The Clark Synthesis Aquasonic (AQ339, formally AC339) is an economical moving-coil design underwater pool speaker providing louder, more bass rich sound than the UW30. Possible uses for the Aquasonic include providing underwater sound for flotation tanks, watsu massage, synchronized swimming, etc. For lap swimming (where very high sound levels are required), the Lubell LL916 underwater speaker is recommended based on reports from high school swim coaches. The Aquasonic is rated at 135 watts continuous @ 4 ohms, and has an attached 100' Enduroflex jacketed 2-conductor cable. Lubell Labs recommends using the Aquasonic with the A-120 PA amplifier listed below exclusively, because amplifier is UL listed, has transformer isolated 4 ohm output, and has 3-prong grounding power cord for connection to GFCI outlet.