ACOUSTICS OF WIND INSTRUMENTS

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ACOUSTICS OF WIND INSTRUMENTS
1. PIPES, HORNS, LIP AND REED VIBRATIONS
REFERENCES SCIENCE OF SOUND (ROSSING, et al.)
CHAPTER 11 THE PHYSICS OF MUSICAL INSTRUMENTS
(FLETCHER AND ROSSING) CHAPTERS 8 and 13

) MUSICAL INSTRUMENTS
(CAMPBELL, et al.) CHAPTERS 5 and 6
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EARLY WIND INSTRUMENTS
ANIMAL HORNS AND SEA SHELLS WERE USED FOR
SIGNALLING SIGNALLING HORN CONVERTED TO A MUSICAL
INSTRUMENT BY CUTTING FINGER HOLES ALONG THE
HORN. CORNETT WAS ONE OF THE EARLIEST OF SUCH
INSTRUMENTS REED INSTRUMENTS MAY DATE BACK TO
300O BCE. REMAINS OF SUMERIAN REED INSTRUMENTS
WITH 3 SIDE HOLES, PROBABLY DESIGNED TO PLAY
WHOLE TONE SCALES, DATE TO 2500 BCE.
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WIND INSTRUMENTS OF GREECE AND ROME
GREEK WIND INSTRUMENTS WERE CHARACTERIZED AS
AULOS (REED) OR SYRINX (FLUTE). AN AULOS OFTEN
TOOK THE FORM OR TWO PIPES, EACH FITTED WITH A
REED, HELD ONE IN EACH HAND THE ROMAN TIBIA WAS
SIMILAR TO THE AULOS. USUALLY MADE OF METAL IT
DATES FROM ABOUT 500 BCE.
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EARLY WOODWIND INSTRUMENTS
THE SHAWM IS A DOUBLE REED INSTRUMENT WITH A
CONICAL BORE DATING BACK TO THE 12TH CENTURY THE
CRUMHORN IS A CURVED WOODEN INSTRUMENT WITH A
CYLINDRICAL BORE AND A DOUBLE REED COVERED BY A
CAP WITH A RAISED SLIT AGAINST WHICH THE PLAYERS
LIP RESTS. IT WAS POPULAR IN THE 14TH TO 17TH
CENTURY.
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RESONANCES OF CYLINDRICAL PIPES WITH OPEN AND
CLOSED ENDS
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RESONANCES OF CONICAL PIPES
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WHAT ABOUT TRUNCATED CONES?
ARE THE RESONANCES HARMONIC?
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RESONANCES OF CYLINDRICAL AND CONICAL PIPES
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OSCILLATIONS IN A PIPE
ONE WAY TO STUDY THE RESONANCES OF A PIPE (OR A
WIND INSTRUMENT) IS TO MAKE A GRAPH OF ITS
ACOUSTIC IMPEDANCE AS A FUNCTION OF
FREQUENCY ACOUSTIC IMPEDANCE IS SOUND PRESSURE
DIVIDED BY VOLUME VELOCITY Z p/U
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GRAPHING ACOUSTIC IMPEDANCE
APPARATUS FOR GRAPHING THE ACOUSTIC IMPEDANCE OF
WIND INSTRUMENTS
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ATTENUATION IN PIPES
ATTENUATION IS MAINLY DUE TO VISCOUS DRAG IN THE
BOUNDARY LAYER WHICH DEPENDS UPON RATIO OF
VISCOUS LAYER TO PIPE DIAMETER THERMAL EXCHANGE
BETWEEN AIR IN THE SOUND WAVE AND PIPE WALLS
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HORNS
HORNS HAVE A NUMBER OF USEFUL APPLICATIONS IN
ACOUSTICS. THEY ARE USED IN LOUDSPEAKERS AS A
SORT OF ACOUSTIC STEP-DOWN TRANSFORMER TO MATCH
THE HIGH IMPEDANCE OF AN ELECTROMAGNETIC DRIVER
TO THE LOWER IMPEDANCE OF AIR. HORN LOUDSPEAKERS
ARE VERY EFFICIENT. THEY ARE USED IN WIND
INSTRUMENTS TO IMPROVE RADIATION EFFICIENCY, BUT
THEY ALSO ARE IMPORTANT PART OF THE INSTRUMENT
RESONATOR ITSELF.
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IMPEDANCE OF CONICAL HORN
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BESSEL HORNS
BESSEL HORNS CAN COUPLE TO A CYLINDRICAL PIPES
WITH LITTLE ACOUSTIC MISMATCH, WHICH MAKES THEM
USEFUL IN MUSICAL INSTRUMENTS. THE FIRST
RESONANCE IS OFTEN OUT OF ALIGNMENT AND THEREFORE
NOT USED IN PLAYING
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BORE PROFILES
ALPENHORN (SOLID LINES) AND FRENCH HORN (DASHED
LINES)
Bb CLARINET
Bb TRUMPET
OBOE
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FEEDBACK
FEEDBACK IS THE ADDITION OF A PART OF THE OUTPUT
OF A SYSTEM TO THE INPUT NEGATIVE FEEDBACK IS
USED TO REDUCE DISTORTION IN AMPLIFIERS,
etc. POSITIVE FEEDBACK IS USED TO SUSTAIN
OSCILLATION IN MUSICAL INSTRUMENTS AND ELECTRICAL
OSCILLATORS
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INPUT VALVES
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REED-GENERATOR CONFIGURATIONS

• Corresponds to a woodwind reed
• Corresponds to brass players lips
• (c) Alternative model of brass players lips

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BENADES WATER TRUMPET
(INPUT VALVE IS CONTROLLED BY PRESSURE FEEDBACK)
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MOUTHPIECE
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LIP ACTION
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OBSERVING THE LIPS THROUGH A GLASS MOUTHPIECE
WINDOW
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COMPARISON OF WIND INSTRUMENTS
f
Pedal Tone
f1 v/2(Lc)
fo (1?)v/4(Lc)
L
f1 v/2L
f1 v/4L
Other Woodwinds
Clarinet
Flute
Brass
c
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STRIKING REEDS
A CLARINET REED STRIKES THE TABLE OF THE
MOUTHPIECE AS IT VIBRATES
AN ORGAN REED STRIKES AGAINST THE SHALLOT
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FREE REEDS
INSTRUMENTS SUCH AS THE AMERICAN REED ORGAN, THE
HARMONICA, AND THE ACCORDIAN EMPLOY FREE REEDS A
FREE REED VIBRATES FREELY OFTEN IN A SLOT IN THE
REED HOLDER. MEASUREMENTS SHOW A NEARLY
SINUSOIDAL REED MOTION
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FREE REED INSTRUMENTS
HARMONICA
BUTTON ACCORDIAN
IN THESE FREE REED INSTRUMENTS THE REED CAN BE
EXCITED BY AIR FLOW IN EITHER DIRECTION (BLOWING
OR DRAWING)
PIANO ACCORDIAN
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ASIAN FREE REED INSTRUMENTS
KHAEN FROM LAOS
CHINESE SHENG