this has been mentioned quite a few times as of late, and since I don’t know nearly as much about whistles as I would like, I have no idea what this is referring to. Is it only something that affects low whistles? Or is something I should be concerned about, since I do not own a low whistle (yet…)? Do I need something to combat it? 
Seriously, what is backpressue?
Dunno,might have something to do with backpressure.
Slan,
D. 
I posted this question a while ago. A long while ago, I think. I’m not sure.
Anyway, backpressure (or back pressure, or back-pressure) refers to the resistance that you get when you play a whistle, basically. Clarks and Shaws have basically no backpressure, for example.
I fear the search engine, unless one is searching for an insanely obscure word or phrase, is of little use anymore because the forum has so many posts.
If you are so inclined, pop off the head of a whistle and fill in the cavity like you would with the sticky tack tweak, only overfill it by a good amount. Mess with it. Shape it and stuff.
It’s just a fun experiment that gave me the epihony: Oh! The whistle is pressing right back at me!
I’m not saying the sticky stuff way is wrong, but I think taking a whistle and putting your shirt over the blowhole while playing will also demostrate backpressure (and not be as messy as the blue stuff has the potential to be).
Yeah, I never really understood this, but for the fact that Overtons have a lot of it. One really erudite whistler just thinks its blowing a lot of air much of which doesn’t contribute to the sound.
Philo
There are two related concepts that relate to how much air a whistle uses, and with how much force it must be blown: resistance and backpressure.
Resistance refers to how little air a whistle uses, irregardless of how hard it must be blown; as the volume of air goes down, resistance goes up.
Backpressure refers to how hard you have to blow, irregardless of how much air the whistle uses.
Usually you find that whistles with low resistance also have low backpressure, some Clarke originals are like this. This type of whistle can be quickly exhausting to play.
My Alba Q1 is an example of a whisle with high packpressure and high resistance.
My Syn D (his later model) I would consider medium backpressure and medium resistance. His earlier model I consider high backpressure and high resistance.
A Feadog I would consider medium resistance and low backpressure.
An Oak I would consider low resistance and medium backpressure.
Susatos have high resistance and medium backpressure.
–James
I’m not sure if this is in line with what James has to say. I’m much less experienced, and I’m not sure I get the distinction between backpressure and resistance, but here goes, anyhow. I’ll just use the term “backpressure” throughout, and someone can correct me if I should be saying “resistance”.
I think it’s mainly related to the size of the windway. Try pursing your lips like you were gonna spit a needle, and then blowing as hard as you can. That’s high backpressure. (Feel the blood pressure rising in your face?)
Now, open your mouth wide enough to insert an egg (hard boiled, not scrambled), relax your throat, and blow. That’s almost zero backpressure. Now, experiment with openings between those two sizes. Start with the smallest opening and gradually enlarge it.
This is just to show how it feels. I also think that the relationship between the size of the windway and the size of the window, and maybe other factors, work together in subtle ways to affect timbre.
One simple point is that the less backpressure there is, the less time it takes to empty your lungs.
I increased the backpressure of my Clarke Original by squashing the windway down to about half of its original height. I accomplished something similar by inserting a drinking straw into the Jubilee practice low D. Both of these whisltles originally took so much air that I found them difficult to play. Others have mentioned inserting matchsticks or toothpicks in both sides of a windway.
On the other hand, there are a few whistles that take so little air that you may have to let some air escape around the tip just to get your lungs empty so that you can get some fresh air into them.
It’s not quite that simple, though. (Is anything, ever?) I have two Whitecaps. One is quiet, one is not. The quiet one has a smaller (top to bottom, not side to side) windway (actually, it tapers), as well as a 33-percent smaller window opening. So, based on my previous argument, you’d expect higher backpressure.
However, it starts to jump octaves at much lower pressures (for both octaves) than the other one. So, when playing the quiet one, even though it has a smaller windway, I never get the pressure up as high as I do with the other, because I’d be going up an octave, instead of just getting louder and a tiny bit sharper. (It’s still very well balanced across octaves–just quieter over all.)
Very good choice of examples to describe it!
Brigitte
P.S. PhilO, there is a lot variation possible regarding the backpressure between one whistle and the other when making it, i.e. 5000th of an inch in windway height can make a BIG difference
thank you all for the explanations. I think I understand it all now…at least relatively speaking since mine have no backpressure. But at least I now know what to look for. Thanks again!
Everybody sees these things differently and I am never quite sure terms to describe whistles mean the same thing to different players. In this light, I have a different take on this than James.
I think there is back pressure and there is volume of air that you use. The less backpressure the more air you need to move through the whistle. The more backpressure the less air it takes. Whistles with high backpressure typically take very little air. Whistles with no backpressure take lots and lots of air.
A whistle with low backpressure can take more or less air. It affects volume and is affected by how efficient the voicing is. If the voicing is very breathy/inefficient you’ll get a whistle that uses much air, but doesn’t play very loud. On the other hand, in my experience, a whistle with high backpressure never takes much air.
Just my take on it.
Back pressure always reminds me of what it’d be like to blow into my thumb, only not quite that bad.
Well, that certainly makes everything clear …
Question 1: If I have whistle X and can play it for 60 seconds before needing to take a breath, then try whistle Z and can only play it 45 seconds before needing a breath (same song) … whistle X has more backpressure?
Question 2: If I have a very quiet whistle and want to “tweak” it to make a louder whistle, do I only need to find a way to increase the backpressure?
The knowledge displayed and shared on this board amazes me – as well as making me feel incredibly stupid, at times 
~Judy
If you have within you the capacity to admit that you are stupid, then you probably are not.
Great questions, Judy! And I too am amazed at the knowledge here, and even more amazed at how everyone seems to WANT to share it! At some point, I hope to know as much as the people here…until then, I suppose I’m destined to ask millions of questions!
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No, it’d be the other way round. But why would you play for 60 seconds without taking a breath?
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I suspect that the whistle will always be quiet which is a Good Thing. Whistles are very high pitched and are louder to other people than you think.
sorry martin, but i think she is correct. no? the higher the backpressure, the greater the resistance, means the longer it takes for you to empty your lungs, meaning the longer you play without having to gasp for air.
am i wrong?
I used to be able to hold my breath for over 2 minutes, but I haven’t tried it while playing a whistle.
I think Martin is right.
You must work harder (expell more air from your lungs) to play the 45 second whistle, which is why you can only play it for 45 seconds.