How much needs to be cut from this BBb tuba?

[imperialbari]

Maybe too late to enter this thread, but the problem will come again.

To retune a tuba from 435Hz to 440Hz (with the tuning slide all way in) you have to change its current theoretical length (TL) from TL*1/1 to TL*435/440. The amount to cut will be TL*5/440 If you do the cutting at the tuning slide, each branch has to be cut half that length. If you want a certain amount of pull on your slide add that amount to the calculated cut.

The theoretical length, because the real length is shorter, as the bell flare has an effect of adding acoustical length to whatever tubing it is added to.

The theoretical length may be calculated precisely for a given temperature, but as the fraction is so small 18’ is good enough as a starting point for a BBb tuba.

(216"x5):(440x2) = 1.227"

Which is a little less than 5/4 of an inch.

If you want the 440Hz tuning with a slide pull of 3/4", you should cut each branch 2".

Klaus

[Michael Bush]

Interesting, Klaus.

For whatever reason, removing a total of a little less than 2 1/2" worked very well. (Maybe when I found 435 was about where it was, I was blowing tight and sharp?)

At any rate, I remain far more satisfied with the intonation of this tuba as it now is than as it was before. It's very close to 440 with the MTS out a bit. I could still push in on a cold day outside. The only issue the cut has introduced is the fourth valve slide has to be pulled out noticeably more now, but even it still has some more to give.

I am pleased with the result. And now I won't be embarrassed to pass it on to someone else when I eventually sell it (since sentimentality about what I played in high school isn't going to be enough reason to keep a tuba I never play around forever).

[imperialbari]

9’ are wrong. The 18’ that you mention are right. I was just thinking in the general C to Bb relation being 8 to 9, forgetting about being in the 16’ contrabass range.

Not to hide my error, but attempting to avoid more confusion, I have edited my previous posting, so that the calc hopefully is right now.

Klaus

[Michael Bush]

9" are wrong. The 18’ that you mention are right. I was just thinking in the general C to Bb relation being 8 to 9, forgetting about being in the 16’ contrabass range.

Not to hide my error, but attempting to avoid more confusion, I have edited my previous posting, so that the calc hopefully is right now.

Klaus

I've edited mine as well, but I think people can still follow the thought.

[ghmerrill]

I did this on my old Buescher Eb (the one in my current avatar) which also tuned to 435 (apparently that's what "low pitch" meant in this case). As I recall, I took off about 3/4" off each side of the main slide, but I'd have to check my records.

Then the valve slides needed to be addressed and I did the 1st and 3rd -- hoping I wouldn't need to do the second because there was almost no room to work on it.

After a couple of months of trying to live with that, I finally bit the bullet and cut the second as well, though it was painfully slow and careful work involving a small hack saw too I made, a Dremel, and file work.

The horn works well, and I tuned it a bit sharp (mostly for winter playing possibilities). Slow and careful wins the race. It took me at least two attempts to get it right on each slide section.

[ghmerrill]

Yeah. Like I say, I'd have to look up the final results since I did this. It was close to four years ago. It's quite possible that the initial cut was 3/4", but then I cut it again. I was being careful not to take off too much. I didn't view it as a "do it once and get it right" approach.

Also, determining the "exact pitch" that a horn plays at is difficult since it depends on several factors. Once I decided that the horn was playing high and mapped the pitches, it originally seemed to me that it was pitched at 438. But I couldn't get entirely consistent results, though I later decided it was closer to 435. I think there's necessarily some trial and error involved in this.

I was really unhappy at having to cut the 2nd valve slide, but the rest of the horn was behaving well and I just couldn't get the 2nd valve combinations at pitch without some degree of lipping.

[Michael Bush]

I took it to community band tonight. Played about half of a really simple part before going back to the CC. I'm just not smart enough to keep both sets of fingerings in my head at once. It sounds sweet though.

[Michael Bush]

Whelp. This tuba with the help of my own head has taught me a lesson I have learned too many times before: The quest for "perfection" is the enemy of "perfectly satisfactory", especially when you're a beginner just figgering stuff out.

It was fine. I undertook to make it better than fine and screwed up a part completely. So now I'm going to be calling around looking for parts or help or whatever.

[Michael Bush]

As you intuitively knew from experience, Joe, (while graciously holding out the possibility that it wasn't so) it was a slide tube. But it wasn't a problem of cutting off too much. I'll call you after while.

[Michael Bush]

As you intuitively knew from experience, Joe, (while graciously holding out the possibility that it wasn't so) it was a slide tube. But it wasn't a problem of cutting off too much. I'll call you after while.

If/when, could have have the o.d. of the tube available?

Yep. It will be a little while later in the day, though.