Speaking in generalities, what does a bells diameter do in regards to...

1. Large vs. smaller= volume less, more

2. Sound vibrant or dampened

3. Volume at the players ear louder, softer

4. Volume at listeners ear louder, softer

5. Anything else?

I haven't made a big study of it, bit in the few situations where I got to play different bell sizes of similar horns, the difference was centered tone vs more diffuse sound. The smaller bell sounded slightly more compact.

Not that those other things you mentioned aren't there, just that I only noticed the centered/diffuse thing.

Bell taper affects volume more than the final diameter.

Bell final diameter does effect the radiation of higher overtones, but only when the horn is built responsively.

Volume at listener's ears, broadly speaking, will be greater with a larger diameter bell.

Bell placement probably affects the player's volume more than changes to the bell itself.

I've been thinking about making a post similar to this, even diving into other measurements of the trombone (i.e. bore size). But here is my 2 cents

1. Large vs. smaller= volume less, more

I feel like the smaller the bell the more focussed the sound is. But it's possible to be too focussed and not open enough.

2. Sound vibrant or dampened

When messing with different bass trombone bells I find that the bigger the bell the hard it is to control. The sound is too spread on a 10.5", for me.

3. Volume at the players ear louder, softer

In my experience, the bigger the bell, the softer it is to the player. I've recently been playing on an 8.5" bell with a medium bore slide. I know that I'm playing loud, and probably louder than normal, but because the sound it more spread out than I'm used to with a 8" or 7.5" bell (small bore) it appears to be softer. But I've had other people tell me that I'm louder on that specific horn.

4. Volume at listeners ear louder, softer

I don't have enough experience with this to have an opinion. There's probably a point where you get too big and your volume is negatively affected by that.

5. Anything else?

Thanks for reading my mind. I've been wanting to post/read up on this myself.

Any thoughts about taper to bell ratios? There are some early Conns that have large throats and small bell diameters that are described as having a lush sound, but great punching power when needed.

--Andy in OKC

This is a discussion that you might want to take to the tuba forum, or at least research it there. Tubas have a wide range of bell dia/flare and taper/dia ratios that definitely have an effect on the sound. There are tubas where the flare is nearly flat, and tubas with a much more truncated flare. And they certainly have opinions on that stuff over there.

In the trombone world, you find much less experimentation with diameter, flare, and taper.

German trombones have generally bigger flares but tend to be not as loud as their American counterparts. But I am unsure whether this is just caused by the flare because there are other differences as well. Even within German trombones the shape of the bell can be different. For instance, the Kruspe Weschke becomes wider much slower than the Kruspe Virtuosa. The maker must have had a very good understanding of how all these parts work together.

Would be nice to have a systematic study of it. This should be facilitated by trombones for which the bell can be switched easily.