Underwater speaker
From Beam Reach Wiki
We use an underwater speaker (intended for synchronized swimmers) to measure how sound propagates in different environments. The Lubell system (model 9816, akin to the caged LL916C projector has a maximum output level of 180 dB re 1 microPa @ 1 m for a 1 kHz tone. In spreading lab exercises off the Friday Harbor Lab docks, we have measured source levels of about 160 - 170 dB re 1 microPa @ 1 m with a typical sound sample and gain settings.
