Aurar 501 Architectural Acoustics Unit 4

8/13/2019 Aurar 501 Architectural Acoustics Unit 4

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UNIT 4

Environmental Noise ControlNoise sources, air borne and structure borne sound, NC curve,Propagation of noise of mechanical operation and impact noise,sound transmission through wall and partition, Vibration isolation

control of mechanical noise, floating floor, wall, ceiling treatment.

Design Principles-reduction of noise at the source, Reduction of noise near the source.Application of sound absorption material, Reduction of noise byTown Planning and Regional Planning consideration.


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Noise Pollution[Environmental Noise]


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It is any unwanted , disturbing or harmful sound that impairs orinterferes with hearing, causes stress, hinders concentration and work efficiency, or causes accidents.

1. Definition of Noise

It can also be defined as displeasing human or machine created soundthat disrupts the activity or happiness of human or animal life .

The sensation of loudness is related to the intensity of the energycarried by the sound waves and is measured in units of decibels (dB).

Sound pressure becomes damaging at about 85 dB and painful ataround 120 dB At 180 dB it can kill.

Human ears can take sound up to about 60dB without damage orhearing loss.


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The source of most noise worldwide is1. Transportation systems , motor vehicle noise, but also including air

craft noise and rail noise.

2. Poor urban planning may give rise to noise pollution, since side-by-side industrial and residential buildings can result in noise pollutionin the residential area.

3. Office equipment, factory machinery, construction work, appliances ,

power tools, lighting hum and audio entertainment systems.4. The sound of an automobile is about 70 dB; the sound of a jet air

craft taking off, about 120dB; sound level in the interior of a home isabout 45 dB So, prolonged exposure to sound levels above 85dB cancause permanent hearing damage .

5. Noise in the range of 50-60 dB is sufficient to interfere with sleep ,producing a feeling of fatigue upon awakening.

2. Sources of noise pollution


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1. Can have a detrimental effect on animals by causing stress ,

increasing risk of mortality by changing the delicate balance in

predator/prey detection and avoidance .2. Interfering with animals use of sounds in communication especially

in relation to reproduction and in navigation .

3. Can lead to temporary or permanent loss of hearing to animals .

4. Very loud noise may affect plant growth indirectly because it

produces vibrations that shake the plants .

3. Environmental effects


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1. Total energy

2. Sounds pitch

3. Frequency

4. Time pattern and,

5. Length of exposure to the sound.

4. Environmental effects of noise depends on


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Pain 130 dB120 dB

Aircraft taking off 110 dBLoud Rock Music 100 dBSemi Truck (short term hazard) 90 dBJack Hammer 80 dB

Traffic (occupational limit) 70 dBConversation 60 dBBackground office noise 50 dBWindmill 40 dB

30 dBQuiet bedroom 20 dB

10 dBThreshold of hearing 0 dB

5. Noise levels of common sounds


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1. Noise and People

6. Noise and Noise Control

Noise is unwanted sound. It can not be completely eliminated but its intensitycan be reduced by proper treatment, such as

1. Proper design, insulation and maintenance2. Placing massive structure around the sound source to reflect sound before it

reaches the receiving-room.

3. Using interference and resonance attenuators4. Anti-vibration mountings5. Flexible belows6. Anti-vibration hangers

7. Acoustic louvers8. Layers of soft resilient materials on floors to isolate vibrating , noisyequipments from conveying vibration to structures. Such prefabricatedmounts and bases are commercially available.

9. Make conduit and pipe-connections flexible and floppy . Isolate themfrom main structure by resilient materials and make them air-tight.


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2. Noise Pollution and People

Noise pollution creates obstruction for carrying out normal, desired activities in

three ways

1. Physically E.g. Sleep Interferences

2. Psychologically E.g. Annoyance

3. Physiologically E.g. Health Hazards



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2.1 Physically E.g. Sleep Interferences

1. Delayed onslaught i.e. delay in falling asleep

2. Fatigue (a) Walking in sleep

(b) Loss in efficiency in normal working

(c) Disturbed sleep (Noise above 50 dB)

Rhythmic-noise can be tolerated but intermittent noise with sharp peaks has

pronounced effects.



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2.2 Psychologically E.g. Annoyance

1. Sudden changes in noise level (above 60-70 dB) makes concentration on

the work at hand.

2. The intensity, spectral complexity i.e. different frequencies of sound,

duration etc. contributes to annoyance.

3. The degree depends upon the individual and also upon the age group.



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2.3 Physiologically E.g. Health Hazards

1. Prolonged exposure to noise of low level can lead to degeneration of ear cells .

High level can lead to structural changes, called Acoustical Trauma .

2. Sensitivity of the ear decreases due to continuous exposure to noise from air-port,

Heavy traffic, Working with noisy machines etc.

3. The middle-ear is damaged by noise level above 120 dB , when the ear-drum can be

ruptured .

4. Abrupt changes in sound pressure is also dangerous (e.g. Explosions, Firing etc.)

5. The inner ear is sensitive to even low-levels if these are prolonged. Working for 8

hrs. per day in a factory with 80 dB lvl. may lead to Deaf-ness .



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Measures to control noise effects

1. Use of barriers of better STC

2. Isolation by floating floors

3. Prevention of flanking and leaks

4. Sound proof doors and windows

5. Construction, keeping separation between sensitive and noisy area



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1. Ear Protection2. Modifying noisy activities and devices3. Shielding noisy devices or processes4. Shielding workers or other persons from the noise5. Moving noisy operations or machinery away from people6. Using anti-noise (a technology that cancels out one noise with another).7. Use of noise barriers8. Limitation of vehicle speeds,9. Limitation of heavy duty vehicles.

10. Use of traffic controls that smooth vehicle flow to reduce braking and acceleration11. Aircraft noise can be reduced to some extent by design of quieter jet engines,12. Redesign of industrial equipment, shock mounting assemblies and physical barriers

in the workplace.13. Research now shows that plants can also help to reduce background noise levels

inside buildings by up to 5 decibels14. Interior plants can absorb, diffract or reflect background noise in buildings, thereby

making the environment more comfortable for the occupants [especially plants withlots of small leaves]

15. Law enforcements.

7. How can we reduce noise pollution


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1. Always wear hearing protection when working around loud noises

2. Take breaks when working in noisy areas

3. Limit exposure to loud music

4. Have regular hearing tests for any loss of hearing

5. keep indoor plants

8. Learning to protect yourself from Noise Pollution


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1. Perfect silence can not be tolerated.2. It proves to be highly disturbing. Some back-ground sound in the

form of Acoustical perfume is not only acceptable but alsodesirable.

3. It is privacy rather than silence that we usually want.4. External speech-sound do not particularly disturb us until they

become distinct enough to carry information .

5. On the basis of extensive research in human responses andperformances a set of contours, similar to that of equal to loudnesscontours, have been developed.

6. These contours are termed as Noise Criteria Curves.

7. These specify the maximum level, in the frequency band, which willbe acceptable.

9. Noise Criteria (N-C Curves)


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8. The acoustical environment for activity spaces can be broadlyspecified as Quiet area : testing audiometry, recording studio, Bedroom, Study-

room etc. having NC range 15-20 dB. Hearing : Drama Cinema, Lecture-room, Assembly Hall, Court-room,

Conference- room, Residences, Hospitals etc. hving NC range 20-30dB.

Normal Activity Area: offices, class room, Library etc. having NCrange 30-35 dB. Moderate Activity Area: Laboratory, corridor, shops, etc NC range 35-

45dB. Noisy area: Hotels, Kitchen, Bank, garrage etc. NC range 45-50 dB. Very Noisy Area: Air Port, Railway, Factory, Parking, Market etc. NC

range 55-75dB.



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9. Human ear can tolerate high intensity sounds of low frequencies andlow intensity sound of high frequencies. This tolerance is expressedby background NC curves. This tolerance is depends upon bothsound pressure and frequencies and is derived from experience withspaces intended for different functions.

10. NC curves specify acceptable sound levels at different frequenciesand are based upon the sensitivity of the human ear . Analysis of the

noise is plotted on the top of the standard curves.



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1. Noise level in the source room

2. Background noise level in the source room3. Background noise level in the receiving room4. Transmitted noise level from the source room to the receiving room


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1. Unwanted sound can pass on through air routes and seriously throughinter connecting solid structures .

2. Floor should be treated with resilient materials or properly carpetedand in stead of flat ceiling to get sound dispersion and diffusion .

3. If possible provide false ceiling so that the air column between falseceiling and the real, rigid ceiling will provide cushion for soundabsorption.

10. Floor ceiling construction for impact isolation and otherflanking cases.

Enclosure with resilient mount resilient mount with doubleenclosure and lining


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1. Impact sound includes foot steps , slammed doors and windows ,noisy pipes , vibrating machines etc. This sound results into structureborn sound also.

2. It is necessary to distinguish between air born and impact sound . Asingle noisy source will generate both types . Foot steps on a floorwould be heard mainly as impact sound in the room below but it willbe heard as air born in the room above.

3. Impact sound also results into flanking Transmission. These indirectsound paths can be numerous and complex .

4. For Impact noise Use carpeting and resilient tiles to cushion theimpact.

5. These are effective at the middle and high frequencies but lowfrequencies can still pass through.6. Impact noise rating (INR) for flat concrete slab is -17. for concrete

slab with floating floor it is +1 and for concrete slab on steel bar

joists, carpet on foam pad etc, it is +26.

11. Impact and Structure Born Sound


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1. For ceiling the materials should not only be absorbent but that whichcuts down sound transmission.

2. For walls and ceiling, perforated mufflers which, allow air movementbut reduce sound transmission.

3. For partitions, use heavy weight materials but of low stiffness. Avoid

materials being both; stiff and light.

11. Impact and Structure Born Sound

11.1 Choice of Materials

1. Proper orientation and planning2. More critical functional rooms be away from noise source.3. Noise reduction at source.4. Acoustic plaster are cheaper for noise control in school and offices.

11.2 Defence against noise


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1. The insulation of a floor must be maintained at all junctions with thesurrounding walls in order to prevent flanking transmission andimpacts.

2. The separation of the two parts of a floating floor must continuearound all the edges by the use of resilient materials and air tightplugging, if STC rating needed is above 65 dB, floating floor is must.

12. Floating floors

1. Floated concrete floor2. Glass fiber board around perimeter to prevent

flanking at perimeter.3. 12.5 mm. exterior plywood panels4. Resilient layer of pre-compressed glass fiber to

have initial deflection of about 15% to allowfloated slab to move while structural slab

remains stationary.5. Layer of polyethylene on top of ply wood

panels and over inside face of perimeterinsulation board to protect it from moisture.

6. Concrete structural slab7. Mastic caulking around perimeter.


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1. Urbanization has forced us to construct such buildings. Such buildings haveserious acoustical problems; such as impact noise, transmitted sounds, lifttransport in addition to external noise.

2. We have to note that we can only try to minimize the noise level to

acceptable limits, In residential flats, we should try to keep less criticalfunctional spaces ; such as kitchen, drawing room, passages etc. along thelift/ stair-case.

3. Then toilet- bathrooms and at the end our study-room and bedroom . Thus

some isolation of critical area from the noisy area and adjoining flat can beachieved. Sound flaking, sound transmission by pipe-line connections etc.can be reduced by proper caulking, using mufflers and absorbents. Mainentry-door to the flat should be heavy and sound leak proof.

4. The partition wall materials for inner room should be of proper STC value .In the study/ bed room , the best method would be have back ground noiseas suggested by noise criteria. This, called Acoustic Perfumes, will helpto give privacy even in noisy area.

5. For a highly confidential and delicate working condition , the space musthave a floating floor, in addition to other noise-reduction-methods .

13. Problems in Multi-storeyed and Multifunctional Buildings


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1. Less critical spaces should face the road side as these spaces act as barrierfor outdoor noise.

2. If possible, dense planting should surround the structure. A single row of trees does not provide sound insulation because of inter reflections between

the trees. Hence multiple layer closely spaced rows, 50m wide can providenoise reduction up to 6 dB.3. Compound wall can also act as a barrier for external noise. When the sound

source is near the barrier wall, height of the wall should be greater.

4. If the distance between the wall and sound is 1m and height of the barrierwall will be 1.2m. i.e. H > LHereH = Height of compound wall

L = Length of the source to compound wall

14. Outdoor barrier for sound control


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Sound Insulation/ Reduction/ Insulation

Sound transmission through wall and partition


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1. Mass Law

The Sound Reduction Index (SRI) increase by 6 dB with eachdoubling of Mass or Frequency.

SRI in dB = LP1 LP2 10log A/SHereLP1 = Sound pressure level in source roomLP2 = Sound pressure level in Receiving roomA = Absorption in the receiving room

S = Surface area of the partition wall

T = Et / EiHereT = Sound Transmission coefficientEt = Transmitted EnergyEi = Incident Energy

Hence

T=0 means sound leak surface and T=1 means sound transparent surface


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1. Mass Law

1/T = E i /E t = (E t /E 0) x (E 0 /E t)10Log(1/T) =10log(E t /E 0) - log(E t /E 0)Thus,10Log(1/T) = Incident power level - Transmitted Power Level= SRI in dB.NRC (Noise Reduction Coefficient)

It is the average of a Materials sound absorption coefficients at 250, 500, 1000, and 2000 Hz i.e.

NRC= ( 250 + 500 + 1000 + 2000) / 4

It is the single number index of sound absorbing efficiency of a material.NR (Noise reduction)

From source room to receiving room

I.e. NR = Difference in intensity level = I 1 I 2 in dB.

Also NR = TL + 10log(a2/S) Here

TL= Transmission loss in partition-wall,

A2= Absorption in receiving room.

S = Area of partition wall (It acts sound source in receiving room)


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1. Mass Law

PARTITIONS WALL

TL due to thickness = 20log 10(f.M) + K in dB.

Where

f = frequency of sound in Hz

M = Mass per unit surface area of the partition wall in Kg/m 2 : K = A constant. It is 47 when M is

in Kg/m 2

DOUBLE WALL PARTITION WALL(With a cavity of width d)

TL = 20log10 (d.M) + K

Here d in meter

M in Kg/m 2 and K = 34

This is valid in the range 100-3200 Hz.


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Aurar 501 Architectural Acoustics Unit 4

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