Scout / Police whistle experiments

[JonL]

After following some of the other posts on whistles with interest I've got my hands on an Acme City whistle of the kind policemen used to use. It would appear that there are lots of collectors so they crop up quite a lot on eBay. The one I have is tatty nickel plate but wire-wheeled back to brass quite quickly with no perceptible change in tone.

After reading others experiments on this forum I have tried the airline at 80 psi with a 10mm gap between the nozzle and the mouthpiece to allow it to induct air between the two; also as an experiment I sealed it entirely to the nozzle so that the only air going through was being supplied by the airline. The sound with the 10mm gap was far superior; I'd be very happy to have that as my whistle. My idea is to have a soldered on nozzle similar to an injector or gas mixing valve on a gas hob, possibly threaded to allow me to make adjustments to the gap. I'll record and document the results here if there is interest.

Photos to follow shortly.

[mbrown]

Interesting... but my hunch is that your 10mm gap is simply lowering the volume of air through the annulus to something close to (a policeman's) lung power.

LBSC got the same result by soldering a nipple into the mouthpiece with a small hole through it - about 1/16" IIRC. I did the same with the slightly smaller Boy Scout whistle and got a good result.

I am all for experimentation, so I will be interested in your result - but, to me, it looks like doing things the hard way!

Malcolm

[JonL]

My intention is to use this as a test rig, you could be right about the volume drop, but I don't know enough about the physics of it to work out exactly what is going on at this stage. I think I'll experiment with nozzles and distances etc until I get the best result I can, then work out the physics after!

As you say, it should be interesting even if I don't adopt the final result. Initial experiments were a good loud clear tone, so I'm fairly hopeful. Of course this is with cold, dry compressed air rather than steam.

[JonL]

As arrived prior to cleaning 




After a quick coat of looking at. Blows with a pleasing note, the two notes pleasantly discordant if that makes sense. Unlike a "warbling" whistle it seems to not get too shrill on compressed air. The airmans whistle I tried on compressed air left my ears ringing.

Next up I'm planning to make an adjustable nozzle.

[mbrown]

That looks identical to eh Boy Scout whistle I used, except mine was plated in a bronze finish!

Malcolm