Evaluation of playback sounds by a newly developed dolphin-speaker

It is important to playback broadband sounds for the research of communication and echolocation of dolphins. Acoustic studies of dolphins mainly focus on recording of vocalizations and hearing abilities, but relatively few playback experiments have been conducted. To improve our understanding of their communication and echolocation abilities, an extremely broadband speaker, which is able to project communication sounds, whistles and burst-pulse sounds, and echolocation clicks, is anticipated. We developed a prototype Dolphin-speaker covering the frequency range from 30 kHz to 150 kHz within +/- 15 dB. Although the transmitting sensitivity of the prototype was almost flat at frequency band higher than 30 kHz, the sensitivity lower than 30 kHz was worse and it had some dips. Using two techniques, composition of the prototype and a Langevin-type element that has resonance at about 10 kHz and equalization for the ripples, the newly developed Dolphin-speaker has been improved having flat transmitting sensitivity from 5 kHz and 150 kHz within +/- 6 dB. A variety of sounds from captive dolphins were played back by the Dolphin-speaker. Visual and numerical comparisons of the playback sounds and originally generated sounds will be presented.