byDr.Kadim Karim Mohsen Ali

Thi-Qar UniversityCollege of Engineering)

2012

Analysis of Penetration of Noise Waves to the Human Body

الضوضاءo ( : � هونا األرض على يمشون الذين الرحمن وعباد تعالى . قال

-) الفرقان سالما� قالوا الجاهلون خاطبهم 63وإذاo - ) ( : صوتك من واغضض مشيك في واقصد تعالى قال

19لقمانo الله رسول أراد ( وعندما الناس ص) لتبليغ طريقة اختيار

ورفض ذلك في أصحابه استشار الصالة وقت دخولأو الطبول أو الناقوس باستعمال بعضهم اقتراحاتإلى أدعى ألنه اإلنسان بصوت األذان واختار األجراس،

ألنه ألدائه بالًال� واختار الصخب، عن والبعد والسكينة الهدوء � صوتا أندى

o  ،عباداته في الضوضاء إحداث عن ينهى اإلسالم كان وإذاالتلذذ هدفسوى بغير الضجة يحدثون الذين بهؤًالء بالك فماأو سياراتهم، زمور إطالق أو الناسبصراخهم بإيذاء والتمتعوسواها التسجيل آًالت أو لمذياعهم الصوت مكبرات رفعهذا كل يريدون، ًال ما سماع على وإجبارهم جيرانهم وإزعاجوأقرتها اإلسالم احترمها التي الشخصية الحرية على تعد\

الدولية .الشرائعo مريضفي من كم الضجيج، يحدثون الذين هؤًالء يعلم أًال ثم

مضطربفي مسن شيخ أو والنوم، الراحة إلى يحتاج البيوتوالمذاكرة الدراسة إلى يحتاج علم طالب من أو . نومه،

Objective of the Work

What is Sound and what is Noise?

o The word noise is derived from the Latin word NAUSES which means "seasickness" the unpleasant sounds made by seasick passengers or sailors

o Britannica encyclopedia defines  Noise as  Unwanted sound  and U.S. Encyclopedia as Undesirable sound  

o From the legal view point may be defined as wrong pollution  is from the air, causing a material wounding of the right of individuals

o Noise is a form of energy which is emitted by a vibrating body and transmitted by pressure fluctuation which the human ear can detect and on reaching the ear causes the sensation of hearing through nerves.

o When one is speaking, the vibrating of vocal chords set air particles into vibration and generate pressure waves in the air, the person nearby may then hear the sound of the speech when the pressure waves are perceived by the ear.

o Sound can also travel through other acoustic media, such as water or steel or Gases

o Sounds produced by all vibrating bodies are not audible. The frequency limits of audibility are from 20 Hz to 20,000 Hz.

<20Hz 20Hz to 20000Hz > 20,000Hz

Infrasonic - inaudible sonic-Audible Ultrasonic - inaudible

Human hearing and Frequency

0 20 Hz 20 kHz 5 MHz

Animals that can hear altrarasonic sound oFish  oDogs oWhalesoSnakesapplication seismographs use for monitoring earthquakesAnimals that can hear infrasonic sound oBatsoElephantsapplicationSonarUltrasonic welding Ultrasonic disintegration bacteria

Noise health effects  consequences exposure to elevated sound levels.oTemporary and sometimes permanent hearing lossoPresbycusisoHypertensionoHeart diseaseoTinnitusoAnnoyance and sleep disturbanceoChanges in the immune system oBirth defects , exposure of the pregnant woman in trouble and become unstable neurological condition which affects the fetusoIschemic oVasoconstriction and other cardiovascular impactso Impairment

o Stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors.

o Human life decrease from 8 to 10 yearso Mental Autismo Excess secretion of certain glands cause high blood sugaro The headaches and fatigue and insomniao Stomach ulcerso Blood pressure in school children in the vicinity of the airport is

higher than the school children away with him, and their speed in solving mathematical problems less, and at their failure to resolve the matter quickly throw aside what they are not trying to re-solve.

o Speech interference: if children who are learning to read cannot understand their teacher

o Mental collapse

The power of jet noise

The power of jet noise

A new study was published present a link, between jet noise and mental illness. The study find that the rate of mental illness hospital admission was 20 percent higher in Inglewood , where the los Angeles International Airport is located , than in El Segundo , about five miles away.The researchers chose El Segundo for comparison because census data showed its residents to be very much like those of Inglewood in age, race and Socio-economic background. The main difference was the jet noise level: above 90 decibels in Inglewood, 60 to 65 decibels in El Segundo.A study by British psychiatrists produced similar results .Mental hospital admission were 31 percent higher among people living close to London’s Heathrow Airport than among those who lived farther away.

1- Hearing loss is the number one of disability of the world

2- hearing loss is the most preventable disability in the world

3- the number of people who need hearing aid 25 million

4- 15 every 1000 people under 18 yrs have hearing loss

5- 3 out of 100 school children are affected by hearing loss

6- percentage of people loss their hearing before age of 3 is 5.4 %

7- percentage of people who loss their hearing between 3 to18 yrs. is 14.2%

8- percentage of people who loss their hearing at age of 19 yrs. is 76.3 %

General statistics

Sources of Noiseo Vehicles, trains, aircraft o Radio and television o Children playing o Household gadgetso Road traffic o Transportation systemso Construction work - construction of buildings, highways, and

streets cause a lot of noise, due to the usage of air compressors, bulldozers, loaders, dump trucks, and pavement breakers.

o Industrial noise o Boilers, generators, air conditioners, fans, plumbing and vacuum

cleanerso Prolonged exposure to loud music

o Sound can be produced by many other sources - man's vocal cord, a running engine, a vibrating loudspeaker diaphragm, an operating machine tool, and so on.

Unpleasant, unwanted, disturbing sound is generally treated as Noise

The nature of noiseoNoise , phenomena of vibration, travels in wave patterns through solids, liquids and gases.oThe waves, caused by vibration of the molecules, follow sine functions, characterized by the amplitude and wavelength (or frequency)oNoise waves of equal amplitude with increasing frequency from top to bottom

o When the medium is the air and pressure fluctuations falls on the air the hearing is produced

o Sound is form of energy and is transmitted by collisions of air molecules one against the next and so on.

o It may represented as a series of compressions and refractions in the density of air molecules which travel away from source

Sound is a disturbance that propagates through a medium having properties of inertia ( mass ) and elasticity. The medium by which the audible waves are transmitted is air.

Basically sound propagation is simply the molecular transfer of motional energy. Hence it cannot pass through vacuum.

Frequency: Number of pressure cycles / time

also called pitch of sound (in Hz)

Guess how much is particle displacement?? 8e-3nm to 0.1mm

The disturbance gradually diminishes as it travels outwards since the initial amount of energy is gradually spreading over a wider area. If the disturbance is limited to one dimension ( tube / thin rod), it does not diminish as it travels ( except loses at the walls of the tube )

Classification of noise

#according to frequency

High frequency Saw sound

Law frequency Grinders sound

White noise Boiler sound

#according to duration

Continuous noise Spinning & weaving

industry

Interrupted noise Traffic noise

Impulse & impact noise

explosions

Combines the noise pulse and random noise and has a spectral bandwidth over a flat area of influence White Noise is a set of noise or sounds that brings together all the frequencies that humans can hear, which is located in the area of the frequency spectrum between 20 to 20000 Hz

White noise 

Noise problemConsists of three inter-related elementsosourceoreceiver otransmission path. Transmission path is usually

the atmosphere through

which the sound is propagated,

but can include the structural materials of any building containing the receiver

Characteristics of noise and the Decibel Scale

Characteristics C/CS of noise and the Decibel Scale

1- Frequency of noiseo Is the number of pressure fluctuation per second o Measured in (Hz) oThe higher the frequency, the more high-pitched oThe sounds produced by drums have much lower frequencies than those produced by a whistleo

2- Loudness oA loud noise usually has a larger fluctuation and a weak one has smaller pressure fluctuation.oLoudness of a sound is depends on the amplitude of the fluctuations above and below atmospheric pressure and frequency oAre expressed in Pascal (Pa) oAmplitude is the magnitude of pressure fluctuations compared with atmospheric pressure (1000 millibars =1bar= 105 N/m2 (Pa))

Threshold of Hearing (20x10-6 Pa=20µPa) Threshold of pain(sensation of pain) (2000 Pa = 2x109 µPa) 1000000 times larger

Range of Pressure

To express noise in terms of Pa is quite inconvenient because we have to deal with numbers from as small as 20 to as big as 2,000,000,000.

LOUDNESS INDEX

Loudness Level (Phon) useful for comparing two different frequencies for equal loudness

The phon is a unit of loudness level for pure tones

 1 phon is equal to 1 dB of SPL at a frequency of 1 kHz

0Phon: threshold of hearing

Sone A unit of perceived loudness equal to the loudness of a 1000-Hz tone at 40 dB above threshold

Direct relationship between Loudness Level ‘P’ (Phons) and Loudness Index ‘S’ (Sones)

8 Sones is twice as loud as 4 Sones

40

102P

S

Sound pressure level Bels and decibels

Quantifying Sound

Root Mean Square Value (RMS) of Sound Pressure

1

22

0

1[ ( )]

T

p p t dtT

o The ‘rms’ pressure is the square root of this time-averaged value. o In calculation of the ‘rms’, the values of sound pressure are

squared to make them all positive and time-averaged to smooth out fluctuation.

Sound Power level

Sound Intensity : Average rate of energy transfer per unit area

22

W/m 4

WI

r

22 2

0

4 4 Watt p

W r I rc

Sound Power Level: 1010logref

WSWL

W

dB

A sound in free space radiating sound uniformly in all directions as a sphere of radius r SPL=SWL-10 log 4πr2

Speed of Light: 299,792,458 m/s Speed of sound 344 m/s

For air, 0c 415Ns/m3 so that 0.16 dBSPL IL

Reference Power Wref =10-12 Watt (0dB)

Peak Power outputPeak Power output:

Female Voice – 0.002W, Male Voice – 0.004W,

A Soft whisper – 10-9W, An average shout – 0.001W

Large Orchestra – 10-70W, Large Jet at Takeoff – 100,000W 15,000,000 speakers speaking simultaneously generate 1HP

Situationand

sound source

sound powerPac

watts

sound powerlevel SWL

dB re 10−12 W

Rocket engine 1,000,000 W 180 dB

Turbojet engine 10,000 W 160 dB

Siren 1,000 W 150 dB

Heavy truck engine orloudspeaker Rock concert

100 W 140 dB

Machine gun 10 W 130 dB

Jackhammer 1 W 120 dB

Excavator, trumpet 0.3 W 115 dB

Chain saw 0.1 W 110 dB

Helicopter 0.01 W 100 dB

Loud speech,vivid children

0.001 W 90 dB

Usual talking,Typewriter

10−5 W 70 dB

Refrigerator 10−7 W 50 dB

o Unless there is a 3 dB difference in SPL, human beings can not distinguish the difference in the sound

o Sound is perceived as doubled in its loudness when there is 10dB difference in the SPL.

SOUND BITS

Typical suburban sound and their levels

Levels in decibels calculationoIt is practical measure of the amplitude of pressure fluctuations. oThe human ear responds to a very wide range of intensities from the threshold of hearing TOH 20 µPa at 0 dB to the threshold of pain –feeling (loudest sound) TOP 20 X106 µPa is 120 dB.

COMBINATION OF SEVERAL SOURCES

Total Intensity produced by several sources

IT=I1+ I2+ I3+…

Usually, intensity levels are known (L1, L2,…)

31 2

1010 1010 10 10 10 ...LL L

TL Log

1210

10T

T

IL Log

1

1 1210

10

IL Log

Sound Intensity

Addition of sound or Noises (decibels) levels Combination of sounds

adding 60 decibels to 60 decibels gives 63 decibels. The following formula explains the general principle of adding sounds on the decibel scale.

One can use the above formula to add three sounds together - 60 dB, 65 dB and 70 dB.

Addition of sound or Noises )decibels( levels Combination of sounds

Addition of sound levels can also be done simply using the following chart.

Let us try adding the three sounds of 60 dB, 65 dB and 70 dB by using the chart. In using the Chart, two sounds are added together first. The resultant sound is then added to a third sound and so on. Please

For e.g. The effective sound level from two air conditioners 60 dB (A) each, say is not 60 + 60 = 120 dB (A) but 60 + 3 = 63 dB(A).Similarly, the effective sound level of 57 dB, 63 dB, 63 dB, 66 dB and 69 dB is 72 dB. The computation is illustrated below.

Noise AttenuationoProcess of removing noise from a signal. oor is the reduction in amplitude and intensity of a signal.oAttenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/m dB/km, etc) and is represented by the attenuation coefficient of the medium.

o They are used to cover the audio frequency spectrumo They have lower frequency fL and upper frequency fU o A normal human ear is able to hear sounds with frequencies

from 20 Hz to 20,000 Hz. called the audible frequency range.o The sounds we hear of various frequencies. o The entire audible frequency range can be divided into 8 or

24 frequency bands known as octave bands or 1/3 octave bands

o Every 3 1/3 octave bands comprise one octaveo A particular sound or noise can be seen to be having different

strengths or sound pressure levels in the frequency bands

Frequency analysis bands

Instruments for analysing Noise

Constant Bandwidth Devices

Proportional Bandwidth Devices

2U

L

f

f

c U Lf f fAbsolute Bandwidth ∆f= fU - fL

1/32U

L

f

f

1/102U

L

f

fFor 1/10th Octave filters,

2nU

L

f

f

n=1 for octave band,

n=3 for 1/3rd octave

octave bandy center frequency

Octave Filters

Frequency Weighting Networks

Frequency Weighting scales

o A-weighting dB (A) : adjusts overall scale so it better matches what the human ear would hear

o C-weighting dB (C) : adjusts scale for loud or low frequency sounds

o B-weighting dB (B) : adjusts by factors that are “in between” the A-weighted factors and C-weighted factors (rarely used)

o D-weighting dB (D) : for Aircraft Noise

o A-weighting dB (A) : adjusts overall scale so it better matches what the human ear would hear

o C-weighting dB (C) : adjusts scale for loud or low frequency sounds

o B-weighting dB (B) : adjusts by factors that are “in between” the A-weighted factors and C-weighted factors (rarely used)

o D-weighting dB (D) : for Aircraft Noise

The responses of the sound level are modified with frequency-weighting networks that represent some responses of the human ear.

Weighting Characteristics

A-weighting: 40Phon equal loudness level contour

C-weighting: 90Phon equal loudness level contour

D-weighting for Aircraft Noise

Sound propagation

o Most sounds or noises we encountered in our daily life are from sources which can be characterized as plane or point or line  sources.

o Plane source -Points of same sound pressure (for example, in the cross-section of the duct) form parallel planes

o If a sound source produces spherical spreading of sound in all directions, it is a point source

o For a point source, the noise level decreases by 6 dB per doubling of distance from it.

o If the sound source produces cylindrical spreading of sound For a line source, the noise level decreases by 3 dB per doubling of distance from it

Radiation from Source

Radiates sound waves equally in all directions (spherical radiation)

W: is acoustic power output of the source;

Constant term Depends on distance from source

22 2

0

4 4 Watt p

W r I rc

Point Source (Monopole)

If the point source is placed on ground,

it radiates over a hemisphere,

the intensity is then doubled and

Line Source

(Long trains, steady stream of traffic, long straight run of pipeline, stream of motor vehicles on a busy road at a distance)

10 101210log 10log

10

WIL r

Sound sources whose dimensions are small compared to the wavelength of the sound they are radiating are generally omni-directional;

otherwise when dimensions are large in comparison, they are directional

DIRECTIVITY OF SOUND SOURCE

Directivity of the source must be taken into account to calculate level from the source power

Environmental effect

Environmental Effects

Wind Gradient

Temperature Gradient

Hot Sunny Day

Cool Night

Velocity Gradient (-)

Wind & Temp effects tend to cancel out

Increase or decrease of 5-6dB

Hearing Damage Potential to sound energy

depends on its level & duration of exposure

Equivalent Continuous Sound Level (Leq)

1010

1

10 10jLN

eq jj

L Log t dB

tj : Fraction of total time duration for which SPL of Lj was measured

Total time interval considered is divided in N parts

with each part has constant SPL of Lj

100 70

10 1010

1 710 10 10 91

8 8eqL Log dB

Regulations:

Basis of 90dB(A) for 8hr a day.

ISO(1999): Increase in SPL from 90 to 93dB(A) must reduce time of exposure from 8 to 4 hours

OSHA: with every 5dB(A) increase, reduce exposure by half

Occupational Safety and Health Administration

Errors of the order of 6dB around 400Hz due to reflections

USEPA United States Environmental Protection Agency, is an agency of the federal government of the united charged with protecting human health and the environment,oThere are direct links between noise and health. o Noise pollution harmfully affects the lives of millions of people.oNoise pollution can damage physiological and psychological health.oHigh blood pressure, stress related illness, sleep disruption, hearing loss, and productivity loss are the problems related to noise pollution.oIt can also cause memory loss, severe depression, and panic attacks.The World Health Organization (WHO) Organization stated that “Noise must be recognized as a major threat to human well-being”

Perception of noise- Human Ear

The ear comprises of three parts:

(a )the outer or external ear,)b( the middle ear, and)c( the inner ear.

The outer ear

The middle ear

The Inner Ear

Response of the Human Ear to Noise

oSound with a high frequency is said to be high-pitched sound women & children, scream, fire-alarm, siren, whistle, airplane

oSound with a low frequency is low-pitched. grass, flowers, worm

Audible range of the human earAudible range of the human ear

International conventions and conference

International conventions and conference

International conventions The Control of Noise at Work Regulations 2005

(Commencement date April 2006) The Health & Safety at Work etc. Act 1974 C148 Working Environment (Air Pollution, Noise and

Vibration), 1977Conference International Noise Conference Australia 2011 International Noise Conference USA Tour 2010 International Noise Conference Euro Tour 2009 International Noise Conference SXSW Austin2009 International Noise Conference Spokane WA 2008 International Noise Conference Seoul South Korea 2008 International Noise Conference Toronto  2008 International Noise Conference USA Tour 2008

o Planting bushes and trees (e.g. Tamarind , Banyan , Neem , Casoria ) in and around sound generating sources

o Regular servicing and tuning of automobiles , lubrication of the machinery and servicing

o Buildings can be designed with suitable noise absorbing material for the walls, windows, and ceilings.

o Workers should be provided with equipment such as ear plugs and earmuffs for hearing protection.

o Soundproof doors and windows o Regulations should be imposed to restrict the usage of play loudspeakers in crowded

areas and public places.o Factories and industries should be located far from the residential areas.o keep schools and hospitals all sources of noise.o Keep cities and populated areas airports a distance of not less than 30 km.o railway lines and highways Must be away from residential areas as possible.o Community development or urban management should be done with long-term

planning, along with an aim to reduce noise pollution.o Social awareness programs should be taken up to educate the public about the causes

and effects of noise pollution. o Acoustic insulation by good glazing can cut down noise

Prevention of noise induced hearing loss

Medical measuresEnvironmental measures

# reduce exposure to noise

#substituation of noisy machines or noisy operation by less noisy one

# segregation of noisy machines in remote places

# isolation of noisy machines by using sound absorbing materials to reduce noise

* Pre employment audiogram

* Periodic medical examination for hearing levels

* Personal protective devices as ear plugs & ear muffs

* Health education about hazardes of noise

Different types of noise barriersDifferent types of noise barriers

Vertical vegetation wallsVertical vegetation walls