OUTLINE Woodwinds single reed, double reed, air reed bores: cylinder, cone resonances, harmonics register holes, tone holes
Woodwind Classification Woodwinds can be classified by the type of reed that disturbs the air. single and double reeds: thin piece of wood air reed: disturbed stream of air Woodwinds can be classified by the type of bore (shape of the air column inside) cylindrical bore conical bore Any combination of reed and bore.
Woodwind Pitch String, and vocal instruments get their pitch from the source of disturbance (string or vocal folds), not from resonators. Woodwind instruments get their pitch from the resonances in air column, not from vibrating reed or air stream. The reed (or air reed) is very light, and is driven by the mass of air in column.
Bernoulli Principle When relaxed, the reed(s) of woodwind are open. When you blow past the reed(s) why doesn’t the air just go through? Why do the reed(s) close? Moving air sucks, that’s the Bernoulli principle. Reed is sucked closed, but when closed no Bernoulli, opens up to get sucked closed again…
Reeds are Pressure Driven The vibration of a reed is driven by pressure in the air column: When a low pressure reaches the reed, reed sucked closed & cannot equilibrate to atmospheric pressure. When a high pressure reaches the reed, reed pushed open & puff of high pressure air is blown in. Again cannot equilibrate to atmospheric pressure.
Resonances of Tube Because the air column cannot come to equilibrium at the reed end, that end acts somewhat like a closed end. The clarinet is a cylindrical-bore reed instrument. We know the resonant frequencies of a tube closed at one end: where v = speed of sound in air L = length of tube n = only odd integers
Clarinet Resonances Resonances of cylinder-bore reed instrument, such as clarinet: At low freq acts like tube with one end closed only odd harmonics: 1, 3, 5 At higher freq affected by bell all harmonics: 6, 7, 8, 9, 10… Missing 2 nd and 4 th harmonics make a tone sound “woody”
Conical Bore Saxophone, oboe, bassoon have a cone-shaped bore Resonances of a conical column of air are the same as a tube open at both ends where v = speed of sound in air L = length of tube n = all integers compare fig. 12.13 and fig 12.16 timbre of sax is not woody
Air Reed Flutes, recorders, flue pipes, whistles blow air stream past obstruction. Air flow is disturbed, starting a sound wave.
The vibration of air reed is driven by flow of air in the column: When high pressure reaches end of air column, stream of air is blown away from the opening, air flows out of column. When low pressure reaches end of air column, stream of air is pulled into the opening, air flows into the air column, Air Reeds are Flow Driven
Resonances of Tube Because the air can flow in and out of air column at the embouchure end, that end acts like a open end. Flute is a cylindrical air-reed instrument. We know the resonant frequencies of an open tube: where v = speed of sound in air L = length of tube n = all integers Flute also doesn’t have woody quality.
Recall To play notes in higher register on brass instrument increase the freq of lip vibration. To play notes in higher register on string instrument suppress the lower resonance by placing your finger on string you force a node where the lower mode has antinode.
Register Holes To play notes in higher register on c larinet Suppress the lower resonance. By opening a register hole allowing air in and out, you force a node where the lower mode has antinode.
Clarinet Fig 12.12 shows position of register holes for clarinet-like instrument. note odd harmonics 3f 1 is (2)(3/2) is an octave plus a fifth 5f 1 is (4)(5/4) is 2 octaves plus a major third
Overblowing To play notes in higher register on flute Suppress the lower resonance. If the air stream crosses the embouchure hole too quickly low freq resonances not excited. Changing embouchure and blowing speed to bring out overtones is called overblowing.
Flute Fig 12.24 shows resonances that can be overblown on flute. note all harmonics 2f 1 is an octave 3f 1 is (2)(3/2) is an octave plus a fifth
Tone Holes How to play the notes in between on woodwind: An open tone hole along the air column is almost like an open end. The open hole effectively shortens the air column. To raise the pitch one semitone, how far from end should you open a tone hole? approx 1/18 the (remaining) length How many notes between on flute? On clarinet? 11 18
Woodwind Demo Listen to timbre. Observe spectrum. Play chromatic scale using tone holes. Which holes are closer together? Why? How many tone holes? Play in different registers. what technique is used? Where are nodes? What intervals can be played with same fingering? Change of timbre with dynamics
Summary Pitch of woodwind, determined by tube resonances. Cylindrical reed instruments missing 2 nd and 4 th harmonic Conical reed instruments, and cylindrical air-reed instruments all harmonics Play in upper registers by using register holes or overblowing Play chromatic scale using tones holes