Posted by Rick Denney on June 24, 2002 at 12:50:53:
In Reply to: Re: Converting a BBb to a CC posted by Gus Pratt on June 23, 2002 at 20:33:46:
The taper design of a tuba has a huge effect on how in tune it plays in addition to the tone. One key parameter in that design is the ratio of cylindrical to tapered tubing in the overal bugle. If you cut too much from the cylindrical section, you might affect both intonation and sound positively or negatively, depending on what you are starting with.
When Rusk talks about remvoing a lead-pipe tuning slide to make most of the conversion, he is also replacing the valve body with valves of a larger bore. This has the effect of maintaining to some extent these ratios.
Fred Young made an observation a few weeks ago that when scaling instruments one should maintain the dimensionless ratios of the instrument, including the ratio of bell size to bore, tapered length to cylindrical length, mouthpiece throat to bore, mouthpiece cup volume to instrument volume, and so on. Many of these are too fuzzy in the small change from BBb to CC, but some are still important.
I agree with Lee Stofer that this should be attempted only be people who want to hack on a horn more than they want a playable result, unless they've sufficient experience so that they don't need to ask questions such as these. When I did my project, I did it for fun and got better results than I deserved, but the result is still not a horn I'm tempted to play more than for its conversation-piece value. In that horn, about two thirds of what I removed was cylindrical and the remainder tapered, with the result that several key ratios were modified. In so doing, the low register, below the staff, lost both intonation and sound, though the upper register worked out okay.
Rick "caveat hackor" Denney