Backpressure 101

[Mikethebook]

As a beginner to whistles, I'm trying to understand the results of backpressure, rather than the actual dynamics so that I can buy a second Low D (currently playing a Kerry Optima) but I'm struggling. I understand that high backpressure results in reduced breath requirements and vice versa. Beyond that I've no idea how it affects tone,volume, note dynamics. Given my main desire it to play expressive airs and Spillane/McNally slow pieces should I be choosing high backpressure or what? Can someone please explain how backpressure affects everything else. I'm thinking of going to Colin Goldie to get a low whistle made but want to know more about what i should be asking for.

[DrPhill]

I have my theories on this subject, but I am not a physicist, neither am I an expert player nor a skilled whistle maker.

That said, I see it like this:

For a given whistle it is air speed across the labium that determines the oscillations of the air column that we perceive as a note. If the air speed is too low we get no note, as the air speed rises we begin to get an impure note. As the air speed rises still the purity of the note increases, then decreases. In this portion of the response we get a mixture of tones including the first harmonic (second octave). As the air speed increases the first harmonic note gets stronger and we get a more pure second octave note.

I think that the expression in a whistle comes from utilising the small variations in tone that can be accessed close to the desired note. This requires very precise control of air speed, and the control over air speed is helped by an increase in 'back pressure'. This is because I am less aware of the volume of air that I am moving, and more aware of the pressure that I am exerting.

So, for example, assume that I can vary my breath pressure between zero and ten pounds per square inch. I have no idea if this is a reasonable figure, but let us just assume for simplicity.

Now a whistle that plays the first octave note at a quarter pound per square inch and the second octave note at a half pound per square inch will not give me as precise control as one that requires four and eight pounds per square inch respectively.

That is how it feels to me when I play my Goldie medium-blower: I can more easily hit the precise spot in the whistles airflow/tone spectrum than I can on a low pressure whistle such as an Onyx. The Onyx is a good example, because there are some lovely complex tones there, but I find them hard to access reliably because of the fine control of air flow required.

Does that help any?
Do other people agree or disagree?

[Mikethebook]

Thanks for that DrPhill. So would you say backpressure provides more "room/space" on an individual note to create effects like, for example, flattening off a note as it fades away and that such effects can be created more accurately with said back pressure?

[Lars Larry Mór Mott]

Good analogy Phil!
I also see it like this - it's easier to aim and hit with a garden hose when you put a finger almost covering the opening, thus increasing pressure

[DrPhill]

Thanks for that DrPhill. So would you say backpressure provides more "room/space" on an individual note to create effects like, for example, flattening off a note as it fades away and that such effects can be created more accurately with said back pressure?

Indeed, and that is a far more concise way of putting it.

Good analogy Phil!
I also see it like this - it's easier to aim and hit with a garden hose when you put a finger almost covering the opening, thus increasing pressure

An interesting analogy, but not quite the way I look at it. But I am no expert in these matters, so who knows. Who was it that said 'If it works, its true'?

[hans]

Interesting to revisit this subject! I never liked the term "backpressure", I found it contradictory and confusing. I think I know now, as I can agree with much of Phill's description. Phill, you describe "air flow" and its variation and effect on tone: with higher air flow we find it easier to vary the flow rate and thus can influence pitch in minute ways, bending a note for instance, or changing the volume, etc. To be precise it is not just higher air flow but higher variance of the flow, for a given note, from a low flow rate to a high flow rate.

I don't understand why this is called "back pressure", as "back pressure" technically is the resistance to flow (see http://en.wikipedia.org/wiki/Back_pressure), thus more flow resistance (through a more constrictive wind way for instance) = more back pressure, technically. Just the opposite of what has been described as backpressure here!

I did some actual crude pressure measurements by using a manometer (U-pipe with some water in the bend) and one end of the pipe in my mouth while blowing various notes on various whistles. So I measured roughly what the air pressure was inside the mouth cavity while blowing a whistle. A normal playing range over two octaves was from 20mm to about 100mm water column, but some notes would speak with as low a pressure as 5mm H2O, and for some notes the pressure could go up to 200mm. The differences from low to high end are very large, and the variance for each note could be quite large as well. If you wonder about the units: 100mm H2O is about 10millibar (9.8millibar) or 0.142psi (pounds per square inch).

Anyway, to cut this short and not bore you with a lot of numbers: my wide bore low G whistle could be played with much more pressure and more variation than it could after I inserted a whittled down match stick into one side of the wind way, thus reducing the size and restricting the flow. Pressure, volume and ability to vary each note was drastically reduced by this restriction. I observed the same comparing different whistles: if the whistle did allow to be played with higher pressure and higher variance in pressure for a given note, then it allowed easier pitch and volume variations.

I am still not comfy with the term "back pressure", and wish it could be dropped in the context of whistles. Rather talk about "air flow" and especially the variance of air flow for each note. Of course that is a far more complex picture, than calling a whistle having high or low backpressure! Personally I like a whistle which blows easily, but can also be "leaned into" giving it extra air flow. That for me gives the most expressive capacities (combined with good voicing). Such a whistle can be played softly and loudly.

[AvienMael]

I disagree that a whistle with high "backpressure" will have less air requirements. My Goldie whistles use as much air as my Copelands, for the most-part - and they are at opposite ends of the spectrum in terms of "backpressure."

I have often thought in the past, that the advantage of backpressure is it gives you more dynamic control (in some whistles) - in fact maybe "more" is a misleading word... "easier" might be a better choice here.

The other thing I would point out about "back pressure" is that you may find the idea of "back pressure" sort of loses relevance as your breath control improves. In the case of some whistles, I have found that as I have become accustomed to the whistle, the higher degree of backpressure I perceived when I first got the whistle, actually seems to disappear with continued practice on that whistle, to the point where I no longer notice it much at all. In my mind, this means that a whistle which has a higher perceived "backpressure" actually seems that way because it needs to be blown a bit differently than one may be used to. In other words, it's requires more breath control, and not necessarily a harder breath - even though it may be playable with both. Sindt whistles, which are often referred to as having a tendency toward being quiet, are a good example of how poor breath control can leave one with a misleading impression of a whistle's playing characteristics. A Sindt can be competitively loud, for example, if you take the time to learn how to play it that way.

"Backpressure" seems to be generally understood as referring to a whistle's tendency to want/need to be blown hard, but it may actually be a good indicator of how your breath control is progressing. I have, over the years, noted many accomplished whistlers mentioning that the very idea of "backpressure" has no meaning to them whatsoever... some claim they don't even know what we are talking about - and they play the same whistles we do.


Food for thought...

[DrPhill]

"Facts are meaningless. You could use facts to prove anything that's even remotely true." - H. Simpson.

That was an interesting idea Hans, to measure the pressure. It is reassuring that the differences are measurable, and the figures can give us a more realistic magnitude in examples.

Interesting to revisit this subject! I never liked the term "backpressure", I found it contradictory and confusing. I think I know now, as I can agree with much of Phill's description. Phill, you describe "air flow" and its variation and effect on tone: with higher air flow we find it easier to vary the flow rate and thus can influence pitch in minute ways, bending a note for instance, or changing the volume, etc. To be precise it is not just higher air flow but higher variance of the flow, for a given note, from a low flow rate to a high flow rate.

I don't understand why this is called "back pressure", as "back pressure" technically is the resistance to flow (see http://en.wikipedia.org/wiki/Back_pressure), thus more flow resistance (through a more constrictive wind way for instance) = more back pressure, technically. Just the opposite of what has been described as backpressure here!

I am afraid you might have misunderstood me Hans. I actually said that it is a higher resistance to flow that seems to give me greater control over the (micro?)tonality. It allows me finer control over the air speed across the blade, under the assumption that the speed of the air is the important factor. If by 'air flow' you mean 'air speed' then we are agreeing violently .
Your dictionary definition of back-pressure defines exactly my personal use of the term. I always understood back-pressure to mean that resistance to flow, and I am not sure that I have seen any other description. My post above should make this clear, and if not then I apologise. My 'medium blower' Goldie is my highest back-pressure whistle. It feels harder to move air through (more resistance to flow) than, say, a Copeland, which I consider a low back-pressure whistle.

In contrast to AvienMael I notice a very real difference in the length of phrases I can play on the two whistles. I can play longer phrases on the Goldie than on the Copeland. I wonder if this effect is exaggerated in low whistles - I have not had anywhere near as much experience of different high whistles. Or it could be my lack of expertise, of course, but it would seem to make sense that a whistle with more 'resistance to flow' would require less air, but perhaps my physics is too rusty.

[Mikethebook]

I'm getting a little more confused now . . . especially regarding what I should ask Colin Goldie for when I order a whistle and whether backpressure does have an inverse relationship to breath requirements seen in terms of notes per lungful. Given I'm a beginner with an interest in playing expressive airs (often with long drawn out notes), I would like solid notes that I can control in terms of volume and exact tone (e.g. flattening a note as it dies away) AND to maximise the output I can get from one lungful. I half relate to Hans when he says "I like a whistle which blows easily, but can also be "leaned into" giving it extra air flow. That for me gives the most expressive capacities (combined with good voicing). Such a whistle can be played softly and loudly." But this sounds to me like low back pressure when I'm assuming high back pressure is the ideal, though not for a beginner. I'm confused.

[Peter Duggan]

Hi Mike, I'd suggest maybe waiting a while (remember your Optima may be closer to the spec. you're chasing than you realise), but in any case not asking for anything custom unless you're sure you're asking for the right thing. Or, if you're determined to go ahead soon, give Colin Goldie the whole description you just gave here and let him advise you.

[Mikethebook]

Good advice Peter. I know the Optima is not the right spec for me but I bought it knowing that as a beginner's whistle. I definitely will consult Colin Goldie but I have the kind of analytical/scientific mind that likes to understand things and take them apart! Understanding would also help me know what i want/need. At the end of the day I suspect a middle ground back pressure will be what I need.

[DrPhill]

Hi Mike, I'd suggest maybe waiting a while (remember your Optima may be closer to the spec. you're chasing than you realise), but in any case not asking for anything custom unless you're sure you're asking for the right thing. Or, if you're determined to go ahead soon, give Colin Goldie the whole description you just gave here and let him advise you.

Seconded.

Though if you talk to Colin he will probably encourage you to get a medium blower (or at least that is what he encouraged me). He was quite likely right, too - I find his whistle the most playable of my collection (it seemed harder work initially). Remember though, I have not played an 'easy' or a 'hard' blowing Goldie to compare.

[ecohawk]

I love this topic as I can completely relate to nearly all the answers from my personal journey over the past three years when I first picked up a tin whistle and became immediately obsessed. \

These are my opinions based on my personal experience.

In the beginning you will notice breath pressure requirements much more than when you become more experienced. Then you will simply become aware that a particular whistle is different from others in many ways and requires adjustments. You won't necessarily experience that as back pressure. For me, the Copeland doesn't have much "back pressure" at all but can tolerate being pushed when required. The Goldie high D I have is the prototypical "medium blower" which at first seems to require a little more push to get clean notes. I also have a Goldie/Overton in A and a Brass Chiefain in A, both of which are described as "hard blowers" meaning there is an extraordinary push necessary to get notes started and keep them clean. I also have many others such as Busman high D which requires a breath pressure somewhere in the middle.

When I first played these, I perceived that those requiring more push also gave me more control over dynamics; or how far below or above pitch I could go with breath alone before the note broke - either squeaking or jumping to the next octave. It caused me to put the Copeland away since it didn't require hardly any push, therefore I couldn't achieve the same dynamic range. It also seemed that the push caused me some slight discomfort, but was more efficient as no breath was wasted so I could play longer on a single breath. Knowing where to breath is crucial to becoming proficient with a whistle so I viewed this as a big advantage for the Goldies.

Now that I've got some time and quite a lot of practice to fall back on, I've learned that these assumptions are just plain false, at least for me. Dynamic control is not dependent on back pressure but on fine breath control which comes from playing a lot. I can achieve the same length of playing time between breaths with the Copeland and Busman as the Goldie and all of these have all the volume one could ever want while covering all aspects of the back pressure spectrum. Once you learn how much breath it takes to achieve a certain volume and pitch on each whistle, you will adjust accordingly and become less aware of the effort required. It will simply be one more of the myriad differences between whistles. That's why we have WHOA to depend on!

Of course, there are whistles at the extreme's which I find to be simply exhausting to play, and the lower the pitch, the more air required to make them sound good. Take Shaw for example. They require no pressure at all and I love the look but can't make them sound good at all. Many others love their sound and characteristics. But, that's personal isn't it?

Listen to all the advice you've received and particularly Peter Duggan's. If you just want a Goldie, then talk to him about what you need and he'll accommodate you as will most of the other quality whistle/flute crafters around. But don't just buy another whistle because you believe at this point that you need more back pressure. If you can afford to spend the money and you want to test everything personally, then go for it. Experience at just playing will bring all this into focus for you.

Hope I haven't just added to the confusion.

ecohawk

[killthemessenger]

Who was it that said 'If it works, its true'?

Could be Jung: Wirklich ist, was wirkt. Although he had something slightly different in mind.

[Tommy]

I am still not comfy with the term "back pressure", and wish it could be dropped in the context of whistles. Rather talk about "air flow" and especially the variance of air flow for each note.

I agree. Breath control is when air flow becomes a reflex in response to what each note in each whistle requires.