Development of the Dolphin Speaker

To gain new insights into how dolphins communicate, we created an extremely broadband speaker called the “Dolphin Speaker”. To communicate or to detect their surroundings and prey, dolphins rely on a combination of a variety of vocalizations and vastly better acoustic abilities than humans have. Acoustic studies of dolphins have focused mainly on recording vocalizations and assessing hearing abilities; there have been relatively few playback experiments, which are very important for gaining a better understanding of dolphins' acoustic abilities. This is because there have been no speakers that could project broadband sounds in the range that dolphins use, from several Hz up to more than 150 kHz, although some could project low-frequency sounds or parts of dolphin sounds. In 2011, we succeeded in developing a prototype broadband transducer for an echosounder by using new types of piezoelectric elements that had never been used for underwater acoustic transducers. We applied this technique to our Dolphin Speaker, and it can now project sounds from 8 to 170 kHz within ±6 dB. The Dolphin Speaker's beam width is 17.5° at 120 kHz. The structure of the Dolphin Speaker and the dolphins' playback sounds by using it are also described.