I believe that whistle voicing can be more versitile. Would you like a whistle that plays “string tone”? “horn tone”? There are many types that can be used to expand the choice of voices in whistles. You can find some variations here…
http://www.organstops.org/_apps/Illustrations.html
These organ voicings would be easy to adapt to whistles. Opinions?
Thomas Hastay.
Wow, That’s a great resource Thomas. I could spend years in that site!
There is a lot of pipe organ technology in modern whistles. As for adapting these voicings, one would have to spend a year touring installed organs and transposing methods to determine voicing and application.
Come to think of it -I think that’s one of the main functions of WhOA.
Thanks for answering Mitch.
The Tuba and Violoncello types use an harmonic “bridge bar” to set up negative feedback at the voicing and give them fast string or slower horn frequencies, depending on diameter and distance from the voicing.
Violoncello
http://www.organstops.org/v/Violoncello.html
Tuba
http://www.organstops.org/t/LabialTuba$.gif
The round “flute” voicing more closely resembles a real flute sound than a labium ramp on whistles and requires less breath pressure.
Flute
http://www.organstops.org/o/OrchFlute.html
I’ve had very good luck with the “Ti-Tsu” flute style that has a “Kazoo” membrane located at the cetral node between the voicing and the top hole.
This gives a deep “reed tone” to the instrument but must be a long hole to cover the scale. It has many imperfections but I believe placing the membrane in the plug face, like a Mirliton, would achieve beter overall results. Humming in tune while blowing gives interesting results(still testing 
The double voicings of Seraphonflote “beat” against each other for a twin flute sound.
http://www.organstops.org/s/Seraphonflote.html
Thomas Hastay.
I looked at those organ pipes, and it made my head spin!
I have a feeling that not too many of those modifications would work on something as short as a D whistle. Fascinating stuff though…