Presentation on theme: "by Dr.Kadim Karim Mohsen Ali Thi-Qar University College of Engineering) 2012 Analysis of Penetration of Noise Waves to the Human Body."— Presentation transcript:
by Dr.Kadim Karim Mohsen Ali Thi-Qar University College of Engineering) 2012 Analysis of Penetration of Noise Waves to the Human Body
الضوضاء o قال تعالى : ( وعباد الرحمن الذين يمشون على الأرض هوناً. وإذا خاطبهم الجاهلون قالوا سلاماً )- الفرقان 63 o قال تعالى : ( واقصد في مشيك واغضض من صوتك ) - لقمان 19 o وعندما أراد رسول الله ( ص ) اختيار طريقة لتبليغ الناس دخول وقت الصلاة استشار أصحابه في ذلك ورفض اقتراحات بعضهم باستعمال الناقوس أو الطبول أو الأجراس، واختار الأذان بصوت الإنسان لأنه أدعى إلى الهدوء والسكينة والبعد عن الصخب، واختار بلالاً لأدائه لأنه أندى صوتاً o وإذا كان الإسلام ينهى عن إحداث الضوضاء في عباداته، فما بالك بهؤلاء الذين يحدثون الضجة بغير هدف سوى التلذذ والتمتع بإيذاء الناس بصراخهم أو إطلاق زمور سياراتهم، أو رفع مكبرات الصوت لمذياعهم أو آلات التسجيل وسواها وإزعاج جيرانهم وإجبارهم على سماع ما لا يريدون، كل هذا تعدٍّ على الحرية الشخصية التي احترمها الإسلام وأقرتها الشرائع الدولية. o ثم ألا يعلم هؤلاء الذين يحدثون الضجيج، كم من مريض في البيوت يحتاج إلى الراحة والنوم، أو شيخ مسن مضطرب في نومه، أو من طالب علم يحتاج إلى الدراسة والمذاكرة.
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. 20,000Hz Infrasonic - inaudible sonic-Audible Ultrasonic - inaudible
Human hearing and Frequency 0 20 Hz 20 kHz5 MHz
Animals that can hear altrarasonic sound oFoF ish oDoD ogs oWoW hales oSoS nakes application seismographs use for monitoring earthquakes Animals that can hear infrasonic sound oBoB ats oEoE lephants application Sonar Ultrasonic welding Ultrasonic disintegration bacteria
Noise health effects consequences exposure to elevated sound levels. o Temporary and sometimes permanent hearing loss o Presbycusis o Hypertension o Heart disease o Tinnitus o Annoyance and sleep disturbance o Changes in the immune system o Birth defects, exposure of the pregnant woman in trouble and become unstable neurological condition which affects the fetus o Ischemic o Vasoconstriction and other cardiovascular impacts o Impairment
o Stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors. o Human life decrease from 8 to 10 years o Mental Autism o Excess secretion of certain glands cause high blood sugar o The headaches and fatigue and insomnia o Stomach ulcers o 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 Londons 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 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 Noise oVoV ehicles, trains, aircraft oRoR adio and television oCoC hildren playing oHoH ousehold gadgets oRoR oad traffic oToT ransportation systems oCoC onstruction 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. oIoI ndustrial noise oBoB oilers, generators, air conditioners, fans, plumbing and vacuum cleaners oPoP rolonged 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 noise oNoN oise, phenomena of vibration, travels in wave patterns through solids, liquids and gases. oToT he waves, caused by vibration of the molecules, follow sine functions, characterized by the amplitude and wavelength (or frequency) oNoN oise 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 Hz White noise
Noise problem Consists of three inter-related elements o source o receiver o transmission 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 noise o I s the number of pressure fluctuation per second o M easured in (Hz) oToT he higher the frequency, the more high-pitched oToT he sounds produced by drums have much lower frequencies than those produced by a whistle
2- Loudness o A loud noise usually has a larger fluctuation and a weak one has smaller pressure fluctuation. o Loudness of a sound is depends on the amplitude of the fluctuations above and below atmospheric pressure and frequency o Are expressed in Pascal (Pa) o Amplitude is the magnitude of pressure fluctuations compared with atmospheric pressure (1000 millibars =1bar= 10 5 N/m 2 (Pa))
Threshold of Hearing (20x10 -6 Pa=20µPa) Threshold of pain(sensation of pain) (2000 Pa = 2x10 9 µPa) 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 kHzdB of SPLkHz 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
Sound pressure level Bels and decibels
Quantifying Sound Root Mean Square Value (RMS) of Sound Pressure 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 Sound Power Level: dB A sound in free space radiating sound uniformly in all directions as a sphere of radius r SPL=SWL-10 log 4πr 2 Speed of Light: 299,792,458 m/s Speed of sound 344 m/s For air, 0 c 415Ns/m 3 so that Reference Power W ref = Watt (0dB)
Peak Power output Peak Power output: Female Voice – 0.002W, Male Voice – 0.004W, A Soft whisper – W,An average shout – 0.001W Large Orchestra – 10-70W,Large Jet at Takeoff – 100,000W 15,000,000 speakers speaking simultaneously generate 1HP
Situation and sound source sound power P ac watts sound power level SWL dB re W Rocket engine1,000,000 W180 dB Turbojet engine10,000 W160 dB Siren1,000 W150 dB Heavy truck engine or loudspeaker Rock concert 100 W140 dB Machine gun10 W130 dB Jackhammer1 W120 dB Excavator, trumpet0.3 W115 dB Chain saw0.1 W110 dB Helicopter0.01 W100 dB Loud speech, vivid children W90 dB Usual talking, Typewriter 10 5 W70 dB Refrigerator10 7 W50 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 calculation o It is practical measure of the amplitude of pressure fluctuations. o The 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 X10 6 µPa is 120 dB.
COMBINATION OF SEVERAL SOURCES Total Intensity produced by several sources I T =I 1 + I 2 + I 3 +… Usually, intensity levels are known (L 1, L 2,…)
Addition of sound or Noises (decibels) levels Combination of sounds 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 = 120 dB (A) but = 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 Attenuation o Process of removing noise from a signal. o or is the reduction in amplitude and intensity of a signal. o Attenuation 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 spectrum o They have lower frequency f L and upper frequency f U 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 octave o 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 Absolute Bandwidth f= f U - f L For 1/10 th Octave filters, n=1 for octave band, n=3 for 1/3 rd octave octave bandy center frequency
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.
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 termDepends on distance from source 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)
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 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 (L eq ) t j : Fraction of total time duration for which SPL of L j was measured Total time interval considered is divided in N parts with each part has constant SPL of L j
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, o There are direct links between noise and health. o Noise pollution harmfully affects the lives of millions of people. o Noise pollution can damage physiological and psychological health. o High blood pressure, stress related illness, sleep disruption, hearing loss, and productivity loss are the problems related to noise pollution. o It 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 o Sound with a high frequency is said to be high-pitched sound women & children, scream, fire-alarm, siren, whistle, airplane o Sound with a low frequency is low-pitched. grass, flowers, worm
Audible range of the human ear
International conventions and conference International conventions and conference
International conventions T he Control of Noise at Work Regulations 2005 ( Commencement date April 2006) T he Health & Safety at Work etc. Act 1974 C 148 Working Environment (Air Pollution, Noise and Vibration), 1977 Conference I nternational Noise Conference Australia 2011 I nternational Noise Conference USA Tour 2010 I nternational Noise Conference Euro Tour 2009 I nternational Noise Conference SXSW Austin2009 I nternational Noise Conference Spokane WA 2008 I nternational Noise Conference Seoul South Korea 2008 I nternational Noise Conference Toronto 2008 I nternational 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 measures Environmental 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