This post is a continuation of a series based on a circa 1980 clinic handout from Lawson Brass Instruments, Inc. (now Lawson Horns). The first post dealt with the importance of the leadpipe in determining the playing characteristics of a horn, while this one considers the role of those sections between the leadpipe and the bell tail. (Italics indicate direct quotations from the handout, annotations are non-italicized and in brackets  ).
THE CYLINDRICAL SECTION: This section includes the valves, slides and connecting tubing:
1) Bore – Inside diameters vary in the cylindrical section, but in the U.S. they are usually .468″ ID. Some European instruments are larger, up to .476″ ID. [In the case of Paxman’s “Dual Bore” system, the ID of the F side is .500″]. The size of the bore has an effect on the performance of the instrument. Manufacturers can control this, however, in other areas.
2) Valves and slides – If these leak, the instrument will not play in an efficient manner and the pitch and center of the sound will be affected. If they do not operate properly, playing technique is hindered.
3) Length of the slides and connecting tubing – The overall pitch of the instrument and the relationship between the various harmonic series are controlled by these lengths.
4) Design of the bends in the tubing or wrap of the instrument – Sharp bends have some effect on the resistance of the instrument and removal of water should be considered in the placement of the bends.
5) Assembly – The parts should be fitted carefully so that the bore is as smooth as possible, the slides are parallel and the soldered joints are strong.
6) Artistic consideration – An instrument can be beautiful or ugly depending on the design of the curves, placement of slides, design of the braces, attention to ornamentation and finish of the metal service.
The taper of this connection between the cylindrical section and the bell tail controls:
1) Slurs – The ability of the instrument to slur easily or with difficulty in different registers and dynamics.
2) Stability – The pitch should remain stable, not float up and down while holding notes.
3) Attack – The notes in all registers should not bounce when started at high dynamic levels.
4) Register – First branch tapers control the ease of playing in the different registers.
5) Sound – The sound should have no roughness and should not growl at high dynamics, but should have the same quality throughout the dynamic range in all registers.
6) Intonation – The pitches of the harmonic series are affected by the first branch taper.
I like this handout because the language is plain and practical, and it is full of tons of great information, rather than being a glorified advertisement for Lawson horns. In fact the characteristics listed would make an excellent checklist when trying new horns or various modifications to your current horn. Check back soon for the final post in this series: the bell tail and bell flare.