intonation (open bugle)..?

[jon112780]

If I have a horn that plays a bit sharp in the upper regieter, and a bit flat in the lower register, how do I 'smush' the otcaves closer together?

I sem to remember someone mentioning here on TubeNet that the mouthpiece might be too far in the reciever, and making the shank a bit larger (stick out farther) would make the horn play more in tune overall...

Does that mean that if the opposite was true, I would have the opposite problem?

Back to the 1st question. Would it be possible to cut a 1/4" off the end of the reciever, and would this have much impact (make the mpc stick out farther) and bring the partials slightly closer together?

EDIT: I don't suppose it would be possible to slightly enlarge the shank of the mouthpiece itself? How would you do this, a couple coats (only on the outside of the shank) of laquer or silver?

[imperialbari]

Cutting the receiver would make no sense, as the mouthpiece would keep its placement relative to the narrowest (venturi) point and to the overall conical progression.

Some older instruments played with modern mouthpieces appear to have stretched octaves. In my experience the main problem in such cases may be, that the 2nd partial goes flat with the larger throats on modern mouthpieces.

A medium (relative to the instrument) mouthpiece throat would keep the partials reasonably in line. According to Vincent Bach and others, the top range will go flat with a narrow throat. A moderately large throat will raise the pitch of the upper register. A very open throat will also raise the pitch of the lower register, so that the mid-range will come out flat compared to the outer registers.

Klaus

[MaryAnn]

Since I have one of these too (an old American 3-valve Eb) I'll go look through my mpc collection and see what is the narrowest throat I have. But it does this with a 32E (not your favorite mpc, as I recall) which I would think has a pretty narrow throat. The difference in the intonation over the range is sufficient that I stopped trying to play it pretty early on; I'd have to use the main slide as well as the valves to get it in range, and that is more than I want to deal with. The former owner had no troubles with it but I found I could not lip it; first I had to cut it to get it up to pitch and then the stretched-range problems caused me to give up. Sharp high, flat low. My other tubas don't do this, so I don't think it's me.

MA

[iiipopes]

Having tried the entire range of PT mouthpieces this summer on several horns, I can give personal experience that the models that are otherwise similar, but have narrower throats, and probably narrower backbores to match, tended to flatten the upper register on the horns I tried them on, basically the entire PT contrabass line, both CC & BBb, and a few others, like the Nirschl 4/4 CC.

Sometimes it is the better investment in the long run just to get a new mouthpiece and keep going. If you have a mouthpiece that you like the rim and cup geometry, call Jeff Rideout at Custom Music and see what he recommends as a similar model in the PT line with the narrower throat.

[bill]

To partly answer your questions about mouthpiece shank diameters, the simplest way to increase the diameter, temporarily, for experimentation, is to use Scotch Tape. Note where the mouthpiece encounters the lead pipe and put the top of the tape there and increase it one layer at a time until you get a change of up to about 5/8" in how much shank is in the lead pipe. If this does what you want, you have two options. One would be to have the shank increased by someone like Matt Walters, at Dillon, for $40-$50. The other is to get that clear package sealing tape and do the same number of wraps, on the entire shank as you did for the Scotch tape. You will need to trim the tape at the end of the shaft but you will have a semi permanent shank increase. Waterproof adhesive tape can also work but it is not so permanent. http://acattanach.users.btopenworld.com ... isons2.xls is a source for comparisons of mouthpiece bore and other dimensions but it does not give shank dimensions. Dave Werden's Chart http://www.dwerden.com/mouthpieces/tuba.cfm is also a good source for dimensions. It has the added advantage that you can compare smaller sets of mouthpieces but clicking on the Rim dimension. It will give you similar mouthpieces and their dimensions.

Hope this leads to some ideas for you to try.