I made my 5th slide circuit about 24" when the slide is pulled about an inch. All my other measurements worked out well, but this one did not. AI said it needed to be around 35.5" on an uncompensated f tuba. My math says one thing, it agrees with the measurements on other charts, and to lower any F, Eb, or CC tuba to play a low Bb, the total number of inches is the same.
HOWEVER… AI said that for a tuba in F, that much straight tubing through the valves will cause a LOT of resistance and cause massive response issues, just like with the low C. Something about impedance valleys.
For the other tubas, the Bb would be the same length, but for an F, it would need to have about ten inches more pipe than what mine has when pushed all the way in, almost exactly where I have been noting the slide wants to be, but that I have to tape it in place because it is just beyond the end of its pull. Dead on.
In the past, I have noted that on old rotary Fs with the classic crappy low C, on some of them with a long 4th slide, you could put it where it seemed to be designed to go and get this horrible, nasal, hole-in-the-horn tone. It was in tune, yes. It was *okay*, yes. But it sounded lousy and responded quite slowly (if at all) unless you wasted an inordinate amount of time learning to mangle your mouth to coax it out. Regarding my old Mirafone 180 F, I recall discussing back in the late 1990s on this board that the very long 4th slide allowed me to pull it out to more than a half step flat, and then suddenly it became "amorphous," and then with the pull of another 1/8" this clear, fat, in-tune C sang out. However, all other 4th notes above that had to be played 13. (Really only the bottom line G on that tuba.)
The AI I dumped on tonight claims that this longer 5th slide would net a low Bb in tune played 45, with 4 tuned to a C (which I can do since I have the 24 tuning fixed with 46). I do not know why this disagrees with the math so much, but it seems to work. So my measurement of a 5th side of between 24 and 26 inches, WHICH MATCHES EXACTLY HERR KURATH'S MEASUREMENTS (and shares this issue of a crappy low Bb), is wrong, and this weird 35.5" length is correct. And I came up with this same number independently, before I asked the AI bot. So I do not think the AI just hallucinated (as they are wont to do) and that this is correct.
BUT WHY?
A Bb is a Bb is a Bb, right? Shouldn't the length be the same on an F as on the other three instruments? The F is. The 4th valve C is. Why is the longer loop working for me on my F, and why did AI suggest that length to me without prompting?
Is this the end of life as we know it?
I want to revisit the old, sweet, rotary F tubas with the craptacular low range. Could all the disagreement about learning to play them be because some folks learned to pull 4th out really far, while the complainers did not? Was that all it was? I detest not understanding stuff…
Anyway, the upshot of this is that I am building a new 5th slide. I have the correct crook. I have enough outer tubing. I am short of the inner tubing unless I use brass, but it will be the *only* slide out of nine with brass legs. Silly, but that would indeed bug me. One solution is to install a spacer on the short side. (One runner comes up an inch shorter than the other.) I have enough for the long side's ferrule and the extended inner and outer tubes. I have the outer tube and ferrule for the other side. And as luck may have it, my first 5th slide layout used internal spacers to take up the gaps, and one of the legs was the length needed, and I reused the slide, so the internal sleeve is already installed, and the exact length needed. So I can do this as a trial thing without using a single part from the current slide assembly. If it sucks, I can easily switch them back.
Alternatively, I could build a longer slide using brass inner legs using the extra crook, and just use it without altering the outer legs until I know whether I want to do this.
I think I will do the latter. I am almost as lazy as Joe claims to be, so building a new, temporary slide using the existing outer tubes is an attractive idea.
I will give this a shot this week. Photos when it is done…
How things are right now: You can see that the numbers I came up with really do seem to be short. If you include the runners (and 2nd has a very long one underneath), 5th is not really twice the length of 6th as it should be. And double that would be just about what seems to work out with the tuner. So we shall see…
