acoustics lesson 1
TRANSCRIPT
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Acoustics lesson 1
Steve VanlanduitDepartement of Mechanical Engineering
u ng , roomE-mail: [email protected]
1-10-2012 1Herhaling titel van presentatie
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Consult
For any remark/question/complaint/etc.Concerning the Bruface program
Electromechanical Engineering During the Acoustics and vibrations
lectures
By e-mail: [email protected] After appointment (room ZW113)
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Acoustics and vibrations Courseoverview
,S. Vanlanduit,4 lectures,
Tuesday 10-12AM weeks 1-4
Vibrations part 1,A. Preumont9 lectures
Thursday 2-4PM, weeks 1-8
,P. Guillaume,
5 lectures, Tuesday 10-12AM week 5-7and Friday 8-10h weeks 8+9
Labs
Excercices
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Acoustics course content
Overview: Ph sics of sound Hearing Acoustics in enclosed spaces
European legislation
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Environmental noise
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Noise on the workfloor
c i t a t e d
f i n c a p a
e r s o n s
u m b e r
p
Source: Belgian Fund for Professional
Vibrations Noise Asbetos OtherSilicosis
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Introduction
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Acoustics course content
Overview: Ph sics of sound Hearing Acoustics in enclosed spaces
European legislation
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Basic physics of sound
Definition of sound: Longitudinal waves in a medium (air, water)
Pressure variations (sound pressure in Pa,Bar,atm) Frequencies: 20Hz-20kHz
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Basic physics of sound
The dB scale oun pressure eve :
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Basic physics of sound
Pressure dB conversion factors:
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Basic physics of sound
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Basic physics of sound
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Basic physics of sound
Logaritmic frequency division
Tertz bands
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Basic physics of sound
Propagation of sound
Simplified sound sources: Plane source plane sound wave
Point source spherical wave
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Basic physics of sound
The plane wave equation:
Solution:
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Basic physics of sound
The speed of sound: Gasses
Solids
helium 0 972air 0 331air 20 340water 0 1402water 20 1482sea water 20 1522iron 0 5130brass 0 4700copper 0 3560gold 0 3240
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Basic physics of sound
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Basic physics of sound
Types of sound signals:
Periodic
Impulse
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Basic physics of sound
Spectral analysis:
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Basic physics of sound
Spectral analysis:
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Basic physics of sound
The acoustic impedance:
Acoustic impedance
MKS unity:
In air: z=4 Ray
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Definities geluid: impedantieBasic physics of sound
Use of impedance:
Acoustic absorption: 14
z
za
Resonators
See lesson 2
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Basic physics of sound
RMS value:
Equivalent sound level:
Ldn :
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Basic physics of sound
Correlated uncorrelated sources:
. o eren source:RMS 2 (totaal sound) RMS 2(source1) + RMS 2 (source2)
2. Incoherent sources:RMS 2 (totaal sound) = RMS 2(source1) + RMS 2 (source2)
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Basic physics of sound
Sound Power in Watt : = energy flux through a closed surface Sound power level L W in dB:
Lw
= 10log(W / W0) with W0 = 10 -12 Watt
Sound Intensit I in Watt m2:
energy flux through 1m2 surface Sound intensity level L I in dB:
S
IdS W
= og w t = - att m
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Basic physics of sound
Sound intensity:
For p ane waves:
I is a vector quantity!
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Basic physics of sound
Relation between power and pressure:
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The hearing system
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The hearing system
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The hearing system
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The hearing system
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Measurement of sound
Type 1
Type 3
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Measurement of sound
Measurement microphones
Principles: ezoe ec r c Inductive
Condenser E ectret
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Measurement of sound
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Measurement of sound
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Measurement of sound
f d
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Measurement of sound
M f d
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Measurement of sound
M f d
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Measurement of sound
Measurement of sound
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Measurement of sound
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Measurement of sound
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Measurement of sound
Measurement of sound
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Measurement of sound
Octaves and Tertz band analysis25 31,5 40 50 63 80 100 125 160
200 250 315 400 500 630 800 1000 1250
1600 2000 2500 3150 4000 5000 6300 8000 10000
12500 16000 20000
Measurement of sound
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Measurement of sound
Measurement of sound
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Measurement of sound
n x r l v l:
Measurement of sound
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Measurement of sound
Sound intensity measurement:
Measurement of sound
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Measurement of sound
Limitation of the frequency range
Sound power measurement
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Sound power measurement
Different possible techniques:
. s ng measurements:
2.Using sound intensity measurements
ISO 9614 series
Sound power measurement
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Sound power measurementISO 3741 to 3747Procedure: Choice of a surrounding surface
SPL measurements at discrete points on the surface A weighted In octave or tertz bands
Variants depending on: Type of surface Acoustical environment (anechoic room?) Required accuracy
Background noise A lication area re uired information
Sound power measurement
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Sound power measurement
ISO 3744 Semi-anechoic, outdoor, large
room
< All types of sound In frequency bands Surrounding surface:
Parallellepipedum
Sphere
1 210logwS
L L K K 0.1110 log 10 pi N
L p L
0 1i
Sound power measurement
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Sound power measurement
Comparison method: ISO 3747 Accuracy = 4 to 5dB Fixed non-mobile machines
- No limitation on the volume of the source All stationary sound Method:
Power of the
reference source
Avg. SPL referencesource
Avg. SPL of
unknown source
Sound power measurement
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Sound power measurement
Using sound intensity: : e erm na on o soun power eve s o
noise sources using sound intensity
Definition of an arbitrary surrounding surface ur u y r
surface
i ni iW I S 10log iW L W
Sound power measurement
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p
Elimination of background noise
Nearfield measurements
Sound power measurement
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p
Disadvantages: Limite requency range
Directivity Cost of the instrumentation
Sound power measurement
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p
ISO 9614-2 :
Sweep method
Example exam questions
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p q
Ma or uestion: Explain the working principle of the human
hearing system. Discuss the working principle of a sonometer and
an intensity meter. Explain how one can measure sound power in
practice.
Minor questions: Calculate dB level (by heart) Give order of magnitude of acoustical quantities