Back pressure in a flute

[Doug_Tipple]

Back pressure in a flute can be the result of the design of the embouchure or the restrictions in the bore of the flute. But is back pressure necessary for a good performing flute? Some players maintain that the inherent backpressure present in a given flute allows them to play longer passages without requiring a breath. They like to blow against a back pressure in the flute.

My question is whether the same condition can be achieved by a good embouchure of the player? I know that when I play my digeridoo, even though the bore is quite large, by having a tight embouchure I can blow a sustained note without having to use much breath in the process. With a tight embouchure it feels like I am blowing against back pressure, when in fact I am not. The only pressure is caused by the compression of my lips. With a tight embouchure it is possible to sustain a note on the digeridoo, filling the cheeks with air and breathing while sustaining the note. Good players can use this same circular breathing technique techinique with the flute, as well.

Is my analogy with the digeridoo appropriate for the playing the flute? What are your thoughts about this.

[Terry McGee]

Whereas I'd say that one can detect "resistance" in a flute, I wouldn't go so far as saying one can detect "back pressure". The flute is unique among wood winds in being a flow-driven instrument - all the others - clarinet, oboe, etc are pressure driven. In a flow operated instrument, pressures are extremely low (hard to get up much pressure in a short tube open at both ends!).

To be able to transmit pressure to and sense back pressure from an instrument, our mouth would have to be closely coupled to it. In the clarinet and oboe, the mouth is entirely closely coupled, clamped around a reed connected to the tube. Pressures are higher and couple directly back to the player. It's not in the flute - there is an air gap of some mm. Any pressure - not that there is much - can dissipate in that gap. When you fill your car tyres with air at the garage, you have to make sure the hose is coupled on well. How long would it take to fill the tyres if you held the hose 3mm away from the valve?

The didge is a pressure-operated instrument, and I guess a member of the brass family, relying on lip vibration. So it works at pressure, with little flow; the exact opposite of the flute which works at high flow, little pressure. You can circular blow a didge, you can't do that with a flute. Circular blowing requires that you can breath in while storing enough pressure of air to operate the instrument in your cheeks - in the case of the flute you can't because there's nothing there to maintain pressure against.

So, since there can't be "back pressure" in a flute, we have to look at the question of "resistance" which we do seem to be able to sense. A conical tube does offer more resistance than a cylindrical tube or the Boehm bore. Those used to a conical bore can feel a little bewildered playing a cylindrical flute at first - as if they are blowing into the vacuum of outer space. Equally, Boehm players can find the conical flute a little stuffy at first. Even more interesting, players can detect the different resistances of different embouchure cuts and even foot joint bore profiles. So it's all real and therefore important for us to understand. Unfortunately, I don't know anyone researching it.

I don't think back pressure has anything to do with conserving air. Remember there's a gap between the lips and the flute - any amount of air can escape there even if the flute has been filled with concrete. Conserving air for the flute player is more to do with efficiency of the flute - it's ability to turn a limited amount of air flow into a satisfactory amount of sound. The flute is a notoriously inefficient instrument - Prof Neville Fletcher estimates about 1% of the energy put in comes out as sound. So it's vital we conserve every bit of that energy. That means we get both our acoustics and aerodynamics working as well as we can.

Terry

[Dana]

Terry, you took the words right out of my mouth. I've nothing to add.

Dana

[kothz]

You can circular blow a didge, you can't do that with a flute.

(I realise that this isn't the point of the post, but... Unless I'm confusing the terms, and circular blowing isn't the same as circular breathing, I used to do this all the time with the flute. Sure, it's not easy to learn, but it's a usable technique.)

[Maihcol]

So, since there can't be "back pressure" in a flute, we have to look at the question of "resistance" which we do seem to be able to sense. A conical tube does offer more resistance than a cylindrical tube or the Boehm bore. Those used to a conical bore can feel a little bewildered playing a cylindrical flute at first - as if they are blowing into the vacuum of outer space. Equally, Boehm players can find the conical flute a little stuffy at first. Even more interesting, players can detect the different resistances of different embouchure cuts and even foot joint bore profiles. So it's all real and therefore important for us to understand. Unfortunately, I don't know anyone researching it.

Terry

I did some experiments last year with the short D-foot and the long C-foot with four different models of flute, those being based on the Pratten, a large-holed Rudall, a medium-holed Rudall and a simple system Boehm model. I was the only player involved in these experiments so that leaves open the question as to how it would pan out for other players.
But I think there are some indications from discussions on the Flute list about the Foster extensions available to Boehm players (For anyone who doesn't know, these are just a way of making the footjoint a bit longer). I followed some of these discussions but there didn't seem to be any definite conclusion about their overall usefulness to players in general. Some said they were an improvement, others said they changed nothing, some said that they found them an advantage on one of their flutes but not on others...and I expect it would be something similar in the case of the D-foot and C-foot.

In my case I couldn't notice any difference using the short or long foot with either of the two Rudall models, nor with the Boehm Model. But with the Pratten it was noticeable - the short D-foot caused a loss of focus for me, particularly on the bottom D but also up through the rest of the bottom register, although the flute still played well so I would describe it more as a strong preference in my case for a long foot on a Pratten, rather than an absolute necessity. I also did some back-reaming experiments with these feet but found these less conclusive...the traditional C-foot seems to be fine for me!

I think it would be interesting to send a travelling flute with short and long foot round to players and see how people respond...but based on my experience, you would get more information if you sent both Pratten and Rudall types and even a Boehm type!

Garry

[Akiba]

I believe I have had a close encounter with "resistance", specifically comparing the Casey Burns Large Hole model and the Casey Burns Rudall. The Large Hole has no resistance I can detect, and I attribute that to the Pratten large bore model, i.e. there is not enough of a cone to create resistance. In fact, I put blu-tack in the very bottom of the flute to create some resistance on the low D which I find helps to get a fatter and easier low D sound.

The Rudall model has more resistance than in any other flute I've tried. I attribute this to its small bore and small holes. Thus, I think that possibly the smaller the bore and/or more pronounced the conical taper, and/or to a lesser extent the smaller the holes, the greater the resistance. I wonder if the GLP model of Terry's has a lot of resistance; I would think it might.

As a result of the resistance in the Rudall model, I think that helps to play a bit faster (for me) and to "push" notes more in a particular way difficult to describe. Thus, I think resistance may be a key for many players, particularly those with a huffy pulse-driven style. As a comparison, Matt Molloy sounds different on the Rudall he played in Bothy Band as compared to the Boosey Pratten he plays thereafter and the Olwell Pratten after that. I think his Bothy Band sound is due, obviously, to the Rudall design but also to the inherent resistance found in the Rudall.

Jason

[Rob Sharer]

In my case I couldn't notice any difference using the short or long foot with either of the two Rudall models, nor with the Boehm Model.

Just to offer a counterpoint (big surprise), I own an Olwell small-holed Rudall in boxwood, for which I have both a long and a short foot. There is a huge difference between the two, and the changes extend right up the flute. The whole instrument sounds more focused with the longer foot, which is also tighter at the nether end. The short foot rewards a gentle, beginner-style blow, but it doesn't offer up enough resistance to stand up to a more advanced blow, i.e. doesn't allow the player to really dig out the more interesting tones. Cheers,

Rob

[Terry McGee]

All of which varied response has been my experience too. I can only conclude that some of us generally prefer (or, at least, benefit from) a free-flowing flute and others from a higher-resistance flute.

For example, I (like Boehm), do better with a rounded rectangular embouchure, while many clearly prefer the elliptical hole. I prefer and do much better with a wide bore foot, while I've found some who prefer the narrowly tapering C foot, and many who can't tell the difference. I haven't attempted to correlate the preferences for free-flowing at both ends of the flute, but it seems probable and it certainly works for me. The difference, as I perceive it, is not minor, so it would come as no surprise to me that a player like Rob at the other extreme would be equally emphatic.

What I con't know (and suspect nobody knows) is whether either is better in the long run if you persevere. I made my current flute (a Rudall 5088 6-key) with an elliptical embouchure to see if I can "wean myself" off the rectangular embouchure. A year or more later, I'm not noticing any improvements, and when I'm testing a rectangular embouchure flute for a customer I can once more and readily appreciate the benefits. (Sigh, the pain I go through for my art!). So, my guess is that my preference for free-flowing is not something I can unlearn, just as I'd probably have some difficulty convincing Rob of the error of his ways.

All of which says to me that those players who are doing really well have likely found the resistance that suits them, while those who struggle may benefit from trying a flute at the other extreme. Don't struggle, don't give up, find out!

Terry

[cadancer]

I think the question of whether the embouchure matters to the perception of "back pressure" is an interesting one. I think the answer is a definite yes. I believe it is related to being able to focus the air stream where it will do what you want it to.

I am, admittedly, a newbie "Irish" flute player. However, I have been playing Bulgarian kaval for some time. The kaval is just an open pipe as it is end-blown. Kaval masters can play continuously for many minutes by using a "circular breathing" technique. I doubt if that would be possible without a focused embouchure, which (in my mind) has a smaller mouth opening and, therefore creates more "back pressure" inside the mouth allowing the player to "circular breathe".

On the other side of the coin, beginning flute players often get light-headed from blowing (like blowing up a balloon). They also can lose the tone altogether even though they are blowing pretty hard. I think the beginning player often has a more open embouchure and struggles with even moderately long phrases due to a lack of a focused embouchure. There is another active thread where a beginning player discusses losing his sound altogether because of his embouchure. I think people just get tired mouth muscles until they get in enough practice.

I do play kavals in multiple keys. When you pick up a new, larger one, the first time, it feels like you are starting all over again. The behavior is similar to what I describe above for beginning players. The effort is well worth it as anyone who plays a "C" or "Bb" "Irish" flute will tell you (I assume). My kavals are in "D", "C", and a monstrous "A" (thank god for the piper's grip). These larger instruments do require more air, I believe, but also require a more focused embouchure to get a proper tone.

As far as a given flute having inherently more or less back pressure due to it's construction, I will leave that to our panel of experts.

...john

[Rob Sharer]

Of course, the funny thing to me, which no one who wasn't familiar with the vagaries of my own instrument would find funny, is that I've always kind of lived and died by the free-flowing nature of my flute*. My Olwell has always had a long foot which nevertheless is wide open on the bottom. It's kind of like a Nicholson which transitions to a Pratten somewhere around the F# sounding-hole. The Pratten section I acquired later to go with the same head and foot is even wider in the same area than a normal Pratten - I think Patrick was experimenting. It was only after I started playing on antique flutes that I came to appreciate the difference that having a tighter foot can make. Coincidentally, on my first visit to the Olwell shop after coming back to America, I discovered that Patrick and Aran had started making the Nicholson model with a tighter foot, for similar reasons.

I still use the wider foot sometimes, but having also acquired a tighter foot for my Nicholson I find myself being drawn to that sound/feel. I find it's more work, and seems to require a more flexible embouchure, with more change up and down the instrument, especially at the bottom. Oddly, I love what the tighter foot seems to do to the top end of the second octave. I guess you could call me a convert, but I certainly do understand and appreciate the free-blowing concept as well; it might still qualify as the way to go for a true session cannon of a flute. Cheers,

Rob

*I have to confess that the first thing I typed here was "free-flawing," a Freudian slip for the ages!

[Cork]

Has anybody considered the sonic limits of a flute?

That, after all, is the true limit of what any given flute can do, as the ultimate point of resistance.

[jemtheflute]

Has anybody considered the sonic limits of a flute?

Nooooo. But if I can just find my sonic screwdriver....... I'll give yours a (suitably ultimate) tweak if you like .

(Signed: The Doctor)

[Maihcol]

I still use the wider foot sometimes, but having also acquired a tighter foot for my Nicholson I find myself being drawn to that sound/feel.

This discussion is pushing me to go back and deepen my investigations of the long and the short of footjoints…but I’ve already got too many other priorities falling off the shelf so it will have to wait. I did open up the flare (the reverse taper) on the Pratten footjoint, using the topjoint reamer from the smaller-holed Rudall and I have an inkling that I can feel an “easing” at the bottom end with this as compared to the standard traditional C-foot but I can’t be sure whether that inkling is due to some sort of logical expectation influencing my perception…In any case it would only be a slight difference for me – and that on Prattens only and not Rudalls on which I can’t sense a difference between long and short feet independent of the bore of the foot. The thing with experiments like this though is that you really need to spend days playing the various configurations up and down before you can be confident of your perceptions - although some things will be obvious at the start.

I suppose the thing to do would be to send out three footjoints with a flute - the short D-foot, a wide bore C-foot and the traditional narrower bored C-foot and then the player sends back two...or keeps all three!

Garry

[Cork]

Has anybody considered the sonic limits of a flute?

Nooooo. But if I can just find my sonic screwdriver....... I'll give yours a (suitably ultimate) tweak if you like .

(Signed: The Doctor)

Seriously, sound represents waves of sonic pressure, or pressures, depending on circumstances, for instance, melodic sound versus harmonic sounds, etc.

So, while air pressure could be a medium by which sound could be transmitted, it appears there's also a sonic "pressure" to consider, too.

A flute, after all, is a sonic radiator, and perhaps some of that radiation could come back up through the embouchure hole, as well.

Moreover, could a flute player detect such a phenomenon, at the embouchure?

[Doug_Tipple]

Even though the flute is a flow-driven instrument, as Terry mentions, you don't have flow without an internal pressure gradient, with the pressure being higher at the embouchure and lower at the tone holes and end of the flute where the air flow is exiting. Anthing that impedes this flow (small embouchure, less-than-aggressive embouchure cut, smaller bore diameter, conical bore, extended foot) acts as resistance to the flow of air, so it is not hard to see how the decrease in the pressure gradient (less flow) caused by the aforementioned resistance could be spoken of as a back pressure, although I agree with Terry that resistance is probably a better term. Even though there is an air gap between the lips and the embouchure of the flute, this subtle resistance in the flute can be sometimes be felt, as has been mentioned.

My original query has to do with the design of cylindrical-bore flutes, where I have a personal interest with my pvc flutes. Say, for example, you have a 6-hole cylindrical-bore flute with a bore diameter of 20 mm and an 10.5mm x 12mm oval embouchure hole with a rather aggressive embouchure cut (letting in a lot of air). Now this flute is not going to offer much in terms of resistance. My question is whether there is any disadvantage of having a flute that is this open? Is this flute going to take more air to play than a similar flute that offered more resistance, perhaps with a smaller embouchure hole, smaller bore or longer foot joint?