WTT - Window proportions - Makers especially wanted to reply

Whistle
1

Of course, if you’re a user who wants to gimme some knowledge, too, I’ll be most happy to listen!

I’ve been struggling with window proportions recently. There seems to be a wide variation in what works, and what doesn’t work, and how well. Over the past month, I’ve been reviewing my heads, and as a result, did a complete redesign based on my own ideas, plus a design I got from Stacey O’Gorman of Alba, and some ideas I noted in my Busman that I liked. (Both Paul and Stacey know about all this - no question of “theft” of intellectual property.) Anyhow, here’s what I’ve come up with - it gets real measurement-oriented here, so bear with me…

The new head was prototyped in a new model of the Polly, for the sake of simplicity. (you can see a picture of it here: http://www.serpentmusic.com/development/brassypolly.html - the beak hasn’t been cut on these). When Stacey saw the pic, she mentioned that the opening looked too long, and would make the octave shift more difficult. Here are the original measurements I used:

Tubing OD = 0.625
Tubing wall thickness = 0.070
Nominal ID = 0.485 - variations +/- 0.005
Embouchure slot length = 1.25"
Windway width - 0.25
Blade angle approx. 32 deg
With fipple plug installed, and the bell end of the brass collar parallel with the end of the plug, my original window opening from the end of the fipple plug to the bottom of the blade curve, was 0.375.

With those dimensions, I got a fine bell note, good response in the initial octave shift, – BUT – you have to really “lean into it” to go into the top of the 2nd octave, and low end of 3rd.

I finally settled on a window opening (lengthwise) of 0.30, which seemed a good compromise. Shorter, and the bell note gets really “difficult”, longer, and the upper end suffers.

To my question (finally - whew!):
Is there an equation that anyone knows about, for calculating this stuff based on all the above variables, and the range of the whistle? There almost has to be, but I can’t find anything at all!

TIA, hopefully, :confused: :slight_smile:
serpent

2

Think of the way flautists (traverso) change registers
and compare with the way whistlers do…

Theoretically, the hole length (windway to blade) should be crossed by the airstream in the same time as the duration of one half-wave of the favored frequency. Suppose you aim for concert A the you should cross the window in 1/880 s.
Now equate this with the stream speed, if you can get hold of a miniature anemometer :wink:

If you make the window shorter, you’ll flip up too easy.

If you blow faster, you’ll hit next register.

According to this rule, you may note that Alba’s original moon-shaped blade may favour a pretty wide gamut of frequencies, rather than one alone. A slanted blade would act similarly…

3

Hmmm… the curved (crescent) blade is an artifact of the milling process cutting into a cylinder on an angle. Mine is also a crescent. Perhaps that’s where the problem lies, but given the rest of the construction, there’s really no way to avoid it without (yet another) redesign! One shot on Stacey’s site shows a hog mill cutting into a tube longitudinally, which makes perfect sense WRT her blades. (The SE is anomalous in that respect, using a flat laminar and straight-edged blade). So, I guess another approach is to toy with the width of the windway, as well as the length of the window. In my narrow-bore Brassy Polly, that would have a pronounced effect on the exposed blade circumference. Unfortunately, it would also decrease the backpressure and increase the air requirement. Still, might be worth a try!

Thanks, Zoob, and if you find a source for the teensy anemometer ( maybe “Anemometers “R” Us” ?? :laughing: please do put me onto it!
Cheers,
serp

4

Just a word on the anemometer thing..

You can probably get one of those medical lung-power-measuring-things, blow as you would blow into a whistle, and calculate from the volume of air moved to find how fast it goes through.

5

(Gosh, how I’m wishing for a “Bill the Cat” emoticon!!!) :boggle: :astonished:

MORE EQUATIONS!!! I thought I got outta that stuff DECADES ago!!! :smiley:
Yikes!
serpent

6

A true anemometer, else than a meteorological one (sort of windmill where you measure the speed of rotation, or the electrical output of a generator) would be rather uncomplicated:

Suffice a U shaped transparent plastic tube, held vertically, and half-filled with a coloured liquid. Mix it with some wetting agent (Photo-Flo), for the narrower the tube, the better, but surface tension (“sticking” to the walls) is a limitation.

One end (branch of the U) is left open to the air (brings in the “static” pressure); the other connects to a duct opening in front of your windway (dynamic pressure). The shorter this duct line, the better.

  • mark the zero (balance point of the two liquid columns.

  • take the whole contraption on top the back of your pick-up (every true Westerner drives a pick-up, right? :stuck_out_tongue: ), mark the lines for 30, 60 on your speedo. Have someone else drive, if you want my inmate tip-onion…

  • Your anemic mater is now cow-liberated. (Trying to speak Western here.) The nice thing is the progression is linear. Half the mark for 30 mph= 15 mph.

  • If you know a good mechanic, the kind into racing/tuning, esp. for motorcycles, he has a depressiometer * made to balance carbs throughput. You could start from that stuff, using two out of the usual four quicksilver-filled columns. You’ll need to pencil out the reference marks anyway.

  • Now all you have to do is hook the probe in front of a whistle duct, measure typical speeds for fundamental octave and overblown regimes.

  • PS: I’m the one measurably depressed, and deprecattled: OutOfBreath hints it’s called a vacuum gauge with you cowboys and knnnnigggets.
7

Zoob, you are amazing! :smiley:



Frightening, :astonished: but amazing!

Cheers, :smiley:
serp

8

Would that be what we cow-liberating westerners would call a vacuumn gauge?

Hmm, come to think of it, seeing as how most cars are EFI now and loaded with sensors, you could probably get suitable and fairly accurate sensors from your local wrecking yard. Of course, you might want to make real good friends with an automotive engineer for access to interfacing information… :laughing:

John

9

Hey Bill,

The answer from my standpoint is, no. No equations. There might actually be some, but I don’t know of them.

My measurements vary between .15"-.2" depending upon what characteristics are desired. I also find that the longer the measurement, the stronger and bolder the lower end - with the sacrifice being in the upper end (both in over-volume and stability). I will also vary the width in quieter whistles, though I am looking for a different approach for this.

I came to these measurements by trial and error, but based my original try on measurements taken from various wind instruments. I, of course, was very wrong, but eventually honed in on “a” right setup.

Erik

10

How do these measurements vary for different keys of whistle?

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Jerry, take Erik’s measurements. Enter them in the equation I reminded–presto, you can infere the correct size for another tone.

In other terms:
Window1 (length) * Frequency1 (Hz) = Window2 * Frequency2

What I can see, though, is that all this rule has also to be–this try and error–moderated by the slope of the blade.
Typically, my Rose’s labium is farther away from the windway than my Sweet’s, yet it’s the Rose which climbs up easiest. Now, the Rose has a sharper blade wedge.

Btw, interestingly enough, the Sweet has also the narrowest window, yet is the loudest by a good margin. I picked these two because of the materials used, bores* and wind demands, being almost identical. So much for rules of thumb…

  • Note the Sweet has a smaller bore in the upper part, down to the tuning assembly, i.e. a bit à la Boehm
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A true anemometer, else than a meteorological one (sort of windmill where you measure the speed of rotation, or the electrical output of a generator) would be rather uncomplicated:

THe windmill device thingie might be found on an existing product. IT is called a “Sherpa” its a Watch / relative humidity / altitude / temperature and wind speed measuring thingie that fits in your hand. Unfortunatly it costs about $180, and it might not exactly work. (probably the resolution is a bit too wide)