8.3 Metal Forming
393
under development (see Sect. 4.2.1). The associated software can make suggestions
for bore profile optimisation.
One feature of modern brass instruments is the great attention given to the first
section of tubing following the mouthpiece, known as the mouthpipe or ‘leadpipe’
(Buick et al. 2002). In some models there is a step down in bore diameter positioned
at the end of the mouthpiece: this reduces or eliminates the sudden expansion
in bore where the mouthpiece stem abruptly ends. The bore constriction often
continues for a couple of centimetres before an approximately conical expansion
towards the tuning-slide or valves. In trombones there is often a cylindrical portion
in the mouthpipe narrower than the main bore of the descending inner slide. This
mouthpipe constriction is often termed the ‘venturi’, an inappropriate term since
the Venturi effect concerns the steady flow of incompressible fluids through a
constriction while air is compressible.
The term ‘leadpipe’ is often used as a synonym for ‘mouthpipe’ to denote
the mouthpiece receiver together with the following section of instrument tubing.
However, some high-quality instruments are made in which this initial section of
tube is removable and interchangeable. Here the term ‘leadpipe’ is more usual. A
detachable leadpipe is 150–250 mm long including the mouthpiece receiver and
is inserted into an outer sheath which forms part of the body of the instrument
(in the case of trombones, the leadpipe extends into the descending inner slide).
Players of such instruments can select a leadpipe to optimise the instrument for their
requirements or equip themselves with a number to choose from to suit a repertoire
or performance situation. The bore profiles of alternative leadpipes supplied for
a particular instrument have interior diameters that vary by a only few tenths of
a millimetre, but even such small changes noticeably affect the response of the
instrument.
8.3 Metal Forming
A cylindrical or conical tube can be formed from flat brass sheet. Before the
nineteenth century, the tubing for instruments was made by hand from strips of brass
rolled around a rod (known as a mandrel) and seamed by brazing; today factorymade tubing is used. Very few parts of brass instruments are purely conical: most
sections if not cylindrical gradually increase in rate of expansion from one end to the
other. This is most perceptible in bell flares, where the rate of expansion noticeably
increases towards the bell end. The shape of actual instrument bells (and other
sections) does not follow a simple mathematical formula. Gently expanding sections
can be approximated by an exponential curve; flaring sections such as trumpet and
trombone bells can be close to a so-called Bessel horn (Sect. 4.3.7). Although actual
bells only rarely follow a Bessel horn over their entire length, a Bessel horn fit can
be useful for representing bell flares over portions of their length (Braden 2006).
One factor which makers can control is wall thickness. We saw in Sect. 6.6 that
the structures of brass instruments vibrate when played at loud dynamics, although
393
under development (see Sect. 4.2.1). The associated software can make suggestions
for bore profile optimisation.
One feature of modern brass instruments is the great attention given to the first
section of tubing following the mouthpiece, known as the mouthpipe or ‘leadpipe’
(Buick et al. 2002). In some models there is a step down in bore diameter positioned
at the end of the mouthpiece: this reduces or eliminates the sudden expansion
in bore where the mouthpiece stem abruptly ends. The bore constriction often
continues for a couple of centimetres before an approximately conical expansion
towards the tuning-slide or valves. In trombones there is often a cylindrical portion
in the mouthpipe narrower than the main bore of the descending inner slide. This
mouthpipe constriction is often termed the ‘venturi’, an inappropriate term since
the Venturi effect concerns the steady flow of incompressible fluids through a
constriction while air is compressible.
The term ‘leadpipe’ is often used as a synonym for ‘mouthpipe’ to denote
the mouthpiece receiver together with the following section of instrument tubing.
However, some high-quality instruments are made in which this initial section of
tube is removable and interchangeable. Here the term ‘leadpipe’ is more usual. A
detachable leadpipe is 150–250 mm long including the mouthpiece receiver and
is inserted into an outer sheath which forms part of the body of the instrument
(in the case of trombones, the leadpipe extends into the descending inner slide).
Players of such instruments can select a leadpipe to optimise the instrument for their
requirements or equip themselves with a number to choose from to suit a repertoire
or performance situation. The bore profiles of alternative leadpipes supplied for
a particular instrument have interior diameters that vary by a only few tenths of
a millimetre, but even such small changes noticeably affect the response of the
instrument.
8.3 Metal Forming
A cylindrical or conical tube can be formed from flat brass sheet. Before the
nineteenth century, the tubing for instruments was made by hand from strips of brass
rolled around a rod (known as a mandrel) and seamed by brazing; today factorymade tubing is used. Very few parts of brass instruments are purely conical: most
sections if not cylindrical gradually increase in rate of expansion from one end to the
other. This is most perceptible in bell flares, where the rate of expansion noticeably
increases towards the bell end. The shape of actual instrument bells (and other
sections) does not follow a simple mathematical formula. Gently expanding sections
can be approximated by an exponential curve; flaring sections such as trumpet and
trombone bells can be close to a so-called Bessel horn (Sect. 4.3.7). Although actual
bells only rarely follow a Bessel horn over their entire length, a Bessel horn fit can
be useful for representing bell flares over portions of their length (Braden 2006).
One factor which makers can control is wall thickness. We saw in Sect. 6.6 that
the structures of brass instruments vibrate when played at loud dynamics, although