PH 105

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PH 105
Wind Instruments
Dr. James van Howe Lecture 11
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Name the artist/group

• The Wailers (Bob Marleys band)
• Jimmy Cliff
• The Police
• The Clash

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Brass and Woodwinds
At a rudimentary level, they both are simply
closed tubes of resonating air
Mouth Piece
Bell
L
l/4
3l/4
In general
only odd harmonics exist
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Your responses

• I am not surprised because I have heard this
  argument before. However, experience has proven
  this wrong for me. And I will never feel foolish
  for buying my fancy silver instrument. It
  sounds better no matter what the physics says. I
  have played the exact same model of a flute made
  of different metals and there was a clear
  difference in tone quality and timbre. Physics is
  correct in ideal conditions, and we do not live
  in an ideal world. I will stick with my solid
  silver flute.
• We could prove that the material does not matter
  if we played instruments composed of different
  materials, with the same quality of construction.
  By playing them into a microphone, we could see
  the waves it produces to give it the certain
  sound. If the waves were the same, then the
  material would not be important.
• There is no scientific way of proving that the
  wall material matters because scientific
  reasoning cannot coincide with artistic
  reasoning.
• Experimentally we could use instruments of
  different materials, but same quality, and play
  the same note. We could then observe that note on
  the computer-drawn graph. If the peaks are
  closer, further, higher, or lower then the
  material would affect the sound waves. This
  experiment wouldn't be 100 accurate due to human
  error and the players skill level.

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Your responses cont.

• It was surprising because when I was in band, I
  remember the trumpet section eventually switched
  from brass to silver instruments. When I read
  that it didn't matter, it was surprising that
  musicians put so much unnecessary focus on the
  material of the instrument. The wall material
  doesn't matter because the things that do matter
  are wall thickness, to stop wall vibrations, and
  air resistance, which could be prevented if the
  walls were smooth enough. I wouldn't be
  interested in a metal clarinet because it would
  be too heavy and a fiberglass flute wouldn't be
  ideal because the walls would be too thin and the
  vibrations would disrupt the sound.
• I think that the person who wrote this could not
  have been a brass player. For example, cheap
  instruments are made of lacquer sprayed on hard
  plastic, which makes a bright sound. This creates
  a brighter sound that is not ideal for
  non-beginners. Silver can create dark or bright
  sounds, unfinished brass has the best resonance,
  and gold plating, while very expensive, has an
  amazing sound. I would never play on a day-to-day
  basis on a wood trumpet, or a lacquered one.

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Your responses cont.

• As long as the craftmenship of the instrument is
  good, and there is minimal friction inside of the
  instrument wall, the sound quality will remain
  good. And although the wall material of a
  woodwind instrument would have little effect on
  sound quality as well, I think that there would
  be many other reasons for choosing different wall
  materials (such as how easily the material
  cracks, what sort of weather is the instrument
  going to be played in, etc.)
• Talking with my clarinet teacher just the other
  day, we discussed the matter of clarinets. 
  Although argued that matter doesn't matter, she
  believes that there is an audible difference to a
  trained clarinetest.  One could argue however
  that plastic clarinets are not made to the
  standards of a professional wooden clarinet, but
  here's the catch.  Different woods sound
  differently.  Many professionals are buying
  different barrels and bells for the clarinets
  made from different wood.  The 'secret' is that
  different woods have different wood grain,
  causing a different sound.  A metal clarinet
  technically should sound the same as a wooden
  clarinet, but there is not warm quality that the
  wood (wood grain) can produce.  A metal clarinet
  also has thinner walls so the vibration amplitude
  would increase far more rapidly than a wooden
  clarinet would. Comparing frequencies of these 2
  instruments could prove this, but to the clarinet
  player there will always be a difference.

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Brass and Woodwinds

• Unlike the violin, the material of instrument is
  not very important the walls radiate negligible
  sound energy
• How the air resonates inside the
  tube and radiates from the bell
  is most important!
• Any material will do, though to
  minimize damping of the sound,
  the walls should be thick
  and smooth

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How to get the air resonating
Brass vibrating lips of the player
Steady puffs of air at right time (frequency)
cause resonance in the tube

• Like pushing the child on the swing at the right
  time
• Or shaking a rope at one end (other end fixed) at
  the right frequency to get nodes
• Or like holding the right tuning fork over the
  end like you did in lab (lips variable tuning
  fork)

Embouchure lip position used when playing wind
instrument
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Help from reflection
Reflection of the sound pressure wave back from
the bell helps the lips open and close at the
right time regenerative feedback
Pressure controlled valve
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Impedance
Change in density caused reflection
Denser medium slower speed
Part of pulse Reflected
Part of pulse Transmitted
Reflected Pulse Transmitted Pulse Incident
Pulse
We sometimes use the word impedance mismatch to
describe the mismatch between two media in which
waves propagate
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Impedance matching Systems
Anti-reflection coating
Medium 1
Medium 2
Medium 2
All light goes through to reduce glare
Ossicles in the ear
Medium 1
All sound goes through to increase hearing
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Acoustic Impedance
A cross sectional area
P pressure
U flux, (velocity) x (area)
If Z changes over length of tube, reflection
occurs, like change in density
Bell sends pressure wave back to mouth piece
since impedance mismatch
Inside trumpet reflected waves build up, 100x
louder than a jet
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Impedance Curves

• 1. Frequency down-shift
• 2. High-frequencies radiated
• out

Odd numbered harmonics
140 cm pipe with bell
140 cm pipe

• Peak 2 Bb3, 233 Hz

Pipe with Bell and Mouthpiece
Mouthpiece enhances 750-850 Hz
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Details
Well-designed bell and mouthpiece bring
frequencies close to a harmonic ratio, in phase
at mouthpiece better help for lips
Mouth Piece
Bell
Pressure wave
Closest antinode towards bell turning point
Length grows with frequency
In phase here helps lip open helps hit all
harmonics
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Details

• Soft blowing sinusoidal lip motion, peak 2 most
  important
• Hard blowing complex shaped motion more
  harmonics, peaks 4, 6, 8 strong
• Missing fundamental (should be at 117 Hz) can be
  excited by other harmonics pedal tone

• Peak 2 Bb3, 233 Hz
• Peak 4 F4, 351 Hz
• Peak 6 F5, 698 Hz
• Peak 8 Bb5, 932 Hz

Peak 9 C6, 1046 Hz hard to play, lip muscles get
little help from reflection
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Reeds
Blowing over reed causes it to flap up and down,
letting puffs of air in and out at a regular
frequency like lips of brass player
Bernoulli Effect Increase flow in velocity
results in lower pressure
Self demo take two strips of paper and blow
between them, What happens?
Ever notice this when passing a big semi-truck on
the highway?
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Vibration of Pipe-Reed
Puff air lowers pressure reed brought up-wards
negative pressure under reed pushes it down-wards
Positive pressure
negative pressure
One cycle of reed
negative pressure pulse closes reed
Positive pressure pulse opens reed so that
another puff can be introduced