A while ago I posted that I had made a very quiet pennywhistle. Today I was thinking more about such things, in the context of what instruments to give to small children [1], and dug up this whistle:

normal whistle, then quiet whistle

You can hear it's much quieter than a typical whistle. Comparing it with my Generation and measuring SPL [2] I get:

	Low D	Low G	High D	High G	High B
Generation	52	53	59	66	64
Quiet	35	38	45	57	52

(Compare to some other methods, but note that our measured numbers are in very different ranges.)

The basic idea is to make the hole in the fipple much smaller than usual, and make the holes smaller as well. Ideally it would also be a smaller diameter, but that's the size of PVC tubing I could get.

[1] It's not actually a very good fit for that purpose. It requires very careful breath control to make any noise at all, so someone who didn't already play whistles would probably get frustrated and bored without figuring it out.

[2] SPL in dB at one meter measured with Sound Meter Lite on a Moto X, uncalibrated. Background noise registered 33dB, which means the low notes on the quiet whistle were barely loud enough to register and so are likely inaccurate.