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I have tried a bunch of sizes on a bunch of tubas and my personal experience seems to bear out what bloke said. I currently use a Yamaha Jim Self on a VMI 3301(.748), Miraphone 184(.705) and an Olds O-99(.656). This is a rather robust mp at 32.8mm rim and 8mm throat. It feels about the same on all 3. I have tried smaller rim and throat sizes on the smaller tubas and don't like them at all. Not reading any German, I'd like to know what kind of problems I am supposed to experience when using an 8mm throat on a .656 bore horn. I'll start looking for them specifically.

I'd go further to ask whether anything relates to `bore' size in a consistent and meaningful way. (well, other than weight - clearly the weight of the valve section will have a positive relation to the bore size, all other things held equal.)

But in terms of acoustics, tubas are, after all, essentially conical. At the big end they are very big, whatever the size of the arbitrarily located valve section, and at the small end, rather small. With no valves engaged, the valve/bore section takes up only a few inches of the tuba's length, where it seems unlikely to make a great difference in how it sounds. If it doesn't sound much different with valves engaged, then QED, bore size per se is not significant.

That might be a good relational starting point, if tubas worked with "flow theory," like carburettors to intake manifolds. But they don't, so I would consider that concept a guideline to get a mouthpiece choice in the right universe with a tuba.

For example: My Besson works best with a Wick 1 with a .332 throat and a short leadpipe to a .730 valve block. But the 38K works just as well with a similarly short mouthpiece-to-block, if you count the two bits, gooseneck and leadpipe, with a PT-82 .323 throat to a .734 bore. And my 186, with its long leadpipe and .770 bore, works equally well with my .324 Curry or the .331 PT-34.

Length of leadpipe is a critical dimension too often left out: short leadpipe makes the bore effectively "larger," and a long leadpipe effectively makes the bore "smaller."

All brass instruments huh? Then let's talk about something I know a bit more about than tubas, ie. bass trombone. Over the last 53 years I have played almost everything out there at one time or an other. I settled on a custom throated Schilke 60(5/16 inch or .3125) to give the very best compromise of range, sound and intonatation on my Besson 943(.563 bore). That is a ratio of 1.80. If I were to use 2.4 as my yardstick I would have to go to a mp with only .234 inch throat. That's less than 1/4 inch. That is smaller than the throat in my Bach 6 1/2AL that I use for my .500 bore jazz tenor. Either my math is way wrong or............................

BTW I wrapped the the 6 1/2 in plumbers tape and tried it in my bass, you wouldn't want your worst enemy to have to hear that sound.

Al, I use my 6.5AL in my bass for the rock band and although it does sound just a bit off to me when I heard the recording it was probably the best trombone sound I have ever made. Even on lower notes, though nothing below a low E save one pedal A.

iiipopes wrote: Length of leadpipe is a critical dimension too often left out: short leadpipe makes the bore effectively "larger," and a long leadpipe effectively makes the bore "smaller."

It's simpler to just recognize that the bore is effectively immaterial.

Given any tuba, and any size valve set, there is some point where the valve bore matches the bugle tubing. That leads to the relation you describe between leadpipe length and bore size, but the relation is such that the two simply cancel each other as factors.

Donn wrote:

iiipopes wrote: Length of leadpipe is a critical dimension too often left out: short leadpipe makes the bore effectively "larger," and a long leadpipe effectively makes the bore "smaller."

It's simpler to just recognize that the bore is effectively immaterial.

Given any tuba, and any size valve set, there is some point where the valve bore matches the bugle tubing. That leads to the relation you describe between leadpipe length and bore size, but the relation is such that the two simply cancel each other as factors.

What Donn said. Yes, I could have simply said bore is immaterial, but I'd rather state one reason why is it immaterial.

Donn wrote:It's simpler to just recognize that the bore is effectively immaterial.

As long as you are talking about valved instruments, I would agree 100%. However, I jumped on the trombone thing partially because it is material in that instance, only to have my doors blown off by Kolada. I really would like to hear that low range on a 6 1/2 AL. By the way Bob, I'm not talking about the large shank 6 1/2 but the small tenor shank, which has appx. 1/4 inch throat.

I have the Reynolds version of the Dr. Young mpc. This has no backbore - it funnels directly into the shank with the same inner diameter. I've used this in a 1291, 20J, 186 and 5/4 Rudy with great success. It gives a very focussed sound to these horns but does require a tad more air. This seems to confirm the above opinions about the bore being immaterial.