PHY2464 - The Physical Basis of Music
PHY
-2464
PHY-2464
Physical Basis of Music
Presentation
Presentation 18
18
Stable
Stable Notes
Notes in
in Wind
Wind Instruments
Instruments
Sam
Sam Trickey
Trickey
Mar.
Mar. 15,
15, 2005
2005
Note
Note –– Figures
Figures are
are from
from Hall
Hall “Musical
“Musical Acoustics”
Acoustics” 33rdrd Ed.
Ed.
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
REMINDER:
• Wind instruments are characterized by a pulsating
source (edgetone, reed, buzzing of lips).
•Flutes, recorders, etc. are open pipe instruments
• Reeds and brasses are closed pipe instruments.
Question: how are the pulsations stabilized?
Put differently– why are some notes playable
and others not?
PHY2464 - The Physical Basis of Music
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Input acoustic
impedance →
pressure/flow at
mouthpiece.
Input impedance of
a stopped cylinder
tells a lot about why
a piece of hose has a
characteristic note.
Recall the
hosaphone™
hosaphone™!
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Input acoustic impedimpedance of a cornet.
Compare to stopped
cylinder. Note the
effect of the bell,
beginning about 1000
Hz & especially from
1500 Hz up. Any note
above mode 10 is by
the lips alone. Also
note mouthpiece
resonance between
500 and 1000 Hz
PHY2464 - The Physical Basis of Music
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
An oboe has many
harmonics in its
played note, whereas
an alto saxophone has
few. This makes the
“color”
color” or timbre of
the two instruments
very different.
Return to this topic in
Unit 19. Both
instruments are
conical. What makes
the difference?
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Regime of oscillation:
oscillation: favorable coincidence of note harmonics
and impedance extrema (minima for open pipes, maxima for
stopped pipes). Notice the match of harmonics of the desired
fundamental with impedance peaks for these notes of the trumpet.
PHY2464 - The Physical Basis of Music
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Here are progressively harder notes to play on the trumpet. Why?
Why?
Because the regime of oscillation involves progressively fewer
impedance peaks.
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
The trumpet pedal tone has almost NO fundamental! We hear the
fundamental by synthesis from the overtones, which are strong. It
It
is a hard note to play in the sense of musical consistency.
PHY2464 - The Physical Basis of Music
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Lowest note input impedance of clarinet. The instrument plays at
at
147 Hz as fundamental even though the first peak is at 150 Hz.
The “mistuning”
mistuning” of modes compared to harmonic is such that a
clarinet in upper registers actually has even harmonics. What
does this say about timbre?
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
Bassoon plays a little below the first mode resonance because this
this
frequency matches peaks 7,9, 13 against harmonics 5,6,8 as well
as 1, 2, & 3.
PHY2464 - The Physical Basis of Music
PHYPHY-2464
Pres. 18 Stable Notes in Wind Instruments
UNUNPLAYABLE
instrument!
PHYPHY-2464
Pres. 19 Stable Notes in Wind Instruments
Summary •
•
•
•
•
The pitch of a wind instrument is determined by the length
and shape of its air column.
The effective length of the air column is controlled with
holes, valves and slides.
Feedback from the resonances of the pipe select the
frequency of oscillation of the jet, reed or liplip-valve.
The feedback approximately matches harmonics to
impedance maxima to establish a regime of oscillation.
The excitation, transmission and emittance of the sound in
the horn determine the timbre of the instrument.