I think I may be asking the impossible here but I’ll give it a try. I suffer from headaches all the time and can’t cope with loud or shrill second octave notes. So ideally I’m wanting to buy a high D whistle that is quiet in the second octave, requires some blowing - since my main whistle is a low D, I really don’t want a whistle with hyper-low breath requirements - and is as inexpensive as possible. And a Parks Whistle, good as they are, just doesn’t do it for me. Any ideas?
You could make a Low Tech Whistle. That way you’d have the breath requirements just the way you like, can adjust the volume a bit, and it’ll cost more time than money.
Although my Dixon polymer whistle is quieter in the second octave than my Freeman bluebird, the bluebird is still not that loud to me and much better tuned. I recommend the bluebird. Very sweet whistle to play!
Thanks for your replies. I don’t really have the time or the ability to make my own. As far as the Bluebird is concerned it may not sound loud to you, but because I’m sensitive to “noise” it still may well be too loud for me. Jerry Freeman’s quietest D whistle is the Blackbird which is a possibility though I think it may still be a bit on the loud side.
You can make an effective whistle “mute” by cutting a narrow strip of card stock (business card), then folding it and placing it in the window of the whistle so that it wraps around the edge of the blade. There are better instructions if you do a quick search. IT might take 45 seconds to make this if you are really slow about it.
You could also buy one of Carey Parks excellent whistles which have a built-in mechanism for quieting the instrument as needed. It’s a great instrument even if this wasn’t a feature.
ecohawk
Earplugs. Seriously … earplugs.
For a mute, drop a paper clip into the window. Just don’t scratch the blade.
Thanks for the suggestions. I would rather do without earplugs if and when I can. I have special musician-quality earplugs but even with them, there is a loss of tonal quality and hence enjoyment. I want to enjoy the whistle unimpeded if possible. I have tried the mute but without success. Maybe I should try again and wasn’t doing it properly. Isn’t there the risk of damaging the blade and I would think card would soon get soggy. If I can I would rather have a whistle that is playable without tweaking it. And as I said at the start, I’ve tried Parks and didn’t like the tone it produced with the ring in place. A pain aren’t I? 
After being much of the opinion of the OP in that high D whistles would be best quiet and sweet, I’ve come to the opinion that really, it’s a whistle- for the most part, a good whistle that maintains excellent intonation will experience at least some increase in volume and “shrillness” in the higher notes. Certain whistles, archetypically narrow bores (i.e. Burke narrow bores, gens, feadógs) will be quieter and sweeter in the upper octave, but depending on the environment you’re playing in even those can be too loud. If you want a sweet, quiet instrument, get a flute. Otherwise, earplugs are an excellent way to get a feel for how your whistle might sound when “blended” among other instruments in a session, or how it will sound in a noisy environment.
This may sound like heresy to some, but a recorder-like thumb hole on a whistle allows venting as required, which allows the second octave to be very much quieter 
For reference (aka “what I’ve done”), on a Generation D, is an approx. 3mm thumb hole, 161mm from the bell-end of the instrument. This was tuned as an “all digits off” D#, which also gives a very reasonable o XXO OOO alternative C# and an alternative D as o OXO OOO. It just makes for variations in fingering “over the break” and a degree of fingering similarity between my whistle and my recorder.
As always, YMMV on a different instrument and I’d not recommend anything as drastic as an extra hole in anything you might anticipate wanting to sell on.
Of course, use of this extra hole remains optional, all original fingerings still work as normal with the thumb-hole closed.
Hoover whistles are awesome.
I’ve got multiple white heads and a narrow bore brass.
Great whistles.
http://praisewhistlers.org/mackhooverwhistles/
Yep, very true. I sometimes use earplugs (or equivalent) as part of evaluating a whistle, for exactly that reason.
30+ dB plugs aren’t necessary. Something like ~10 dB musician’s plugs, with minimal tonal alteration. Or just try a bit of cotton (cotton wool).
Very little risk if you use a plastic-covered paper clip. Takes 2 seconds to drop one in and try it. 
Another idea: An untweaked Clarke original is mellow to begin with with a large breath requirement and a relatively quiet 2nd octave. Mute to taste.
But you didn’t say why the Parks doesn’t do it for you. It might help if you elaborate.
I was at a whistle workshop a few weeks back and, though I learned some good stuff, the sound of six high whistles playing together did my head in completely and I had a migraine for a couple of days. Trouble is earplugs wouldn’t have helped because I needed to hear the soft-spoken instructor in between! Anyway I have NO desire at all to play in a session or therefore to hear how a whistle sounds amid ten others and, as regards headaches, I’m afraid earplugs create their own particular problems for me. Something to do with pressure.
The paperclip. Do you just let in lie in the whistle? With a Parks I just didn’t like the tone I got with the ring adjusted enough that it worked for me. Great whistle though.
Mack Hoover’s whistles are fantastic. I had one Whitecap which was beautiful but as I said at the outset, because a low D is my main whistle I struggle with a whistle with such minimal air requirements. D’you think he could make me a Whitecap or a brass high D that required more air but was still relatively quiet in the 2nd octave?
Oh, I see. I’ll give it a try but with a plastic paperclip.
Are you completely locked in to a high D? I’ve owned many inexpensive and a few high priced high D’s, but even my favorite Burke sometimes annoys me on the upper octave. It’s a perfectly fine whistle, it’s just the nature of the beast (any high D) to be beyond my sensitivities at times. Since your main whistle is a Low D, I’d suggest something in between, perhaps an A. No compromising breath requirements, easier on the ear, and if you’re comfortable fingering a low D, an A would be a piece of cake. I recently bought a Dixon polymer A for all the above reasons, and have been quite pleased with the sound and quality, well worth the $50 I paid, and it doesn’t jangle my nerves in the upper octaves. Just a suggestion.
Nice idea ketida and I’ve thought about that but I think I need a high D. First, while I’m learning another low whistle with piper’s grip may only confuse my muscle memory. A high D is like a different instrument. Second, If I go to classes, it is what I need. You can’t fit in with anything else. Third, I want it for playing while at my desk during breaks, something I can just pick up and practice tunes or ornamentation on. Finally, I do like the high D when it’s not shrill. Listen to the opening air to The Secret on Roan Inish. It’s so haunting and gorgeous and it’s on a high D.
Although mine eventually broke, I recall the Walton’s Little Black Whistle having an oddly quiet 2nd octave. The sound was “thinner” than what I get from other whistles. And it’s pretty quiet in the 1st octave too. You should be able to get one for under $10 US.
It’s also probably EQ’d to a fare-thee-well with the top end rolled off, and compressed/limited like a squashed bug to balance the octaves. Add in some “haunting” reverb and voilà! - the magical whistle that doesn’t really exist.
It shouldn’t be. Muscle memory has mostly to do with finger actuation, which is the same regardless of the whistle. High or low, EZ Grip or standard. Thinking of high/low whistles as different instruments is a mistake, IMO. The “low” designation is historical, not functional. They’re just whistles in different pitches/keys.
And for that you’ll want a whistle that your instructor can hear properly and which behaves as a normal whistle, so that your instructor can evaluate your playing against a known standard. If you have idiosyncratic hearing tolerances in that setting, then it’s really up to you, not everyone else, to adjust. Plus, a quiet whistle won’t help your ears when the rest of the class are wailing away.
If you can’t tolerate earplugs, then maybe consider over-the-ear headphone type sound mufflers. The kind that construction workers or gun enthusiasts wear. Move them off to hear the instructor, back on to play.
I do wonder, though, why your instructor wouldn’t simply allow you to use your low D in the class.
For that purpose, a quiet whistle will generally be a breathy whistle, because breathiness is part of what reduces the carrying power. The Parks, Big Whistle “Shush”, and muted whistles all work the same way. You can’t have perfect tone and inaudibility at the same time.
Something like the Hoover very narrow bore D is voiced with a quiet but clear tone. I also have a Romanian frula with similar voicing, and a very tiny fipple. But these whistles take very, very little breath and I think would still be quite audible in a quiet office setting.
As for breath requirement, it should be more or less proportional to the size of the whistle. If you have a small fipple that takes a big breath, that air has to go somewhere - and it will exit the small window with a breathy sound. Exactly like the Clarke original I described above.
Whistles, like all acoustic instruments, are bundles of physical and acoustical compromises. If you emphasize one characteristic - tone, volume, breath - it will likely be at the expense of other characteristics. Different applications may require different instruments.
And really, I hope all this discussion is helpful.
Six whistles! Six, just six!. 
Try 30 or more at one go.
But seriously, earplugs (or other protection) are the way to go. You’re not alone with this particular issue. I know I can’t take a room full of high D’s anymore myself. My ears basically shut off at some point. Head aches! I can’t hear much else for hours afterwards. So I have gone to using earplugs when I go to a workshop. Actually the earplugs are usually in the whistle bag just in case. It is workable. I know others that do the same as well.
Of course with Joanie Madden’s classes “the soft-spoken instructor” description might not always apply.
A quiet practice whistle is still a good idea. I just mute a normal D whistle or play using the “whisper method”.
The opening theme can also be played on a low A whistle, if that helps you. The same motifs are played on a low D in other parts of the movie. Good movie! Nice music. John Lynch as Tadhg is terrific.
Feadoggie
Or a G whistle, since the piece is effectively in G Major. An A whistle puts you in C-nat fingering, which works but with a few half-holed F-nats.
Actually, I realized I have the soundtrack, and just listened to what I guess is the theme in question (track 3). It’s not as heavily processed as I guessed, which is a pleasant surprise. The EQ, compression and reverb are fairly light. But the compass is only a 9th, up to E, which makes things easier.
The whistle sounds like a Generation D to me. But who knows.