TubeNet

The width or choke of the bell can have an effect on pitch between bells that are the same length. No sure why, but I experienced that when I swapped bells a few years ago. On the other hand, I'm not sure if just that extra 2 or 3 inches of the "blossom" has much to do with the pitch, or it just creates a difference to the response and timbre. Maybe someone like Rick Denny or Dan Schulz might be able to shed some light on this one. I would defer to them on most issues.

Don't forget the "end effect" of the bell: effective tube length = actual tube length + (0.6 * bell diameter) The working length of the tuba actually extends past the end of the bell, and bell diameter makes a difference.

Changing out an entire tuba bell.

As opposed to doing it slice by slice?

Eighteen feet is just a 'rough' figure that represents about ONE HALF of the actual wave length of a BBb tuba.

That eighteen feet does extend a bit beyond the end of the bell and is somewhat influenced by the diameter of the flare. I have some literature that pictures what might be considered to be a parabola extending beyond the bell. I tend to think of it as just the radius of the flare.

I honestly think we are often 'fooled' by bell size because of the vibrations that we physically feel coming from the horn rather that what are ears are hearing.

The bell is basically just an amplifier. A few inches of bell length has little affect on intonation as compared with the same length of 'pull' on the main tuning slide. Along the same line of thinking... an inch of leadpipe means more than an inch of tubing elsewhere in the horn.

Nothing is conclusive in acoustics. Designing is called 'prototyping' and can only be done by trial and error.

Several years ago I had a Conn 36J with a 22" one piece bell that was swapped for a Meinl Weston 6/4 bell (I forget the model it was from - this was roughly 10 or more years ago).

It made the absolutely crummy 3rd partial open F (almost E) a little less crummy.

If I recall correctly, the original Conn bell had less "throat" and more "pancake" than the MW bell.

As a side benefit, it made the horn able to fit in the trunk of my 1979 Volare (damn, I miss that car)!

P.S. to bloke - I never knew that recording bells ever went out of style in the first place (at least as far as I'm concerned)!

UncleBeer wrote:Don't forget the "end effect" of the bell: effective tube length = actual tube length + (0.6 * bell diameter) The working length of the tuba actually extends past the end of the bell, and bell diameter makes a difference.

Otherwise known as the terminal node.

Before changing out the bell on my detachable bell Miraphone, it had the following characteristics:

1) When the 16 1/2 inch upright modified St. Pete bell was on, the low range octaves were a little compressed, 1st ledger line Eb was a little insecure, and the tone was really dark, heading towards Alex territory. This bell was a little short, and had to have the tuning slide extended.
2) When the stock 22 inch recording bell was on, the dreaded flat fifth partials were at their worst, but it had the "American" pancake bell tone, leaning towards souzy territory. I had to get another tuning slide that was the stock length, because as set forth above, the bell made the horn effectively longer.

Now, having changed the stack out for a 17-inch Besson BBb bell, which when trimmed was exactly the right length and diameter for the stack ferrule, the octaves are where they should be, Eb is secure again, the fifth partials are not so bad, indeed, 2nd space C is right on, and it has a nice, round, foundational tone that is not too dark and not too bright, with reasonable "core." I use the same long tuning slide I had with the St. Pete bell, and as an added benefit, the tuba is not top-heavy anymore by getting rid of the extra brass necessary to have a collar and tenon.

Shifting length of tubing from the bell to narrower areas like a longer tuning slide and/or a tuning bit will move nodes to areas where the designer never had planned them to be. You may be lucky that the intonation stays good or even improves, but the odds are that the intonation will be unpredictable.

Klaus

lost wrote:This helps. I'm pretty sure if i swapped bells on a potential horn, the new bell is shorter. Good to know the tuning slide could help it. Plus maybe a bit.

Not necessarily. Changing the relationship between the bell and the tuning slide changes the proportion of conical tubing to cylindrical tubing at different points on the horn. Intonation will change. I got lucky. Mine changed for the better. It could make it worse, depending on where proportionally the added straight tubing is in the grand scheme of things. Cylindrical tubing tends to expand the octaves, conical tubing tends to contract the octaves. The bell taper and throat were wider on the stock bell stack, trying with the recording bell to emulate the tonality of a Martin or Holton. The bell taper and throat are smaller on my Besson bell, which gave me the bonus of a suspended lead pipe. So the octaves expanded a little in the low range, and brought up the 5th partials a little bit, but selectively C is fine, Db is lippable, D is at the limit of lip, but actually has to be settled down when played 1+2. It will be different on each horn. Mix-and-match is a black art at best.