CHAPTER 4SOUND

Describe precisely relationship between man and its envirobnment on the aspect of sound, room acoustics and sound transmission.Learning Outcomes 1

Students would be able to:

Introduction to AcousticsObjectivesTo develop controlled environment for human comfort. Helps occupants realize the orientation and direction.

1.0 FrequencyWhat is frequency?The number of cycles per unit of time is called the frequency. For convenience, frequency is most often measured in cycles per second (cps) or the interchangeable Hertz (Hz) (60 cps = 60 Hz)1000 Hz is often referred to as 1 kHz (kilohertz) or simply '1k

The characteristic of sound

Frequency is related with a complete cycle , T through a formula:

For a wave to have velocity v and wave length (lamda) , frequency is given as: The range of human hearing in the young is approximately 20 Hz to 20 kHzthe higher number tends to decrease with age (as do many other things). It may be quite normal for a 60-year-old to hear a maximum of 16,000 Hz

2.0 Wave length

Wavelength, is the distance between 2 repeated waves. The length of a wave is measured in meter (m).When The frequency increases , the wavelength decreases.When the velocity of a sound increases, the wavelength also increases.

It means that wave length is direct propotion with velocity and reverse propotion with frequency.

2.0 Velocity

Moving distance in a second at fix direction.Unit SI in m/sSimbol From the wave behaviour, when wave lwngth is multiplied with frequency, it is the samae as the distance that sound moves in a second which is called velocity.Standard velocuty for sound in buildings is340 m/s

Example;For a sound that has a frequency of 340 m/s, What is the length of the wave?Given the frequency of the sound is 1000 m/s.

SOUND MEASUREMENTS

What is decibel?Sound level whether it is sound power level, Sound intensity level or Bel(B)One Bel indicates the ratio of 10 and 2 Bel is equal to 100 and so on. Any measurement using Bel will produce large number.

So the suitable unit is Decibel. Decibel is equal to 1/10 bel .So the number measured will be reduced.

SOUND PRESSURE MEASUREMENTSound Pressure P is an average atmosphere pressure which is caused by sound and the unit is Pascal (Pa).SOUND POWER MEASUREMENTThe total sound produce from a sound source and is measured in Watt(W).SOUND INTENSITY MEASUREMENTWhen a sound comes out from a source will reduce its intensity because the sound distributes to the vast hemispherical surface.

SOUND INTENSITY (I) MEASUREMENTPicture below shows the sound intensity at the center point of the sound source and distribute at the spherical surfaces where intensity reduces with distance.I IntensityUnit = W/mI p

Inverse relation ship between sound intensity and distance

SOUND LEVEL MEASUREMENTIt is comparison to the standard hearing level Sound Power Level

SWL = 10 log ( W/W) dB

Where; W = Sound Powerdalam WattW = Standard sound power 10 -12

SOUND LEVEL MEASUREMENTSound Intensity Level

SIL = 10 log ( I/I) dB

WhereI = Sound Intensity (w/m)I = Standard Sound Intensity 10 -12 W/m

SOUND LEVEL MEASUREMENTSound Pressure Level

SPL = 20 log ( P/P) dB

Where;P = Sound pressuredalam PaP = Standard Sound pressure 20 X10 -6 Pa

Calculation

QUESTION 1Value the Sound Power Level for a given power source of 50 X 10-3 watt. Use the standard sound power of 10 -12 Watt.

(107dB)

QUESTION 2A sound produces a sound intensity of 3.16 X 10-4 W/m . Calculate the Sond intensity level in dB. The standard intensity is valued at 10 -12 Watt.

(85dB)

QUESTION 3Measure the Sound Pressure Level of a machine which has a sound pressure of 7.96 X 10-2 Pa. Used the standard sound pressure of 20 X 10 -6 Pa

(72dB)

SOALAN 4Kirakan tekanan sebenar sebuah measin yang menghasilkan aras tekanan bunyi 55 dB.

(1.12 X 10 -2Pa)

QUESTION 4Calculate the Sound intensity of the given sound which has the sound Intensity level o101 dB. (0.0126 W/m)

QUESTION 5Measure the power of a machine that produce a Sound Power level of 75 dB.

(3.162 X 10-5 W)

Additional Sound Level Decibel cannot be added using normal additional calculation methods.Example 100dB + 100dB is not equal to 200dBBut sound intensity and sound pressure can be added using given formula:

Itotal = I + I Ptotal = P1 + P2

QUESTION 1Calculate the total sound intensity which is produces by 3 machines where each machines produces 70dB, 73dB dan 65dB?

QUESTION 34 machnes works simulteneously. Calculate the total sound pressure when each macine produce 85dB, 80dB 89dB and 90dB . Calculate the total SPL of the four machines.

Question 3A Factory has 2 machines which produce 100 dB and 95 dB sound level. Calculate the total sound pressure level in that factory.

Question 43 machines are positioned close to a discussion room. The sound intensity of each machines is 89dB, 85dB and 90dB. Calculate the total sound intensity of the machines when operated simulteneously.

Question 5For a sound that has a frequency of 440Hz with a velocity of 340 m/s, what is the wavelength of that sound?Question 6Calculate the intensity of a sound and sound intensity level for a sound that has a sound power of 3.14 X 10 -6 Watt. Given the value r = 5mQuestion 7If a machine has a sound intensity level of 76 dB. What is the sound power level of that machine that has a value r=2m.

Question 1The total SPL of an area which has 1 machine that produces 79 dB. When the machine is not in operation , the SPL measure is72 dB (background noise) in that area. Calculate the SPL of that machine.Question 3Find the difference in dB for the 2 machines that have the intensity value of 4.16 X 10 -3 W/m2 and 2.61 X 10 -4 W/m2.

Estimation measurement of any sound level ( addition)Differential value between 2 sources10 dB above6 9 dB4 5 dB3 dB2 dB1 dBSubtraction from the highest sound level 0dB1 dB2 dB3 dB5 dB7 dBdB subtraction- Estimation

For example:Source A = 98 dBSource B = 100 dBDifference between 2 sources100 dB 100 dB = 2 dBFrom the estimation table the Decibel additional measurement :

Difference : 2dB --Addition from the highest sound level= 2 dB

Highest value + 2 dB = 100dB + 2 = 102 dB

CALCULATIONQuestion 1Estimate the total sound level which are produced by 3 sources as given : 95 dB, 93 dB & 98 dB.Question 2Estimate the total sound level which are produced by 4 machines : 75 dB, 90 dB, 100 dB & 80 dB.

EAR COMPONENTS

NOISE AND ITS EFFECTSDefinition of noiseNoise is unwanted & loud sound. Noise can be produced by many sources - man's vocal cord, a running engine, a vibrating loudspeaker, an operating machine, and so on. Effects of noise to humanReduce/loss of hearingSpeech interference.Reduce work performancesSleep disturbanceDisturb healthDisturb health and way of life.Damage to the ears

NOISE EFFECT ON HUMAN DAILY LIFEIt can cause the voice of the speaker difficult to be heard.Difficult to understandImpression of direction is lost.Incease the % of sufferer Blood circulation problem Heart problemBalancing problemJeopardize the work quality. Lack of conteration / focus.Disturb deep sleepDepends on the age, gender and the quality of sleep factors.Temporary deafPermanent deaf

EFFECT OF NOISE TO HUMANSOUNDNOISEINTENSITYFREQUENCYSOUND DURATION/ EXPOSURE.TONE CONTENTSLOCATION OF THE NOISEDISTANCE OF SOUND SOURCEFactors that can convert sound to noise

INTENSITYHigh intensity sound will cause loud sound. FREQUENCYSound with high frequency level are easy to be heard by normal human ears. SOUND DURATION/EXPOSUREExposure to sound in a long time will cause disturbace of human life.LOCATION OF THE SOUNDSound source that is far from human is less disturbing.Source with several location will cause great disturbance.DISTANCE OF SOUND SOURCE.Indirect proportion with intensity.Sound source that is far cause less noise.TONE CONTENTSound with information cause less disturbance compare to sound that content unclear and not easy to understand.

METHODS OF EVALUATE THE ACOUSTIC INTERFERENCE/DISTURBANCEThere are a few index level in measuring the level of interference/disturbance(sound or vibration)ARAS GANGGUAN PERBUALAN (SIL) SPEECH INTERFERENCE LEVELKRITERIA KEBISINGAN (NC NOISE CRITERIAARAS BUNYISOUND LEVEL4. ARAS PENCEMARAN BUNYI (NPL) NOISE POLLUTION LEVEL

SOUND INTEFERENCE LEVEL (ARAS GANGGUAN PERBUALAN) (SIL)It describes how far a person can hear clearly in different back ground noise level.

This index measures the ability sound interferes the communication between 2 people in a room

SOUND INTEFERENCE LEVEL (ARAS GANGGUAN PERBUALAN) (SIL)The SIL graph shows the relationship between SIL and distance. The SIL index helps to determine the speech interference level when 2 people communicate at certain distances. 4 normal, raised, very loud or shouting voice to be understood.

Choosing an appropriate noise criteria is important when specifying acceptable levels of noise. Most organizations use a particular index based upon practical experience. Recommended maximum noise levels for different types of rooms and standards are indicated in the table below

Type of Room - OccupancyNoise Criterion - NC -Noise Rating - NR -db(A)Very quietConcert and opera halls, recording studios, theaters, etc.10 - 202025 - 30Private bedrooms, live theaters, television and radio studios, conference and lecture rooms, cathedrals and large churches, libraries, etc.20 - 252525 - 30Private living rooms, board rooms, conference and lecture rooms, hotel bedrooms30 - 403030 - 35QuietPublic rooms in hotels, small offices classrooms, courtrooms30 - 403540 - 45Moderate noisyDrawing offices, toilets, bathrooms, reception areas, lobbies, corridors, department stores, etc.35 - 454045 - 55NoisyKitchens in hospitals and hotels, laundry rooms, computer rooms, canteens, supermarkets, office landscape, etc.40 - 504545 - 55

NC index is widely used in measuring the disturbance of build environment (inside and outside of the buildings)

Index NC is widely used in measuring noise inside or outside of the buildings.NOISE CRITERIA (KRITERIA KEBISINGAN) (NC)(NC) is a single numerical index commonly used to define design goals for the maximum allowable noise in a given space.

The criteria curves define the limits of octave band spectra that must not be exceeded to meet occupant acceptance in certain spaces

NOISE CRITERIA (NC)

NC SURROUNDINGS ASSUMPTION< NC 25VERY QUIETNC 25 - NC35QUIETNC 35 - NC 45MODERATELY QUIETNC 45 - NC 50MODERATELY NOISYNC 50 - NC 55NOISYNC 55 - NC 70LOUD

Typical NC valuesApplicationNC Curve Conference rooms25 - 35Hospitals / Libraries30 - 40 General offices35 - 45Factories50 - 70

SOUND LEVELmeasure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noiseSound level meters The sound level depends on the distance between the sound source and the place of measurement, possibly one ear of a listener.The SOUND LEVEL METER measures the strength of sound. The unit is in decibels (dB) and is usually measured with a dB meter. The threshold of quiet sound is zero dB and the onset of painful sound is 100 dB

HEARING ASSUMPTION ON SOUND LEVEL

SOUND LEVELHEARING ASSUMPTIONAround 120 dBdeafeningaround 100dBVery loudSEKITAR 80loudSEKITAR 50quiet

HEARING ASSUMPTION ON SOUND LEVEL

SOUND LEVEL(dB)HEARING ASSUMPTION44-69Whispering & private talk50-75Normal voice56-81Loud voice62-87High voice68-93Shouts

the degree of loudness of annoying or physically dangerous noise in a persons environment, taken as a measurement.NOISE POLLUTION LEVEL (NPL)This pollution is increasing due to the rise in the utilization of heavy duty machineries of industrial facilities and vehicles.Noise pollution can affect health, yet the effects are very difficult to quantify. It is believed that persistent exposure to noise, especially at night, may lead to psychological distress

A guide to noise levels is:normal conversation 50 - 60 dB(A) a loud radio 65 - 75 dB(A) a busy street 78 - 85 dB(A) a heavy lorry about 7 meter away 95 - 100 dB(A) a pighouse at feeding time 110 dB(A) a chain saw 115 - 120 dB(A) a jet aircraft taking off 25 meter away 140 dB(A). (HSE, 2000

Combinations of noise exposure levels and maximum duration time are expressed in the table below:

Exposure Level (dBA)Duration Time - t - (s)HoursMinutesSeconds8025248120108216831242841058588662187528848931090231

91292135931169419547379637489730982349991859100151011154102927103730104557105443106345107259108222109153110129111111

NOISE POLLUTION LEVEL (NPL)

Sumber: Jabatan Alam Sekitar. (1998). Laporan kualiti alam sekeliling.

Jadual 1: Pencemaran bunyi di bandar-bandar utama di Malaysia

Bandar 1998 1992 Klang 83.8 83 Johor Bahru 82.3 81.3 Kuala Lumpur 81.3 81 Kuala Terengganu 80.1 79.6 Ipoh 78.9 78.3 Alor Setar 78.8 76.6 Kota Bharu 78.6 77.6 Pulau Pinang 80.5 73.1 Seremban 78.2 76.8 Kuantan 77.9 76.8 Kangar 76.4 75.4

SOUND IN ROOMS

When a sound wave hit any surface in a roomThe sound behavior when it encounters the end of the medium or an obstacle, they will reflect, absorb and transmit .Reflection, absorption and sound transmission

A sound wave doesn't just stop when it reaches the end of the surface or when it encounters an obstacle in its path. Angle of reflection = angle incident

Sound is reflected in different ways depending on the shape of the reflecting surface: Concave surfaces

Convex surfaces

Flat SurfaceIt distributes the sound evenlyIt also amplify the reflected sound.

The speakers voice is blocked from reaching the back row audience.METHODS IN INCREASING THE SPEAKERS VOICE TO BE HEARD BY ALL THE AUNDIENCE. Build a stage or increase the speakers level. This will lift some of the obstruction by front row audience. The back row still have problem hearing the speakers voice.Build a reflector on the stage ceiling. This will reflect and distribute the sound evenly. The front and middle rows will listen clearly. The back rows still have the problem of hearing the sound clearly.Step 1Step 2Step 3

Step 4Step 5Step 6The reflector is angled 45 to reflect the sound to the back rows. The sound will reach the back row but the front rows will face a problem of hearing the clear sound.The reflector is angled 45 to reflect the sound to the back rows. The seating arrangement is designed as steps. So that the sound will reach the back without any obstruction.The reflector is angled 45 to reflect the sound to the back rows. Another reflector is placed horizontally to reflect the sound evenly to the front and middle rows. This is the best design as all the audience will hear a clear voice from the stage.

HOW TO WIDEN THE SOUND DISTRIBUTION.Reflected sound will be widely distributed if 2 reflected ceiling are placed at different angle.

The prolongation of the reflected sound is known as reverberation.

Reverberation When a reflected sound reach the receiver at different time and delayed.The reverberation sound is heard differently from the original sound.It creates echo.Reverberation is not wanted in a room depending on the function of the room.

Alternate Time reflection

The effect of sound reflection (amplifier, sound mixer or reverberation) depends on the time difference between the original sound and the reflected sound at the receiver.

Time difference (second)effects0.00 0.020.02 0.030.03 0.07>0.07OPTIMUM AMPLIFIERGOOD AMPLIFIERMIXED SOUNDECHOES

Reverberation time (RT) the time it takes for sound to die away to inaudibility after the source is stopped. It is usually measured from the slope of the sound decay and extrapolated to represent a 60-dB decay. RT increases with room volume and can be decreased by adding sound-absorbing material to the room.

RELATIONSHIP BETWEEN EFFECTS OF REFLECTION AND DISTANCE TRAVELLED BY A SOUND. The distance difference is the length taken by the sound from the source to the receiver.This distance must be controlled.The distance difference shouldnt be more than 11m and the best is not more than 7m.CDifference in distanceDistance travelled by direct soundDistance travelled by reflected sound-=

Describe the condition of the reflected sound that reach the listener/ in the roomFrom the table, the effect of the reflected sound is :

Time difference(s)Effect< 77 - 1111 - 23> 23Optimum amplifierGood amplifierMixed soundEchoes

QUESTIONs1. Explain the condition of a space when a sound is reflected by a flat ceiling as shown below:

ABSORPTIONThe Purpose Reduce the noise level.Avoid the sound reflection which can cause mixed, confused and echoes sound.Reduce the Reverberation time.(RT)Noise from the equipments in AHU room.The noise is transmitted out The noise is contained inside. The sound insulation to absorb the sound.

Need reflectorReflection at this points will cause mixed and echoes sound.Reflector is placed at this point. To amplify the sound.Absorbers at the ceiling will absorb the sound and prevent echoesCeiling is being installed with reflectors and absorbers.Absorption aim is to reduce the reverberation period. That is why the absorption materials is placed throughout the room so that the reverberation period is evenly distributed.

Sounds from reflections compete Sound absorption controls echo

Reverberation Time CalculationThe area of the equivalent total sound absorption and the room volume determine the expected reverberation time (RT).

The Sabine reverberation time equation can be used to obtain a simple estimate of the sound absorption required to achieve a particular reverberation time,A = 0.161 V/RT,

where the room volume is in m3 .For example,

To achieve a 0.5s reverberation time in a 312-m3 room would require a total of about 100 m2 of sound absorption. If each person adds 0.75 m2 of sound absorption, 25 people would add 19 m2. Thus a further 81 m2 would be required to meet the 0.5-s RT goal.To meet a 0.7-s reverberation time goal would require only 72 m2 of sound absorption or 53 m2 in addition to the sound absorption of the 25 people.

Types of rooms and activitiesDifferent activities require different RT.< 1 second is for speech>1 second is for music.

The best RTShorter RT means clearer sound.Longer RT causes mixed sound (good for music)

How to measure RTUse Sabine formulaRT = 0.16V A RT = reverberation time A = the absorption surfaces area( total area of the components X Absorption coefficient) V = volume of the room/space

Sound absorption is the incident sound that is not reflected back. Sound absorption When a sound wave strikes an acoustical material the sound wave causes the fibers or particle makeup of the absorbing material to vibrate. The more fibrous a material is the better the absorption; conversely denser materials are less absorptive.

Acoustic foam : charcoal grey, fire retardant foamBonded acoustical cotton.Acoustic Popcorn Ceilings- an acoustic sprayAcoustic Wedges Soundproofing most popular industrial noise source absorber Pyramid Acoustic Soundproofing Mineral Fiber Acoustic ceiling BoardGypsum acoustic ceiling board

Acoustic absorption materials3 types :Porous absorptionDiaphragm panel Resonant absorption1. POROUS ABSORPTIONCavity holes.The sound wave vibrates in the cavity space/holesThe friction caused by the vibration will turn the sound energy into heat energy and the sound will reduce. 2 types of porous absorption

1. Bulk typeThe performance of this absorbents is better. For example : Foam and fiber1. CurtainsThe air gap between the glass window and the curtain acts as the cavity space that trap the sound waves.The trapped sound will reflected in the cavity area, slow down and die in the end. The curtain material itself is a good absorber.It gives double impacts to sound absorption.2. CarpetsIt absorbs the sound/vibration on the floor.Types of carpets:Cut pile yarn ( High absorption)Looped yarn (Less absorption)The thickness and weight of the carpet influence the quality of absorption.

3. Akustik plasterIn the form of semi plastic.The plaster is ether sprayed or laidIt absorbs high frequency sound better.

4. Acoustic blanketsMaterials are from rock wool, fiber glass and hair felt (bulu tenunan)It is usually placed in between the wood/steel frame and covered by a thin protection materials such as wire mash.

NRC Ratings for Inexpensive Sound Absorbtion Material:

MaterialNRCAudimute Sound Absorption Sheets0.70Sound Absorbing Carpet with or without padding 0.20-0.55Polyurethane Foam (1" thick)0.30Auralex 1" Studio Foam Wedge0.50Sound Absorbing Drapery, light weight0.05-0.15Sound Absorbing Drapery, medium weight0.55Sound Absorbing Drapery, heavy weight0.60

2. Sheet typesIt depends on the density, area and thickness of the materials. Examples: Fiberglass wool, mineral fiberglass Acoustic fiber panelAcoustic Fiberglass panelFiberglass sheet is placed on board.

2. DIAPHRAGM PANELThis panel will vibrate at the frequency that is the same as the source frequency.But.In reality, this panel in not elastic. That is why the sound energy will be forced to stop vibrating and change it into heat energy.heat energy received = absorbed sound energy. Sound sourcePanelThis absorber is suitable for high frequency sound. f = 60 / md f - frequency m density d distance from the wall

2. Diaphragm panel wallAbsorption panelstudsFor low and medium sound frequency, this absorber is not suitable.

To increase the ability to absorbed sound, blanket type of absorber is placed on the wall surfaces.d

3. RESONANT ABSORPTIONThis types is suitable for rough and tough places like gym, bowling alley, machine rooms factories, bus/train stations and highways.2 types of resonant absorptionCavity resonatorIt consists of a hard wall which has a small hole/opening in front.Inside the block, it has a wide cavity area/space with small and narrow mouth/opening.

Sound that enter the mouth into the cavity space will being reflected continuously till all the sound energy is absorbed.VvAA = Area or the mouthV = Volume inside the block.V = volume of the mouth.

CONCRETE BLOCK RESONANCEThis concrete block consists of a small long mouth in front.It also has hard walls which will create cavity space effects to the sound.It is suitable as sound barrier walls. The outside surface of the walls can be painted without damaging the absorption quality of the wall.

MEASURING THE EFFECTIVENESS OF ABSORPTION OF A MATERIALAbsorption coefficient

It is the ratio of the acoustic energy absorbed and changed into heat energy.Different types of materials and sound frequency has different value of absorption coefficient.

MaterialFrequency (Hz)12525050010002000Unpainted concrete block 0.360.440.310.290.39painted concrete block 0.10.050.060.070.09Brick0.030.030.030.040.04Plastered brick0.130.150.020.030.04Glass window0.350.250.180.120.07

Factors in calculating RTRT cannot be added or subtracted directly. Total RT can be obtained by calculating the absorption unit.Sketch the situation to help finding accurate measurement.Any surface than is not touched, should not be included in the calculationPrepare a table that includes all the related elements in the calculation.Example calculation.

Example 1.

A 2000m3 hall is usually used for assemblies every Monday morning. Assume that the hall doesnt have any absorption materials that causes bad echoes. Calculate the RT of the hall if 200 students with absorption coefficient of 0.46 Sabine use the hall for their activities.A hall with a volume of 1500m has the following finishes that absorb sound at 500Hz.Plastered brick wall --------400m ---------0.02 SabinePlastic tiled floor ----------300m ---------0.05Plaster board ceiling ------300m --------0.10Students ----------100 people --0.46Calculate the RT of the hall when 100 students fill the hall. Calculate the extra area of sound absorption needed to be added in the hall so that it can suitably used for a speech program next week. The optimum RT for speech is 1 second.Example 2.

Example 3

A hall dimension of 30m X 10m X 5m. There is an opening at one of the walls. The opening area is 50 m. The wall is a plastered brick, the ceiling is from hard board and the floor is made of wood block on the concrete. There are also 200 fabric type seats. The measured RT of the emptied hall is 1.5second at 500Hz. Using the table given below, calculate the area of the carpet needed as a sound absorption to reach the correct RT.

MaterialsArea A (m)Absorption coefficient (SABINE)Dinding (-bukaan)3500.03Lantai3000.15Siling3000.05Fabrik seat2000.28Karpetx0.50

Question 1A hall with a volume of 5000m has the RT of 1.6s. Calculate the total extra area of sound absorption needed to reduce the RT to 1 second.

Question 2A 900m room has a RT of 1second. Calculate the total extra area of absorption needed to lower the RT to 0.8 second.

Question 3Calculate the actual RT for a hall that has a volume of 5000m and the following details on the finishes that are in the hall at 500 Hz :

finishesArea (m)Absorption coefficient (SABINE)Brickwork5000.03Plaster on solid 6000.02Acoustic board1500.70Carpet3500.30Curtain700.40Seats5000.30

Question 4From Question 3, Calculate the total extra area of sound absorption needed if the optimum RT for the hall is 1.5second.

Question 5A multi purpose hall has a volume of 120,000m . If the hall is empty, the RT of the hall is 9 second. When there is an assembly, the hall has the RT of 6 second. Calculate the number of audience needed to reduce the RT if each audience acts as sound absorption coefficient of 0.46 Sabine.

more questions will be given at the end of this chapter.

Acoustic transmission in building design refers to a number of processes by which sound can be transferred from one part of a building to anotherIt is the weak sound energy which transmitted through an object but it can damage the building structures.

Airborne transmission - a noise source in one room sends air pressure waves which induce vibration to one side of a wall or element of structure setting it moving such that the other face of the wall vibrates in an adjacent room.Structure-borne transmission Vibration from an operating fan may be transmitted to the interior of the building through building structure when the fan is directly mounted on a supporting structure without proper isolation. The vibration transmitted may activate the building structure to generate noise which causes noise disturbance to residents inside the building.TRANSMISSION

Direct transmission - resonant motion (floor radiating sound to the room below).

Flanking transmission - resonant motion (floor transmitting sound to the adjacent walls which radiate to the room below.

Specific low frequency transmission - non-resonant motion (forced motion of the floor causing the floor to deflect and compress the air in the room below which changes the pressure out the eardrum).

The definition - " The accumulated decrease in acoustic intensity as an acoustic pressure wave propagates outwards from a source." As the acoustic wave propagates outwards from the source the intensity of the signal is reduced with increasing range due to: 1) Spreading 2) Attenuation The transmission loss (TL) The term Transmission Loss (TL), or more commonly Sound Reduction Index (SRI) are used to describe the reduction in sound level resulting from transmission through a material. This is given by:

SRI = 10 log (Wsource / Wreceiver) = 10 log (1/t) = -10 log (t) Sound Transmission Loss (TL);

A doors ability to reduce noise is called its sound transmission loss (TL) effectiveness. TL is a value given in decibels, which is determined by measuring sound pressure levels at a certain frequency in the source and receiving rooms. The calculation also factors in the area of the partition shared by the two rooms, and adjusts for the receiving rooms acoustic liveness (known as reverberation time). The adjusted difference between the two levels is the TL of the door. The higher the TL, the better the result.

Sound Transmission Class (STC):

TL measurements for a door are taken across a range of frequencies, which makes it difficult to compare the effectiveness of different doors. Sound transmission class (STC) ratings solve that problem by giving a single value to acoustical performance for a door. The higher the STC value, the better the rating and the better the performance

When sound is incident upon a building element some of it will be reflected and some will be transmitted through the wall. The fraction of incident energy transmitted is called the transmission coefficient . The sound reduction index , is in turn defined in terms of the transmission coefficient. Transmission coefficient.

SOUND REDUCTION/TRANMISSION LOSS CALCULATION The basic measure of sound insulation provided by a partition is called Sound Reduction Index (SRI) or R or Sound Transmission Loss(TL). The unit is in dB. Sound Reduction Index between 2 rooms:Where Ls = Sound level in the source room (dB) LR= Sound level in the receiving room (dB) S = Partition/wall area (m2) A = Absorption area of the receiving area (m2)

The transmission loss (TL) for a partition and the noise reduction in the room

For composite partitions of n nos. of surface parts, the average transmission coefficient TAV can be found from the following equation: where Ti = transmission coefficients of the ith partAi = area of the ith partA = total area of partition = The transmission coefficient i

Example question 2An office measuring 5m X 7m X 3m is adjacent to the factory hall.. The dividing partition between the rooms is 6m X 3m. The SRI of the wall is 40dB. The sound pressure level (SPL) in the factory is 80 dB. Calculate the estimated SPL in the receiving room if the reverberation time there is 1 second.Example question 1A 5m X 2 m wall is used as a partition between 2 spaces. If the wall SRI is 35 dB, calculate the sound transmission coefficient of the same wall.Example question 4A 20m2 brick wall is placed as an insulated partition with the sound reduction index of 65 dB. A door is built onto the wall with the sound reduction index of 40dB. Calculate the area of the door if the SRI for both components is 50dB.Calculate the average transmission coefficient of the 5m X 5m wall partition that has a door and a window on it. The SRI of the wall is 55dB. The 2m window and 7m door on the wall have the SRI of 35dB and 35dB.Example question 2

Now Actual sound reduction index in dB : It can be seen that the poor insulation of the window of small area reduces the overall insulation very considerably. If the window had fitted badly the insulation would be even lower.

A partition of total area 10 m2 consists of a brick wall plastered on both sides to a total thickness of 250 mm and contains a window of area 2 m2. The brickwork has a sound reduction index of 51 dB and the window 18 dB at a certain frequency. Calculate the sound reduction of the complete partition at this frequency.Example 4Brickwork : if TB is the transmission coefficient of the brick, then Window : if TW is the transmission coefficient of the window, then

VIBRATION

Define vibrationDescribe the 3 types of vibrationDefine air borne and structure borne sound/vibrationList the vibration controlList the vibration isolationWith the aids of a diagram, describe inertia block.Identify the vibration isolators and padding for the BS equipmentDescribe mass spring and mass spring with damper.

What is vibration? Any vibration has two measurable quantities. How far (amplitude or intensity), and how fast (frequency) the object moves helps determine its vibration characteristics. The terms used to describe this movement are frequency, amplitude and acceleration.FrequencyThe number of cycles that a vibrating object completes in one second is called frequency.. Amplitudemeasured in meters (m). The intensity of vibration depends on amplitude. Acceleration (measure of vibration intensity)The speed of a vibrating object varies from zero to a maximum during each cycle of vibration. Speed of vibration is expressed in units of meters per second (m/s)

Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely.

Forced vibration is the vibration resulting from the application of an external periodic force

Free Vibration:

TYPES OF VIBRATIONS.2. Random Vibration:3. Transient Vibration:

1. Periodic Vibration

Vibration is distributed through 2 methods:1, Air borne sound Air borne sound is distributed through air. Air in the atmosphere is used as a medium to transfer sound waves to another place.Conversation, singing, shouting, sounds emitted by animals, sounds of wind instruments and strings (instruments) that do not touch floor, the sound of thunder are the examples to airborne sounds.

Preventation methods

Air borne sound

2,Structure borne sound (bunyi bawaan struktur)It has negative effects on the building structures such as :Cracks in the structures.Damage the building structures.Structure borne sound is sound that is propagated/forced through structures as vibration and subsequently radiated as sound. Machinery noise; due to lifts, plumbing, heating, ventilating and air conditioning (HVAC) systems Impact noise; objects dropping on the floor, footsteps etc. Vibrations due to heavy vehicles Preventation methods

VIBRATION CONTROLENGINEERING CONTROL.CAN BE DONE IN SEVERAL WAYS :CHOOSE A SILENCE MACHINES.Silence machines & silencers.For example : centrifugal fanAC compressor needs sound insulation/dampers/silencers. USE MACHINES THAT IS SUITABLE FOR ITS BURDEN.Machines that are forced to work hard will produced loud noise.SCHEDULE MAINTENANCE.Machines that are not maintain will produce loud noise and will damage.

Architecture control1. Space arrangementMain space must be separated from the services areaAvoid placing them directly on the floor or roof.2. Use vibration isolators.Separate the equipment from the floor & roof - use inertia block & fiber glass spring3. Use the vibration isolationAll vibrated equipments must be separated or lifted using elastic isolators.Examples : inertia block should be separated from the floor using spring vibration isolators.

A vibration problem can also be nicely described by the same source path receiver model we previously used to characterize the noise control problem.

Source: a mechanical or fluid disturbance, generated internally by the machine, such as unbalance, torque pulsations, gear tooth meshing, fan blade passing, etc. These typical occur at frequencies which are integer multiples of the rotating frequency of the machine.

Path: the structural or airborne path by which the disturbance is transmitted to the receiver

Receiver: the responding system, generally having many natural frequencies which can potentially be excited by vibration frequencies generated by the source.

VIBRATION ISOLATION the process of isolating an object, such as a piece of equipment, from the source ofvibrations.VIBRATION ISOLATORA flexible support for anyformof vibrating or reverberating machinery,piping, orductwork, serving to reduce noise or vibrationThevibrationsthat are carried to the remainder of the buildingstructure.

Vibration isolation springVibration isolators for hanging pipes and air handling unit ducting.Spring is enclosed by walls but they do not touch the spring.

Elastic/resilient materials reduce vibration caused by liquid velocity movement sanitation liquid flow from the apparatus through the wall in the sanitation pipe.Vibration that transfer through earth can be prevented Build a ditch/drain that separate the building from the source of vibrationOther types of vibration isolators

CHOOSING THE RIGHT VIBRATION ISOLATORS AND PADDINGS.

Equipments on the roof -

Cooling tower-

Compressor-

AHUDepends on the type of AHU used.-

PumpPump with a power less than 3.7kW -Pump with higher power -

Fan If placed on the floorPower not more than 3.7kW Power more than 4.5kW

Air Ducting SystemUse

Lift& esclator2 noise sources produced by the equipment and banging/stamping on of the car.Reduce the vibration - is placed at the places where vibration and loud noise are produced.

Inertia BlockA concrete block which serves as a base for mechanical equipment such as fans or pumps; the block is mounted on a resilient support to reduce the transmission of vibration to the building structureInertia block thickness is not less than 150mm and usually made from reinforced concrete and at least the same weight as the equipments.

PROBLEMS AND PRACTICAL REMEDIES ON PUMPING SYSTEM NOISEStructure-borne Noise from PumpsetsVibration from an operating pump set may be transmitted to the interior of the building through building structure when the pump set is directly mounted on a supporting structure without proper isolation. The vibration transmitted may activate the building structure to generate noise which causes noise disturbance to residents inside the building.

Provide an inertia block to support the pump set (see Fig. 11) so as to add rigidity and stability to the pumping system, and provide vibration isolators (see Fig.11) to support the inertia block, thereby isolating it from the building structure (see App. VII and VIII). Provide flexible connectors between the pump and associated pipe work, thereby preventing the vibration of the pumps et being transmitted to the pipe work .Practical Remedies

Jisim (m)Merupakan jasad yang rigid/kakuJisim yang menerima getaran akan menerima atau hilang tenaga kinetik bergantung kepada perubahan halaju jasadKerja yang dilakukan adalah hasil darab daya dengan jarak (displacement)Spring (k)Mempunyai daya elastik dan dianggap ringanDaya spring akan berlaku sekiranya spring berubah bentuk dan juga jika terjadi anjakanSpring mempunyai kekejangan atau kekenyalan yang memastikan ianya cuba balik kebentuk asalnya apabila satu daya/beban dikenakan.RendamanAlat rendaman tidak mempunyai sifat elastikDaya rendaman akan berlaku sekiranya ada pergerakan dikedua hujungDaya atau kerja yang berlaku akan dipindahkan kedalam rendaman yang akan menukarkan tenaga kinetik kepada tenaga haba. Ini akan menghentukan gerakan/getaran yang dihasilkan oleh bebanSISTEM JISIM PEGASJisim pegas merupakan satu alat yang bersifat anjalIa boleh kembali ke bentuk asal selepas diberi tekanan kepadanyaGetaran satu jisim pegas ialah jisim bersambung dengan penyambung tegar(spring) dan akan bergerak ke atas dan ke bawah secara pugak.Gerakan ini menghasilkan amplitud getaran

MASS SPRING SYSTEM

Titik alah Pemanjang ynag berterusan akan memutuskan springBeban Pemanjangan HOOKE LAW

A vibratory force, f(t), is applied to the mass, inducing response vibration displacement, X(t). The applied force is typically a random time function having a continuous spectrum over the frequency range of interest. MASS SPRING WITH DAMPER

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