which suprano D would it be, ignoring all attributes?
meir
I’d say Hoover. I have a narrow bore Burke D that is really quiet, but the Hoover is quieter still.
Jef
Of the ones I own (self-tweaked Clarke original, Dixon tuneable, Burke aluminum narrow bore, Whitecap-Feadog), the Whitecap head on the Feadog body is the quietest overall. The Dixon comes in second, but is more difficult to play in the upper half of the second octave. The Clarke is pretty quiet in the first octave, but gets extremely loud in the second.
Of course, all of them require more breath for the second octave, so the volume also increases at least somewhat in every case.
The Whitecap-Feadog also has a very pleasing sound for my taste.
Noah Herbison’s Laughing Whistle is the quietest d whistle available.
I believe the McHaffie sounds like the quietest whistle. The adjustment makes it possible to select the volume you would like. I have not played one but the sound clips are great.
Ron
I have 8 high D whistles inc. Clarkes, Feadog, Generation, Dixon tunable and Alba Q1.
Quietest is Alba Q1. It’s also the quickest and most rhythmical - ie it demands rhythm.
But will investigate Laughing Whistle.
D
My vote is for the Laughing Whistle - it is a regular occupant of my briefcase for whenever I get a minute
Chuck
I had a hoover brass, but not the narrow bore, it was pretty quiet. The Weston copper I have is quieter than that. I have not had the opportunity to compare it to any of the other quiet whistles though.
A little informal testing of my quietest whistles revealed:
Alba Q1 is softest of all,
Clarke original is only slightly louder than the Q1,
Burke brass pro narrow bore is a bit louder and much more projective than the Clarke,
Hoover whitecap on a brass Generation tube is only slightly louder than the Burke but not as projective over distance, and
My standard of comparison is a Generation D brass redtop, which is louder than all the above but not quite as projective as the Burke.
–James
Of all the d’s I have ever played, the Hoover narrow bore is by far the quietest. The amount of air it takes is minimal.
Best.
Byll
Hoovers are quieter than the laughing whistle I own and the others by Noah that I’ve played. The Laughings tend to clog a LOT as well, though I don’t notice the same problems in the Hoover windways. I really like the Laughing whistles, but overall, the Hoovers would be my choice for both volume and clarity.
For what purpose are you needing a quiet whistle? If it’s for playing in an apartment or something like that, some whistles you can cover half the window with tape and still get a very nice sound out. The dixon is easy to halfway tape up and still get a nice tone.
Hoovers take well to taping the window to quiet them. Then they are REALLY quiet. I can practice any where I want to just about.
Most of then gen style whistles I have don’t seem to take well to taping up.
Bud, if you EVER ditch that laughing whistle, I get dibs! Or Max and I will come beat you up! 
The Hoover is well named. You have to blow so easy on D you almost have to suck. I tend to run out of breath more quickly on a hoover. I have to drop a note to breathe out, then another to breathe in. I got a whitecap and stuck it on an Oak barrel. It’s of value for practicing at 2 AM, or in a library.
But the Hoover narrow bore is even quieter! 
/Jens
thanks to all.
i am going to order both.
the hoover cause i got such good recs here.
and the laughing, well, its got to be way cool even if it is the second quietest.
meir
For quietning a whistle check this out:
Brian
so, the happy end of this story. i got both the hoover and the laughing.
the laughing is in fact the quietest, as asserted by the world’s greatest whistle collector.
but i am thankful to jeferson since the hoover is almost as quiet, and amazing in its own right.
my whitecap is on an aluminum tube also made by mack. it has the most incredible second octave of any i have played. it is incredibly sweet. c nat responds better to 0xx xx0 than to 0xx 000, my only whistle to do that. this would be an amazing beginner whistle too, although one would have to learn to switch gears when picking up any other whiste except the laughing. play it with the air and pressure needed by most whistles and you get junk. it does not clog easily. for its price i would call it the best value in whistles today, another feature that recommends it either to beginners or to those who want to move one step up but for whom money is a problem.
my laughing is also amazing. it has more attitude but still alot of sweetness. it clogs more easily than the hoover, and in fact i just did the soap thing and it is drying now. its lower octave is amazing. the middle octave takes more finess. and of course the telescoping feature is incredible.
so thanks everyone for your advice. as you can see, my whoa is in good control probably because my POAD is totally out of control. i never spend more than 100 on a whistle. ok, the copeland low D was a special case. and i guess the goldie G. and the burke’s, well, they are close enough to 100 to call it even…and i buy only in the key of D… well, i had to have a b to play with b pipes, and a C to play along with david power’s pipes…
meir
The one that’s not being played.
The Hoover narrow bore is unbelievably quiet. So much so that it’s actually too quiet, even though I love quiet whistles. It takes so little air, too, that it’s almost difficult to avoid that 3rd octave. If you learn to play it, it’ll be hard to switch back to normal whistles.