6.6 The Influence of Wall Material on Brass Instrument Performance
311
We can conclude from the global view presented by Fig. 6.22 that most of
the playing frequencies are higher than the bore resonance frequencies over the
playing regimes studied here. This is consistent with the predominantly outwardstriking lip behaviour which has been observed in previous studies (see Chap. 5).
Nevertheless, Fig. 6.22 also shows that musicians can sometimes play below the
resonance frequencies, strengthening the view that a single mechanical oscillator
cannot model the complete behaviour of the lip reed.
6.6 The Influence of Wall Material on Brass Instrument
Performance
Relaxation of the assumption of wall rigidity acknowledges the fact that the walls of
brass instruments vibrate when the instruments are played. The controversial issue
of the musical significance of these wall vibrations is the principal topic of Sect. 6.6.
When sounding a fortissimo note on a trumpet or trombone, it is easy for the
player to feel the vibration of the metallic structure, and tempting to identify the
characteristic brassy blare with this metal vibration. As explained in Sect. 6.1,
this intuitively attractive idea is incorrect: the brassy timbre is a consequence of
nonlinear acoustic propagation in the air column of the instrument. A brassy note
can be easily sounded using a trumpet mouthpiece on a suitable length of plastic
hose whose wall has a negligible vibration amplitude.
The only critical requirement for the wall material of a brass instrument is that
it must be capable of providing a smooth and rigid boundary to define the shape of
the internal air column. In Sect. 6.6.1 we review briefly some other considerations
which have influenced the choice of labrosone wall materials. Section 6.6.2 presents
experimental evidence showing that wall vibrations can exert a subtle influence
(of the order of 1 or 2 decibels) in the amplitudes of particular harmonics in the
spectra of brass instruments. Section 6.6.3 describes some studies of thin-walled
metal organ pipes which demonstrate that an injudicious choice of wall material
properties can result in much more dramatic effects, including the disruption of the
normal playing behaviour. The coupling between structural and acoustic modes in
brass instruments is discussed in Sect. 6.6.4, and the possible influence of the direct
communication of mechanical vibrations between the mouthpiece and the lips of the
player is considered in Sect. 6.6.5. The complex bore geometry of brass instruments
makes it difficult to develop an accurate theoretical model of structural vibrations,
but vibroacoustic theoretical and experimental results from a study of cylindrical
tubes, presented in Sect. 6.7, provide some insights.
311
We can conclude from the global view presented by Fig. 6.22 that most of
the playing frequencies are higher than the bore resonance frequencies over the
playing regimes studied here. This is consistent with the predominantly outwardstriking lip behaviour which has been observed in previous studies (see Chap. 5).
Nevertheless, Fig. 6.22 also shows that musicians can sometimes play below the
resonance frequencies, strengthening the view that a single mechanical oscillator
cannot model the complete behaviour of the lip reed.
6.6 The Influence of Wall Material on Brass Instrument
Performance
Relaxation of the assumption of wall rigidity acknowledges the fact that the walls of
brass instruments vibrate when the instruments are played. The controversial issue
of the musical significance of these wall vibrations is the principal topic of Sect. 6.6.
When sounding a fortissimo note on a trumpet or trombone, it is easy for the
player to feel the vibration of the metallic structure, and tempting to identify the
characteristic brassy blare with this metal vibration. As explained in Sect. 6.1,
this intuitively attractive idea is incorrect: the brassy timbre is a consequence of
nonlinear acoustic propagation in the air column of the instrument. A brassy note
can be easily sounded using a trumpet mouthpiece on a suitable length of plastic
hose whose wall has a negligible vibration amplitude.
The only critical requirement for the wall material of a brass instrument is that
it must be capable of providing a smooth and rigid boundary to define the shape of
the internal air column. In Sect. 6.6.1 we review briefly some other considerations
which have influenced the choice of labrosone wall materials. Section 6.6.2 presents
experimental evidence showing that wall vibrations can exert a subtle influence
(of the order of 1 or 2 decibels) in the amplitudes of particular harmonics in the
spectra of brass instruments. Section 6.6.3 describes some studies of thin-walled
metal organ pipes which demonstrate that an injudicious choice of wall material
properties can result in much more dramatic effects, including the disruption of the
normal playing behaviour. The coupling between structural and acoustic modes in
brass instruments is discussed in Sect. 6.6.4, and the possible influence of the direct
communication of mechanical vibrations between the mouthpiece and the lips of the
player is considered in Sect. 6.6.5. The complex bore geometry of brass instruments
makes it difficult to develop an accurate theoretical model of structural vibrations,
but vibroacoustic theoretical and experimental results from a study of cylindrical
tubes, presented in Sect. 6.7, provide some insights.