(placeholder)


Glass blowers first noticed the phenomenon of "singing" tubes or pipes. Lord Rayleigh described the phenomenon in his book, Theory of Sound. Not only does heating the bottom produced sound but he claims so does cooling the top with ice. He gives an explanation for the production of the sound. Interestingly this phenomenon is related to thermo-acoustic engines where the reverse occurs: sound cools one end of a pipe and heats the other.


With classic English understatement Rayleigh discusses "a very effective lecture experiment. For this purpose a cast iron pipe 5 feet long and 4 3/4 inches in diameter may be employed. The gauze is of about 32 meshes to the linear inch, and may advantageously be used in two thicknesses. It may be moulded with a hammer on a circular wooden block of somewhat smaller diameter than that of the pipe, and will then retain its position in the pipe by friction. When it is desired to produce the sound, the gauze caps are pushed up the pipe to a distance of about a foot, and a gas flame from a large rose burner is adjusted underneath, at such a level as to heat the gauze to bright redness. For this purpose the vertical tube of the lamp should be prolonged, if necessary, by an additional length of brass tubing. When a good red heat is attained, the flame is suddenly removed, either by withdrawing the lamp or stopping the supply of gas. In about a second the sound begins, and presently rises to such intensity as to shake the room, after which it gradually dies away. The whole duration of the sound may be about 10 seconds."1 Indeed, the one shown to the left is of similar design and was heard four stories up when demonstrated at Conoco Research Center in Ponca City.


When demonstrating this tube, you may have to adjust the length with a stiff magazine wrapped around the top as shown here to get maximum effect. Talking across the top may amplify your voice. Puffing into the top stops even the loudest honking, as does tipping the tube on its side.


An explanation: an electric heating coil placed on a screen about a quarter the way up the tube heats air. But a sound wave changes the air temperature periodically. When the air is cool near the heater, it dumps energy faster contributing to expansion and the pumping of energy into the next wave cycle. So there is sound stimulated emission of heat into the sound wave, just like stimulated emission of light into a laser beam. Hmmmm....a SASER?


Thanks to Mike Lucas and the Department of Physics Machine Shop for design and construction.


1. The Theory of Sound: J.W.S. Rayleigh (Dover, New York, 1945) Volume 2, page 232.

Rijke Tube