Sewerin Leak Correlator Hydrophone Kit - For SeCorr C200 or SeCorrPhon AC200Hydrophone Kit For SeCorr C200 AC200 Leak Noise Correlator Most leak correlators use microphone type sensors to pick up leak sound traveling down the wall of the pipe or tubing. Sound does not travel the same speed or distance on different materials. Sound on Plastic pipe travels only around 200' limiting the usefulness of most leak correlators in plastic pipe systems. The HYDROPHONES are designed to listen for the leak sound in the water column