolocation pulses (the so-called “clicks”) and its acoustic output is coupled to the melon through the impedance matching nasal ducts; (2) the melon because of its low sound velocity, acts as a “slow waveguide” to form the observed forward-looking beam pattern; and (3) the residual air, forced from the premaxillary sac into the vestibular sec, is “lip modulated” by the interconnecting vestibular Lips, which act as the source of the frequency modulated tonal phonations (the so-called “whistles”)