physics tuba question

[jsswadley]

Why is the inside bore of the tuba not polished and made flat and smooth like the outside? Doesn't the irregularity of the metal on the inside walls create turbulence or friction? John

[Chuck(G)]

Air actually moves very slowly through a tuba; turbulence isn't normally a problem once the flow gets through the mouthpiece unless you're backed by an Ingersoll-Rand air compressor.

F'rinstance, suppose you can actually push 6 liters of air per minute through your horn. At the end of that minute, the air you began with still won't have made it out of the bell of most large instruments.

Acoustics are far more important when it comes to bumps on the inside of a tuba.

[Shockwave]

Ditto

[UDELBR]

Gerhard Meinl (of Meinl-Weston) was looking into this awhile ago; said the "fuzzies" and "slime-ies" that tend to grow inside tubas had a non-negligible negative effect on the instrument's performance. He was looking for a way to make the interior more resistant to revolting clingy things.

I suppose a solution along these lines would also have helped with red rot. No word on what happened with his idea.

(Of course I assume the original poster isn't referring to actual hydraulic loss when he mentions 'friction', but probably early reflections that DO affect the instrument's response).

[Leland]

Gerhard Meinl...was looking for a way to make the interior more resistant to revolting clingy things.

Did you find out what some of his ideas were? I would guess a non-corrosive plating of some kind (nice thing about stainless & titanium mouthpieces; nothing gets a foothold inside).

[UDELBR]

Gerhard Meinl...was looking for a way to make the interior more resistant to revolting clingy things.

Did you find out what some of his ideas were?

Nah; he was just thinking out loud that day.

[Chuck(G)]

(Of course I assume the original poster isn't referring to actual hydraulic loss when he mentions 'friction', but probably early reflections that DO affect the instrument's response).

That's why I qualified my response with lumps and ridges perhaps having a significant acoustic effect akin to lining the innards of one's instrument with pea gravel. But it's pretty clear that the original poster actually meant aerodynamic effects:

Why is the inside bore of the tuba not polished and made flat and smooth like the outside? Doesn't the irregularity of the metal on the inside walls create turbulence or friction?

FWIW, like many other tuba-wranglers on this list, I do my level best to put the factory errors (gaps within ferrules, crowned-over tubing ends, etc.) right when reassembling an instrument.

[jsswadley]

Thanks for your responses. Of course I meant aerodynamic effect within the inner bore of the tuba. To be absolutely clear: look at the bell of your unlaquered or laquered tuba. Then, reach down into the tuba towards the bottom bow and feel the relatively irregular surface on the inside of the tuba. Without any doubt dents must affect an airstream and the question was whether these small surface irregularities would have any aerodynamic effects. Related commentary: an Austrian trumpet maker offers a trumpet with a "hand hammered" oval indentations in the bell. The maker feels that this makes his trumpets sound good. So, apparently this type of indentation would make some sound difference. I hope this is formulated precisely enough for you. John

[Rick Denney]

Then, reach down into the tuba towards the bottom bow and feel the relatively irregular surface on the inside of the tuba.

Consider what it would take to remove those bumps and bring the interior to as smooth a finish as the outside. Tubas and other brass instruments are sanded and polished on the outside. That would be mighty hard to do on the inside, heh, heh.

But also consider that a slightly rough surface actually flows better than a polished surface. I don't remember why, though.

Rick "something to do with boundary layers" Denney

[Chuck(G)]

But also consider that a slightly rough surface actually flows better than a polished surface. I don't remember why, though.

Isn't that why golf balls have dimples?

...but don't ask me to dimple my tuba!

[ai698]

Isn't that why golf balls have dimples?

...but don't ask me to dimple my tuba!

Think about it if you enter you tuba for the ITEC Tuba Throwing Contest.

[Rick Denney]

Isn't that why golf balls have dimples?

No, I don't think so. Golf balls have a spin when struck, and the dimples increase friction and grab the air. The spin uses that friction to make the ball climb on the air, which gives it more height and distance.

At least that's the theory. I've never been able to demonstrate it personally.

Rick "whose therapist has banned golf because of anger and depression" Denney

[Chuck(G)]

http://www.coolquiz.com/trivia/explain/ ... _balls.asp

[tubeast]

My server doesn´t allow me to open the link Chuck provided, but here´s the explanation our fluid dynamics professor provided:
In addition to the effect Rick Denney mentioned, the dimples make sure the airflow around the ball is turbulent rather than laminar even at compareably low speeds.
It´s true that turbulent airflow has more internal resistance than laminar flow, but with laminar flow the "air-shadow" (space which the flow around the ball doesn´t reach because air already is there) behind the ball expands with distance from the ball and adds to its drag resistance.
With turbulent flow, the air-shadow is much narrower, offering less resistance, which makes the ball loose less dynamic energy on its path.

This effect is used in volleball, too. When serving, the players try to give the ball a speed great enough so there will be tubulent flow. The ball goes almost on curved, but basically horizontal line until it lost so much speed that the flow switches to laminar. All of a sudden the ball will change its path, falling much faster.

As to tubas: I´m afraid dimples won´t have that much effect because especially at the end of the tube the air flow is incredibly slow. Plus, the geometry of the horn that has effect on air resistance won´t change, as opposed to the ball.

[windshieldbug]

What was that custom model of F. E. Olds trombone that had that hammered finish?

I believe both the Olds trombones and trumpets with the hand-hammered 'dimpled' bells were known as the "Military" models;
Since there is no real airflow I can only imagine that it was justified by the overtones created/cancelled by this treatment.

[iiipopes]

My Besson has had the dents hammered out of it so many times before I got it that it looks like a hammer peen finish! Doesn't affect tone, as the valves are perfect. As a matter of fact, a band director friend said if he had found it first, he would have bought it for his band!

[Rick Denney]

http://www.coolquiz.com/trivia/explain/ ... _balls.asp

So it is the same. Cool.

Rick "who'll loan Chuck his picking hammer" Denney

[hbcrandy]

From the side of practicality, how does one propose to buff and degrease the inside of the tuba when the smaller tubing is about 3/4" in diameter and several feet long?

[windshieldbug]

From the side of practicality, how does one propose to buff and degrease the inside of the tuba when the smaller tubing is about 3/4" in diameter and several feet long?

Using a very small labor force

[iiipopes]

It's expensive, but if you can find a tech with an ultrasonic bath it works great! I just haven't come up with the $150 yet to do mine.