I know we’ve discussed it in the past, but I don’t think we ever came up with a satisfactory decision regarding concave fipple blocks vs. flat-faced ones.
Almost all whistle makers use flat-faced fipple blocks, and the ones I’ve talked to about it say they can’t tell any diffence between flat-faced and concave… which has been my experience as well, but maybe we’re all missing something! 
It would only take a couple of minutes to add the concave to the fipple block, and I’d gladly add it to mine if it made even the slightest difference … but I just can’t tell any diffrence, even though it seems like it really should make a difference.
Ah…you mean the inside of the whistle…where the fipple block ends? The place you fill in with sticky tac on cheap whistles?
I’ve never been able to discern a difference.
Best wishes,
Jerry
I believe Glenn does this on the Water Weasel.
Yes he does… and aside from an early Silkstone alloy D, my Water Weasel D is the only whistle in my collection that has a concave fipple block.
As for the Silkstone, Paul told me he only made a few with concave fipple blocks because he couldn’t tell any diffence with or without it.
I wonder where the idea originated, and who ever thought it actually made a difference! 
You know how whistles sound very similar when you listen to soundclips as opposed to when you hear yourself playing? I wonder what kind of difference you could tell the same way. Doesn’t sound like you can from what you are saying.
I’ve experimented with one or two concave fipples, and couldn’t tell a bit of difference.
Some people have gone the opposite way on flutes and built a bit of a spike onto the plug, but I haven’t tried this.
The purpose of the spike on the plug of a flute is to adjust the upper register tuning to match the lower. I would be interested in knowing what other whistle makers do to get the tuning to match between octaves.
Best wishes,
Jerry
I have tried various configurations when tweaking inexpensive whistles such as Gens. The only difference I have found is a change in the “raspiness” if I fill the area under the windway. I have tried different shapes and materials for the filler and have not been able to discern any difference.
Ron
I’ve tried the spike before on whistles to adjust upper octave tuning.
Didn’t go any further with it, just an experiement.
What I’ve discovered is that the octave balancing has almost everything to do with the bore size (bore to length ratio). If the octave is flat due to too large of bore a constriction in the bore near the head will sharpen it to bring it into balance. The spike (or some makers use a wedge or tapered head) will achieve this or an insert both of which are perturbations. If the bore is too narrow then the octave may have to be flattened which can be achieved by using the concave plug approach. This can be seen in silver flutes which use an adjustable plug to adjust the octave balance. Sliding the plug open will flatten the octave and the second octave notes by basically increasing the size of the bore (total volume in bore).
Perhaps some of you haven’t noticed any difference because the concave is so slight so as to not make much of a difference.
This observation of mine is not based on anything but experimentation so don’t quote me or do anything foolish like that. Just try it out.
Ronaldo