Re: Howcum?


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Posted by Klaus on January 24, 2002 at 00:32:18:

In Reply to: Howcum? posted by Chuck(G) on January 23, 2002 at 20:34:17:

Maybe because "guard pieces (like bottom bow caps)" are misleading terms. Which have been introduced on the basis of our immediate visual perception of their placements. Which always are on the exposed outer perimeters of bends.

I see "guard pieces (like bottom bow caps)" foremostly as weight adjusters applied for acoustical reasons.

A very few top grade makes and models have their bows made out of specially cut sheet metal, which is hammered into the final shape and then soldered. A technique that was more usual in previous eras of brass making. Both of my Conn sousas (a 40K from 1927 and a 26K from 1928) seem to have their larger branches made that way. Especially the knee with the bell receiving collar appears like a masterpiece in combination of strength and elegance. Brilliantly executed by the craftsmen.

Most modern instruments have their bows pressure formed from cylindrical tubing. Yamaha call their technique hydraulic. I do not know whether water or oil actually is applied. Boosey&Hawkes uses a special technique, that I do not remember the term for. And my description will be clumsy:

In the straight tubing, that shall become a bow, what shall become the outside of the bow is pressured down as a giganting dent, so that the tubing consists of two "half circles" very close to each other. That way the tubing can be bent without being filled with lead or pitch(?). And without cracking.

The bent tubing then is placed inside the steel mold and by means of extremely high air pressure the tubing is expanded to fit the mold. B&H maintains that the procedure doubles as a quality check of the brass. Only the best brass tubing will survive the process without cracks or riples.

Back to my main point: What ever hydraulic/pneumatic pressure-bending-forming procedure has been applied will for simple geometric reasons leave the metal on the outer diameters of the bow stretched thinner than on the inner diameter. For the same reasons the metal is stretched thinner at the wider end of a conical bow.

Of course that leaves the stretched-thinner metal more vulnerable to dents. But it also changes the acoustical response of the metal. To compensate for the potential rattle-o-phonic properties of such bows, they are acoustically damped by the addition of bow caps, wire strips, and other metallic additions.

I have had a first hand experience of comparable instruments with differing additions of caps and strips:

While I waited 3 months for the delivery of my Besson 981 Eb tuba I had the equivalent non compensating 3+1 model from the 700 series on loan. The differences up to the pro model were limited to the leadpipe, the lighter non-comp valve system, and the much less elaborate application of bow caps and strips. My greatest problem with this lightweight instrument was the very uneven response. Not that there were "dead" notes. On the contrary there were notes, that were overly responsive. Most noticeably the top line Ab. The arrival of the 981 was experienced as a revelation, because it was a much more reliable instrument in respect of dynamics and control. I discussed the matter with a friendly B&H employČ (they are hard to come by). He told that the effect was not only based on the extra bow caps, but also by the weight and structural rigidity provided by the compensating valve system (longer pistons, more soldered connections, lesser lengths of free tubing).

If my idea about the application of bow caps is right, why do we the see nickel silver guards on the straight parts of the 2nd branch of some German tubas like the old B&S Symphonie? These models followed one of the German maximes for getting a richness in high range overtones: thin metal. Which needs a bit of acoustical adjustment in form of some extra weight. Which could then just as well be placed, where it could perform its second act as branch guard.

When I met Steven Mead back in 1998, he told about the then current versions of the Sovereign euphs. In the pursuit of lightness of sound and ease of response not only the leadpipe had been lifted off the bell. The guard strips on the 2nd branch had also been shortened.

Sorry for the redundance, if I have written this before. And I have. The single new factor might be, that I do not believe, that non-metallic materials wouth fulfil the desired acoustical functions.

Klaus


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