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Reply by Don Johnson

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Posted on Whistle design

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Don Johnson

604 posts in 1379 days


#1 posted 536 days ago

I think i figure out the deeper the hole the deeper the sound but apart from that it must just be magic.

As I understand it . . . . .

Blowing air across the sharp edge initially causes it to fill up the hole in the body, until the pressure rises so much that no more can get in – then the blown air deflects OUTSIDE the body, and sucks out some of the air inside as it does so (the Venturi effect – as employed in spray guns for example)

When the pressure inside the body drops sufficiently, the air can be deflected inside once again, and the whole cycle repeats.

The time it takes for a cycle obviously depends on the volume of the hole in the body, therefore, so does the pitch of the note made by the process.

For a successful whistle – or organ pipe – the flat on the dowel has to direct the air at the sharp edge, in a pretty thin stream.

In the organ pipes I made for my busker organs http://www.donjohnson24.co.uk/banjo.html the gap is made using cereal packet cardboard, which at 0.5mm is just about right. (The red bit in the diagram below)

Moving the stopper adjusts the pitch. The shape of the pipe affects the ‘quality’ of the sound – and so does the material used.

-- Don, Somerset UK, http://www.donjohnson24.co.uk


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