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Starting with a basic concept.
Years ago, I learned to make a whistle from a fresh willow twig, loosening the bark, trimming the wood inside and sliding them back together. I thought it might be possible to do a similar 3D print design on the same plan, a hollow tube and a sharp edge to break up the air blown in from one end. Of course, it turned out to be "not that simple".

basic design

I did look at the Wikipedia article "The Physics of Whistles", and mostly it was over my head.

Narrowing it down
The trick seems to be to to have the exiting air be split on the sharp edge of the whistle's tube AND get the air flow moving faster at the exit of the mouthpiece. Getting the combination right took me six tries. Along the way, I added a loop to allow a lanyard for hanging the whistle around the neck, and put a hole about 3/4 of the way along the tube to make two tones. Covering the little hole makes a lower whistle.

During the development process, I came to believe this simplified theory of a whistle.

cutaway of whistle

While the first try "looked" essentially like the last, it made almost no noise, just a soft, hollow sound with neither volume nor sharp sound. The fix was to add a wedge to reshape the mouthpiece hole so it lined up better on the sharp notch and also concentrated the airflow (I think).

The design prints vertically, standing on the mouthpiece end. Because the mouthpiece is small, I figured the whistle would need support to keep from falling over. Unfortunately, the support structure not only helped hold up on the outside, there were support filaments inside the tube too. Version zero - fail. I switched to only using a brim for support and the printing worked fine from there on.

Of course, there's more experimentation to come. Moving the position of the tone hole, adding more tone holes, making the tube longer/shorter, narrower, etc. etc.

Maybe you will want to make your own versions based on this design. I'd love to hear from you about your own prints (email in page footer).

Available Files:

(In most browsers, right click each file you wish to download and select "save-as" from the menu options.)

SCAD files for study/modification and STL files for quick prints

whistle06.scad - whistle06.stl appx. 2 ½ hr to print on Lulzbot Mini
GPL3 License