JeffC Hit my point of argument.
A Boehm Baroque flute uses a “Boehm Taper” and a calculated cavity to match the “Cut-off Frequencies”, or as Benade states, the “W” waves between the overblown registers. A Modern Boehm flute uses the entire length of the headjoint as a tapered reflector.
In Recorders without this tuned reflector/cavity, the pinching technique is used to correct for out of pitch, phase shifted second register tones. If a Recorder used a Boehm Taper/Reflector cavity in the headjoint,like a Generation whistle, it would have much better frequency matching of the toneholes between registers. In other words, the toneholes wouldn’t go as flat in the upper registers due to phase shift. A Tin whistle with a flat face fipple plug must use embouchure bending in all the upper registers to correct for the phase-shift flattening effect.
A Generation design uses a 1/2 Parabolic Reflector to gather acoustic energy from the area beneath the voicing, into its upper focus and reflect it strait down the bore in a cylindrical shape(like a flashlight beam) without the ineffecient wasted space around the rim of the flat fipple plug face that causes an increase in “effective cubic volume” under high pressure. If this were a 1/2 Eliptical Reflector it would gather acoustic energy into its upper focus and reflect it to the secondary lower focus beneath the voicing window(like a beam that shines out in an expanding cone after the “cross-over” at the second focus).
If the internal shape is a cylinder with a flat faced fipple plug, the energy wave from the voicing would strike the face of the plug, travel 90 degrees out to the sides, back to the center and then down the bore. This extra travel of the soundwave is much more evident in the high pressure upper registers, resulting in very flat scales the player needs to “embouchure bend” for correction. Any irregularities in the shape of this reflector would be the same as an out of position/warped plug in a flute, causing negative feedback and reduced acoustic response.
Can a whistle do without a Boehm Taper reflector? YES, but the player would have to use skill and a perfect ear to compensate for an inferior design that is unbalanced between registers.
Thomas,
I checked pitches on my favorite tweaked Waltons mellow D whistle. Then I untweaked it.
Absolutely no difference whatsoever in pitch accuracy. The notes that blew sharp with normal playing blew the same degree sharp with or without the cavity filled. The notes that blew flat with normal playing blew the same degree flat with or without the cavity filled.
If you look carefully at the whistleheads, the area under the windway isn’t paraboloid; it’s a nearly pure circular radius.
I remain skeptical of your theory about the purpose of that cavity. I’m still convinced it’s only there to facilitate injection molding.
Best wishes,
Jerry
I agree with Jerry in this. It’s tempting to compare whistles and side-blown flutes, but they’re 2 very different beasts.
g
Well Jerry, you are entitled to your opinion and I guess the Master Acoustic Mathematician, Mr. Arthur Benade, is mistaken and you are correct. I was parroting his research, not my own. Was your test done with an oscilliscope and a regulated wind source? Did you subconsciously correct pitch with your breath control?(unregulated CFM).
I did use an oscilloscope, or a software equivalent of some of an oscilloscope’s functions.
Thomas, I’m not interested in being right. I’m interested in results. If I had found that having the cavity filled or not filled made a difference in the pitches, I would have posted those results.
I need to know the outcome of that test, whether it’s the outcome I had expected or not, because I’m in the business of tweaking whistles. Anything that can provide clues to how to get a whistle to play better, I’m interested in, even if it means I have to change my opinion in the face of a different than expected result.
On that particular whistle, it would take some very contrived playing to blow the notes far enough sharp or flat to offset any significant difference in pitch between the two tests. Playing the whistle, it’s obvious where each note naturally falls.
I’m sorry, Thomas. As I’ve said, I have only the highest regard for your expertise, and I’m grateful for your willingness to share information. And, as I said, I hope you’ll forgive me for disagreeing with you on this one.
Best wishes,
Jerry
WOW! 
I must confess that this is actually the type of point-counterpoint material that I enjoy reading. (I still haven’t tried the test on my own whistles, but Jerry’s results are definitely interesting) Admittedly I know virtually nothing of accoustics, and my whistle tweaking is definitely of the trial and error type. I am very thankful for this forum though, and for the oppurtunity to have ideas presented to one and all. Through this thread I have learned a bit more about tweaking whistles, and as I continue to browse the site I will probably learn more. To learn is actually one of the reasons I am here. 
oh yes, by the way Jerry, you mentioned a tweaked mello-d, I just acquired a LBW and can’t do much with it, do you know of any LBW specific tweaks?
Thanks
JeffC
The main thing with a LBW head is, where does the windcutter blade edge align with the windway? Sight into the mouth end of the whistlehead. If the windcutter blade edge is low relative to the height of the windway (just a little above the windway floor, they tend to tweak up pretty easily. If the blade edge is high relative to the height of the windway (just below the windway ceiling) they’re much harder to tweak. If the latter configuration tweaks successfully at all, it will typically need a blade edge lamination tweak. The former configuration often tweaks well with just filling the cavity under the windway and adjusting the blade edge sharpness (sharper to strengthen the upper register, blunter to strengthen the bottom two notes of the lower register). Also, The Whistle Shop sells LBW heads separately for about $3.50 each. It’s worth asking Thom to check and see if there’s any variation in the ones he has to try to pick a good one (I’ve never asked him, so it’ll be interesting to find out if he’ll look).
oh yes, by the way Jerry, you mentioned a tweaked mello-d, I just acquired a LBW and can’t do much with it, do you know of any LBW specific tweaks?
My personal choice of LBW tweak is to run it over with a car 
Needless to say, I’m not quite a tweaking person
Sometimes the LBW heads are good, though they’re highly variable. Most people throw away the LBW tubes and put the head on a Generation/Feadog/Oak/etc. tube.
This inspired me to tweak my own Gen Bb, what a difference! On this whistle the bottom part of the airway was cracked, i fixed this by filing the whole bottom part down a bit with a custom cut emery(sp?) board. Then I superglueing a little piece of thin plastic in it’s place to make a smooth bottom on the wind way. This reduced the airway a bit, now the whistle needs less air & jumps to the next octave a little easier. Both of which don’t bother me on a Bb anyway. The whistle played better after this. Then I filled in the “pocket” under the airway (with candle wax) & flattened everything out with a coffee stirer & the emery board. This was also a change for the better.
Kla-zam! A good Bb whistle, in retrospect why the hell did I bother doing all of that stuff when I could have bought a new one for $10? I guess it’s the DIY in me.
Hi, Brad.
Laminating a piece of thin plastic to the floor of the windway is one of the tweaks that helps focus the timbre of most whistles. Ususlly, the windcutter blade edge is a little higher than ideal, in relation to the windway floor. In other words, before the tweak, too much air goes under the blade edge and the sound is “muddy” compared to after the windway floor lamination tweak. The tweak also gives a little more back pressure and helps make the whistle more responsive.
Best wishes,
Jerry