TOKYO, Japan -- Dolphins rely on the combination of a variety of vocalizations and vastly better acoustic abilities than humans to communicate with each other or to detect their surroundings and prey in the dark sea. To gain new insights into how dolphins communicate, researchers in Japan created a prototype of an extremely broadband "dolphin speaker" capable of projecting dolphins' communication sounds, whistles, burst-pulse sounds, as well as detection sounds such as echolocation clicks.
Yuka Mishima, a graduate student at Tokyo University of Marine Science and Technology, along with university colleagues and collaborators at Fusion Inc., will present their research at the Acoustics 2012 meeting in Hong Kong, May 13-18, a joint meeting of the Acoustical Society of America (ASA), Acoustical Society of China, Western Pacific Acoustics Conference, and the Hong Kong Institute of Acoustics.
Dolphins can hear and produce not only low-frequency sounds below 20 kHz, which humans can also hear and produce, but go a step further to high-frequency sounds of up to 150 kHz, which are too high for humans to hear. Not only can dolphins produce tonal sounds like humans, they're capable of vocalizing at a variety of frequencies simultaneously.
"Acoustic studies of dolphins that have been done so far focus mainly on recordings of vocalizations and hearing abilities, but relatively few playback experiments have been conducted," explains Mishima. "There were no speakers that could project from low to high frequencies like dolphins, although some could project the low-frequency sounds or parts of dolphin sounds."
Since playback experiments are a very important part of gaining a better understanding of dolphins' communication and detection abilities, the researchers decided to create their own "dolphin speaker."
"Our goal was to develop a dolphin speaker that could project the full range of all of the sounds dolphins make," Mishima says. "We succeeded in developing a prototype broadband transducer for an echosounder last year by using new types of piezoelectric elements that had never been used for underwater acoustic transducers."
They applied this technique to their dolphin speaker prototype, and it can now project sounds in the 7 to 170 kHz range.
"The next step is to faithfully playback the original sounds of the dolphins by using the dolphin speaker. Once the dolphin speaker is completed it will enable us to playback a variety of dolphin sounds to dolphins, which will help to broaden the research of their acoustic abilities," notes Mishima.
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