Posted by Rick Denney on July 01, 2002 at 16:44:47:
In Reply to: Re: Re: Re: Intonation on the 2155 posted by Jay Bertolet on July 01, 2002 at 08:07:54:
I agree with you that the backbore seems to have the intonation effect rather than the cup.
But if I had the formulas to show it, that would be hard analytical proof. Empirical proof is never hard, because it is based on statistics. (You may roast me now for being pedantic, heh, heh.)
When I bought the Doug Elliott mouthpiece, I did so in consultation with Doug. He helped me choose a comfotable rim that fit my face, and then we selected a cup that gave the tuba the sound I was looking for. Then we tried backbores, going up in throat size and shape until intonation started to stuffer, and then backing off. I ended up with a T-6 backbore, which has a bigger throat than any mouthpiece in my box-o-mouthpieces, but it's not Doug's biggest. A bigger cup has intonation effects, according to the theory, but those are likely offset by a larger throat, if I'm remembering the arm-waving that Ken Sloan and I did in his den recently.
So, in terms of primary influences, I would say that the protocol is to select a rim for comfort, a cup for sound, and a backbore for intonation.
Of course, we had to make room for the larger backbore--that required reaming the proper taper in the receiver, which the factory had apparently forgotten to do.
The tuba still has the same basic intonation tendencies it did before, but much less so and within the manageable range.
Rick "whose air stream causes more pitch problems than his tuba" Denney