Re: Hey! Rick Denney...


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Posted by Rick Denney on November 26, 2001 at 11:20:17:

In Reply to: Hey! Rick Denney... posted by Doc on November 25, 2001 at 22:18:33:

I've done too little testing to be able to report "findings." But I do have opinions, based on how horns seem to play and how good players seem to react to them.

Joe S. posted a thread a week or two back that talked about short, fat bells versus tall, narrow bells, and I'm just summarizing what I wrote buried down in that thread.

My own tests had to do with the spectrum of sound frequencies produced by a tuba. That test was extremely simplistic, and was as much a test of my room (and of me) as of my tubas. But with the player and the room held constant, the differences seemed to be that the shorter, fatter bell of the York produced stronger upper harmonics than the taller, narrower Miraphone bell. The Yamaha 621 F tuba is a small instrument with piston valves, but the bell is more like the tall, narrow type in that the shape is more like an exponential horn, and less like the bi-radial shape of the York bell. The Yamaha and the Miraphone were similar in their spectra, and both were different from the York.

But I think the real issue is how the sound propagates in the hall. If I take a recorded York sound and a recorded Miraphone sound, both recorded in an anechoic chamber (or outdoors) to remove room effects, and then played them back in a hall, what would happen? I don't know the answer, but my suspicion is that I could make the recorded York sound like a Miraphone if I played it through an exponential horn loudspeaker, and I could make the Miraphone sound more like the York if I played it through a bi-radial horn loudspeaker.

It seems to me the reason is that the bi-radial horn York bell radiates sound much more widely than does the narrow exponential Miraphone bell. What effect does that have in the hall? The widely-radiated sound will follow many paths through the hall, and a listener will hear more from the peripheral paths and less from the central path, when compared to the Miraphone bell. Now, the Miraphone is still aimed at the ceiling, so that path is still a reflected path, but there will be more from the central path (however it is reflected) and less from the peripheral paths, when compared to the fat bell.

All paths have a different length, and the sound following a short path will get to the listener a bit sooner than the sound following a longer path. So, the two sounds will be a bit out of phase with each other, which can cancel or reinforce some of the higher harmonics. The more variety in the number of paths, the more the tone will be colored by the phases shifts inherent in that variety. I think that's why the fat-belled tubas are thought to have more character out in the hall.

When I think of how these same tubas behave outdoors, I'm not sure these ideas hold up very well, so this is just guesswork on my part. But my ears undeniably tell me that the sound reflected back to me in a live hall from the York is much deeper and fuller than the sound reflected back from the Miraphone. The difference in my dead basement is much harder to discern.

I've become a strong believer in the notion that the timbre of the tuba out in the hall is most closely associated with the shape of the bell stack. Intonation tendencies seem to be determined upstream from the bell stack. Practitioners have held this point of view for a while, and you'll hear the experts saying something like, "I put that wonderful-sounding bell on a really in-tune tuba."

Rick "offering nothing more than a considered opinion" Denney


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