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© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 1 Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot 1. Definitions: sound and acoustics 2. Why is acoustics important ? 3. Acoustics: a very broad research field ! 1. Linear vs. non-linear 2. Aero- vs. vibro-acoustics 3. A few applications of ultrasounds 4. More acoustics research topics

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© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 1

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 2

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 3

What is a sound ?

A sound is a small and rapid fluctuation of pressure around a mean value.

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 4

Mean value

The mean value is either the atmospheric or the hydrostatic pressure

Atmospheric pressure changes with altitude

Hydrostatic pressure

changes with depth

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 5

Small fluctuation: how small ?

0

20,000

40,000

60,000

80,000

100,000

120,000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Pre

ssio

n t

ota

le (

[Pa]

)

Temps (unités arbitraires)

0

20,000

40,000

60,000

80,000

100,000

120,000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Pre

ssio

n t

ota

le (

[Pa]

)

Temps (unités arbitraires)

0

20,000

40,000

60,000

80,000

100,000

120,000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Pre

ssio

n t

ota

le (

[Pa]

)

Temps (unités arbitraires)

0

20,000

40,000

60,000

80,000

100,000

120,000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Pre

ssio

n t

ota

le (

[Pa]

)

Temps (unités arbitraires)

100 dB

160 dB

Time (arbitrary units)

Time (arbitrary units)

Tota

l pre

ssu

re (

[Pa]

) To

tal p

ress

ure

([P

a])

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 6

Rapid fluctuation: how fast ?

1 10 3 10 6 10 9 10 12

20 Hz 16 kHz 1 GHz

Sound Ultrasound Hypersound Infrasound

220 Hz A(3)

440 Hz A(4)

880 Hz A(5)

1760 Hz A(6)

110 Hz A(2)

55 Hz A(1)

27.5 Hz A(0)

3520 Hz A(7)

4186 Hz Do(8)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 7

A typical (stereo) sound recording

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 8

Range of audible frequencies

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 9

Noise (negative) vs. sound (general)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 10

Acoustics

Acoustics is concerned with pressure waves in air but also

in water (underwater acoustics)

in any fluid (e.g. transformer oil)

in any solid (structure-borne sound propagation in vehicles and buildings, P-waves in geodynamics)

Acoustics is concerned with 4 aspects of sounds:

production

propagation

reception and perception

effect on the propagation media

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 11

The three topics of engineering acoustics

Usually sound has no lasting effects on its propagation media

Acoustical engineers are primarily concerned with three aspects of sounds:

its production by a source -> physics of the source (vibration, turbulence, …)

its perception or recording by a receiver -> physiology of the ear, physics of microphones, …

the propagation from the source to the receiver -> propagation, reflection, attenuation, …

Source Path Receiver

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 12

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 13

Why acoustics ? Noise is annoying !

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 14

Why acoustics ? Noise performance is a purchase criteria !

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 15

Why acoustics ? Stringent standards apply !

© CRITT M2A

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 16

European Pass-by noise regulation

Pass-by noise engineering: a review of different transfer path analysis techniques - K. Janssens et al. – ISMA 2014

2016

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 17

Why acoustics ? Noise performance may mean success or failure !

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 18

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 19

Fields of acoustics

Lindsay R.B., JASA., 36:2242 (1964) cited by Pierce A.D. , Acoustics, Acoustical Society of America and American Institute of Physics (1994).

Hearing

Bioacoustics

Oceanography

Physics of Earth and

Atmosphere

Electrical &Chemical

Mechanical

Architectural

Visual Arts

Music

Speech

Psychology

Physiology

Medicine

EarthSciences

Engineering

ArtsLife

Sciences

Seismic wavesSound in theatmosphere

UnderwaterSound

Electro-acoustics

Ultra-sonics

Shock andVibrations

Room andTheatre

Acoustics

Musical scales& Instruments

Psycho-acoustics

Com-muni-cation

FundamentalPhysical

Acoustics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 20

Classification of the Acoustical Society of America

Categories based on the underlying physics or technique:

General linear acoustics

Nonlinear acoustics

Aeroacoustics

Structural acoustics Vibrations

Ultrasonics, Physical effects of sound

Categories related to life science:

Physiological acoustics

Speech-Production, Perception, Processing

Psychological acoustics

Bioacoustics

Categories based on applications:

Architectural acoustics

Music and musical instruments

Noise, its effects and control

Electro-acoustics

Underwater acoustics

Transverse categories

Transduction; Acoustical measurements

Acoustic signal processing

Audio Engineering

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 21

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 22

A 2*B

p(A+2*B) = p(A)+2*p(B)

Linearity ?

Linearity means:

Superposition pA + pB = pA+B

Proportionality pkB=k.pB

The immense majority of acoustic phenomena are linear

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 23

Linear vs. non-linear acoustics

Non-linear phenomena appear when:

Sound levels are very high (jet engines, power ultrasound) ~ 150dB

The source amplitude depends on induced acoustic field (burner noise)

The mechanical properties of the acoustic media change with the sound field (acoustic cavitation)

Examples

Sonic Boom

Acoustic levitation

Sonochemistry

Sonoluminescence

Acoustic streaming

It is in the field of ultrasound that most non-linear acoustic phenomena are encountered

© Wikipedia – Sonic Boom

© http://www.hashmoder.com/ 2010/01/20/acoustic-levitation/

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 24

Sonoluminescence

Felipe Gaitan Larry Crum

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 25

Sonochemistry: improving chemical yield with ultrasounds

© Jean-Louis Migeot, ASA, 1998

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 26

Acoustic streaming

Olivier Dahlem &

Véronique Halloin (1998)

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 27

Science, scientists and engineers in motion pictures ...

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 28

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 29

Aeroacoustics vs. vibro-acoustics

Aero-acoustics:

generation of noise by flows:

• turbulents flows (jets, boundary layer)

• turbomachinery flow

propagation of sound waves in a moving fluid (convected propagation)

flow induced by sound in a dissipative fluid (streaming).

Vibro-acoustics = Sound radiation by vibrating structures:

cars: powertrain, body, transmission, alternator

machines: stamping and forging, printing, electrical devices

home appliances: vacuum cleaner, dishwasher, washing machines

electronics: television, computers

An acoustic phenomenon may always be categorized as aeroacoustics or vibro-acoustics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 30

Aero-acoustics

© ACTRAN / Free Field Technologies

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 31

Vibro-acoustics

© ACTRAN / Free Field Technologies

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 32

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 33

Ultrasounds – Non-destructive Testing

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 34

Ultrasounds in Production Engineering

Emulsification

Homogenization

Welding

Cleaning

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 35

Ultrasounds – Medical Applications

Echography

Cautery

Lithotripsy

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 36

Breaking glass …

The Fat Lady guarding the entrance of Gryffindor Tower © Harry Potter and The Prisoner of Azkaban

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 37

Tif & Tondu vs. M. Choc

CHOC !

What are I have activated my

ultrasound system: the

house will collapse.

Good luck !

you doing !

Tif et Tondu © Will

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 38

Calculus’ sonic weapon

Tintin, The Calculus Affair © Hergé - Moulinsart

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 39

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 40

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. Definitions: sound and acoustics

2. Why is acoustics important ?

3. Acoustics: a very broad research field !

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 41

Classification of the Acoustical Society of America

Categories based on the underlying physics or technique:

General linear acoustics

Nonlinear acoustics

Aeroacoustics

Structural acoustics Vibrations

Ultrasonics, Physical effects of sound

Categories related to life science:

Physiological acoustics

Speech-Production, Perception, Processing

Psychological acoustics

Bioacoustics

Categories based on applications:

Architectural acoustics

Music and musical instruments

Noise, its effects and control

Electro-acoustics

Underwater acoustics

Transverse categories

Transduction; Acoustical measurements

Acoustic signal processing

Audio Engineering

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 42

Physiological acoustics: speaking and hearing

© Blausen.com staff. "Blausen gallery 2014“

Wikiversity Journal of Medicine. © http://training.seer.cancer.gov/head-neck/anatomy/overview.html

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 43

Sense of hearing – Auditory Transduction

Brandon Pletsch

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 44

Psycho-acoustics

Effect of personal, environmental and other non-acoustical factors on noise perception

cumulative aspect of noise nuisance

effect of stress, fatigue, illness, lack of sleep, sex, age, education

perceptive coupling: vibratory, visual

psychological or physical factors (ex: announcement effect)

Differences between objective and subjective noise measures:

definition of psycho-acoustical indices: loudness, pitch, …

Sound quality

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 45

Bio-acoustics: snapping shrimp

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 46

Room and building acoustics

© MJM ACOUSTICAL CONSULTANTS INC © DOUGLAS MICHAEL VERSAGLI

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 47

Electro-acoustics and micro-acoustics

Electro-acoustics

loudspeakers

headsets

microphones

telephones

Micro-acoustics (visco-thermal loss effects in small cavities, ducts and layers)

auditory prosthesis

mobile phones

inkjet printers

solar panels

© ACTRAN / Free Field Technologies

© http://www.hearingaidopinion.com

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 48

Underwater acoustics: civil applications

Acoustic thermometry

Seafloor survey

http://npal.ucsd.edu/thermometry/index.htm

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 49

Underwater acoustics: military applications

Torpedo guiding system

Identification of submarines and other vessels by their ultrasonic echo

Non lethal weapons for underwater warfare

© Ultra Electronics

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 50

Transduction, metrology, signal processing

Microphones, hydrophones, intensity probes

Active materials:

piezo-electric

magneto-strictive

electro-strictive

Measurement techniques:

sound measurement

intensimetry

acoustic holography

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 51

Key Takeaways

Acoustics includes sound production-propagation-perception.

Noise is defined by the time history of acoustic pressure

Acoustics is a very broad topic ranging from very practical to rather exotic fields of research. Key differences between sub-domains:

vibro- vs. aero-acoustics

linear vs. non-linear

audible acoustics vs. ultrasonics

Our focus in the course will be on audible sound propagation.

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 52

Get your hands dirty !

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 53

Think for yourself

Take a few minutes to answer the following questions for yourself:

why is acoustics important for your own company ?

• customer (user)

• citizens

• standards compliance

who (which department(s)) is (are) in charge of the design part, the experimental part, the standards compliance part ?

how do the various actors work together ?

list the tools, technologies, partners that are used by your company to improve your product’s acoustic performance

© Jean-Louis Migeot – MSC Software – Free Field Technologies – Université Libre de Bruxelles – Conservatoire Royal de Musique de Liège – IJK Numerics 54

Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeot

1. What is a sound ?

2. Definition of acoustics

3. Why is acoustic so important ?

4. The wide field of acoustics

1. Linear vs. non-linear

2. Aero- vs. vibro-acoustics

3. A few applications of ultrasounds

4. More acoustics research topics