We know that dolphins and other cetaceans are amazing communicators, capable of making far more sounds than humans, but so far we've been unable to know what they're saying. Scientists at Tokyo University of Marine Science and Technology have developed a technology that may allow us to not only better understand their sounds, but possibly communicate with them too.
There have been plenty of studies that have recorded the sounds that dolphins make, but few that playback those sounds. Dolphins can hear and communicate at frequencies lower than 20 kHz and up to 150kHz, which is too high for humans to hear. They're also able to produce sounds at many frequencies at once. No speakers had existed that could project at that wide range of frequencies.
So, the Tokyo University team developed the dolphin speaker, an extremely broadband speaker that can project all the various communication sounds, whistles, burst-pulse sounds, and echo-location clicks that dolphins make and at frequencies from 7 kHz to 170 kHz. For it to operate underwater, the team used piezoelectric materials in its construction so that it will be powered by the bobbing of the waves.
The speaker is just a prototype right now. The team will next test the technology to make sure it can playback original dolphin sounds. Once they've developed a final version of the speaker, the goal is to conduct playback experiments with dolphins in the water and to observe what happens. These experiments could eventually give us greater insight into dolphin "language" and perhaps even let us directly communicate with them in the future.