Does Bell size matter?

[Alex C]

In an orchestral environment, a larger tuba is currently preferred.

OP did not ask about "a larger tuba". He asked about "a larger bell".

A tuba with a larger bell is a larger tuba.

[Rick Denney]

In an orchestral environment, a larger tuba is currently preferred.

OP did not ask about "a larger tuba". He asked about "a larger bell".

A tuba with a larger bell is a larger tuba.

I don't agree. I don't think a 56J is any bigger a tuba than a 52J, though it has a bigger bell. A Holton is a larger tuba, and it definitely has a bigger sound, but the bell is smaller with respect to width of the rest of the outer branches than any of the three Conn models.

A bell made larger by extending the rim from its current profile (as is the case with the Conn) has a larger amount of bell surface that is at shallow angles to the centerline of the instrument. That provides a larger reflector, but the reflector is not focused, and this will indeed increase dispersion, in the same way that a bi-radial horn loudspeaker is used for wide dispersion and a narrow exponential horn is used for long throw. But it isn't the size of the bell, it's the shape. The shape necessarily becomes more "bi-radial" when you add more material to the rim of an existing bell shape. But you could also make a bigger bell that has the same profile as a smaller bell, in which case I would expect them to propagate more similarly. An example would be a Rudi 5/4 versus a Rudi 4/4, which has a bigger bell but also a bigger throat to match, and the two bells have the same radius of curvature in the profile. The 5/4 makes a bigger sound. But is that the bigger bell or the bigger throat and outer branches? I submit the latter is more likely. Is the sound of a Rudi 5/4 more diffuse? If so, I'd bet the difference owes more to the ratio of overall instrument width to the mouthpiece, and the size of the throat, than to just the difference in bell size.

Changing the shape of the bell changes the tone, because the bell, acting as an impedance matching device, changes the degree to which some frequencies are reflected or projected more than others. I think it's possible that the bigger bell could ruin the mix of frequencies being projected, and make the instrument sound crappy, small, and stuffy.

An instrument with no bell provides very poor impedance matching, and some important frequencies get more fully reflected rather than being allowed to project into the uncontained and unresonant air outside the instrument. The remaining frequencies may create a more strident sound, which has greater ability to penetrate through the sound of the group. That would be perceived as louder, whether or not one would see a change in sound pressure level.

Aside: Remember that sound pressure level ("dB") does not measure loudness in a particularly useful way. Standard SPL assumes a particular profile of frequencies (the "weighting") that is more related to potential ear damage than musicality. The only way to know what's really happening is to do spectrum analysis of the sound to see the relative loudness relative to frequency. And SPL is not a measure of sound "bigness" in any case. It's a measure of intensity. An intense sound vibrates the few air molecules at the test sensor strongly. A big sound vibrates more air molecules. It's like the difference between temperature and heat. A tiny 15-watt soldering iron might make it's small tip as hot (in degrees) as a big 100-watt iron. But the 100-watt iron makes much more total heat, as measured by how big a solder pool it can melt. So, a big sound puts strong vibration all over the concert hall, rather than peeling the paint in just one part of it. I really think it's not "loud" sounds that current tuba players want, but rather "big" sounds. A big tuba, with its large bell, throat, and volume, sets more air vibrating within the instrument and then provides a greater interface between those molecules and the air molecules beyond the bell--including in a wider array of directions.

The bell is part of a system, and it is the system that has to perform, not just one part of it.

Rick "suggesting that an impedance matching device has to be tuned to the resonator to achieve its objectives" Denney

[Alex C]

Rick, I am not disagreeing with your eriudite post but in earlier my earlier posts I made statements which, I think, are consistant or at least not contrary to yours. I did not discuss in the same detail and without the ability to discourse to your degree of technical explanation, however, in the context of three posts, I believe I am consistant in saying that a tuba with a larger bell (flare and stack) is a larger tuba. If there is a tuba with a small stack and small flare which is a large tuba, I haven't heard of it.

[Rick Denney]

If there is a tuba with a small stack and small flare which is a large tuba, I haven't heard of it.

No offense intended--I did not disagree with anything you said except the statement I quoted, and then I went on to address other responses since my first one, some of which explains rather than refutes your observations.

But it was you who used the Conn as a comparison, considering the 56J as a larger tuba just because of its larger bell rim. The stack and throat below the bell rim is, of course, the same across all three Conn models. It the case of the Rudi's, the stack and bell diameter maintains the same ratio across their size range, so that their tubas with bigger bells are indeed bigger tubas.

The body on my York Master is a solid 4/4, and by today's measure pushing 5/4. The bell diameter is 20", which could be anything. But the throat is fairly narrow, owing to a smallish bell attachment ring. My Miraphone 186 has a larger throat and a smaller bell, and even the much smaller King 2341 has a larger throat. These crossovers do indeed occur. But compared to, say, the King (which is also called a 4/4), the York Master is a large tuba. Compared to a Holton, it isn't. All three have about the same bell size. The word "large" by itself doesn't mean much.

And that's why we have to get into specifics, and why I am saying that the diameter of the bell has to be considered as part of its system, and not in isolation.

Rick "thinking the 18 or 19" Kanstul replacement bell for the YM a good idea" Denney

[Wyvern]

A large tuba with a small bell flare is the Meinl-Weston 197 Hilgers model BBb which is based on a 1930's design. That has only 18" bell although a VERY BIG tuba - in height larger than the Fafner. That smaller flare does not seem to impede its sound projection at all. In fact listening to recordings (which is an imprecise way of judging), it seems to project even better than the Fafner.