KiltieTuba wrote:A couple of random questions:
Is it possible to bend an upright bell? I am wondering if a standard upright bell can be converted into a recording bell.
bloke has told of one US maker using the same bell taper for their BBb tubas and for their sousaphones. He better tells the story himself, but the main point was that the same basic funnel was found as the large back bow on their sousaphones and as stack and bottom bow on their tubas.
There is some simple geometric principles behind bending tubing, but the specific formulas aren’t necessarily simple.
A Danish repairman trained in building brass instruments from scratch in the old German masters’ system told that bending relatively small bore tubing like trumpet and horn bells creates wrinkles on the inner perimeter, where material is compressed. These wrinkles were scraped off in the old German school.
On the outer perimeter the material is stretched, which means the wall of the tubing becomes thinner. If the bend is too radical there may occur cracks. Due to the thinned material we see bow guards and caps on the outer perimeter. They obviously shall enforce the tubing in areas where thinness and an exposed placement easily lead to dents.
I however think these guards and caps may have a function much more important than preventing dents: they dampen the oscillation of the tubing when the instrument in question is played. While waiting for my Besson 981 to be made for me, I loaned a sample of the non-compensating equivalent from the 700 series. Especially the top bow lacked guard material. The result was about some notes responding way too loudly from normal even playing. Especially the Ab on top of the staff went off like a rocket with almost no ignition.
This article tells about material thinning by different ways of making bells:
http://www.osmun.com/prod/Schmid/Schmidbell.htm
However tuba and euphonium bells often are made by insetting triangular gussets to avoid too much thinning of the material. On some lacquered bell one may see these inserts.
Hypothetical sample: If you had the right mandrel for bending an existing straight bell, you should ideally cut a slit on what would become the outside of the bent bell. You then should insert a gusset of a shape likely to be somewhere between a rhomb and an ellipse.
The handmade bottom bows of high end tubas are made from two pieces of sheet brass hammered around a mandrel (or inside female half mandrels) and then joined by seams along the inner and outer perimeters.
If you look down the body knee of an old Conn sousaphone you will see silver soldered seams telling that this knee was made of at least two pieces of brass before getting its final shape in the hydraulic press.
With silver or gold plated instruments it is not possible to see, whether the bell knee on Conn sousaphones are made the same way, but my guess would be that they are. And the bell flare obviously was made separately and only was joined after the knee had achieved its shape.
So bending an existing bell is not likely to happen, and the old guys, who made non-detachable recording bells, certainly knew how to subdivide their task when building them from scratch.
Klaus
