[701-0662-00 V] Environmental Impacts, Threshold Levels...

D-USYS • M. Brink • Environmental Impacts - Noise Part 1 Slide 1

[701-0662-00 V]

Environmental Impacts, Threshold Levels and

Health Effects

Lecture 7: Noise - Part 1 (01.04.2020)

Mark Brink

ETH Zürich

D-USYS

Homepage:

http://www.noise.ethz.ch/ei/

http://www.noise.ethz.ch/ei/


EmissionPerception

Effects

Limitation

AssessmentNoise abatement

Rating of noise

Noise regulation

(policy)

Immission

Sound & Noise

Topics of the next six lectures

Hearing


Overview of today’s lecture

► Physical basics of sound

► Sound generation, propagation, and perception (short intro)

► Frequency and wavelength

► Types of waves

► Sound pressure and sound pressure level

► Time and frequency domain

► The Decibel (dB)

► Physiological basis of hearing

► Anatomy of the ear

► Outer ear, middle era, inner ear

► Theories of auditory perception

► The cochlea

► Perceptual organization of sound


Physical basics of sound


Sound generation, propagation, and perception

What is sound?

• Sound is a disturbance that propagates through a medium

that has properties of inertia (mass) and elasticity.

• The medium by which the audible waves are transmitted

is air or water, or even solid bodies (e.g. a wall, a window,

the ceiling of your apartment...)

• Sound propagation is simply the molecular transfer of

motional energy (Hence: sound cannot pass through a

vacuum).



How is it generated?

• By mechanical motion, e.g. from a loudspeaker

membrane, from a vibrating string... etc.

• If the motion is periodical, the sound has (one or

more) distinguishable frequencies

waveform of one second of sound

waveform of 12 seconds of sound



Why can we hear it?

• Because the energy contained in a sound wave puts

the eardrum into vibrational motion

• the eardrum translates the energy of the wave trough

the ossicles of the middle ear onto the cochlea in the

inner ear and the cochlear hair cells

• the hair cells produce neuronal action potentials

which travel through the auditory nerve to the brain

• ... the brain interprets these action potentials as

"sound"

• ... more about auditory perception will follow soon..


Sound generation and propagationSound as longitudinal compression wave


c

f CAir ≈ 340 m/s

CWater ≈ 1400 m/s

place x

pre

ssu

re c

han

ge

Sound generation and propagation

Wavelength and frequency

Propagation speeds:

standard pitch 'A' (440 Hz) → λ = 0.77 m (in air)


wavelength (λ, lambda)

movement

of air moleculesmovement

of tines

tuning fork

sound propagation

high pressurelow pressure

sound pressure

atmospheric pressure

place

medium (air, water)

Sound generation and propagation

Summary


Types of sound waves (in the time and frequency domain)

4 8 12 16 20

4 8 12 16 20

4 8 12 16 20

Zeit [ms]

Sc

ha

lld

ruc

k [

Pa

]

31 125 500 2000 8000

31 125 500 2000 8000

31 125 500 2000 8000

Frequenz [Hz]

Te

rzb

an

dp

eg

el

[dB

]

Pure tone ("Reinton")

Complex sound ("Klang")

Noise ("Rauschen")

white: pink:

So

un

d p

res

su

reS

ou

nd

pre

ss

ure

So

un

d p

res

su

re

Time [ms] Frequency [Hz]

440 Hz

880 Hz


Time domain: one wave

-4

-3

-2

-1

0

1

2

3

4

Wave #1

Time

So

un

d p

ress

ure


Time domain: two waves

-4

-3

-2

-1

0

1

2

3

4 Wave #1

Wave #2

Time

So

un

d p

ress

ure


Time domain: three waves

-4

-3

-2

-1

0

1

2

3

4Wave #1

Wave #2

Wave #3

Time

So

un

d p

ress

ure


Time domain: the sum signal

-4

-3

-2

-1

0

1

2

3

4Wave #1

Wave #2

Wave #3

Sum signal

Time

So

un

d p

ress

ure


Frequency domain: the spectrum of the sum signal

FFT spectrum of the sum signal

Mag

nit

ud

e

Frequency

Wave #3

Wave #2

Wave #1

../../A-Sounds and Movies/Demo on wave summation and frequency decomposition.xls


Demo-Excel sheetdownload at www.noise.ethz.ch/ei



Range of frequencies

audible frequency

range


Sound pressure - time courseS

ou

nd

pre

ss

ure

p in

Pa

atmospheric pressure (ca. 100‘000 Pascal [Pa])

1 Pa = Force of 1 Newton per square meter = 1 N/m2

Time t

Sound pressure fluctuations are very small in

relation to the standing atmospheric pressure


Peff = Effektivwert = Root mean square (RMS)

Sc

ha

lld

ruc

k p

in

Pa

Zeit t

Schalldruck pi zum Zeitpunt ti in Pa

atmosphärischer Luftdruck

Root mean square value

Atmospheric pressure

Sound p

ressure

in P

a

Sound pressure in Pa

ger. “Effektivwert”

1RMS =

2for a sine wave:

Root Mean Square (RMS) value= a measure of energy of a sound wave


Transmission, Reflection and Absorption


Anechoic chamber (A lot of absorption, no reflections)


Echo chamber (No absorption, a lot of reflections...)

Echo chamber at Empa in Dübendorf


Sound pressure: Pressure fluctuations in the air that occur in

a point in space as the sound pressure waves travel

Unit: Pascal (Pa) = 1 N/m2

→ depending on the location of the receiver relative to source

Sound power: Sound energy that a sound source produces

per time unit

Unit: Watt

→ Independent of the location of the receiver

Sound pressure and sound pressure level


Sound pressure level Lp [in dB]: is a logarithmic

measure of the sound pressure of a sound relative to a

reference value. It indicates “how many times” larger is

the measured sound pressure relative to the pressure at

the hearing threshold

Unit: Decibel [dB]

Reference pressure p0: 0.00002 Pa (= Hearing threshold @ 1000Hz)

Threshold of pain: 20 Pa

2

10 2

0

pL 10 log

p

[dB]

Sound pressure level

Note: p is the RMS value in Pascal


Sound

pressure [Pa]

Reference sound

pressure [Pa]

Ratio of

squares

Logarithm Level

[dB]

0.00002 0.00002 1 0 x 10 = 0

0.0002 0.00002 100 2 x 10 = 20

0.002 0.00002 10000 4 x 10 = 40

0.02 0.00002 1000000 6 x 10 = 60

0.2 0.00002 100000000 8 x 10 = 80

2 0.00002 10000000000 10 x 10 = 100

20 0.00002 1E+12 12 x 10 = 120

200 0.00002 1E+14 14 x 10 = 140

Threshold of pain

Hearing threshold

Calculation of the sound pressure level

Bel Deci-bel

Namesake: A. Graham Bell


So

un

d p

ressu

re l

evel

0

20

40

60

80

100

120

140

160

[ Pa ] [ W/m2 ]

10-12

10-10

10-8

10-6

10-4

0.01

1

100

1000

Whisper

Acute irreversible damage

Threshold of pain

Danger to hearing

Speech understandability

Hearing threshold

[ dB ]

Effects:

0.00002

0.0002

0.002

0.02

0.2

2

20

200

2000

So

un

d in

ten

sit

y

Decibel scaleS

ou

nd

pre

ssu

re

Firecracker

Jet taking off

Rock concert

Mp3 player

Rehearsal room

Jackhammer

Noisy road traffic

Conversation

Concert hall (empty)

Source:


80 dB 80 dB+ = 83 dB

Summation:

Averaging:

0 dB + 0 dB = 3 dB

Decibel arithmetic

n

N0.1 L

10

n 1

L 10 log 10

n

N0.1 L

n 1

10

10

L 10 logN


Changes of sound pressure levelQualitative perception

Change of level Perception

1-2 dB barely recognizable change

2-5 dB recognizable change

5-10 dB well recognizable change

10-20 dB large, convincing change

> 20 dB very large change

440 Hz, each tone 1 dB lower




Physiology of hearing


bone conduction

air

conduction

Cochlea

eardrum

ear canal

equilibrium organ

Eustachian

tube

Anatomy of the ear


outer ear middle ear inner ear

eustachian tube

ossicles

(ger. "Gehörknöchelchen")

cochlea

eardrum

oval window

round window

sound pressure

Anatomy of the ear

http://www.musik-service.de/event-tr-8-prx395679770de.aspx


mastoid

Comparison of the perception of

sounds, as transmitted by air or

by bone conduction (through

mastoid).

Procedure:

(1) Put tuning fork on mastoid

When the tone disappears...

(2) hold tuning fork close to the ear

Judge result:

If tone is still audible → everything ok

if not, → Conductive hearing loss

(1)

(2)

Rinne test


Stirrup (tiniest bone of

skeleton)

eardrum

roundwindow

oval window

basilarmembrane

Anvil (ger. Amboss)

Stirrup (ger. Steigbügel)

Hammer (ger. Hammer)

pivotpoint

eustachian tube

Anatomy of the middle ear


inner ear (Cochlea)outer ear

airborne sound liquidborne sound

middle ear

eardrumoval window

Large area, weak force small area, strong force

Impedance matching

../../A-Sounds and Movies/Impedance matching.avi


Base

Apex

in mammals: spiral form

in birds, reptiles: stretched out

Inner ear: cochlea

round window

oval window

../../A-Sounds and Movies/Hearing Summary.avi


Resonance in the Cochlea („place coding“)

high tone

low tone

von Helmholtz

von Békécy

Place theory of pitch perception

http://upload.wikimedia.org/wikipedia/commons/c/c7/Hermann_von_Helmholtz.jpg


Basilar membraneTraveling wave

http://147.162.36.50/cochlea/cochleapages/overview/twhi.htm


Basilar membraneTraveling wave characteristics

• The wave always starts at the base of the cochlea

and moves towards the apex

• Its amplitude changes as it traverses the length of

the cochlea

• The position along the basilar membrane at which

its amplitude is highest depends on the frequency

of the stimulus


Apex

Base (oval window)

440 Hz

880 Hz

1320 Hz

low frequencies

high frequencies

outer

ear

middle

ear

Basilar membraneFrequency decomposition

stiff, narrow

less stiff, wider


../../A-Sounds and Movies/Cochlear animation (Low).mp4


oval window

round window

basilar membrane

Cross section of cochlea, organ of Corti

../../A-Sounds and Movies/Organ of Corti - short version.avi




“The movie shows an outer hair cell which has been patch clamped using a whole cell

recording pipette at its basal end. This allows the membrane potential of the cell to be

varied. The low frequency envelope of RatC is played into the stimulus input socket of

the patch amplifier, with a peak-to-peak amplitude of about 100 mV. The hair cell

changes it’s length.

Source: http://www.physiol.ucl.ac.uk/ashmore/

outer hair cellsinner hair cells

The “dancing hair cell” (Jonathan Ashmore, 1987)

../../A-Sounds and Movies/Dancing hair cell.mpeg


Sound localization cuesInteraural time delay

Interaural level difference

Convolutions of the outer ear


1

2

3

4

5

6

7

"Gestalt"-Principles of auditory perception (Examples)

Auditory figure-ground perception

http://de.wikipedia.org/wiki/Bild:FrereJacques1pt.png

http://de.wikipedia.org/wiki/Bild:FrereJacques1pt.png

Date post:	07-Aug-2020
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