F tubas which sound like medium-large C tubas (less "front", less vibrant, more "bass") have become popular, and most of them feature large mouthpipes, large bell throats, pistons valves and often (trigger warning) intonation characteristics which are a bit difficult.
My model of F instrument was thought of as "tremendously large" when some of them first found their way into the USA in the mid-late 1970's (and certainly early 1980's). After all, the bell flare was as large as a 186, and - by the time the 4th rotor is reached, the bore size is a huge .827" (associated with kaiser tubas) bore. Soon after they found their way here, though (to attempt to morph them into more C-tuba-player-ready instruments), soon MOST of them were outfitted with larger mouthpipe tubes, larger bore sizes in their early rotors, and (not too long afterwards) larger bell throats. Descriptions such as "6/4" began to be associated with some of those F tubas.
Mine features none of those alterations, the initial bore of the mouthpipe tube is a scant .500" (probably actually only .495"), the first rotor encountered is only .669" bore (not much larger than a Conn 5J, etc.) and the bell throat is the original "standard" opening.
I wouldn't trade it for anything, and - F-tuba-wise - I've just about tried everything.
I use my own "Solo" (somewhat shallow bowl cup) mouthpiece with it, and a particular (narrow, no sharp corners) rim profile.
WHEN I'VE WISHED FOR IT TO SOUND MORE LIKE SOME OF THE MORE "ROUND-SOUNDING" F tubas (typically: pistons, larger mouthpipes, some intonation issues), I've used a medium-deep funnel moutpiece (my "Imperial")...but I'm just about to market an altered Helleberg II/Laskey 30H style mouthpiece (my favorite rim profile - rather than either of those, a larger exit bore, and a different throat size), and I've been messing around with it with my F tuba...
...I'm getting even more of the "piston F tuba" type of resonance: rounder-sounding/less "front"...but without issues such as unstable range below the staff nor saggy upper range.
I don't believe I'll use it (with my F tuba) for very much quintet stuff, and maybe only a limited amount of orchestra stuff...but I AM getting that "piston F tuba" sound (yet without the intonation stumbling blocks associated with so many of those)...ie. still (luxuriously - and I realize that I'm lucky) zero slide-pulling.
The quintet players (yesterday) all have more cred's than I have (and are all wonderful players. Even the youngest of the four - w/terminal degree - just won some Carnegie-Hall-related solo competition, and performed a solo recital - of the competition pieces - up there...) ALL FOUR OF THEM told me that they FAR PREFER my REGULAR mouthpiece (shallower) with the F tuba, but IF the thing that I'm attempting to accomplish is "a rounder sound, and less front, yet with the same reliable intonation, etc.", my Helleberg-II-ish thing accomplishes that.
I did notice that (via those sonic characteristics) have to "play out" more to balance this group (particularly - obviously - loud passages).
This wasn't the main purpose of developing this mouthpiece. I've actually noticed that this style of mouthpiece tends to play tubas around 1 or 2 c. (hundredths of a semitone) higher (same main slide position) than some other styles of "deep"-cup mouthpieces, and that it might come in handy for some newer (particularly "signature") models I've encountered out there that tend to play just barely (or not quite) up to pitch with other deep-cup mouthpieces, and I'm also wondering if this Hb-II thing (having also tested it with my compensating E-flat) might also be a good alternate choice for that style of instrument as well.
Finally, I've had a couple of 4/4 C tubas here (minor repairs), and my altered Hb-II mouthpiece offers PLENTY of "front" and "vibrancy" with those tubas (vs. my F tuba).
see...?? I warned you - at the beginning - that this would be boring. I kept my promise and - apparently - you didn't heed it.
