Sunday, February 03, 2008

“You know how to whistle, don't you, Steve? You just put your lips together and blow.”

This post is about the air whistle, (similar to a steam whistle) I designed and wrote about in the last Make Magazine.

This PVC whistle is based on a calliope design that provides a lot of noise at relatively low air pressures. I called it the Super Tritone after a train whistle my friend Steve Cox owns, which is called a Leslie Super Tyfon, (although technically, the Super Tyfon is a horn, not a whistle.)

There are several good articles in Make Magazine #12, the latest issue. I’ve contributed three, including a major project called the Super TriTone Shop Whistle. I’ve written and photographed step-by-step directions showing how to make a really neat whistle from PVC pipe and fittings. If you don’t subscribe to Make Magazine, try to locate a copy. You can subscribe online to this wonderful magazine here.

If you sign up using their autorenew feature (no big deal, you can always cancel) you will get online access to all of Make’s voluminous archives of projects including this one. That's a good deal, believe me. There's a lot in there.

Adjusting the Super Tritone Shop Whistle

The Super Tritone is easy enough to make, see the Make Magazine article for details. But be forewarned -- it takes a while to adjust. There are a number of critical dimensions and if any of them are off, the whistle doesn’t sound, it mostly just hisses. However, adjusting the Super Tritone isn’t that hard, mostly consisting of turning the adjusting nuts on the main shaft, thereby making the whistle throat larger or smaller. At some critical dimension, it will provide a loud shrill tritone.

If you’re still having trouble, first make sure there are no leaks where holes have been machined through the PVC. Those leaks are sound killers so all holes and joints MUST be air tight.

Next, look at the alignment of the bells (the larger PVC pipe with the edge filed into the bottom) with the opening through which the air passes. The air opening is an annular slit, formed by the PVC bowl and a slightly smaller plastic disk called the languid. The placement of the languid is critical.

In connection with that, you’ll need to turn the horizontal adjusting screws on the bell and the bowl to make sure the air escaping the languid goes straight up into the edge on the bottom of the bell.

Finally, use enough air pressure. You’ll likely need 50 psi on up to get a really good sound.

Whistle physics is tricky and therefore, so is making your own whistle. But with enough adjustment and experimentation, your whistle will sound great. Be sure to read read all disclaimers and warnings in the magazine before you start.

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