ph 105 dr. cecilia vogel lecture 19. outline woodwinds single reed, double reed, air reed bores:...

PH 105

Dr. Cecilia VogelLecture 19

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 4n

nvf

L

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 2nd and 4th 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

2n

nvf

L

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.2n

nvf

L

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

clarinet 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 3f1 is (2)(3/2)

is an octave plus a fifth 5f1 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 2f1

is an octave 3f1 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

SummaryPitch of woodwind,

determined by tube resonances.Cylindrical reed instruments

missing 2nd and 4th harmonicConical 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