Clogged Pipes Make A Special Sound, Mathematicians Report

With further development, the method could be used to remotely track down problems in unpleasant areas like sewer lines.

The group built a device that -- like the echolocation used by bats and dolphins -- sends out high-pitched frequencies and listens to the sounds that bounce back. The listening device first records the profile of reflected sound coming back from an empty pipe. When the pipe is blocked, this sound profile changes. Using a signal-processing technique called matched-field processing, Tolstoy picks out the more important changes and calculates how long these frequencies took to bounce back to the two microphones on the device. This time indicates how far along in the pipe the clog is located.

The team has tested the device on a variety of different kinds of pipes -- concrete, PVC, clay -- blocked up with a different sizes and amounts of sandbags and bricks. The technique is not affected by twists and turns in the pipes. For the moment, only empty, air-filled pipes have been tested. In theory, the technique should work just as well with fluid-filled pipes, though further work would be needed to compensate for the dynamics of the fluid.

The talk "Detecting and localizing pipe changes via matched field processing" by Alex Tolstoy et al will be presented at the 157th  Acoustical Society of America Meeting to be held May 18-22 in Portland, Ore.