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That is the difference between the Greenhoe and Rotax valves. A Greenhoe rotor maintains the same, circular inner dimensions as the rest of the valve tubing. (When you mentioned before that both valves were the same, I wondered how it was possible for Gary to get a patent if his valve was simply a Rotax copy.)

Steve Shires early production models of the Greenhoe valve look like swiss cheese. They consist of two valve halves braised together. I think Gary's newest generation are machined out of a single chunk of brass.

Now you are taking the topic down to real business, Joe. And thank you for that!

Basically I am out of a European vocal and recorder breathing school, which advocates a maximum pressure from the outer muscles of the abdominal cavity (like in defecating) balanced by a controlled resistance in the abdomen itself. Some Europeans have been taught to place the resistance in the vocal chords. I find that as dangerous and ridiculous as one of my teachers telling me to place the resistance in the embouchure.

All that said I am extremely aware, that the instrument design also places resistance in crucial areas of the bore sequence.

These have real implications in our perceptions of any given intrument. But they also play with our imagined perceptions of these instruments.

My imagined ideal in short is: large and open leadpipe, large bore, and small to medium bell flare. I like to imagine that I am playing the bell flare, like I have taught bass guitarists in ensembles not to play their instrument, but the cone of their amplifier. Pure voodoo of course.

But then only my King 7B bassbone and my YEP641 euph fit that ideal description of mine. My German trumpets are large leadpipewise but small bore and large bell. My Conn 28D adds a narrow leadpipe to that problematic, but is equally effective as the German trumpets. The Besson 981 Eb tuba combines an open leadpipe with a comparatively moderate bore and a huge bell into a fine music making tool.

Has this anything to do with the Rotax? Oh, yes!

The R&D department of this list often uses the term of impedance. Which is something about how systems in actual working are impeded by obstructions not perceived in static situations or by non-oscillating motions. Of air in this case.

By any theory a plain rotary valve is a nightmare in irregular geometry of the air passage. Sharp edges, restraints and at least one bulb in bore. Irregular shapes of square cuts. All in all ideal generators of turbulences. Which in their own right are very resistance generating. Hence big impe-dancers.

Joe'S analyses of the additional restraints of bore in the Rotax valves are true all the way.

I am not a Rotax endorser. Cannot be one, as I never have had the chance to try a Rotax equipped instrument.




Yet I will say from the very view, that Joe S provided, that the Rotax rotor cuts down on major irregularities in axial as well as square profiles of the air-path. Thereby cutting down on turbulences and hence cutting down on impedance.

Hard to understand? Yes, for me too!

Klaus

Seems that if you wanted a "round all the way through" valve, the Hagmann might come pretty close:



Kanstul's CR valve isn't bad in that department either:

harold wrote:What about the physics?

It seems to me that most of this is smoke and mirrors. Is there some impedence or turbulance created by having pathways that are less smooth than others?

Certainly, but for the most part a human is not capable of moving a column of air fast enough to make any perceived effect statistically significant.

What we are looking at here is in fact voodoo not good science.

It's voodoo only if you look at it from a fluid dynamics standpoint. If you look at it from an acoustics standpoint, any discontinuity in the surface will degrade the acoustic propoerties of an instrument as a resonator.