eupher61 wrote:For many reasons I'm not in these woods as much as I ustabe, but I'm glad to catch up with this thread. Rick D, thanks for finding those pictures. And, Rick F, I think the parallel is significant. A different type of wave production, but it's all the same air.
I can't relate the waveguide example to a tuba beyond the general conceptual similarity of both being frequency-domain questions. "The same air" doesn't do it--that waveguide would work just as well without the air, and in fact waveguide is usually filled with something other than air to eliminate moisture that causes attenuation and corrosion.
And the microwave stuff isn't really moving in the air in any case. It's moving along the inside surface (i.e., skin effect) of the waveguide tubing. That tubing inner surface creates a field that has characteristics of resonance, and that resonance has to be tuned appropriately to minimize the impedance mismatch between the transmitter output and the antenna, but that could happen equally in the vacuum of space. Measuring that impedance mismatch (of which VSWR is one possible measure) is easy compared to understanding the acoustics of a conical tuba.
The pulse made by the sound of the opening lips during the buzz travels down the instrument at the speed of sound, as affected by the impedance of the instrument as it goes. That sound is a series of pressure fronts. When one of those pressure fronts reaches a dent, it causes the pressure to increase a bit, which sends a reflecting pulse back to the mouthpiece. If that return reflection arrives just in time to reinforce the buzz on the low C, it could make that low C easier to play. That timing requires that the dent be positioned at just the right spot. But it seems to me the dent would have to be bigger than The Dent in Steve's F. I tend to agree with Joe that Steve's tuba would probably play as well without the dent, and the correction of the low C problem wasn't as tightly related to the dent as Steve perceives. But it's not my tuba and I doubt Steve is willing to conduct the experiment, heh.
I agree that the Sellmansberger mouthpiece play better in these types of F tubas. The reason is that they provide a better impedance match. Their cup shape also modifies the impedance at the mouthpieces, and gives the player some impedance to work into. That is also why the Geib-inspired cups (like the Blokepiece, Stofer Geib, Laskey 30G, etc.) seem to produce more harmonic color and therefore more sense of resonance. But it takes some control--someone whose sound is overburdened with noise artifacts (like mine) has to be careful not to end up with blatty sounds. It's worth the effort. In any case, the trouble I used to have with the low C isn't so much of a problem any more, even on tubas that have a reputation for such problems. I suspect that has to do with practice.
Rick "suggesting that all frequency-domain systems need some impedance to work into" Denney
No wonder my patent application was rejected.