Woodwind Instruments

1
Woodwind Instruments

• Chapter 12

2
Woodwind Topic Overview

• Pipe-reed system
• Tone holes
• Resonances of cylinders and cones
• Single- and double-reed instruments
• In the flute, collaboration between air stream of
  player and air column in flute.

3
Pipe-Reed System

• Pipe-reed systems are naturally a closed pipe,
  but bore shape can change this
• Conical bores (oboe, saxophone) behave like open
  pipes.
• Reed acts as a valve
• Open at beginning of pulse
• Closed when pulse returns
• Open for next return, etc.

4
Reed Vibrations

• Air inside column has a large mass compared to
  the reed.
• Reed locks in to vibrating frequency of the
  column.
• Possible to triple the frequency of the reed
  vibration through lip pressure alone, but usually
  this is done with a register key.

5
Modes of Oscillation

• Period and Frequency

6
Tone Holes (closed)

• Both open and closed tone holes affect a woodwind
  instrument.
• Closed tone holes have an increased volume of
  air, slowing the speed of the wave traveling in
  the instrument.
• Closed tone holes increase the acoustical length
  of an instrument, and lower its resonance
  frequencies slightly.

7
Tone Holes (Open)

• Open tone holes change the acoustic length of the
  instrument.
• The larger the hole, the more effective the
  shortening.
• When the size of the opening matches the bore,
  the pipe effectively ends at that point.
• Tone-hole lattice more than one open hole.
• Acts as a filter.
• Cutoff frequency of the lattice above,
  frequencies propagate through the openings
  below, reflected.

8
Conical Bores

• Conical bores essentially have the same resonance
  frequencies as an open pipe.
• Same impedance peaks as conical, but points of
  minimum pressure do not lay midway in between
  points of maximum pressure.

9
Register Holes

• Leaking a little bit of air reduces the strength
  of a resonance, making it possible to vibrate in
  another mode.
• Register keys perform this function.
• Placement of key usually is optimal for one or
  two modes.
• Tone holes can provide additional resonance
  keys.

10
Whistles

• Flutes (whistles, recorders, etc.) make use a
  vibrating air stream (jet of air)
• Input flow not controlled by feedback pressure
• Input flow controlled by direction of standing
  waves in air column
• Flow-controlled

11
Flute

• Flow-controlled air stream collaborates with the
  air column to vibrate at frequencies where the
  air column has dips in its impedance curve.
• Cylindrical pipe, open, has fundamental and all
  harmonics.

12
Resonance control

• Player has control over blowing pressure, length
  of the air jet, and area of lip opening.
• Moving lip forward decreases jet length.
• Above, coupled with increased blowing pressure
  gets second mode of vibration.
• Angle of blowing also has an effect.