The exciter mechanism of double-reed instrumentsgsam.sfa.free.fr/.../AAlmeida_LondresSept2006.pdf · 2008. 10. 17. · Exciter Tools for reed characterisa-tion Reed characteristics

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter

Tools for reedcharacterisa-tionReed characteristics

Vibrational analysis

Conclusion

The exciter mechanism of double-reedinstruments

A. AlmeidaC.Vergez, R.Caussé

IRCAM – Centre Georges PompidouInstrument Acoustics and Analysis / Synthesis Teams

Sep 20, 2006 – Musical Acoustics Network Conference,London

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Motivations of my PhD work

General objectiveunderstand the behavior of double-reed instrumentscompare to other reed instruments

Applicationssound synthesisvalidate generic models of reedphysical interpretation for methods of fabrication ofdouble reeds

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

From reed to sound

Instrument

behavior

Sound

Reed

configuration

Material

properties

Fabrication

procedures

Embouchure

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

From reed to sound

Instrument

behavior

Sound

Reed

configuration

Material

properties

Fabrication

procedures

Embouchure

Empirical knowledge

(musician, reed maker)

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

From reed to sound

Instrument

behavior

Sound

Reed

configuration

Material

properties

Fabrication

procedures

Measurements

Physical

parameters

Embouchure

Empirical knowledge

(musician, reed maker)

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Outline

1 Reed instrument modelsResonatorExciter

2 Tools for reed characterisationReed characteristicsVibrational analysis

3 Conclusion

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Instrument models

Pressure varies periodically inside the bore (resonator):

Period of oscillations determined by the bore geometry

Pressure variations cause the reed to open and closeFlow and pressure are modulated by the reed opening,feeding the oscillation in the bore

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Outline



3 Conclusion

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Resonator

Measured oboe impedancefor note B3[Plitnik and Strong, 1979]

Linear systemPressure/flow independent of intensityDepends strongly on frequency

Reeds work on maxima of pressure/flow

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Outline



3 Conclusion

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Exciter modelMechanics

Linear spring model for the reed opening

��

��

��

��

��

��

��

��

pr

pm

S

Displacement of the reed blades proportional to appliedforce [Almeida et al., 2006]Force caused by:

lipspressure difference pm − pr

S0 − S proportional to pm − pr

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Flow

Bernoulli model at the reed entrance

��

��

��

��

��

��

��

��

pm

pr

(∆p)r

Flow induced by the pressure difference betweenmouth (pm) and reed (pr )Flow velocity (v ) proportional to (

√pm − pr )

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Non-linear characteristics

0 5 10 15 20

P P

Pressure

T M

(kPa)

0

0.05

0.1

0.15

0.2

0.25

Flow

(l/s)

RemarksDynamic effects neglectedPT = PM/3

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Comparison between instruments

−5 0 5 10 15 20 25 300

0.1

0.2

0.3

0.4

0.5Pressure flow characteristic

Pressure difference (kPa)

Flo

w (

l/s)

ClarinetOboeBassoon

Clarinet measurementat LAUM[Dalmont et al., 2003]

RemarkBassoon reed is wider than oboeClarinet opening still wider

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Comparison between instruments

0 1 2 3 4 5 60

0.2

0.4

0.6

0.8

1

1.2Normalized pressure flow characteristic

Pressure difference

Flo

w

ClarinetOboeBasoon

Clarinet measurementat LAUM[Dalmont et al., 2003]

ObservationDouble-reeds curve has longer tail beyond curve top(PT ∼ PM/5)Clarinet closer to theoretical model (PT ∼ PM/3)

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Outline



3 Conclusion

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Static characterisation

ObservationsNon-linear characteristic maintains shapeScale is determined by:

Reed elasticityReed opening at equilibrium

Double-reedphysics

Almeida

Motivations

ModelsResonator

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Conclusion

Variability within a same reed

0 10 20 30 40 500

0.05

0.1

0.15

0.2

0.25

0.3

0.35

flow

(l/s

)

pressure (kPa)

natural cane reed no. 4 (humidified)

run 13run 14run 17

ReasonsReed damping changes along one experimentViscoelasticity (memory effects):

reed does not re-open instantly to the same positionmeasurements correspond to different reed openings atequilibrium

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Outline



3 Conclusion

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Dynamic properties of the reed

Reed does not behave equally when subject to a staticforce or to an oscillating onePrevious static characterisation needs to be completedwith an exploration of the dynamic properties of thereedDynamic effects are due to:

Inertia of the reed (cannot move between two statesinstantaneously)Inertia of the airViscosity and damping

In practice, the curve measured for static regimes ischanged when the frequency of oscillation changes

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Patterns of vibration in the reed

RemarksDifferent modes of vibration of the structure respond todifferent frequencies of the diving forceBoth the shape and frequency of these modes changewith the shape of the structure

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Mechanical admittance of the reed

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000−50

0

50

100

Frequency (Hz)

Am

plitu

de (

dB)

Dry5 min soaking30 min soaking

RemarksDifferent modes of vibration of the structureRespond to different frequencies of the diving forceBoth the shape and frequency of these modes changewith the shape of the structure

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Observations

Sound ← Meas. ← GeometryInfluences:

sound amplitude

beating regime

closed/open time ratio

Char.changing S0 scales p,q

changing k scales p,q

admittance peaks⇒harmonic enhancementin final sound

induced flow dependson mode pattern

clarinet[Pinard et al., 2003]:important torsionalmode

Dyn.

Can be easilysimulated with FEMalgorithms

Simple models:clamped beam

Ex: increase tip mass⇒ increase 1st modefrequency

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Conclusion

RemarksBoth measurements shown are incomplete andcomplement each otherVibration modes and elastic properties are related tochanges in timbreComplex relation of measurements to final sound. . .. . . but a step towards understanding the role of thereed details

Double-reedphysics

Almeida

Motivations

ModelsResonator

Exciter



Conclusion

Bibliography

Almeida, A., Vergez, C., and Caussé, R. (2006).Experimental investigation of reed instrument functionning through image analysis of reed opening.Submitted to Acustica.

Dalmont, J. P., Gilbert, J., and Ollivier, S. (2003).Nonlinear characteristics of single-reed instruments: quasi-static volume flow and reed openingmeasurements.J. Acoust. Soc. Am., 114(4):2253–2262.

Pinard, F., Laine, B., and Vach, H. (2003).Musical quality assessment of clarinet reeds using optical holography.J. Acoust. Soc. Am., 113(3):1736–1742.

Plitnik, G. and Strong, W. (1979).Numerical method for calculating input impedances of the oboe.J. Acoust. Soc. Am., 65(3):816–825.

MotivationsReed instrument modelsResonatorExciter

Tools for reed characterisationReed characteristicsVibrational analysis

Conclusion

Documents

The exciter mechanism of double-reed instrumentsgsam.sfa.free.fr/.../AAlmeida_LondresSept2006.pdf · 2008. 10. 17. · Exciter Tools for reed characterisa-tion Reed characteristics