ACOUSTICS



ACOUSTICS, SOUND INSULATION AND NOISE CONTROL

19.0. Scope - This Section covers requirements and guidelines regarding planning against noise, acceptable noise levels and the requirements for sound insulation in buildings with different occupancies.

19.1. Terminology :

19.1.0. For the purpose of this Section, the following definitions shall apply.

19.1.1. Ambient Noise – The sound pressure levels associated with a given environment. Ambient noise is usually a composite of sounds from near and far sources none of which are particularly dominant.

19.1.2. Audible Frequency Range – The range of sound frequencies normally heard by the human ear. The audible range spans from 20 Hz to 20 000 Hz.

19.1.3. A-Weighted Sound Pressure, pA – Value of overall sound pressure, measured in pascals (Pa), after the electrical signal derived from a microphone has been pasted through A-weighting network.

NO : The A-weighting network modifies the electrical response of a sound level meter with frequency in approximately the same way as the sensitivity of the human hearing system.

19.1.4. A-Weighted Sound Pressure Level, LpA  – Quantity of A-weighted sound pressure, given by the following formula in decibels (dBA):

LpA = 10 log10 ( pA / pAo )2

Where,

pA = is the A-weighted sound pressure in pascals (Pa); and

pAo = is the reference sound pressure (20 µ Pa).

NOTE: Measurements of A-weighted sound pressure level can be made with a meter and correlate roughly with subjective assessments of loudness, and are usually made to assist in judging the effects of noise on people. The size of A-weighting in 1/3 octave bands, is shown in Annex A (see A-5). An increase or decrease in level of 10 dBA corresponds roughly to a doubling or halving of loudness.

19.1.5. Background Noise – The sound pressure levels in a given environment from all sources excluding a specific sound source being investigated or measured.

19.1.6. Break-in – Unwanted sound transmission into a duct from outside.

19.1.7. Break-out – Unwanted sound transmission from inside a duct to the outside.

19.1.8. Broad Band Noise – Spectrum consisting of a large number of frequency components, none of which is individually dominant.

19.1.9. Cross-Talk – Unwanted sound transmission between one room and another room or space via a duct.

19.1.10. Decibels – Ten times the logarithm ( to the base 10) of the ratio of two mean square values of sound pressure, sound power or sound intensity.  The abbreviation for ‘decibels‘  is dB.

19.1.11. Effective Perceived Noise Level in Decibel (EPN dB) – The number for rating the noise of an individual aircraft flying overhead is the effective perceived noise level in decibels (EPN dB).  The effective perceived noise decibel value takes into account the subjectively annoying effects of the noise including pure tones and duration.  In principle, it is a kind of time-integrated loudness level.

19.1.12. Equivalent Continuous A-Weighted Sound Pressure Level, Lpeq.T  - Value of the A-Weighted sound pressure level in decibels (dB) of a continuous, steady sound, that within a specified time interval, T, has the same mean squared sound pressure as the sound under consideration that aries with time, given by the formula:

1       pA2 (t)  dt

Lpeq.T = 10 log10      T   tƒo   po2                                                                         

pA (t)  = is the instantaneous A-Weighted sound pressure in pascals (Pa); and

po            = is the reference sound pressure ( 20 µ Pa ).

Note : Equivalent continuous A-weighted sound pressure level is mainly used for the assesment of environmental noise and occupational noise exposure.

19.1.13. Equvivalent Sound Absorption Area of A Room, A – Hypothetical area of a totally absorbing surface without diffraction effects, expressed in square metres (m2) which, if it were the only absorbing element in the room, would give the same reverberation time as the room under consideration.

19.1.14. Facade Level – Sound pressure level measured 1 m to m in front of the facade.

Note: Façade level measurements of LpA are usually 2 dB to 3 dB higher than corresponding free-field measurements.

19.1.15. Free-Field Level – Sound pressure level measured outside, far away from reflecting surfaces.

NOTE – Measurements made 1.2 m to 1.5 m above the ground and at least 3.5 m away from other reflecting surface are usually regarded as being free-field measurements.  To minimize the effect of reflections the measuring position should be at least 3.5 m to the side of the reflecting surface (that is, not 3.5 m from the reflecting surface in the direction of the source). Estimates of noise from aircraft overhead usually include a correction of 2 dB to allow for reflections from the ground.

19.1.16. Frequency – The number of cyclical variations per unit time. Frequency is generally expressed in cycles per second (cps) and is also denoted a Hertz (Hz)

19.12.17. Impact sound Pressure Level, L i – Average sound pressure level in a specific frequency band in a room below a floor, when it is excited by a standard tapping machine.

19.1.18. Indoor Ambient Noise – Pervasive noise in a given situation at a given time. Usually compose of noise from many sources, inside and outside the building, but excluding noise from activities of the occupants.

19.1.19. Insertion Loss ( Lµ) – Insertion loss is generally defined as the difference, in decibels, between two sound pressure levels ( or power levels or intensity levels ) which are measured at the same point in space before and after a muffler or any other noise control device is inserted between the measurement point and the noise source.

19.1.20. Noise – Unwanted sound which may be hazardous to health interferes with communications or is disturbing.

19.1.21. Noise Exposure Forecast (NEF) – The noise exposure forecast at any location is the summation of the noise levels in EPN dB from all aircraft types, on all runways, suitably weighted for the number of operations during day time and night time.

19.1.22. Noise Rating (NR) – Graphical method for rating a noise by comparing the noise spectrum with a family of noise rating curves.

19.1.23. Noise Reduction Co0efficient (NRC) – A single figure descriptor of the sound absorption property of a material. It is the arithmetic mean of the sound absorption co-efficients at 250, 500, 1,000 and 2,000 Hz rounded off to the nearest multiple of 0.05.

19.1.24. Normalized Impact Sound Pressure Level, Ln - Impact sound pressure level normalized for a standard absorption area in the receiving room.

Note : Normalized impact sound pressure level is usually used to characterize the insulation of a floor in a laboratory against impact sound in a stated frequency band .

19.1.25. Octave Band – Band of frequencies in which the upper limit of the band is twice the frequency of the lower limit.

19.1.26. Percentile Level, LAN,T - A-weighted sound pressure level obtained using time-weighting ‘ F

which is exceeded for N percent of a specified time interval.

Example : LA90, th  is the a-weighted level exceeded for 90 percent of 1 h. Percentile levels determined over a certain time interval cannot accurately be extrapolated to other time intervals. Time weighting    ‘ F ‘ or ‘ S ‘ can be selected on most modern measuring instruments and used to determine the speed at which instrument responds to changes in the amplitude of the signal. Time-weighting ‘ F ‘ is faster than ‘ S ‘ and so its use can lead to higher values when rapidly changing signals are measured.

19.1.27. Pin Noise – Sound with an uninterrupted frequency spectrum and a power which is steady within frequency band and proportional to centre frequency.  An example is constant power level per octave band.

19.1.28. Pure Tone – A sound emitted at a single frequency.

19.1.29. Rating Level, L Ar,  Tr  - Equivalent continuous A-weighted sound pressure level of the noise, plus any adjustment for the characteristic features of the noise.

Note: This definition is used for rating industrial noise, where the noise is the specific noise from the source under investigations.

19.1.30. Reverberation Time, T – Tem that would be required fro the sound pressure level to decrease by 60 dB after the sound source has stopped.

Note: Reverberation time is usually measured in octave or third octave bands.  It is not necessary to measure the decay over the full 60 dB range.  The decay measured over the range 5 dB to 35 dB below the initial level is denoted by  T30 and over the range 5 dB to 25 dB below the initial level by T20.

19.1.31. Sound – A vibrational disturbance, exciting hearing mechanisms, transmitted in a predictable manner determined by the medium through within  it propagates.  To be audible the disturbance shall have to fall within the frequency range of 20 Hz  to 20,000 Hz.

19.1.32. Sound Exposure Level, L AE   - Level of sound of 1 s duration, that has the same sound energy as the actual noise event considered.

1 L AE   The of a discrete noise event is given by the formula:

 

1       pA2 (t)  dt

Lpeq.T = 10 log10    to   t2ƒt1   po2

Where,

pA2 (t)   = is the instantaneous A-weighted sound pressure in pascals (Pa);

t2 – t1      = is a stated time interval in seconds (s) long enough to encompass all significant sound energy of the event;

po          = is the reference sound pressure level (20 pa); and

to        = is the reference time interval (1 s).

2 L AE is also known as L Ax (single-event noise exposure level).

19.1.33. Sound Power – The acoustic power of a sound source, expressed in Watts.

19.1.34. Sound Power Level, L w - The acoustic power radiated from a given sound source as related to a reference power level (typically 10 -12 watts) and expressed in decibels as:

 

L w = 10 log10           W 

                            10 -12

Where,

W = Acoustic power in watts.

By definition, 1 W therefore corresponds to 120 dB for L w.

19.1.35. Sound Pressure, p – Root-mean-square value of the variation in air pressure measured in pascals (Pa), above and below atmospheric pressure, caused by the sound.

19.1.36. Sound Pressure Level, L w - quantity of sound pressure, in decibels (dB), given by the formula:

L p = 10 log10   ( P   /  Po  ) 2

Where,

P = is the root mean square sound pressure in pascals (Pa); and

Po = si the reference sound pressure ( 20 µ Pa)

Note: The range of sound pressure for ordinary sounds is very wide.  The use of decibels gives a smaller, more convenient range of numbers. For example, sound pressure levels ranging from 40 dB to 94 dB correspond to sound pressure ranging from  0,002 Pa to 1 Pa. A doubling of sound energy corresponds to an increase in level of 3 dB

19.1.37. Sound Receiver – One or more observation points at which sound is evaluated or measured.  The effect of sound on an individual receiver is usually evaluated by measurements near the ear or close to the body.

19.1.38. Sound reduction Index, R – Laboratory measure of the sound insulating properties of a material or building element in a stated frequency band.

19.1.39. Sound source – Equipment or phenomena which generate sound. Source room is the room containing sound source.

19.1.40. Spectrum – A quantity expressed as a function of frequency, such as sound pressure versus frequency curve.

19.1.41. Standardized Impact sound Pressure Level, L nT - Impact sound pressure level normalized to a reverberation time in the receiving room of 0.5 s.

19.1.42. Speech Interference Level (SIL) – A descriptor for rating steady noise according to its ability to interfere with conversation between two people.  SIL is the arithmetic average of the sound pressure levels in the three octave bands with centre frequencies at 500, 1,000 and 2,000 Hz.

19.1.43. Standardized Level Difference, D nT  - Difference in sound level between a pair of room, in a stated frequency band, normalized to a reverberation time of 0.5 s.

Note: Standardized level difference takes account of all sound transmission paths between the rooms.

19.1.44. Structure Borne Noise – Generation and propagation of time dependent motions and forces in solid materials which result in unwanted radiated sound.

19.1.45. Transient Sound – Sound which is audible for a limited period of time, for example sound from over flight of an airplane.

19.1.46. Third Octave Band – Band of frequencies in which the upper limit of the band is 2 1/3  time the frequency of the lower limit.

19.1.47. Threshold of Hearing – The lowest continuous sound pressure level which will create a auditory sensation for the average human ear.  Any sound below these levels will be inaudible and any sound above the threshold will vary in loudness dependent on intensity.

19.1.48. Vibration Isolation – Reduction of force or displacement transmitted by a vibratory source, often attained by use of a resilient mount.

19.1.49. Wavelength – The length in space of one complete cycle of a sound wave.

y   =    (speed of sound ) =   ( C )

              (frequency)          ( f )

19.1.50. Weighted Level Difference, D w  - Single number quantity that characterizes airborne sound insulation between rooms but which is not adjusted to reference conditions.

Note: Weighted level difference is used to characterize the insulation between rooms in a building as they are; values cannot normally be compared with measurement made under other conditions

19.1.51. Weighted Sound Reduction Index, R w  - single number quantity which characterizes the airborne sound insulating properties of a material or building element over a range of frequencies.

Note: the weighted sound reduction index is used to characterize the insulation of material or product that has been measured in a laboratory.  

19.1.52. Weighted Standardized Impact sound Pressure Level, L nT,w  - Single number quantity used to characterize the impact sound insulation of floors over a range of frequencies.

Note: weighted standardized impact sound pressure level is used to characterize the insulation of floors in buildings .

19.1.53. Weighted standardized Level Difference, D nT,w    - Single-number quantity, which characterizes the airborne sound insulation between rooms.

Note: Weighted standardized level difference is used to characterize the insulation between rooms in a building .

19.1.54. Weighted Normalized Impact sound Pressure Level, L n.w    - Single number quantity used to characterize the impact sound insulation of floors over a range of frequencies.

Note: Weighted normalized impact sound pressure level is usually used to characterize the insulation of floors tested in a laboratory.

19.1.55. White Noise – A noise whose spectrum (level) density is substantially independent of frequency over a specified range and has equal power for any range of frequencies of constant band width.                                    

19.2. Planning and design against outdoor noise

19.2.1. General – Planning against noise should be an integral part of town and country planning proposals, ranging from regional proposals, to detailed zoning, and three dimensional layouts and road design within built-up areas.  Noise nuisance should be fully recognized in zoning regulations.

Noise is either generated by traffic (road, rail and underground railway) or it arises from zones and buildings within built up areas (industry; commerce, offices and public buildings). For planning, the noise survey should examine all the possible cause of noise and consider the various factors causing actual nuisance.

Noise by night, causing disturbance of sleep, is more of nuisance than noise by day. For this reason, housing colonies that adjoined areas with heavy traffic movement during the night are liable to cause serious complaints. Also, the factories that work by night are liable to cause serious complaints if housing estates adjoined them. While planning, care should be taken that housing colonies are adequately setback from busy airports, state and  national highways, factories, main railway lines and marshalling yards.

There are two aspects of defense by planning. The first is to plan so as to keep the noise at a distance. Under this aspect comes the separation of housing from traffic noise by interposing buffer zones, and the protection of schools and hospitals by green belts, public gardens, etc. The second is the principle of shading or screening. This consists of deliberately interposing a less vulnerable building to screen a more vulnerable one or by providing a solid barrier, such as a wall, between the source and the location to be protected.

19.2.2. Traffic noise levels

19.2.2.1. For air-traffic - For guidance, approximate noise levels due to various types of aircraft, measured on ground, when the aircraft’s fly overhead at a height of 450 m, are given in Table 1

Table 1 Typical noise levels of some aircraft types

Sl. No.

Type of aircraft

Fly-over noise levels at 450 m with take off thrust  (EPN dB)

i

Boeing 737

107

ii

Boeing 747–200

103

iii

Airbus A 300

101

iv

Concorde SST

114

19.2.2.2. For rail traffic – Noise levels of some typical railway traffic are given in Table 2.

Table 2 Typical noise levels of railway trains

Sl. No

Type of train

Noise level at 30 m. Measured on the side or in the direction of train, dB (A)

i

Steam train, 60 kmph

85

ii

Diesel; train, 60 kmph

83

iii

Electric train, 60 kmph

77

19.2.2.3. For road traffic -The level of noise generated by road traffic depends upon such factors as the number of vehicles passing per hour, the type of traffic, the preponderance of heavy vehicles, average speed, gradient and smoothness of traffic flow. The smoothness of traffic flow also affects variability of the noise and is governed by such things as roundabouts and traffic lights, and the volume of traffic and pedestrian movement with their effects on stopping, starting and overtaking. The level of traffic noise fluctuates continuously and the way it does has a considerable effect on the nuisance caused. For assessing traffic noise, noise is measured in dB (A). Because of the fluctuating nature of traffic noise, a unit known as L10 or Leq may be used. Typical noise levels due to different volumes of traffic flow with a varying mix of vehicles are given in Table 3.

Table 3 Typical noise levels due to free flowing road traffic

Sl. No.

Type of traffic

Noise level at  30 m from edge of road DB(A)

i

5000 vehicles per 18 hour day (10 percent heavy vehicles), 50 kmph

65

ii

10 000 vehicles per 18 hour day (20 percent heavy vehicles), 60 kmph

70

iii

10000 vehicles per 18 hour day (40 percent heavy vehicles) 80 kmph

75

iv

20000 vehicles per 18 hour day (40 percent heavy vehicles), 80 kmph

77

Note: The values are applicable to free flowing traffic without honking.

Outdoor Noise Regulations

The outdoor noise regulations in force from time to time shall be complied with (see also Annex D)

19.2.3. Planning and design

19.2.3.1. For air traffic – Near airports two sources of aircraft noise should be considered.

a) Fly-over noise - Fly-over noise is that which occurs under flight paths close to airports and is the most serious and common problem. As the aircraft passes overhead the noise level at any particular location rises to a peak and then decreases.

b) Ground noise - The noise emitted by an aircraft during ground operations, is less variable in direction than flyover noise, but is usually of a longer duration.

Aircraft noise may disturb sleep, rest and communication, and as such may be considered potentially harmful to health. It is important that no new development is carried out  within areas where the expected noise levels will cause mental and physical fatigue or permanent loss of hearing. In case development in such areas is essential, adequate sound insulation shall be provided for the building.

As the problems caused by aircraft noise have become more acute, a number of methods have been devised for evaluating noise exposure in the vicinity of airports. They all combine many factors into a single number evaluation. A commonly used criterion is the noise exposure forecast (NEF). The NEF is used primarily to develop noise contours for areas around airports. It has been accepted generally that noise exposure forecast levels greater than NEF 40 are unacceptable to people while levels less than NEF 25 are normally acceptable.

While it is theoretically possible to provide sufficient insulation to achieve an acceptable indoor noise environment in the area of very high outdoor noise, there is a level above which aircraft noise seriously affects living conditions no matter how much sound insulation has been applied to-the dwelling unit. For this reason it is recommended that no residential development be allowed beyond the NEF 35 level.

During summer months, the windows are normally kept open for adequate ventilation. In-view of this, no matter how much sound insulation is provided for the building structure, the noise level inside the room can never be less than 10 dB below the outdoor noise level. For very critical buildings, such as buildings necessary for maintaining and supplementing the airport services, and for commercial development, such as hotels, it is possible to provide sealed windows and to centrally air- condition the entire building. However, it is not feasible for most of the residential developments in the country. In such cases proper zoning regulations and siting of vulnerable buildings away from aircraft noise are of vital importance.

19.2.3.2. Rail traffic - This is a very serious source of noise in built-up areas, both by day and by night. Railway cuttings reduce the spread of noise, whereas embankments extend it. The elevated railway on viaducts or embankments is very common in built-up areas. The elevation increases exposure to noise but in addition the construction of the viaduct may effect the propagation of noise. In this respect solid embankments are preferable to built-up arches, which tend to act as sound boxes. Worst of all are the steel bridges, which greatly magnify the noise due to vibration.  Uphill, gradients are another feature tending lo increase noise, especially of heavy goods trains.

Wherever possible, no residential or public building zone should abut on to rail- way lines, especially on the marshalling yards which are particularly objectionable because of the shrill, clanging and intermittent noise they generate, often at night. The appropriate zones along side railway lines are industrial and commercial buildings other than office buildings. Where, these precautions are not practicable and housing has to abut on to railway lines, every attempt may be made to house as few people as possible in the vicinity of the railway lines.

The underground transportation system is being introduced in India. Experience with subway trains in the western countries has indicated that they can be both noisy and uncomfortable to passengers. Also wayside vibration can be a major cause of disturbance for the neighboring community.  Very high noise levels are propagated to long distances by the underground high speed railway, as a result of wheel rail interaction. Both air-borne noise and ground or structure-borne vibration are potential sources of complaints. Noise control measures, therefore, need to be considered for the following:

a) In stations, where high noise levels are produced at the arrival and departure of trains;

b) In tunnels, during high speed train movement:

c) Where an underground rail transit system passes close to existing structures or high rise buildings adequate attention should also be paid to the problem of ground vibration transmitted to the building, and proper isolation should be provided for critical areas: and

d) In transit cars, where sound insulation is of vital importance to provide comfortable conditions for the commutators.  .

19.2.3.3. Road traffic

Convoys of long-distance heavy trucks at night moving past through built-up areas cause serious noise complaints. On busy roads, the noise of continuous traffic may be a worse nuisance than that of railways. At least the same precautions may, therefore, be taken in the planning of dwellings in relation to arterial and truck roads as with railways. Care may be taken that local housing roads do not provide short cuts for heavy traffic through residential areas. Hilly roads present the additional noise of gear changing. Trees with heavy foliage planted on both sides of carriageway help slightly to muffle the noise, provided the foliage extends for a considerable distance (30m or more).

Road traffic may give rise to serious nuisance particularly on busy thoroughfares, between continuous high buildings in main streets, at the traffic lights, near bus stops, on steep slopes and  in  parking spaces and enclosed yards.

For zoning and planning new buildings in urban areas it is recommended that external  L10 is limited to a maximum of 70dB(A) when the dwellings are proposed to have sealed windows and 60dB(A) when the dwellings are proposed to have open windows. Indeed it is desirable to confine major new residential development to locations subject to levels substantially lower than those given above.

It is recognized, however, that within  the large urban areas, the use of sites where the external L10 is greater than 60-70 dB(A) cannot always be avoided. In that case it is suggested to utilize such design solutions as barrier blocks-in order to reduce external L10 noise levels to at least 60-70dB(A) at any point 1.0m from any inward looking facade. When the orientation of site and the density of development are such that this cannot be fully achieved, some form of dwelling insulation will have to be provided. It should be appreciated that where/open windows are a must; the occupants would have to put up with discomfort if the above conditions are not met.

Certain other methods can often be utilized to provide economical and effective protection from noise:

a) Method may be adopted to improve the smoothness of flow and reduce number of stopping and starting. This leads to an improvement even if it leads to increased flows. Flow linking of traffic lights, for example, may reduce noise nuisance.

b) Use of roads passing through residential areas may be prohibited to heavy commercial vehicles. An alternative would be to limit use by commercial, vehicles to certain times of the day.

c) Use of honking may be prohibited near sensitive buildings, such as hospitals and the like.

19.2.4. Zoning -The zoning of the different cities shall be done by the town planning authorities, taking into account besides other aspects, the noise levels from different occupancies. Wherever necessary, experts in the Field may be consulted. For detailed information on noise reduction for town planning schemes, reference may be made to good practice [see IS: 4954-1968)

19.2.5. Green belts and landscaping – Where relief from noise is to be provided by means of .green belts these may be of considerable width and be landscaped. (In case of railway tracks, a minimum distance of 50m to 70m may be provided between the buildings and the tracks.) The extent of relief that may be derived from the above may be estimated only after considering other environmental factors. Only thick belts of planting (greater than 30 m) are of real value. Strong leafy trees may be planted to act as noise baffles. Shrubs or creepers may also be planted for additional protection between tree trunks, artificial mounds and banks should be formed where practicable. As little hard paving and as much grass as possible may be used. The creation of green belt is particularly advisable on the perimeter of aerodromes, along railway lines and arterial roads, through or past built-up areas and adjoining noisy industrial zones.

3.7. Highway Noise Barriers

Barriers are often the most effective means of reducing traffic noise around residential areas. They have the great advantage that they generally protect most or all of the site. In nearly all situations, a well-designed barrier of even a modest height (say 3m) can at least ensure that all areas of open space are free from excessive noise levels.

There are two types of barriers that can be built to protect sites; one which are build solely for the purpose of reducing noise and two, which from part of the building complex (barrier blocks). Free standing walls and artificial mounds are typical examples of the first type while single and multi-storeyed dwellings and/or garages are the most common form of the second.

Of the two types, barrier blocks are more widely used because they are cheaper and also tend to form a more effective barrier overall because of their greater height and width. Barrier walls or mounds are more limited in their effect than barrier blocks for they protect little more than the area of the site close to ground level essentially because of the lack of height, as continuous walls much higher than 3m are often difficult to construct.

3.8. Special Problems Requiring Expert Advice

The purpose of noise control is to ensure that people are neither harmed not disturbed by noise. In addition to provisions given in this section, special advice may be required for more complex situations, such as those listed in Annex E.

19.3. Planning and design against indoor noise

19.3.1. Acceptable indoor noise levels in buildings - The generally acceptable noise levels inside buildings from point of view of comfort, economy and practical consideration under the conditions prevailing in this country maybe taken as given in Table 4.

Table 4 Acceptable indoor noise levels for various buildings

Sl. No.

Location

Noise level dB(A)

1

2

3

i

Audotoria and concert halls

20 – 25

ii

Radio and TV studios

20 – 25

iii

Music rooms

25 – 30

iv

Hospitals and cinema theatres

 35 – 40

v

Apartments, hotels and homes

35 – 40

vi

Conference rooms, small offices and libraries

35 - 40

vii

Court rooms and class rooms

40 – 45

viii

Large public offices, banks and stores

45 – 50

ix

restaurants

50 - 55

19.3.2. Vulnerable buildings - Some buildings or parts of buildings are specially vulnerable to noise, for example, recording and radio studios, hospitals and research laboratories. These should not be sited near loud noise sources. Most vulnerable buildings contain some areas which are they noisy and in such buildings the less vulnerable elements should be planned to act as, noise buffers. Most noisy buildings also contain quiet accommodation, which equally may be planned to act as a buffer between the noisy part of the building and adjoining vulnerable building.

19.3.3 Site and internal planning and insulation requirements. these details are covered under individual occupancies (5 to 9) as applicable to the respective character and sources of noise in different buildings.

19.3.4. Sound insulation of non-industrial buildings by constructional measures –The desired (acceptable) noise levels and the recommended insulation values for the various areas may be achieved by providing sound insulation treatments by constructional measures. The details of the same are given in Annexure 19-A.1. The recommendations given in Annexure 19-A.1 are applicable to non industrial buildings like residences, educational buildings, hospitals and office buildings.

19.4. Residential buildings

19.4.1. Sources of noise nuisance

Outdoor noise - The main sources of outdoor noise in residential areas are traffic (aeroplane, railways, and roadways), children playing, hawkers, services deliveries, road repairs blaring loud-speakers and various types of moving machinery in the neighborhood and building operations.

Indoor noise - As far as indoor noises are concerned, conversation of the occupants, footsteps, banging of doors, shifting of the furniture, operation of the cistern and water-closets, playing of radios, gramophones, etc. contribute most of the noise emanating from an adjacent room or an adjacent building. Noise conditions vary from time to lime and noise which may not be objectionable during the day may assume annoying proportions in the silence of the night when quiet conditions are essential.

In the case of flats the main sources of noise are from other flats and from stairs, lifts and access balconies. Plumbing noise is another cause, in semi-detached buildings, outdoor noises from streets, are noticed more than indoor noises from neighbors.

19.4.2. Recommendations

19.4.2.1. Site planning - The most desirable method is to locate the residential buildings in a quiet area away from the noisy sources like the industrial areas, rail tracks, aerodromes. Roads carrying heavy traffic, etc.

To minimize ground reflection, the maximum amount of planting and grassed areas and the minimum amount of hard surfacing should surround the dwellings. This applies particularly to high-density areas. Where for maintenance reasons a large amount of hard paving is necessary, it should be broken up by areas of planting and grassing.  Narrow hard paved courts should be avoided between adjacent tall buildings.

Roads within a residential area should be kept to a minimum both in width and length, and should be designed to discourage speeding. Area-wise planning, with zones from which vehicular traffic is altogether excluded will greatly help to reduce noise.  Through traffic roads should be excluded from residential areas, but where sites have to be developed adjacent to existing major roads the same principles should be observed in the siting of blocks as, with railway lines as covered under 19.2.3.2.

Play areas for older children should be sited as far away from dwellings as possible. Special care should -be taken with old people’s dwellings. They should not be placed immediately adjacent to service entries, play spaces, or to any entrances where children may tend to congregate.

19.4.2.2. Internal planning - The orientation of buildings in a locality should be planned in such a way as to reduce the noise disturbance from neighborhood areas. The non-critical areas, such as corridors, kitchens, bathrooms, elevators and service spaces may be located on the noisy side and the critical areas, such as bedrooms and living space, on the quiet side.

Windows and doors – Windows and doors should be kept away from the noisy side of the building as given below wherever possible:

a) When windows of a building, particularly those of bedrooms in apartments or flats, face roads carrying heavy traffic or other noises where the external noise is of the order of 80 to 90 dB (A) the building should be located at a distance of about 30 m from the road, but .a distance of 45 m or more where possible, should be aimed at for greater relief from noise:

b) When the windows are at right angles to the direction of the above type of noise, the distance from the road should be arranged to be about 15 to. 25m: and

c) In case another building, boundary wall or trees and plantations intervene between the road traffic and the house; flat further noise reduction is achieved and in such cases the above distances may be reduced suitably.

Layout plans - It is desirable that rooms adjoining party walls and above/below party floors should be of similar use. By this means, bedrooms are not exposed to noise from adjoining living rooms, and there is less risk of disturbance of sleep.

In semi-detached houses, the staircase, hall and kitchen should adjoin each other on each side of the party wall, thus providing a sound baffle between rooms requiring quiet conditions.

Open fireplaces on party walls should be avoided as far as possible: bedrooms should not be planned alongside access balconies, and preferably not underneath them. Where the approach is by an internal corridor, a sound barrier may usefully be provided by arranging internal passages and bathrooms between the corridor and the living room or bedrooms.

Water-closets should not be planned over living rooms and bedrooms, whether within the same dwelling or over other dwellings. Soil pipes should not be carried in ducts, which adjoin living rooms or bedrooms unless the side of the duct next to these rooms is a solid wall containing no inspection openings. Refuse chutes should not be planned next to living rooms or bedrooms.

19.4.2.3. Sound insulation

19.4.2.3.1. Reduction of air-borne noise - 'The average sound insulation for air-borne noise (over the frequency range 100-3150 Hz) between individual rooms or apartments of a building unit shall be as given in Table 5. These values may, however, be suitably increased, where required, for critical areas.

Table 5 Sound insulation between individual rooms (air-borne)

Sl. No.

Situation

Average sound insulation in dB (100-3150 Hz)

i

Between the living room in one house or flat and the living room and bed rooms in another

50

ii

Elsewhere between houses or flats

45

iii

Between one room and another in the same house or flat

35

Note 1: Where communicating doors are provided, all doors should be so designed as to provide recommended insulation between the rooms.

Note 2: There are cases when a set of houses or flat have to be built for the people who work at night and sleep during the day. It is desirable to consider the design of at least one such room in each of the houses or flat, which will provide an insulation of about 45 dB in the room.

Note 3: The insulation values referred to are applicable with doors and windows shut.

19.4.2.3.2. Suppression of noise at the source itself - All items of equipment that are potentially noisy should be selected with care. Water-closet cisterns should not be fixed on partitions next to bedrooms or living rooms. Plumbing pipes should be isolated from the structures. Lift motors should be mounted on resilient supports. Access doors from machine rooms to internal staircases should be  well  fitting  and  of solid construction.

19.4.2.3.3. Reduction of air-borne noise transmitted through the structure - Reduction of air-borne noise requires the use of rigid and massive walls without any openings. Openings are the major cause of penetration of noise through a barrier. While designing it should be borne in mind that all components should provide a sound transmission compatible with that of the rest of the barrier so that an equivalent amount of sound energy .is transmitted through each portion of the barrier.

Ventilating ducts or air transfer openings where provided should be designed to minimize transmission of noise. For this purpose, some sound attenuating devices may be installed in these openings.

All partitions should be sealed effectively where they butt against rest of the structure. All doors and windows should be properly gasketed where a high degree of sound insulation is desired.

19.4.2.3.4. Reduction of structure-borne noise - This requires the use of discontinuous or non-homogeneous materials in the construction of the structure.

19.4.2.3.5. Reduction of impact noise –The floor of a room immediately above the bedroom or living

room shall satisfy the grade 1 impact sound insulation given in Figure 1. For example, 150mm thick concrete floor with thick carpet (12mm) covering would satisfy this requirement.

19.4.2.3.6. Main staircases in blocks of flats are often highly reverberant. Some of the surfaces at least (for example, the soffits of stairs and landings) should be finished with sound absorbent materials wherever required.

 

Fig 1 Grades of impact sound insulation

19.5. Educational buildings

19.5.1. Sources of noise nuisance

Outdoor  noise -The  outdoor sources  of  noise  produced  on  school premises, which cause disturbance within the school,  include  the  noise  arising  from playgrounds,  playing fields and open air swimming pools. Though playgrounds are used mainly during break periods, they are also used for games and physical education at times when teaching is in progress in the adjoining class rooms.

Indoor noise – Indoor sources of noise are as follows:

a)  Singing, instrumental and reproduced music which may take place in class rooms and in dining and assembly hall particularly in primary schools. In secondary schools, specialized music room is generally provided;

b) The movement of chairs, desks and tables at the end of one period may disturb a class engaged in a lesson in a room below:

c) The shutting and opening of doors and windows which may occur at any time during teaching periods:

d) Wireless and television reproduction in class-rooms, and films with sound track

e) Wood and metal workshops, machine shops (engineering laboratories), typing rooms etc, which produce continuous of intermittent sound of considerable soundness:

f) Practical work carried out in general teaching areas;

g) Gymnasium and swimming pools;

h) School kitchens and dining spaces where food preparation and the handling of crockery and utensils persist for the greater part of the school day;

j) Corridors and other circulation spaces and

k) Plumbing and mechanical services.

19.5.2. Recommendations

19.5.2.1. Site planning - Where outdoor noise nuisance exists from local industry, busy roads, railways, airfields, sport ground or other sources beyond the control of the school authority, school buildings should be sited as far away as possible from the sources of noise. Rooms should be planned in a manner so that the minimum amount of glazing is placed on the side facing the external noise.

Noises arising from the activities of a school and from the use of the buildings after school hours may constitute a nuisance to occupants of surrounding property: therefore. It is desirable to place playgrounds, workshops, swimming pools, music rooms, assembly halls and gymnasia as far away as possible from buildings which require a quiet environment.

19.5.2.2. Internal planning -The following principles should be observed in the detailed planning of educational buildings:

a)  Grouping - Noisy rooms should be separated from quiet ones, if possible. In general, it is desirable that rooms should be grouped together in accordance with the classification given in 19.5.2.4.

b)  Windows and ventilators - Windows of noisy and quiet rooms should not open on to the same courtyard or be near to one another. Roof lights and ventilators over noisy rooms should be avoided, if they are likely to be a source of nuisance to adjacent upper floors.

c) Doors - Swing doors into rooms should only be used where no problem of sound transmission exists. Reduction of insulation between rooms and corridors due to doors must be borne in mind. The type and method of fitting of doors is important and necessary care shall be paid in this respect.

d) Sliding partitions should only be used where, essential.

e) Open planning and circulation areas - Where open planning, is used to permit spaces, such as assembly halls, dining rooms or entrance halls to be used in association with each other or for circulation, the degree of disturbance caused by interfering noise to teaching areas needs careful consideration; traffic through such areas should be strictly controlled; full use should be made of sound absorbent treatments to reduce the spread of noise from one space to another (see 19.5.2.3).

If rooms have large glazed panels or ventilation openings facing directly on the circulation areas, human traffic passing by the rooms should be controlled. Preferably baffled ventilation system or double windows should be used. (Fan-lights over doors should be fixed and glazed.)

f) Furniture - In all educational buildings, regardless of the character of the floor finish, rubber buffers should be fitted to the legs of chairs and tables.

19.5.2.3. Noise reduction within rooms - Sound absorbent materials plays a useful part in reducing the built-up or air-borne noise at source.  In rooms such as class-rooms, assembly halls and music rooms, a fairly short reverberation time under occupied conditions is one of the requirements of the acoustic design. The maximum reverberation times permissible for this purpose are usually short enough to give adequate noise control but in addition, the reverberation time should not be excessive

under empty conditions, because noise may occur in these rooms with very few occupants. Table 6 gives the reverberation times often arranged in occupied rooms for acoustic reasons and the maximum times recommended in the empty rooms for noise reduction; the times given are for a frequency of 500 Hz, but they should not be greatly exceeded at any frequency. When rooms are used for a variety of purposes, the reverberation period appropriate to the major use should be adopted.

Special attention should be given to noise reduction in schools for the deaf and schools for the blind. Deaf children are taught by means of hearing aids which cannot be used satisfactorily in high noise levels or in reverberant conditions. Blind children depend on good hearing for understanding speech and for detecting changes in environment. In both these types of schools, noise levels should be kept low and reverberation times short. As an example, the reverberation times in empty class-rooms should not exceed one second in schools for the blind or 0.5 second in schools for the deaf.

Table 6 Reverberation times in schools

Sl. No.

Room

Reverberation times

Usual for acoustic reasons (full)

Maximum* for noise control (empty)

i

Assembly halls

1.0 – 1.25

according to size

1.5 – 2.5

according to volume of hall

ii

Music teaching rooms

0.75 – 1.25

1.5

iii

Gymnasium and indoor swimming pools

----

1.5

iv

Dining rooms

----

1.25

v

 Class-rooms

0.75

1.25

vi

Headmasters room and staff rooms

0.5 – 1.00

1.0

* Shorter reverberation times are desirable for noise control whenever possible.

Special attention should be give noise reduction in schools for the deaf and schools for the blind. Deaf children are taught by means of hearing aids which cannot be used satisfactorily in high noise levels or in reverberant conditions. Blind children depend on good hearing for understanding speech and for detecting changes in environment. In both these types of schools, noise levels should be kept low and reverberation times short. As an example, the reverberation times in empty class-rooms should not exceed one second in schools for the blind or 0.5 second in schools for the deaf.

19.5.2.4. Sound insulation

Air borne noise – For purposes of sound insulation, rooms in educational buildings may be classified as follows:

Class A

Noise producing

Workshops

Kitchens

Dining rooms

Gymnasiums

Indoor swimming pools

Class B

Producing but needing quiet at times

Assembly halls

Lecture halls

Music rooms

Typing rooms

Class C

Average

General class rooms

 

 

Practical rooms

Laboratories

offices

Class D

Rooms needing quiet

Libraries

Studies

Class E

Rooms needing privacy

Medical rooms

Staff rooms

The recommended minimum sound reduction (average over 100 – 1350 Hz) between rooms of the same class is as follows:

Class A

25 dB

Class C or D

35 dB

Class B or E

45 dB

Where a room is likely to have a dual use, for example, a dining room to be used as a class-room, the higher sound insulation value should be used.

The recommended minimum sound insulation between rooms in different classes is 45 dB  subject  to  the  following:

a) In schools or institutes with a technical bias where noisy activities, such as sheet metal work, plumbing and woodwork are likely to be practiced extensively in normal hours, workshops should be regarded as a special category requiring more than 45 dB insulation from rooms of any other class.

b) Assembly halls and music rooms are special cases in that, as well as producing noise, they also require protection from it and may need more than 45 dB insulation from rooms in Class A. if the latter are very noisy.

c) Circulation spaces may vary from a long and frequented corridor to a small private lobby and it is therefore difficult to give precise recommendations to cover them. For partitions between rooms in Class C and most corridors. 35-dB insulation for the partition itself is adequate. For partitions between rooms in other classes and corridors, more or less insulation maybe necessary, depending upon the specific usage.

d) The problem of noise in circulation areas is as a rule greatly mitigated in schools by the fact that classes usually change rooms together at regular times. In colleges and evening institutes, however, this is much less true and in such buildings particular attention should be paid to insulation between rooms and corridors.

Open plan schools - A new concept in school planning is the use of a large teaching area with simultaneous instructions imparted to several groups of students. These open plan-teaching areas offer a different set of problems. Because of the limitations in achieving a great deal of attenuation across the space and related difficulties in noise control and speech interference, lecturing to a large number of students is not possible without interfering with neighboring groups. The shape of such spaces may be as linear as possible with a width to height ratio of 5:1 or greater. In addition, special measures are required to be introduced to reduce the level of intruding speech to an acceptable value so that the various teaching groups are not disturbed and adequate privacy is maintained, judicious positioning of partial height barriers can improve the sound attenuation between teaching groups and the use of reflective screens can reinforce the speech locally without reflecting it to unwanted areas.

Impact noise - In these cases of schools, the concrete floor of the room immediately above the teaching rooms shall meet Grade II standard for impact insulation shown in Figure 1. For example a covering of 6 mm linoleum or cork tiles on concrete floor (hollow or solid) weighing not less than 220kg/m will usually meet the above requirement.

19.6. Hospital building

19.6.1. General - Problems of noise control vary from hospital to hospital but .the principles outlined below apply to all types. A quiet environment in hospitals is desirable for patients who are acutely ill.

Staff requires quiet conditions for consultations and examinations and also in their living and sleeping

quarters. There have been rapid rises in noise levels in hospitals due to the higher levels of outdoor noise, to increasing use of mechanical and mobile equipment (some of which is now brought much nearer to the patient in order to facilitate nursing procedure) and the introduction of loudspeaker, radio, television and call systems. Noise control in the hospital is made much more difficult by the extensive use of hard washable surfaces, which reflect and intensify the noise.  In most hospitals, windows to the open air and fanlights to corridors are usually open for the purpose of ventilation, admitting noise from outside and allowing it to spread through the building.

19.6.2. Sources of noise nuisance

Outdoor noise - This may be classified into two main categories:

a) Noise from sources outside the hospital premises, for example, traffic and industrial noises; and

b) Noise from sources outside the building but usually within the control of the hospital authority, for example, ambulances. Motor-cars and service vehicles, fuel and stores deliveries, laundries, refuse collection, trucks and trolleys.

Indoor noise - A hospital is a complex building with many services and the numerous internal sources of structure-borne and air-borne noises are grouped into three main categories:

a) Noises consequent upon hospital routines - This category includes sources, which transmit noise through both structure-borne and air-borne paths, many of which may be quite near to patients particularly those in wards such as the following:

1) Wheeled trolleys of various kinds for food and medical supplies:

2)  Sterilizing equipment;

3)  Sluice room equipment including bedpan washers:

4) Ward kitchen equipment:

5) Footsteps:

6) Doors banging:

7) The handling of metal or glass equipment:

8) Noises caused during maintenance and overhaul of engineering services: and

9) Vacuum- cleaners, mechanical

b) Loudspeaker, radio or television, audible calls system, telephone bells and buzzers. and other air-borne noises, such as loud conversation; and

c) Noises from fixed or mobile equipment and services not directly concerned with hospital routines. These include all the fixed services as given below:

1) Plumbing and sanitary Fittings

2) Steam, hot-and cold water and central heating pipes

3) Ventilation shafts and ducts

4) Pans

5) Boilers                     

6) Pumps

7) Air compressors

8) Pneumatic tubes

9) Electrical and mechanical motors and equipment

10) Lifts

11) Laundry equipment: and

12) Main kitchen equipment (refrigerators. mixers, steam boilers, etc).

19.6.3. Recommendations

19.6.3.1. Site planning - Hospital sites with their high degree of sensitivity to, outside noise should be as far away from outside sources as may be compatible with other considerations,  such  as  accessibility  and availability of services. The building should be so arranged on the site that sensitive areas like wards, consulting and treatment rooms, operating theatres and staff bedrooms are placed away from outdoor sources of noise, if possible, with their windows overlooking areas of acoustic shadow.

19.6.3.2. Detailed planning – There is a very large number of unit and room classification in hospital design and in planning the units in relation to each other and to the common services, (such as X-ray departments, operating theatre suits and main kitchens). noise reduction in the sensitive areas should be weighed carefully against other design factors. Special care in overall planning and internal planning against noise is required in the planning within the building of units which are themselves potential noise sources, for example, children’s wards and outpatients departments, parts of which require protection against noise.

Unloading bays refuse disposal areas, boiler houses, workshops and laundries are examples of service units which should be as far from sensitive areas as possible.

The kitchen is a constant source of both air-borne and structure-borne noise and should preferably be in a separate building away from or screened from the sensitive areas. If this is not possible and the main kitchens must form part of a multi-storey building, noise control is easier if they are placed below and not above the wards and other sensitive rooms so as to 'facilitate the insulation of the equipment and machinery in order to reduce the transmission of structure borne noise to a minimum.

Inward units, the kitchens, sluice rooms, utility rooms, sterilizing rooms and other ancillary rooms, need to be placed quite near to the beds if they arc to fulfil their purposes, which are all sources of noise. Some form of noise baffling between open wards and rooms of this kind will be needed.

19.6.3.3. Reduction of noise at source - In view of the difficulty of suppressing noise in  hospital  buildings,  it  is  important  to eliminate  noise  at  its  source  wherever possible.

a) Use of resilient material – Mats of rubber or other resilient material on draining boards and rubber-shod equipment will greatly reduce noise from utility rooms, sluice rooms and ward kitchens. The use of plastics or other resilient materials for sinks. draining boards, utensils and bowls would also  reduce .the  noise.  Many items of equipment especially mobile equipment, such as trolleys and beds, may be silenced by means of rubber-tyred wheels and rubber bumper and the provision of resilient floor finishes (see 19.6.3.4.1). The latter also reduces footstep noise. Silent type curtain rails, rings and-runners should be used. Lift gates and doors should be fitted with buffers and silent closing gear.  Fans and other machinery should be mounted on suitable resilient mountings to prevent the spread of noise through the structure.

b) Other measures - Noise from water or heating pipes may be reduced by installing systems, which operate at comparatively low pressures and velocities. Silencing pipes and specially designed flushing action reduce water closet noise at source and make structural measures easier to apply. The ventilation system should be designed so as not to create a noise problem. Silent closers should be fitted to doors.

19.6.3.4. Reduction of noise by structural means -

Insulation - Since the various departments or units may be planned in many ways, only general guidance on the insulation values for walls and partitions are given as below:

a)  It is recommended that walls or partitions between rooms should normally have an insulation value of at least 40dB. Higher values of insulation of at least 45 d B are necessary where a noisy room is adjacent to one requiring quiet. Doors should be solid with close fitting in the frames.

b) There is little insulation value in double swing doors and where these are fitted to a noisy room the opening should be planned so that it is screened from areas requiring quiet by a baffle lobby lined with absorbent material.  Very high insulation values may be necessary in special cases and exceptional measures may be required.

c) Solid floors with floating finishes and resilient surfaces are necessary particularly between wards and other parts of the building. Ordinary timber board on joist floors should never be used.

d) Conduits, ventilation ducts, chases, etc, should be constructed so as not to form easy by-pass for disseminating noise about the building, and should be provided with sufficient sound insulation. Pipe ducts should be completely sealed around the pipes where they pass through walls or floors. Ducts carrying waste or water pipes should be lined with sound insulating material to prevent noise from the pipes passing through duct walls into the rooms through which they pass.

Absorption - Most surfaces in hospitals should be easily cleanable so as to prevent the build-up of bacteria, which may cause cross-infection. Many sound absorbent materials of a soft nature and difficult to clean are unsuitable for use in some hospital areas and lose much of their effectiveness, if painted for hygienic reasons.

Some porous materials with very thin non-porous coverings (like mineral wool covered with thin plastic sheets) have good sound absorption and when covered with a perforated sheet metal lacing can be used in most areas requiring a washable acoustical treatment. In noisy areas, such as corridors and waiting rooms, however, a wider choice of absorbents is available.

In the ward, bed curtains, window curtains etc, add to the absorbent properties of the room and help reduce reverberation in otherwise hard surfaced surroundings.

Sensitive areas such as operation theatres, doctors' consultation rooms, intensive care units (ICU) require special consideration against noise control. Apart from outdoor noise, a common problem is the transmission of sound .between the consulting room and the waiting room. To ensure silence, a sound reduction of 45dB (A) between the rooms shall be provided. If a single communicating door directly connects the doors it will not be possible to achieve these values of insulation. To obtain 40-45 dB (A) insulation between communicating rooms, it is necessary to provide two doors separated by an air gap, such as a lobby or corridor.

19.7. Office buildings

19.7.1.  General - Modern  office .buildings  are often noisier than older buildings due to the use of thinner and more rigid forms of construction, harder finishes, more austere furnishings and use of business machines.

19.7.2. Sources of noise nuisance

Outdoor noise - The outdoor noise is mainly traffic noise, noise from an industry if any located  nearby  or  from  any  other source depending upon the location of the office  building.  The methods of defense against outdoor noise as given in 19.2 shall also be used in addition to those given in 19.7.

Indoor noise - Main sources of indoor noise include the following:

a) Office machines, such as typewriters, and calculating, tabulating and punching machines:

b) Telephonic conversation;

c) Noise from the public admitted to the building,

d) Footsteps, voices and slamming of doors in circulation spaces, lift doors and gates

e) Sound reproduction in staff training rooms and cinemas and machine noise in projection rooms, recreation rooms, etc;

f) The handling of crockery and utensils in canteens and kitchens; and

g) Ventilation plant and lift machinery

19.7.3. Recommendations

19.7.3.1. Site planning - Rooms demanding quiet conditions should be placed on the quiet side of the site. Even on quiet thoroughfares, these rooms should not be planned at street level. They should also not be planned on enclosed yards used for the parking of cars, scooters, etc.  Where, however, the problems cannot be resolved by planning, the provision of double windows may be necessary

19.7.3.2. Detailed planning

Noise reduction within rooms – These reverberation times should not exceed one second in all general offices of the types listed below. In small private offices, the reverberation time should not exceed 0.75 second, in very large offices the reverberation time may be increased to 1.25 seconds.  For canteens, the recommended maximum reverberation time is 1.25 seconds.

Large general offices – The grouping of departments and machines together in one room should be avoided wherever possible.  Where supervision is necessary the provision of glazed screens carried up to the ceiling should be considered. If it is essential to the work of an office for machine operators and clerks to work side by side in the same room the machines should be enclosed by panels or low screens lined with absorbent material and the ceiling should be sound absorbent. In addition, the machines should be as quiet as possible in operation and mounted on suitable resilient mountings.

Note: A quiet area should be planned for prolonged telephonic conversation.

Light weight construction - Modern construction methods and economy dictates the use of lightweight construction for many office buildings. While the lightweight materials lead to fast fabrication and erection and also effect considerable economy in the building structure, they may lead to tremendous sound insulation problems between adjacent offices and areas. Lightweight construction is also frequently employed for the subdivision of large space into executive cabins and secretarial areas. Where such construction is considered desirable, efforts should be made to provide a double-skin panel. The panels should be isolated from each other as far as possible either by the use of separate framing or by the use of elastic discontinuities in the construction, and a sound absorbing material may be introduced in the air cavity between the panels. The partitions should be full height up to the bottom of the roof above and any openings required for air movement should be provided with sound attenuators compatible with the rest of the partition.

When lightweight floors are provided in multi-use buildings, adequate attention shall be paid to the question of air-borne and structure-borne noise transmission from the upper floors to the floors below. For effective reduction of air-borne, noise, a double panel hollow floor construction may be employed with some heavy sound damping material introduced between the panels and the panel isolated from each other. The sound damping material could be sand, mineral wool, etc. In case impact noise isolation is also required, the upper panel should be effectively isolated from the rest of the floors and building structure. The choice of the isolation layer would of course depend upon the lowest frequency of interest.

Another point to be kept in mind when going in for lightweight construction is to ensure that the light weight panels are not in resonance with the natural frequencies of any mechanical equipment installed inside the building. Lightweight materials have high natural frequencies well within the audio range and may resonate or vibrate due to an applied vibratory force. This vibratory force is caused by mechanical equipment, road traffic, rail traffic, etc. Special measures also need be taken to isolate either the source or the building so as to reduce the amount of vibration transmitted to the building structure.

Open plan offices - A new concept in office planning is the use of open plan offices.  Large open floor spaces are converted into an office area with senior executives, junior executives and secretarial staff all seated within the same area without the use of any partitions or walls. While this method of planning is appreciated, it leads to a problem of inadequate acoustical privacy between adjacent workspaces. Special design measures are therefore, required to reduce the level of intruding sounds at work places to acceptable low value so that people are not disturbed and adequate privacy is maintained.

Some special measures, which might considered for such open plan offices are the use of an acoustical ceiling together partial height barriers between workspaces. All designed to provide adequate privacy between adjacent workspaces. In addition use may have to be made of a background masking noise system which provides a constant level of a generally acceptable background noise in the entire office area. The masking noise system is a very useful concept in open plan office design because by raising the background level at every workplace, intruding noises are made less disturbing.  A background music system cannot serve as a noise masking system because the music does not have a constant spectrum or  sound  level.  In fact the background noise masking system must be introduced gradually without the feeling of employees, the air-conditioning system can also be used to generate background masking noise if the noise level from the fans, ducts and grills is suitably tailored to generate the desired frequency spectrum. However, it is not simple to predict the noise level of air-conditioning components accurately. On the other hand, the electronic system enables both the level and the spectrum of the background noise to be finally adjusted to suit individual job requirements.

Office equipments rooms – It is important that machines like typewriters, printers etc, should be quiet in them and also be fitted with resilient pads, to prevent the floors or tables on which they stand from acting as large radiating panels. It is desirable to locate machine further apart and. to apply sound absorbent treatment to the ceiling.   

Banking halls - If banking halls are large and lofty, noise nuisance tends to be aggravated.  It is advisable to avoid high reflective ceilings. The worst effects may be reduced by segregating the noise from the quiet operations and screening one from the other and by applying sound absorbent materials to the surfaces of the ceilings, screens and nearby wails.  Resilient flooring is also recommended.

Public offices and waiting spaces - Noise nuisance may be minimized by the provision of resilient flooring, sound absorbent ceilings and heavy full height screens between the public space and the clerical office.

Canteens -The   provision of a sound absorbent ceiling, resilient  flooring and the use of plastics trays and tables with 'quiet tops are recommended.

Circulation spaces – The effective length of long corridors should be limited by providing swing doors at intervals. Hard floor finishes and board and batten floors in corridors should be avoided. The provision of a sound absorbent ceiling in corridors recommended.  Floor ducts should be planned on one side of corridors.

The noise from slamming of doors may be reduced by fitting automatic quiet action type door closers. Door buffers are useful but may reduce insulation of air-borne sound due to the inevitable gaps between buffers. Continuous soft, resilient strip let into the doorframes is preferable. The use of quiet action door latches is recommended.

Staircases and lifts should be isolated from quiet rooms and shall have silent type doors.

19.7.3.3. Requirement of sound insulation - With open window (single or double) the net insulation will be 5-10 dB, and with sealed double windows it will be 40-45 dB. Intermediate values are obtainable with closed openable windows (single or double) but only, of course, at such times as ventilation may be dispensed with.  Having to choose between ventilation and noise exclusion is a serious handicap to efficient working in offices.  In large office blocks on noisy sites, consideration should be given to the provision of sealed double windows and mechanical ventilation at least in the offices on the sides of the building exposed to noise.

The insulation necessary between adjoining rooms, both horizontally and vertically depends upon the amount of noise created within the rooms, the amount of intruding noise and whether it is important that conversation should not be overheard between rooms. Generally a sound insulation value of 30 dB between one room and another room in office is recommended.

The following list may be considered as broad classification of noise producing rooms and rooms requiring quiet though many offices fall into both categories. Where room in opposing categories is planned adjacent to each other, a sound reduction of at least 45 dB should be provided between them.

Noise producing rooms

Rooms requiring Quiet

Entrance halls, staircases and corridors used by the public

Executive's rooms Conference rooms and Board rooms

Lifts and lift halls

Interview rooms

Motor and plant rooms

Offices for one of two persons

Lavatories

Medical officer's rooms

Public offices

Sick rooms

Canteen and kitchens

Rest rooms

Office machine rooms and typing pools

Libraries

Recreation rooms

Telephoning rooms

Large general offices

 

Cinemas and projection rooms

DW

a) Rooms requiring quiet (as listed above) on a quiet site where privacy is required

45 dB

b) Rooms requiring quiet (as listed above) but on a noisy site or where a lower degree of privacy is tolerable

40 dB

c)   Clerical offices in which noise does not constitute a major nuisance

20 – 30 dB

It is recommended that the minimum sound reduction index Rw for floors should be 45dB, and the floors should have a resilient finish.

19.8. Hotels and hostels

19.8.1. General - Hotels and hostels are primarily used as dwelling units, and hotels also provide for public entertainment. The most serious risk of course is disturbance to sleep, and adequate care, therefore, need be taken to protect the occupants from disturbing outdoor and indoor noise.

Outdoor noise - Hotels near railway stations, airports, highways and those situated in highly urbanized areas are specially vulnerable to outdoor noise. The outdoor noise in many of the areas is of a high level even late at night and in the early morning, The noise could also be due to other types

of activities such as building construction activity (pile driving, concrete mixing etc) and various types of portable utility equipment, such as compressors or generators.

Indoor noise - In so far as indoor noise is concerned, the noise could be due to the occupants themselves, which is transmitted from one room to the other. It could also be due to public functions and late night use of restaurants located, in the hotel as also due to miscellaneous utility equipment installed for providing and maintaining the services in the hotel, such as air-conditioning equipment, pumping equipment, power laundry and kitchen.  Sometimes hotels equipped with standby generators are a potential source of noise. Only other source, which could lead to disturbance to the occupants, is the plumbing.

19.8.2. Recommendations

19.8.2.1. Site planning - While it is desirable, to locate the hotel, or hostel away from an area where there is a high ambient noise level, many a times these have to be located in noisy areas for public convenience. Hotels near airports and railway stations are becoming popular because they are convenient for passengers in transit. Hotels located in the commercial areas of a city are also a commercially viable proposition and many a time this factor outweighs the other problems associated with such a location. When a reasonably quiet location  is not possible,  it  is desirable that adequate measures be considered to provide a comfortable acoustical environment for the occupants.

19.8.2.2. Internal planning - Where a hotel is located in a noisy environment, the provision of sealed windows (single or double) and an air-conditioning system is desirable for rooms exposed to noise. The requirements for the windows would of course, depend upon the level and character of noise in the area.

The general recommendation for satisfactory acoustical design of hotels and hostels are given below;

1) Hotels of all classes shall by necessity provide, good protection against indoor noise. Since hotels can be considered as flats, the standards of protection recommended for flats are also applicable to hotels. Partition between guestrooms and between room’s corridors and floors shall not be less than 115 mm brick wall plastered or equivalent. The floors shall have proper impact insulation Special attention should be paid to built in wall cupboards as these are potential areas of sound leakage.

These will not serve as sound insulating partitions and may not be relied upon to increase the insulation value of partitions against which they may be built. In fact, partitions between adjoining rooms should continuous behind the cupboards. Use of silent type door gear and cupboard catches is also highly desirable.

2) Door openings on opposite sides of corridors shall be staggered and doors are provided with gaskets on head, sides and threshold.  Inter-communicating –doors should be double doors, fully gasket. Doors should also have quite action latches whenever possible; rooms should be entered through a baffle lobby. Wherever possible, corridor walls should not have ventilators unless they are doubling glazed and non-openable.

3) Corridors and staircases may have resilient floor coverings and sound absorbent ceilings are desirable unless the corridor is fully, carpeted. Staircases and lift wells may be cut off from corridors by means of swing doors and, if possible, isolated from guestrooms by linen stores or similar rooms. Room service pantries on floors can also be a source of noise and may be separated from corridors by baffle lobbies, unless the rooms themselves have baffle lobbies.

4) Except within the same suite, bathrooms should not be planned next to bedrooms. 'Where this is unavoidable, internal pipe shafts with heavy walls, unpierced on bedrooms side may be used as means of separation. It is important to choose quiet type of sanitary fittings and to design the plumbing system so as hot to create noise that is by avoiding sharp bends, restrictions of flew, quick-action valves that might cause water hammer, etc.

5) Air-conditioning system should be quiet in operation. Care should also be taken that the air-conditioning ducts do not lead to a cross-talk problem between rooms. Suitable acoustical lining would need to be provided in the ducts consistent with the fire safety requirements of the buildings.

6) Large hotels often have banquet halls and conference halls, which are separately hired out for public and private functions. Late night restaurants and night dubs are also popular and functions in all these areas may go on well into the night. It is therefore essential that these rooms be effectively isolated from bedrooms and effective insulation from all possible noise source, is considered. Here it is not only necessary to consider the air-borne  sound  insulation  but  it  is  also necessary   to   consider-  the   question   of structure-borne and impact noise transmitted from areas where there might be dancing late into the night.

7) While most of the noise problems encountered in hotels are applicable to hostels, the latter are normally of more economical construction and, therefore, cannot cater for special sound insulation provisions. However, as far as possible, precautions should be taken to provide comfortable conditions in hostel rooms. This is specially true for student hostels where each room is also a living room.  Students might play music or have loud discussions, late into the night. This may disturb  sleep  or  study  of  other  students. Proper precautions should, therefore, be taken  to  provide  satisfactory  conditions.

19.9.    Industrial buildings

19.9.1. General - Industrial buildings are primarily producers rather than receivers of noise. The level of industrial noise commonly exceeds that from any other source with the exception of aircraft. As compared with traffic noise, its effects are less Widespread but it is often more annoying in character.

Many industrial noises contain very strong high frequencies whines, screeches and clatter these components are relatively more attenuated by passage through the air and by the insulation of light structure than are lower frequencies.

Intermittent noises are either isolated explosions or reports, or noises of a periodic nature, such as those of pressure relief valves or blow off, or the noises of work occurring at random intervals, for example, hammering grinding and sawing operations; the latter class may be especially irritating because of high frequency components.

19.9.2. Sources of industrial noise

Noises in industrial buildings are mainly of indoor origin. Noise in factories and workshops is generally caused by machine tools and by operations involved in making and handling the product and they are classified into the following groups, depending upon how the noise energy is generated.

1) Impact - Noise caused by impact is the most intense and widespread of all industrial noises.  It is normally coupled with resonant response of the structural members connected to the impacting surface. Common sources of this type of noise are forging, riveting chipping, pressing, tumbling, cutting, weaving, etc. Intense impact noise may also be produced during handling of materials as in the case of sheared steel plates failing one over another in collecting trays in a steel factory. Impact noise is usually intermittent and impulsive in character, but it may also be continuous as in the case of tumbling.

2) Friction - Most of the noise due to friction is produced in such processes as sawing, grinding and sanding. Friction also occurs at the cutting edge on lathes and other machine tools and in brakes and from bearings. The spectrum of frictional noise often predominates in high frequency and is very unpleasant in character.

3) Rotation and reciprocation - A rotating or reciprocating machine generates noise due to unbalanced forces and/or pressure fluctuations in the fluids inside the machines. In many cases, the moving surfaces radiate noise directly and in other cases, the pressure fluctuations are transmitted to the outer casings of the machine from where they are radiated as noise. Interaction of rotating component with the fluid stream can also give rise to pure tone components, such as the whine in a turbine. Since most machine casings have radiation efficiencies of unity in the higher frequency range, the amount of sound radiated is often substantial,

4) Air turbulence - Noise may be generated by rapid variation in air pressure caused by turbulence from high velocity air, steam or gases. Common examples are the exhaust noise from pneumatic tools

and jet engines. The noise is intense, and broad based in character and the frequency criteria depends on the size of the jet. The intensity increases rapidly with the velocity of that air stream.

5) Noises with pure tone components - Whining noise from turbines and humming noise from transformers come under this group. 

19.9.3. Noise criteria

1) Hearing damage- risk criteria - Continuous exposure to high noise levels may result in permanent noise induced hearing loss in the course of time. Damage-risk criteria specify the maximum levels and duration of noise exposure that may be considered safe. Generally accepted damage-risk criteria for exposure to continuous, steady broad band noise are shown in Table 7. Whenever-the sound level at the workers position in a factory exceed the levels and the duration suggested, feasible engineering controls shall be utilized to reduce the sound to the limits shown. If such controls fail to reduce sound levels within the levels of Table 7, personal hearing protection equipment shall be provided and used to reduce sound levels within the level shown.

2)  Interference with communication - In factories where audible warning signals are used, or where an operator follows the operation of his machine by ear, the background noise should not be so loud as to mask the signal or desired sound (the information sound) to be heard. Noise may be the cause of accidents by hindering communication or by masking warning signals.

19.9.4. Methods of reducing noise

3) Noise control by location - Machines, processes and work areas, which are approximately equally noisy, should be located together as far as possible. Areas that are particularly noisy should be segregated from quiet areas by buffer zones that produce and may tolerate intermediate noise levels.

4)  Noise reduction by layout – The office space in a factory should be as far as possible segregated from the production area and located preferably in a separate building. This building should not have a wall common with the production area. Where a common wail is unavoidable, it should be heavy with few connecting doors and no permanent openings.

5)  Noise reduction at source

i) Selection of machinery - Noise should be reduced as near the source as possible. While the operational processes in a factory may be fixed and may have no quieter alternative, careful selection of the machine tools and equipment to be used may considerably help attaining lower noise levels in the machine shop.

ii)  Reducing noise from potential sources - Impact that is not essential to a process should be quietened. Noise from handling and dropping of materials on hard surface may be reduced by using soft resilient materials on containers. Fixing rubber tyres on trucks, trolleys, etc. Machine noise may be kept to a minimum by proper maintenance. Proper lubrication will reduce noise by friction conveyors, rollers, etc.

iii)  The noise from the radiating surfaces may be reduced by reducing the radiating area. For example, if the area is halved, the noise intensity will be reduced by 3dB and at low frequencies the reduction will be much greater.

Table 7 Permissible exposure limits for steady – state noise

(Clause 19.9.3)

Sound level dB(A) (Slow response)

Time permitted. T Hr. min.

85

16 – 00

86

13 – 56

87

12 – 08

88

10 – 34

89

99 - 11

90

8 – 00

91

6 – 58

92

6 – 04

93

5 – 17

94

4 – 36

95

4 – 00

96

3 – 29

97

3 – 02

98

2 – 50

99

2 – 15

100

2 – 00

101

1 – 44

102

1 – 31

103

1 – 19

104

1 – 09

105

1 – 00

106

0 – 52

107

0 – 46

108

0 – 40

109

0 – 34

110

0 – 30

111

0 – 26

112

0 – 23

113

0 – 20

114

0 – 17

115

0 - 15

Note1: Where the table does not reflect the actual exposure times and levels, the permissible exposure to continuous noise at a single level shall not exceed the time, T ( in hours) computed  from the formula:

             16

 T  =  -----------------   

          2[ 0.2 (L - 85) ]

Where L is the work place sound level measured in dB(A)

Note 2: When the daily noise exposure is composed of two or more periods of different levels their combined effect should be considered rather than the individual effect of each. The combined levels may not exceed a daily noise dose, D of unity where 1) is computed from the formula:

           C1          C2          C3                           Cn

D  =  ------  +  -------  +  --------  + ……….+   -------

          T1         T2            T3                              Tn

Where C1, C2.............. Cn indicate the total duration of exposure (in hours) at a given steady-state noise level, and T1, T2.....Tn are the noise exposure limits (in hours for the respective levels given in the table or computed by the equation in Note 1. Exposure to continuous noise shall not exceed 115 dB (A) regardless of any value computed by the formula for the daily noise dose, D or by the equation in the Note 2,

Supporting structures for vibrating machines and-other equipment should be frames rather than cabinets or sheeted enclosures.  If an enclosure is used precaution should be taken to isolate it and line it on the inside with sound-absorbent material. The noise radiated by machinery guards can be minimized by making them of perforated sheet or of wire mesh.

v) Reducing transmission of mechanical vibration – A vibrating sources does not usually contain a large radiating surface but the vibration is conducted along mechanically rigid paths to surfaces that can act as effective radiator. If the rigid connecting paths are interrupted by resilient materials, the transmission of vibration and consequently the noise radiated may be greatly reduced. The reduction depends on the ratio of the driving (forcing) frequency of the source to the natural frequency of the resilient system. The natural frequency may be determined from static deflection under actual load as given in Fig.1. Higher the ratio between the two frequencies, lesser is the transmissibility, which is defined as the ratio of the force transmitted through the resilient isolator to the exciting force applied to it. Transmissibility and the equivalent noise reduction for various frequency ratios are given in Fig.2. For satisfactory operation, a ratio of 3:1 or more between the driving and natural frequencies is recommended.

Materials for isolators and their position are given below:

a) Material for isolators - Vibration isolators are usually made of resilient materials like steel in the form of springs, rubber, cork and felt.

1) Because of the large range of deflections obtainable in coil springs, they may isolate vibrations over a large spectrum of low frequencies. Metal springs transmit high frequency (from about two hundred to several thousand c/s) very readily.  Transmission of these frequencies can be reduced by eliminating direct contact between the spring and the supporting structure. Rubber or felt pads may be inserted between the ends of the spring and the surfaces to which it is fastened.

2) Rubber in the form of pads may be used to isolate very effectively engines, motors, etc. It may be used in compression or in shear. Some rubber mountings use rubber-in shear as the primary elastic elements and rubber-in-compression as a secondary element which furnishes snubbing action if the mounting is subjected to an overload.

3) Felt or cork or both may be used as resilient mats or pads under machine bases. The load per unit area shall be chosen to produce enough deflection for the isolation required and shall be such that at this deflection, it is not loaded beyond its elastic limit.

b) Position of isolator - The normal position of the isolators is between the machine and its foundation. However, if the forcing frequency of the machine is low (less than 10Hz) and vibration isolators with the requisite deflections for this location are not available, the machine may be bolted directly to an independent heavy inertia concrete base and the available vibration isolators used below the concrete base.

1) Large press and drop hammers which create serious impact vibration in heavy machine shops may be mounted rigidly, on very massive blocks of concrete having weights many times greater than the weights of the supported machines. The inertia blocks may, in turn, be isolated from the building structure by large wooden blocks and with thick pads of cork.

2) In critical installations (see Note), attempt should be made to locate the resilient mounts in a plane which contains the centre of gravity of the mounted assembly. It is also preferable to locate the mounts laterally as far away as possible from the centre of the machine.

Note - Critical installations are those installations where transmission of vibration from these installations will seriously hamper the normal working.                 

3) Rigid mechanical ties between vibrating machine and building structure, short-circuits or reduces the effectiveness of isolators. Loose and flexible connections should be inserted in all pipes and conduits leading from the vibrating machine. Where flexible connections are impracticable, bends should be inserted into the pipes or the pipes themselves should be supported on vibration mounts for a considerable distance from the source.

4) Flexibility of foundation - The effect of flexibility of the foundation on the isolator transmissibility shall be considered in the selection of practical vibration isolating mountings.  The simplified vibration isolation theory assumes a completely rigid foundation. However, in practice, this can never be achieved.  The foundation is never actually completely rigid. Generally, the relatively low stiffness of

the isolation system permits the assumption of the foundation to be rigid. However, if the stiffness of the isolator is allowed to become comparable to the foundation stiffness (or greater), the deflection of the isolator will become smaller and the foundation will also deflect with increased transmissibility and decreased isolator efficiency. In a dynamic sense, supporting foundation or floors should have natural Fig 2 Relation between static deflection and natural frequency frequency as high and be as stiff as possible compared to the system being isolated. Good design practice requires that the isolators should be designed assuming a rigid foundation with the stipulation that .the selected machine isolation system frequency should be well below the foundation frequency.  This point should specially he kept in mind when installing machines at upper levels in buildings because supported slabs generally have lower natural frequencies (low stiffness) than slabs on grade in basement or ground floor locations.

19.9.4.1. Noise reduction by enclosures and barriers

Enclosures - Air-borne noise generated by a machine may be reduced by placing the machine in an enclosure or behind a barrier. The enclosure may be in the form of close fitting acoustic box around the machine such that the operator performs his normal work outside the box and thus is not subjected to the high noise levels of the machine. The enclosure may be made of sheet metal lined inside with an acoustical material. Where size of the machine, working area and the operation does not permit close-fitting enclosures, the machine may be housed in a room of its own. The inside of the enclosure should be lined with sound-absorbing materials to reduce the noise level of the contained sound. The bounding walls of the enclosures shall also have adequate transmission loss to provide desired insertion loss.

Fig 3 Transmissibility and equivalent noise reduction for different ration of forcing and natural frequencies

Barriers - A partial reduction of noise in certain directions may be obtained by ‘barriers’ or partial enclosures or partial height walls. Two-sided or three-sided barrier with or without a top and invariably covered on the machine side with acoustic absorption material should face a wall covered with sound-absorbing material. If the top of the enclosure is open, the reduction may be increased by placing sound-absorbing material on the ceiling overhead.

19.9.4.2. Acoustical absorption devices

Acoustical treatment of ceilings and side walls - In order to reduce the general reverberant noise level in machine shops, acoustical material may be placed on the ceiling and side walls. With this treatment 3 to 6 dB reduction of middle and high frequency noise may be achieved. While the noise level at the source, affecting the operator, may not be reduced materially, the treatment would bring down the general noise level away from the source in reverberant field.

Functional sound absorbers - For efficient noise reduction functional sound absorbers' may be clustered as near the machines as possible. These units may be suspended and distributed in any pattern to obtain lower noise levels within the machine shop. Compared on the basis of equal total exposed surface areas, functional sound absorbers have slightly higher noise reduction coefficients (arithmetic average of absorption coefficients at 250, 500. 1 000 and 2 000 Hz) than conventional acoustical materials placed directly on ceilings and walls.

19.10. Laboratories and test houses

19.10.1. Sources of noise

Outdoor noise - In a test house or laboratory, where research workers and scientists are engaged in performing sophisticated experiments, the external noise is mostly contributed by noise emitting buildings  (workshops, machine -rooms), aerodromes railway stations and general traffic noises. The outdoor sources of noise in a college laboratory include noises produced in a playground as well.

Indoor noise - The following sources mainly contribute to indoor noises in research institutions, college laboratories:

a) Workshop, machine rooms, cafeteria etc;     

b) Air-conditioners and exhaust fans,

c) Noise produced within the test house or laboratory while performing experiments, and

d) Typing or other machine noises, telephone service lift sanitary services, etc.

19.10.2. Recommendations

Site planning - While planning for a laboratory or test house, care should be taken in the design that no noise emitting installations should exist in its neighborhood. However, where outdoor noises exist such as from local factory, heavy traffic aerodromes, railway lines, sport grounds or busy markets, buildings should be kept as far as possible away from the source of noise.

The window and door openings towards the noise sources should be minimum. Minimum amount of glazing should be placed on walls directly facing the noise sources.

19.10.2.2. Internal planning

Noisy places should be kept separate from the quiet ones. The location of laboratories or test houses should be so chosen that it be cut off from the noisy zones. Where there are offices attached to a laboratory, provision should be made to treat the offices and to use acoustical partitions, to achieve a sound insulation of at least 35 dB.

In a laboratory, mostly hard reflecting surfaces and bare furnishings are found, which produce very reverberant conditions. The noise condition still deteriorates when noise-producing instruments are switched on or a heavy object is dropped on the floor. Under these conditions, sound absorbing treatment of the space is very essential. Sound absorbing ceilings are recommended to deaden such noises. Rubber buffers may also be fitted to the legs of furniture.

In large span laboratories or test houses where scientists and researchers are engaged in work and / or simultaneously busy in calculations or deskwork requiring high degree of mental concentration, use of sound absorbing screens is recommended.

Noise reduction between the test house or laboratory and corridors or general circulation space should be well kept in mind and due care should be taken of the type of doors and the manner of their fittings etc. Transmission of noise through service ducts, pipes, lifts and staircases should also be guarded. Telephones should preferably be placed in a separate small enclosure or acoustically efficient telephone booth.

To isolate a laboratory or a test house from structure borne noises originating from upper floor, sand witch type floor construction is recommended.

Wherever the provision of double glazed windows is necessary to reduce the heat losses care should be taken to provide sealed double windows rather than double-glazing in a single window.

Note: Double glazed windows for sound insulation should have a minimum gap of 100 mm between the two glasses.

19.11. Miscellaneous buildings

19.11.1. Law courts and council chambers - It is important that law courts and council chambers be protected from the intrusion of outdoor noise and from indoor noise arising both from ancillary- offices and circulation spaces. The general recommendations on site planning given in 19.2 apply to law courts and municipal buildings, but in the larger buildings at least further protection against outdoor noise can be obtained by planning offices and other rooms around the court rooms or chambers, and separating the offices from the central rooms by means of corridors. This arrangement is usually convenient to the function of the buildings.

The wall between the corridors and the central rooms should have a sound insulation value of not less than 50 dB (for example 230 mm brick) to insulate against airborne noise in the corridors. Entrances from halls or corridors into court rooms or council chambers should be through baffle lobbies with two sets of quiet action doors. Sound absorbing treatment on ceilings and upper parts or walls of entrance lobbies is recommended.

The whole of the floor of the court room or chamber including steps and seating areas set aside for the public should have a resilient floor finish to reduce the noise of footsteps and shuffling, of feet. Any tip-up seats should be quiet in action. Sound absorbing treatment applied for acoustic purposes serves also to reduce the build-up of noise within the room and, part of the treatment should be applied in a band to the perimeter of the ceiling to absorb intruding outdoor noise; it is often desirable to keep the centre part of the ceiling free of absorbent material for acoustic reasons.

19.11.2. Libraries, museums and art galleries - Quiet conditions for reading and study are essential in these types of buildings and, since their occupancy is not noise producing, intruding noise is more noticeable and distracting. Every opportunity therefore should be taken to plan for noise defense, both in respect of siting of the building and internal  planning.  When possible, stack rooms, storerooms and administrative offices should be planned to screen reading rooms, print rooms and lecture rooms from noise sources. In public libraries, the reference library and lecture rooms should receive first consideration; the lending library, newspaper and periodical rooms have a higher background noise and are secondary, in importance.

In large libraries, museums and art galleries echoes from lofty, large domed or concave ceilings are often a nuisance. Small noises such as footsteps, coughs, chair scraping and closing of books are reinforced by reverberation, and concave surfaces even when treated with a sound absorbent may focus these noises. Treated oat ceilings, if not too high obviate these troubles. Books on shelves in libraries constitute a valuable wall absorbent.

Floor finishes are important.  The impact noise of footsteps on marble, terrazzo or wood block flooring, and especially on hardwood strip and batten flooring, can be disturbing both within the room in which the noise is generated and the rooms below. On solid floors, resilient floor finishes, such as rubber, cork and linoleum on an underlay, are highly desirable. In the children's sections of libraries and museums they are essential. In existing buildings, rubber, linoleum or vinyl asbestos tiles laid over the floor in the traffic areas are often a solution to the problem.

Reference libraries in universities, research establishments, office buildings and science buildings having machines and testing benches, should he planned in a quiet part of the building.  Walls enclosing the library should normally have a sound reduction value of not less than 50 dB (for example 225 mm brick) and baffle lobbies should be planned between the library and halls and corridors. Walls facing on to corridors or other noisy areas should not have fanlights or borrowed lights unless they are double glazed and not openable.

19.11.3. Auditoria and theatres - The sources of noise that have to be considered in concert halls, opera houses, theatres, cinemas and similar auditorium buildings are as follows:

a) Outdoor noise entering through walls, roofs, doors, windows or ventilation openings,

b) Noise from any other hall in the same building, especially if let out separately for revenue.

c) Noise from foyers, service rooms and other ancillary rooms, particularly rehearsal rooms: and

d) Noise from air-conditioning plant, etc. and the cross-transmission of other internal noises via ventilating duct system.

Because of greatly increased outdoor noise, all auditorium buildings now need more care in siting than formerly. For listening to speech or music, a very low background noise level is desirable: in concert halls especially the quietest possible conditions should be provided because the pauses and moments of silence, which are an essential element of music, cannot otherwise be given full value. Therefore, sites at crossroads or close to steel railway bridges or near churches where bell ringing is practiced should be avoided unless very high standards of structural sound insulation are contemplated. Sites adjoining under ground railways may also prove unsatisfactory at basement levels owing to low-pitched noise or rumble transmitted through the ground: special isolation measure need to he adopted for isolating large buildings from ground vibration of this sort.

Whenever possible, for concert halls and theatres on city sites a- noise survey of the site should be made a suitable sound reduction value for the structure of the building can then be chosen so as to keep down to certain maximum noise levels within the auditorium. The maximum octave-band sound pressure levels (S PL) recommended are given in Table 8.

Table 8 Maximum sound pressure levels due to external and mechanical equipment noise in auditoria (dB)

Type of auditorium

Centre frequency (Hz)

63

125

250

500

1000

2000

4000

8000

Concert halls

[ dB (A) – 25 ]

51

39

31

24

20

17

14

13

Drama theatres

[ dB (A) – 30 ]

55

44

35

29

25

22

20

18

The minimum standard of sound reduction index Rw likely to be required for the envelope of an auditorium in a city to protect it against external noise is of the order of 65 dB for a concert hall or  55-60 dB for a theatre. This reduction should be provided on all sides, but it would be reasonable to make the Rw for the roof 5-10 dB less, provided the building is not unduly exposed to noise from aircraft in flight. Surrounding the auditorium with ancillary rooms and foyers is an obvious and invaluable planning method of obtaining the required insulation against outdoor noise. 19.16.3.A Ventilation intakes and returns are vulnerable features in the defence against external noise, they should be positioned so as to avoid exposure to noise, and in addition a sufficient length of both inlet and outlet ducts should be provided with carefully designed silencers. The ventilation system should also be designed to avoid transmitting or adding to internal noise.

The most serious internal noise problem arises when there are two halls meant for separate use in the same building, especially if one of them a concert hall; the-latter is a very loud potential source of noise and requires a high standard of protection against extraneous noise. In these circumstances it is doubtful whether a 'single' wall can be adequate for insulating the two halls unless it is designed with a wide un-bridged cavity. Separation by planning is preferable.

Other sources of internal noise are rehearsal rooms, scenery bays and workshops, stages of other halls where rehearsals or erection of stage sets might be in progress and foyers and bars where loud conversation might occur. The insulation of the internal walls should be adequate to protect the auditorium from these noise sources and the insulation should not be by-passed by openings, doorways, etc. The general noise due to banging of doors also needs to betaken care of: soft sealing materials should be provided for all doors to ensure quiet closing.

For detailed acoustical design of auditoria and conference halls reference may be made to good practice (refer IS: 2526-1963)

19.12. Public address system

19.12.1. Cinemas

The main objective of the design should be to control noise from adjacent screens, the projection area, the foyer, and outside the cinema. The first of these, controlling noise from adjacent screens, is likely to be the most difficult with modern digital sound systems. As most cinemas are air conditioned, there will be some noise from services. To ensure reasonable listening conditions, this should be limited to 30 dBA. This will provide some masking of the noise from adjacent screens but a high performance partition will still be essential. Masonry or lightweight construction may be used, and a typical performance specification for a lightweight wall separating two screens is given in Table 9. Cinema design, however, normally required specialist acoustic advice.

Table 9 Typical sound insulation specification for wall separating

two cinema screens (clause 12.4)

Octave Band HZ

Sound Reduction Index R, dB

3-63

38

125

44

250

50

500

61

1000

57

2000

58

4000

57

8000

55

19.13. Noise from building services

19.13.1. Mechanical. Electrical, air conditioning, heating and mechanical ventilation, and other services are provided in almost all large buildings excluding residential, commercial and industrial buildings. Noise control measures should be incorporated during the design and installation of such services to adhere to the recommended outdoor and indoor noise criteria for the kind of occupancy. For detailed design of noise control for services, specialist advice should be sought.

Some basic design techniques for noise control in air conditioning, heating and mechanical ventilation system are given in Annex G

19.13.2. Control of noise from mechanical equipments can also be done by specifying noise control requirements while purchasing the equipments (see Annex H)

* * * *