Questions About Bernoulli’s Principle and Brass Playing

How does the Bernoulli’s Principle apply to brass playing? I’m not a physicist (almost completely self-taught in that area), so I must acknowledge that this is an area where I just may be way off base. So rather than try explain this in detail, I’m going to simply offer my understanding at this time and ask my readers to help me fill in the gaps and correct any misinformation. I’ve heard contradictory statements about this from sources I trust, so perhaps this is another area where even experts still disagree.

First, what is the Bernoulli Principle? The relevant part for brass playing is that a fluid (or air, in our case) moving with a change in pressure will also be accompanied by a change in speed.  This physical law is often cited (including by me) as the reason why brass players change the level of tongue arch according to the range being played.  The higher the register, the higher in the mouth the tongue will arch, resulting in the air moving through a smaller area inside the mouth.  The general reasoning here is that this results in the air striking the lips with faster speed/higher pressure, making the faster vibrations for the high register easier.

I recently got an email from Darryl who is trying to help me come to grips with why this might be wrong.

The pressure that one can create by lung pressure is the maximum pressure that will exist just before the embouchure, regardless of how one “narrows” the path before the aperture. The total pressure of the air is, at best, exactly the same as the lung pressure. Regardless of the air’s velocity of flow as it approaches the aperture.

As I understand things, he’s definitely correct that there is a maximum pressure that can be created in the thoracic cavity before internal mechanisms engage to protect you from an internal injury.  I’m going by memory here, but I recall Arnold Jacobs writing about how this maximum amount of internal pressure is actually quite small (the context was, I believe, how we need not work as hard as we sometimes feel to breathe well for playing).

But I get a little lost trying to understand fully the context of Darryl’s corrections.  Some of my confusion may be due to certain assumptions that I’m making regarding the dynamics of how the air behaves prior to striking the lips.  First, I’m assuming that friction and viscosity aren’t changing around the model enough to be irrelevant to the tongue arch.  Secondly, I’m assuming that the air behaves similarly to how it would traveling through a tube of varying size.  For the sake of increasing my understanding, for now let’s just assume that this is the case.  I think we can all agree that there are lots of variables here and that it’s not only impossible, but also unnecessary to consider them at this time.  We’ll start burning those bridges later.

This web site has a nice description for us laymen regarding Bernoulli’s Principle.  From it, I’ve learned some new things.

As a fluid passes through a pipe that narrows or widens, the velocity and pressure of the fluid vary. As the pipe narrows, the fluid flows more quickly. Surprisingly, Bernoulli’s Principle tells us that as the fluid flows more quickly through the narrow sections, the pressure actually decreases rather than increases!

First, it appears that I had an important point backwards.  As the air gets forced through a smaller opening (e.g., in the oral cavity because of a higher tongue arch) the pressure actually decreases as it flows faster.  Still, I’m left a bit confused because assuming the air flow through the body behaves as a fluid passing through a pipe, then Bernoulli’s Principle would indicate a difference in speed or pressure as it gets blown through the smaller “pipe” created by a raised tongue arch, contrary to Darryl’s correction.

Another web site addresses my confusion somewhat by differentiating between what’s called static pressure and ram pressure.

Static pressure should not be confused with ram pressure, which is the pressure felt by an object because it is moving relative to the fluid. Basically, the fluid is ramming into the moving object, or vice versa.

The ram pressure increases when the speed increases. This explains the stronger force felt by your hand when it is held a fast moving current. In the faster current, your hand is deflecting more flowing fluid from its original path.

So perhaps what we need to consider with regards to the tongue arch and how it affects the air pressure isn’t so much the static pressure inside the mouth, but the ram pressure of the air as it strikes the compressed embouchure formation.  Again, assuming that the air inside the body behaves similarly to a fluid moving through a tube of varying sizes, I don’t understand Darryl’s corrections.

Can Darryl or any other physicist types out there with expert understanding of these principles want to chime in and help me better understand what’s going on?  What is actually happening to both the static pressure of the air as it moves through a more narrow path due to the raised tongue arch?  How does this affect the ram pressure of the air against the lips?  Lastly, how does this make it easier for brass players to play in the higher register?  Please leave your comments below.

Jeff Garrett

Wilktone,

Try looking at this web site:
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

This will give you a much better explanation of Bernoulli. Most important is the fact that Pressure will be sacrificed (transformed) to velocity as it passes thru the restriction. Pressure lowers as it passes thru the restriction. Once passed the restriction it assumes the previous pressure. The Bernoulli equation is based on a “perfect” fluid. That is one that has no viscosity. This is an impossibility. It dose not make it any less useful. It only bods to efficiency. Even though it may be less efficient, the effect still works.

Dave

Thanks for the resource, but remember you’re talking with a musician, not a scientist. I found that resource before, but a lot of it assumes a prior background that I personally don’t have. I need more basic info before I can effectively make use of that page.

Darryl Jones

I appreciate the discussion.

In the case of air approaching the aperture you can not add the ram pressure of the approaching air flow velocity without also considering the equal reduction in the static pressure which is proportional to that velocity.

The aperture only knows and “feels” the total pressure. Which is exactly what the lungs provide ( discounting frictional effects)

More later..

Dave

I would think that the aperture feels the ram pressure. I never meant to imply that ram pressure should be completely separated from static pressure, but just that there was more refinement that needed to be made in this discussion.

Darryl Jones

Also, to clarify:

When I said “maximum” air pressure applied I was referring to the maximum available of a specific pressure.

There is nothing one can do to achieve greater pressure at the aperture than what the lungs are supplying at that moment. Regardless of if the lung pressure is high or not.

In other words. The most air pressure that will exist at the aperture at any instant is the pressure in the lungs at that instant. Regardless of velocity of flow.

Dave

I’m afraid you’ve lost me again. Based on what I can tell (here’s the latest page I just read about this), in a tube the pressure of a fluid inside will change according to the diameter and length. Of course, I’m assuming that the path the air takes from the lungs to the lips will be sufficient to act similarly. If so, why would arching the tongue higher and narrowing the “tube” the air flows through not make for an accompanying change in pressure and speed?

Paul T.

This is an interesting point.

My understanding on this “dilemma”, as a total non-physicist, is that Bernoulli’s principle may not be applicable to a static fluid. A fluid moving through a pipe clearly is affected in the manner described: narrow the passage, and the velocity (and thus the ram pressure) increases.

However, the air in the lungs (and mouth cavity) is much closer to static when playing a brass instrument, particularly in the upper register.

Considering the air inside a brass player’s body as a static fluid, Bernoulli’s principle (and the level of tongue arch) seems entirely irrelevant to the pressure in the mouth.

So the question is–and this is a question for someone who knows far more than the little I do about physics–is the air in the body of a brass player closer to being a static fluid or a fluid in motion? At what point do which rules apply?

svenne larsson

Bernoulli’s princip is very much applied to brass playing, and also woodwind playing.
The airflow hitting closed lips will open the lips to an aperture. When the airflow pass the lips,witch create a smaller tube then the mouth cavity, the air flow does accelerate. (Yes it does)
The faster airflow create a sub pressure that close the lips, this procedure is going very fast.
So airflow opens the aperture, airflow close the aperture.
You can make a simple experiment and see this like this: you need two empty soft drink cans, a drinking straw, a flat table and something like a book a couple centimeters thick.
Place the cans on the table close to each other and to the book, blow through the straw between the cans from the other side from the book. If I explained it right and you executed it right, the separated to and aperture and immediately closed, open and closed very rapidly as long as you blow. This usually creates a loud high tone.
I used to do this trick in brass classes to surprise the audience and get them to understand some of the embouchure principle.

And old explanation about this used to be: The air stream opens the aperture and the muscles of the embouchure close the aperture. That would need muscles varying their tension very very fast.
The muscles does not vary its tension as long as the tone and loudness is constant.

Many brass players do not start the tone with closed lips. That does obviously work very well. (They play good)
For them the airflow close the aperture before it opens the aperture.

Darryl

It is more than air flow that opens and closes the lips. There are two very important, (and more influential) factors. One is the pressure variation in the mp cup. The other is the elasticity of the aperture.

Dave you are still getting some poor interpretation of Bernoulli, from some of the above posts.

Dave

Thanks, Darryl. I don’t think anyone meant to imply that other factors also come into play, just that Bernoulli’s Effect relates to brass playing too. Incidentally, since our original discussion here I’ve asked a college physics professor, a high school physics professor (who plays trumpet), a middle school science teacher (horn player), and a former NASA engineer (euphonium) about this topic. They all suggested that raising the level of the tongue arch would indeed increase the air velocity at the lips. It’s possible that they are mistaken, as you feel, but the teachers were very good at explaining the principle to me and why they agreed.

Darrl

I never said that it is impossible for the air velocity to be REALTIVELY greater over a raised tongue arch. But even if it is, this does NOT mean that the air has more total pressure at the embouchure due to some increase in the “ram” (or dynamic) pressure. That is the misundertood nuance of what the Bernoulli law really refers to.

Raising the tongue will not, and can not, increase the pressure of the air acting on the embouchure nor will it increase the velocity of the air THROUGH the embouchure.

I dont think you presented the actual “contentious” issue to your experts.

I would be happy to discuss it with those you listed involved.

Dave

Hi, “Darrl.”

If you use the same login every time you leave a comment you shouldn’t have to wait for it to be approved by me. 🙂

Raising the tongue will not, and can not, increase the pressure of the air acting on the embouchure nor will it increase the velocity of the air THROUGH the embouchure.

I’m perfectly willing to accept this, even though it goes against my current understanding of the physical laws being applied. Your problem isn’t in convincing me to change my mind, it’s that in spite of me asking several times for you to explain why, you only want to rephrase your points over again. The folks I mentioned above at least made an effort to answer my questions and teach me about the science. It’s definitely possible that my confusion here meant that I was asking the wrong questions to them.

I would be happy to discuss it with those you listed involved.

That’s such a bad idea for many reasons, but I do understand your motivation here. It’s easy for me to find advice on brass embouchures that are based on misinformation and at times I have contacted folks out of the blue to offer a correction. The problem is that when I do so it comes across as less about educating the public and more about proving myself right through proving someone else is wrong. I prefer the strategy of educating people and giving them the tools to understand not just what we know, but how we know it. It won’t help me personally come to a better understanding for you to spam strangers out of the blue to tell them where they got it wrong. I would much prefer you help explain the principles involved to me, not to my friends and colleagues.

In order to facilitate your corrections, let me try to break down what I think I know and you can jump directly to the point where I have it wrong.

1. Moving a fluid through a tube we will be able to measure the pressure both along the sides of the tube and at the end of the tube where a valve is. Pressure measured along the sides of the tube will be lowered than pressure measured at the valve at the end of the tube because the kinetic energy of the moving fluid is being converted to pressure.

2. When we make the tube more narrow the liquid/gas begins to move faster. This results in a decrease of the pressure along the sides of the tube. The amount of pressure felt at the valve, on the other hand, will be increased because there is more kinetic energy being converted to pressure there.

3. Assuming that these same physical principles apply to what a brass player does inside his or her oral cavity when playing due to changing the level of the tongue arch, is it correct to assume that if a brass player raises the tongue and effectively narrows the “tube” the amount of pressure felt at the “valve” should be felt to be stronger? If so, would this increased ram pressure at the embouchure help contribute to higher pitches?

You suggest that this is incorrect. Can you please help me understand this better and not only tell me where I have it wrong but explain to me why it’s wrong. For me, this is not about proving my theory about tonguing techniques right, it’s about learning more about how the science applies to my interests.

Thanks,

Dave

Fred Richardson

Darryl focuses on pressure, but that is not really the point. Yes the pressure can be no more than produced by the lungs. And yes the ultimate air velocity will be determined by the pressure and the smallest opening (the aperture). The challenge is how to transform air pressure into air velocity and to control the resulting pitches. A smaller mouth cavity for high notes means that some of the increase in velocity has already taken place before the aperture is reached. This can mean more than one control point (think coarse adjustment with tongue arch and fine adjustment with the aperture). For some this allows for better control and less strain on the embouchure. That is how tongue arch can help some and how it is linked to the Bernoulli effect.

Darryl Jones

You make 2 poor assumptions. 1. That air velocity anywhere, especially NOT at the embouchure, has any influence on pitch. 2. That increase of flow velocity before the aperture increases the molecular velocity AT the aperture. It doesn’t.

Dave

Please quit talking past each other (and me) and site sources. Darryl, my gripe with the way you discuss this (and Fred, you’re doing the same here) is that you state with absolute confidence that what you say is correct and others are wrong – but you don’t explain how and why.

Don’t just tell us what you know, tell us how you know what you know so that we can better evaluate your ideas.

Thanks,

Dave

Paul T.

My understanding of this issue aligns with Darryl’s. The inside of the human body (during the activity of playing a brass instrument) is much more like a balloon full of air under pressure, escaping at a small hole (the aperture) than it is like water flowing through a pipe.

Do you think a great deal of air is passing through your mouth and over your tongue when you play? Unless you’re playing extremely loud in the lowest register of your instrument (which isn’t generally what people associate tongue arch with), the air in your mouth is basically static when you play. It’s under pressure, and a bit of it escapes through the aperture at the lips, little puffs escaping hundreds of times per second.

You create the pressure by compressing the lungs: this increases the pressure inside your body until it’s significantly greater than the air pressure outside the body. That muscular contraction is responsible for your ability to “blow”.

Like a balloon which is being squeezed, making a squeaking sound as air escapes from its “nozzle”. If you put a tube or pipe inside that balloon, will the air come out faster? No. Only the pressure inside the balloon (and the properties of the aperture where the air escapes) matter.

Darryl, would you agree with this? (I wrote about this earlier, up above in the comments, as well.)

(It’s also worth noting that the “airspeed” explanation of the tongue arch has other issues. For instance, if Bernoulli’s laws apply, the airspeed velocity increases as the space between the tongue and the roof of the mouth decreases (like a narrowing tube). But most people do not actually touch the aperture with the tip of their tongue when they are playing.

This means that, before hitting the aperture, the hypothetical “airstream” would pass through the constricted passage above the tongue and then into a more open space (once it has passed your tongue, but before it has reached the aperture). At this point, if the air was indeed in motion and operating under Bernoullian principles, the pressure and airspeed velocity would all drop dramatically, undoing all the work you’ve just done (just like how the flow of a fluid *after* the Bernoullian acceleration has taken place would slow down again once it’s “out of the pipe”). You’d expect, in this case, a drop in performance (or, at best, an equal performance), certainly not any kind of increase.

This whole model of air traveling through a tube (and the tongue in the mouth forming a “narrower tube” and “speeding up the air”) seems pretty inappropriate to me.

The body compressed the air inside it, and it escapes at the only place it can: the aperture the player is allowing to form. There is no “airflow” inside the body (or very little, anyway), just a gradually diminishing air pressure. There is a little air escaping from the lips, of course, and there we could measure airspeed, but I doubt the tongue arch would change it.

Fred Richardson

A few comments.

1. Some posters indicate or appear to indicate that there is no Bernoulli effect, or it would be minimal for tongue arch. Given the videos that exist and the teaching on trumpet, horn, and trombone associated with tongue arch. It would appear that the “no” case was the one that had to be proven.

2. A poster suggested that there was no air flow in the body. Inhalation and exhalation are air flow. No air flow = death.

3. A poster indicated that even if tongue arch speeds up the air, going into the mouth (a less constricted space) will undo the effect. Well, if I take a piece of paper, hold it at arm’s length, and blow, it moves. That is going from the mouth to an infinitely open space at a distance of 2+ feet, not from a tongue arch across a mouth cavity of about 3 inches. The “undoing” will be less if the tongue arch is toward the front of the mouth (see Pops McLaughlin’s diagram on his website).

4. When I place the paper at a distance where I really have to focus the embouchure to make the paper move and see how long I can go (inhaling and exhaling in a timed pattern) before the embouchure muscles give out and I can no longer make the paper move, I find that I can go about 25% longer using tongue arch than not using tongue arch. With dozens of students over a 15 year period (who are not told what to expect) the variation is around 10% to 30%. This leads me to conclude (rather than assume, in fact I make neither assumption that Dave claims I do) that the tongue arch may reduce the DIFFERENCE between the velocity before and at the aperture and therefore reduce the work that the aperture muscles have to do to focus the resulting airstream to generate a particular velocity to support a particular pitch. So my conclusion is not that tongue arch increases overall velocity (that will still be determined by the smallest opening), but rather it reduces the work the aperture muscles have to do to achieve that velocity. Are there other conclusions possible? Maybe, if anyone has one, I would like to see it. Is this publishable in a scientific journal? No. But then I retired from my physics day job long ago (after 30 years, and I have been playing horn for 40) and have no need to go back to the lab to try to be helpful answering a question on a website. Anyone is free to test this on their own, or not, as they see fit.

5. There are measurements being done of intraoral pressure taken at several points in the oral cavity. I am not sure if their are similar multisite measurements of air speed as well. Google intraoral pressure measurements to see what is out there. These techniques applied to the question would be the best way to find evidence on what is happening.

Dave

This leads me to conclude (rather than assume, in fact I make neither assumption that Dave claims I do) that the tongue arch may reduce the DIFFERENCE between the velocity before and at the aperture and therefore reduce the work that the aperture muscles have to do to focus the resulting airstream to generate a particular velocity to support a particular pitch.

Thank you for taking the time to clarify your ideas, Fred. I think you meant to direct that comment towards Darryl.

Dave

Dave

Darryl, would air velocity correlate with air pressure? If so, Arnold Jacobs did measure intra-oral pressure of different brass players and concluded that the higher the pitch the higher the air pressure inside the mouth. I don’t have that reference handy, however, so take my memory with a grain of salt.

Now I don’t know that we can conclude that air velocity is the sole determination of pitch. Perhaps the increased pitch (or the mechanical changes that make for a higher pitch) is what increases the air pressure. There does appear to be a correlation, though.

Dave

Michael Reuss

Hi Dave,
first of all let me say thank you for your great website and for sharing your passion and enthusiasm!

As a trombone playing physicist I cannot resist to add my two cent to this thread 😉

With some thought models I had difficulties to understand them or to align them with my physic. Nevertheless a lot of correct statements and observations have been mentioned and maybe just have to be sorted and straightened a bit.

E.g. Yes, the Bernoulli effect is local to those regions in the ‘tube’ model, where the aperture is smaller. If the ‘space’ – or lumen as I would call it – would open again after the tongue was close to the ‘roof’ at the back of your mouth, the velocity would decrease again, the pressure increase etc.

I don’t see a conceptual difference between a narrow region in the tube and an (open) valve. If the diameter is too small, friction will increase which limits the amount of air that can pass through with a given initial (lung) pressure. But still Bernoulli applies and at the most narrow position there will be the highest velocity and the lowest pressure.
If the valve is closed of course, there can be no air flow, no velocity, no Bernoulli and – neglecting travelling shock waves – there’s only static pressure.

And since the aperture at the lips is much smaller than at the tongue, as physicist I would tend to neglect the tongue anyhow… 😉

I fully agree with Svenne in that the actual buzzing is a result of a kind of resonance between static pressure opening the lips and Bernoulli closing them through relative low pressure. And I would assume, the stiffer the lips, the higher the frequency and the higher the needed velocity to close them resp. the higher the pressure to open them?
Or was it the smaller the pinhole, the lighter the affected part of the lip… ?!

The last comment I want to give to the tongue/tube model: according to the Hagen-Poisseuille equation the amount of air flowing through a tube under a given pressure difference decreases with the length of the tube and the radius to the 4th! I.e. if I lift my tongue too much I can hardly get any air out at all, let alone move a sheet of paper in a distance. And we’ve not even touched the turbulence…

BUT, I’d like to suggest some additional thoughts about the position of the tongue and how I think it affects the pitch:
The shape of the mouth and the throat determines which frequencies are intensified by resonance.
In singing this is called formants. By shaping your mouth to an ‘ah’ you emphasize lower frequencies than by lifting the tongue for an ‘eh’. Listen e.g. to overtone singers for a demonstration.
Simplified, brass playing is all about exciting the proper partial. If the position of tongue and throat would form formants of resonant frequencies I’m sure it would help a big deal.

I think we observe that a certain tongue position is not absolutely necessary for a certain tone but facilitates certain registers. I conclude that the intraoral velocities and pressures do not directly influence the pitch. A certain embouchure firmness may be easier with a certain tongue position.
My gut feeling is, that the effect of resonant formants might be equally important.

Please take everything I wrote with a grain of salt since both my university was some years ago and I never managed the very high register personally yet.

Micha

Your email address will not be published. Required fields are marked *