46
2 The Scientist’s Perspective on Brass Instrument Behaviour
mechanical shaker, which was attached to the instrument body and driven by a
computer generated signal which created the same amplitude of bell vibration as that
measured during the playing test. Again the radiated sound was measured. Since in
the second test there were no sound waves in the instrument air column, the only
sound source was the vibroacoustic one. It was found that the sound pressure level
was around 40 dB lower than the level when the player was performing.
Although direct sound radiation from the bell is probably insignificant, this does
not mean that wall vibrations have no effect on the radiated sound. Recent research
has demonstrated that under some circumstances coupling between acoustic and
structural resonances can significantly change the internal sound field, thus indirectly modifying the radiated sound. It must also be borne in mind that the player’s
perception could be different from that of a listener if wall vibrations transmitted
mechanically from the mouthpiece to the lips provide additional feedback. A full
discussion of this topic is given in Sect. 6.6.
2.1.7 Warming Up a Brass Instrument
We conclude this section by considering an aspect of brass instrument behaviour
familiar to all players: the dependence of the playing properties of the instrument on
temperature. When a player picks up an instrument which has been for some time
on a stand in a rehearsal room, the internal air column will be at the temperature
of the room, which we will assume to be 20 ◦ C. The musician usually starts a
playing session by ‘warming up’ the instrument, which typically involves playing
arpeggios over an increasingly wide pitch range. Air enters the mouthpiece from the
musician’s mouth close to the body temperature of 37 ◦ C. After a few minutes of
steady warm-up, a stable temperature profile is created in the instrument, decreasing
from near 37 ◦ C at the mouthpiece to near 20 ◦ C at the bell. It is difficult to measure
this temperature profile precisely, but an idea of its nature can be obtained using a
thermal imaging camera which allows the external temperature of the metal to be
shown using infrared thermography (Fig. 2.13).
The temperature scale, shown at the right side of the image in Fig. 2.13, ranges
between 26 and 19 ◦ C. The photograph was taken a short time after warming up the
trombone, but it is evident that the instrument has already cooled down significantly
since the mouthpiece receiver is only at 26 ◦ C. A second trombone which had not
been played can be seen behind the warmed-up instrument; as expected, it has a
uniform temperature close to 20 ◦ C.
The temperature profile of the warmed-up instrument, derived from the information in Fig. 2.13, is shown in Fig. 2.14. The temperature shows a global decrease
from the mouthpiece to the bell, apart from a large peak around 1.5 m from the
mouthpiece. This is the position at which the left hand of the player holds the
instrument, and the temperature rise is clearly due to additional heating by the
player’s hand.
2 The Scientist’s Perspective on Brass Instrument Behaviour
mechanical shaker, which was attached to the instrument body and driven by a
computer generated signal which created the same amplitude of bell vibration as that
measured during the playing test. Again the radiated sound was measured. Since in
the second test there were no sound waves in the instrument air column, the only
sound source was the vibroacoustic one. It was found that the sound pressure level
was around 40 dB lower than the level when the player was performing.
Although direct sound radiation from the bell is probably insignificant, this does
not mean that wall vibrations have no effect on the radiated sound. Recent research
has demonstrated that under some circumstances coupling between acoustic and
structural resonances can significantly change the internal sound field, thus indirectly modifying the radiated sound. It must also be borne in mind that the player’s
perception could be different from that of a listener if wall vibrations transmitted
mechanically from the mouthpiece to the lips provide additional feedback. A full
discussion of this topic is given in Sect. 6.6.
2.1.7 Warming Up a Brass Instrument
We conclude this section by considering an aspect of brass instrument behaviour
familiar to all players: the dependence of the playing properties of the instrument on
temperature. When a player picks up an instrument which has been for some time
on a stand in a rehearsal room, the internal air column will be at the temperature
of the room, which we will assume to be 20 ◦ C. The musician usually starts a
playing session by ‘warming up’ the instrument, which typically involves playing
arpeggios over an increasingly wide pitch range. Air enters the mouthpiece from the
musician’s mouth close to the body temperature of 37 ◦ C. After a few minutes of
steady warm-up, a stable temperature profile is created in the instrument, decreasing
from near 37 ◦ C at the mouthpiece to near 20 ◦ C at the bell. It is difficult to measure
this temperature profile precisely, but an idea of its nature can be obtained using a
thermal imaging camera which allows the external temperature of the metal to be
shown using infrared thermography (Fig. 2.13).
The temperature scale, shown at the right side of the image in Fig. 2.13, ranges
between 26 and 19 ◦ C. The photograph was taken a short time after warming up the
trombone, but it is evident that the instrument has already cooled down significantly
since the mouthpiece receiver is only at 26 ◦ C. A second trombone which had not
been played can be seen behind the warmed-up instrument; as expected, it has a
uniform temperature close to 20 ◦ C.
The temperature profile of the warmed-up instrument, derived from the information in Fig. 2.13, is shown in Fig. 2.14. The temperature shows a global decrease
from the mouthpiece to the bell, apart from a large peak around 1.5 m from the
mouthpiece. This is the position at which the left hand of the player holds the
instrument, and the temperature rise is clearly due to additional heating by the
player’s hand.