Physics%201251%20The%20Science%20and%20Technology%20of%20Musical%20Sound - PowerPoint PPT Presentation

About This Presentation
Title:

Physics%201251%20The%20Science%20and%20Technology%20of%20Musical%20Sound

Description:

Title: Physics 1251 The Science and Technology of Musical Sound Author: alanb Last modified by: matteson Created Date: 1/9/2001 2:27:14 PM Document presentation format – PowerPoint PPT presentation

Number of Views:186
Avg rating:3.0/5.0
Slides: 23
Provided by: alan3167
Learn more at: http://www.phys.unt.edu
Category:

less

Transcript and Presenter's Notes

Title: Physics%201251%20The%20Science%20and%20Technology%20of%20Musical%20Sound


1
Physics 1251The Science and Technology of
Musical Sound
  • Unit 3
  • Session 27 MWF
  • Flutes and Flags,
  • Fipples and Fingering

2
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • What are the first three harmonics of a pipe
    closed on one end that is a length of 0.30 m?
    Assume T20 C.

Only odd harmonics in stopped pipe f1 344/4
L 344 /(4 ? 0.30) 286.7 Hz f3 3 f1
3(286.7) 860 Hz f5 5 f1 5(286.7) 1424 Hz
3
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • 1' Lecture
  • Flutes and flue pipes are driven by fluid flow
    instabilities at their mouth.
  • Standing waves in open air columns of flutes
    determine the pitch.
  • Open holes in the flute tube change the effective
    length of the air column.

4
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • The Flute
  • The transverse flute is acoustically driven by
    the fluid flow instabilities whose frequency is
    controlled by the feedback of the resonances of
    the pipe.

Standing wave frequencies
Flow Instability
Feedback
5
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • The Flute

Head Joint
Body
Foot Joint
6
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Transverse Flute
  • 80/20The flute is driven by air flow against the
    edge of the embrochure.

Air flow
Embrochure
7
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Edge Tone
  • 80/20An air stream striking against an edge
    produces a fluctuating instability in flow.

Air Stream
Edge
The flow alternates sides.
8
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Flow instabilities appear from the small to the
    very large.

Winds in Pacific Ocean
Thread in flow
9
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Foolscap Fipple
  • 1. Gently blow air from you mouth as in
    whistling.
  • Below a certain velocity the air flow is stable,
    but faster than this critical velocity the air
    flow oscillates.
  • Blow against the edge of a piece of paper.
  • Blow harder and softer. Move the paper closer and
    farther away from you lips. Notice the change in
    the sound.

10
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Fluid Flow Instability

11
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Why does the stream oscillate?

Short answer positive feedback.
  • When the stream bends to the left, the stream
    moves faster on the right side.
  • Bernoullis Principle tells us that the faster
    the flow, the lower the pressure.
  • Therefore, the left-flowing stream will bend
    back to the right

12
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Bernoulli Effect
  • 80/20The pressure in a fluid decreases as the
    velocity increases.

Hold the foolscap by the edge and blow across the
top. What do you observe?
13
Physics 1251 Unit 3 Session 27 Flutes et
cetera.
  • So why does a flag wave?

http//usflag.org/toc.html
14
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Edge Tone

fedge 0.4 vjet / 2 b 0.2 vjet /b
u 0.4 vjet
b
b
vjet
u
15
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Feedback from the acoustic standing wave locks
    the frequency of the oscillation if the edge tone
    is near the fundamental frequency.

fedge 0.2 vjet /b fn n v/ 2L
fedge fn
Displacement wave
16
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Flue and Fipple

Recorder Mouthpiece
Flue
Fipple
Air Column
17
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Recorder
  • Baroque Flute

fn n v/2L
Fipple
L
What happens when you over blow?
The instrument jumps to a new register, n2 or 3.
18
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • The Problem with Flutes
  • Only about 1 of the energy of the air stream
    produces sound.
  • Playing louder means more air flow.
  • More air flow means higher jet velocity
  • Edge tone goes sharp
  • Worse in Recorder than in Transverse Flute
  • Player must lip tone into tune

19
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • How does one play the notes?
  • By effectively changing the length of the air
    column.
  • Opening holes introduces reflections that change
    the standing wave length.

Displacement wave
f n' n ? v/2Leff
20
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Cross Fingering
  • 80/20The position and size of the open holes
    modify the effective length of the air column and
    consequently the pitch.

21
Physics 1251 Unit 3 Session 27 Flutes et cetera
  • Why does the size of the hole matter?
  • Z p/U
  • Impedance pressure/flow

Displacement ?Flow U
Z '
Z
22
Physics 1251 Unit 3 Session 27 Flutes et al.
  • Summary
  • Flutes and flue pipes are open columns of air,
    with fn n v/2L, n 1,2,3,4.
  • Flue pipes are excited by flow instabilities of
    the air steam in the embrochure or fipple.
  • The frequency range is selected by the edge tone.
  • The pitch is determined by the effective length
    of the pipe.
  • Open holes determine the effective length of the
    pipe.
Write a Comment
User Comments (0)
About PowerShow.com