This is a rectangle of plastic pipes with T connectors in the middle of both long sides. Through the use of telescoping tubes, either end of the interferometer can be extended out in a manner similar to a slide trombone. When a monotone is generated by a speaker in one of the T connectors, its energy splits and travels around both sides, recombining at the second T. By adjusting the extensions, the recombination can be made constructive or destructive. A microphone can be placed in the second T and connected to an oscilloscope. This permits the demonstration to be done quantitatively. You can use the apparatus in a few different ways: