Tea Kettle Acoustics
Ambience: Tea kettle whistle
Announcer: How does a tea kettle make its whistling sound? Like many things in the world of science, the answer isn’t a simple as it may seem. I’m Jim Metzner and this is the Pulse of the Planet. Ross Henrywood is a researcher in the Engineering Department at Cambridge University in the United Kingdom.
Henrywood : Now in a kettle, we have a spout, which is a length of pipe, and in the end there is this whistle. In most tea kettles that use this whistling arrangement, there are two small plates, typically about an inch in diameter and separated by about half an inch, and there’s a small hole through the middle. So the steam has to come up through this large duct and contract to go through whistle. It’s that contraction that forms a jet. We’re trying to work out why that jet made a noise.
A typical tea kettle’s produces a suite of sounds that builds to a crescendo.
Henrywood: When the kettle just starts to boil, the whistle actually behaves like what you get when you blow over an empty wine bottle. The air inside the neck of the bottle starts bouncing up and down. But when flow increases when the kettle boils more vigorously, it switches to another mechanism.
Announcer: In its final stage, the whistle produces is shrillest sound.
Henrywood: You can imagine that if you’re playing a recorder..and you’re playing nice low notes, but If you suddenly blow much harder you get a higher note.
Announcer: A similar phenomenon occurs inside the spout of the tea kettle as the acoustic wave inside bounces back and forth at a higher rate.
Ambience: Tea kettle whistle
Ross Henrywood’s findings may also have a bearing in situations where a whistle is unwanted.
Henrywood: This goes on for various things: household plumbing, car exhaust, industrial pipelines anything that involves a pipe with two constrictions that whistles, might be due to this mechanism. If it is, we can potentially take steps to eliminate it.
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