Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeothomepages.ulb.ac.be/~aderaema/vibrations/02-Definition_and_Scope.pdf · Acoustics: Definition and Scope Jean-Louis Migeot

© 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











What is a sound ?

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


Mean value

The mean value is either the atmospheric or the hydrostatic pressure

Atmospheric pressure changes with altitude

Hydrostatic pressure

changes with depth


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]

)


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]

)


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]

)


100 dB

160 dB

Time (arbitrary units)

Time (arbitrary units)

Tota

l pre

ssu

re (

[Pa]

) To

tal p

ress

ure

([P

a])


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)


A typical (stereo) sound recording


Range of audible frequencies

../../../DataMovie/20Hz to 20kHz (Human Audio Spectrum).mp4


Noise (negative) vs. sound (general)


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


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











Why acoustics ? Noise is annoying !


Why acoustics ? Noise performance is a purchase criteria !


Why acoustics ? Stringent standards apply !

© CRITT M2A


European Pass-by noise regulation

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

2016


Why acoustics ? Noise performance may mean success or failure !











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


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











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


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/


Sonoluminescence

Felipe Gaitan Larry Crum


Sonochemistry: improving chemical yield with ultrasounds

© Jean-Louis Migeot, ASA, 1998


Acoustic streaming

Olivier Dahlem &

Véronique Halloin (1998)


Science, scientists and engineers in motion pictures ...











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


Aero-acoustics

© ACTRAN / Free Field Technologies


Vibro-acoustics












Ultrasounds – Non-destructive Testing


Ultrasounds in Production Engineering

Emulsification

Homogenization

Welding

Cleaning


Ultrasounds – Medical Applications

Echography

Cautery

Lithotripsy


Breaking glass …

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

../../../DataMovie/Fischetti/Verre brisé.MOV


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


Calculus’ sonic weapon

Tintin, The Calculus Affair © Hergé - Moulinsart












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


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


Sense of hearing – Auditory Transduction

Brandon Pletsch


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


Bio-acoustics: snapping shrimp


Room and building acoustics

© MJM ACOUSTICAL CONSULTANTS INC © DOUGLAS MICHAEL VERSAGLI


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


© http://www.hearingaidopinion.com


Underwater acoustics: civil applications

Acoustic thermometry

Seafloor survey

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


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


Transduction, metrology, signal processing

Microphones, hydrophones, intensity probes

Active materials:

piezo-electric

magneto-strictive

electro-strictive

Measurement techniques:

sound measurement

intensimetry

acoustic holography


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.


Get your hands dirty !


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



1. What is a sound ?

2. Definition of acoustics

3. Why is acoustic so important ?

4. The wide field of acoustics





Chapter 2 Acoustics: Definition and Scope Jean-Louis Migeothomepages.ulb.ac.be/~aderaema/vibrations/02-Definition_and_Scope.pdf · Acoustics: Definition and Scope Jean-Louis Migeot

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