90 degree bends instead of smooth curves .....

[Brassdad]

I'm no engineer, nor do I even play one on TV,

Choo, Choo!!!sorry, couldn't resist...

[windshieldbug]

Never played one, seen one, etc., but thought this might be of interest:

This tuba, from Daniel Kunst's shop in Bremen definately has the 90 degree bend thing down...

Except that to be functional, the valves still either contain 90° bends, or contain airways that have to cross, which STILL means you have to have the "dreaded" 90° bends... (work it out!)

[windshieldbug]

Choo, Choo!!!sorry, couldn't resist...

I'm in Durango, Colorado right now. My wife and I have tickets on the narrow gauge railroad here for tomorrow morning.
Jealous?

Yes

Likewise!

[Rick Denney]

Has anyone tried to measure the actual airspeed through valve combinations? I'm no engineer, nor do I even play one on TV, but I'd be very surprised if much air actually flows THROUGH the horn. I thought this was mostly about standing waves, and the air flowing through the lips to initiate them.

I am persuaded that "stuffy" means lack of resonance, not lack of air movement. If a note's ease of speaking is picky about the air flow or embouchure (or both) we complain that it's stuffy, or that it backs up on us.

Some instruments lose their characteristic resonance when air flow exceeds a certain amount, and this could be because of pressure pockets caused by the geometry of the tubing. The things that project into the air flow cause these anomalies, but I think the taper design is still much more important to basic resonance.

A good buzz requires air flow to work against the elasticity of the lips. Good resonance reinforces that buzz by adding each pulse of air from the lips to the pressure waves reflecting back from the bell efficiently. More air does not mean more pressure--pressure is not produced by air supply, but rather by restrictions on its subsequent movement. When our pulses fit neatly into the standing waves inside the tuba, it's easy to let more air flow into it without having to push. So, poor resonance can provide a restriction on air flow. Powering through that restriction can sometimes cause alternate resonances that are unmusical. More often, though, we don't play in tune with the resonance of the instrument by putting in a clean and efficient buzz, and try to compensate by pushing more air. That produces noise in the vibration, which we think of as a spreading or unfocused sound.

An ideal instrument provides just enough natural air resistance to allow the buzz to maintain efficiency, and an abundance of natural resonance to make full use of the buzz we produce. Distance from that ideal undermines our buzz and the product of our buzz, and that's what makes a tuba stuffy. But both characteristics have to work together. Air resistance may or may help or hurt buzz efficiency in any given instrument.

Rick "for whom 'open' means 'resonant'" Denney

Edit: On the subject of air speed, for uncompressible fluids flow equals velocity times area. Let's assume air is not compressible (which is a false assumption, but useful). Further, let's assume that we can empty our lungs on a pedal tone in two seconds. We will be dumping perhaps 2 liters per second, which corresponds fairly closely to Jacob's measurements of 140 liters/minute for low, loud notes on the tuba.

A liter is 1000 cubic centimeters, so we are moving 2000 cm^3/second through the mouthpiece throat. The mouthpiece throat is perhaps .84 cm in diameter, which has an area of .55 cm^2. If we were blowing water instead of air, velocity would be 3.6 m/sec, which is about 25 mph. When that flow expands to fill a .75" tube, velocity would drop by a factor of five, to .7 m/s, or maybe 5 mph. At a 20" bell, the velocity drops by a factor of 3600, to .001 m/s or .007 mph. Air is compressible and pressure will increase in smoothly in response to restrictions, with the sound pressure waves riding on top of it. But it gives you a notion of how much air speed slows down in the instrument. You can feel that difference in warmth when playing on a cold day.

R "who forgot to answer the question first time around" Denney

[windshieldbug]

I am persuaded that "stuffy" means lack of resonance, not lack of air movement. If a note's ease of speaking is picky about the air flow or embouchure (or both) we complain that it's stuffy, or that it backs up on us

That sure resonated here!