2.1 Scientific Measurements of Brass Instrument Behaviour
37
0
1
2
3
4
5
6
Time (s)
-5
0
5
Pressure (kPa)
0.95
1
1.05
1.1
1.15
Time (s)
-2
0
2
Pressure (kPa)
4.25
4.26
4.27
4.28
4.29
4.3
Time (s)
-5
0
5
Pressure (kPa)
(a)
(b)
(c)
Fig. 2.3 (a) The acoustic pressure inside the mouthpiece of the trombone sounding the note F4
illustrated in Fig. 2.2a. (b) Zoom to 230 ms of the mouthpiece pressure signal starting at t = 0.92 s.
(c) Zoom to 50 ms of the mouthpiece pressure signal starting at t = 4.25 s
greater that the pressure in the radiated sound. The peak-to-peak pressure amplitude
at t = 1.1 s inside the mouthpiece is 2.8 kPa, compared to 0.46 Pa 50 cm outside
the trombone bell; at t = 4.3 s the mouthpiece peak-to-peak pressure amplitude is
10.6 kPa, while the radiated pressure amplitude is 3.3 Pa. It is a remarkable feature
of all wind instruments that the radiated pressure amplitude is a tiny fraction of the
internal pressure amplitude.
37
0
1
2
3
4
5
6
Time (s)
-5
0
5
Pressure (kPa)
0.95
1
1.05
1.1
1.15
Time (s)
-2
0
2
Pressure (kPa)
4.25
4.26
4.27
4.28
4.29
4.3
Time (s)
-5
0
5
Pressure (kPa)
(a)
(b)
(c)
Fig. 2.3 (a) The acoustic pressure inside the mouthpiece of the trombone sounding the note F4
illustrated in Fig. 2.2a. (b) Zoom to 230 ms of the mouthpiece pressure signal starting at t = 0.92 s.
(c) Zoom to 50 ms of the mouthpiece pressure signal starting at t = 4.25 s
greater that the pressure in the radiated sound. The peak-to-peak pressure amplitude
at t = 1.1 s inside the mouthpiece is 2.8 kPa, compared to 0.46 Pa 50 cm outside
the trombone bell; at t = 4.3 s the mouthpiece peak-to-peak pressure amplitude is
10.6 kPa, while the radiated pressure amplitude is 3.3 Pa. It is a remarkable feature
of all wind instruments that the radiated pressure amplitude is a tiny fraction of the
internal pressure amplitude.