Posted by Rick Denney on October 26, 2001 at 09:50:00:
In Reply to: Re: Short Action vs. "Regular" Piston Valves posted by Lew on October 26, 2001 at 08:40:59:
Lew, it isn't a question of fluid dynamics, but a question of acoustics. Tubas would still sound like tubas if there was no airflow at all, except that we can't make our lips vibrate without the airflow.
To the original poster:
Any variation in shape can cause a modification in the phase of some of the sound waves traversing that variation, which can strengthen or weaken that harmonic. Whether short-action valves, per se, have this effect (or, more accurately, whether the tubas that use them work around any resulting problems effectively) hasn't ever really been demonstrated. The tubas that used the short-action valves are very large instruments, however, and those instruments have strengths and weaknesses inherent in their size and taper design.
Even the 3xJ tubas from Conn, which were as large as the 2xJ tubas with short-action valves, had similar intonation problems. I think it would be hard to say which sounded better than the other. Based on the continued popularity of the 2xJ instruments, I'd have to say that short-action valves aren't much of a problem, if any.
And sousaphones with short-action valves are among the most popular sousaphones ever made.
Rick "thinking that valve-port shape is just another design parameter to be worked around" Denney