SOUND INSULATION OF BUILDINGS

ANKITA SIKDER

1554003

CONTENT

• General discussion on effects of sound• Types of Noise• Transmission of noise• Sound Insulation vs. Sound Absorption• Transmission loss• Maximum noise levels• Means of noise control and sound

insulation.

GENERAL DISCUSSION ON EFFECTS OF SOUND

High noise conditions not only result in uncomfortable living conditions, fatigue, inefficiency and mental strain, but prolonged exposure to such conditions may cause temporary deafness or nervous break-downs.

Sound-proofing is absolutely essential in case of film studios, radio-broadcasting stations, television stations, sound recording studios etc.

The insulation of noises is important for office buildings , hospitals , educational institute , hotels etc.

Though it is difficult to prevent the outdoor noises coming into the building but acceptable indoor noise levels can be achieved by adequate planning of building and its components and by suitable constructional measures using insulating materials.

TYPES OF NOISE

‘Noise’ is defined as unwanted sound. Noises from their origin point of view are of the following two types:

1. Outdoor Noises.2. Indoor Noises.1. Outdoor Noises: These noises have their

source of origin outside the room or building, such as rood traffic, railways, aero-planes, lifts, loud speakers, moving machinery in the neighborhood or in adjacent buildings.

2. Indoor Noises: These noises have their source of origin inside the room or building, such as conversation of the occupants, foot steps, banging of doors, shifting of furniture, in water closets, working of typewriters, playing of radios, gramophones etc.

Another Classifications: From the viewpoint of the analysis of sound insulation problems, the noises are again classified into two types:

1. Air-borne Noises or Sounds.2. Structure-borne Noises or Impact Noises or

Sounds.1. Air-borne Noises or Sounds: It is

generated in the air and is transmitted through the air directly to the human ear. This types of sound travels one part to another through small gapes or openings or by vibrating the partition walls or doors.

2. Structure-borne Noises or Sounds: They are originate and progress in the building structure. It is caused by impact and transmitted as air-borne noises.

TRANSMISSION OF NOISE

The noise is transmitted in the following 3 ways.1. Through the air.2. By the vibration of Structural Members.3. Through the Structural Members.The 1st type of noise transmission, being common is

important.The 2nd type becomes prominent only when the

enclosing walls, floors, ceilings etc. are of thin construction.

The 3rd type is prevalent where mechanical vibrations are caused, particularly in case of factories, work shops, public buildings, offices etc.

SOUND INSULATION vs. SOUND ABSORPTION

The distinct function of sound absorption is the prevention of reflection of sound waves where as the function of sound insulation is the prevention of transmission of sound, may be by any means. Sound insulation is used to indicate the reduction obtained when sound passes from one room to another room or from one side of partition to the other side.

Porous materials, which are generally good sound absorbents, are poor sound insulators and vice versa.

TRANSMISSION LOSS

During transmission of air-borne sound from the source to the recipient; a reduction in the sound intensity takes place and this is termed as ‘Transmission Loss’. This transmission loss is numerically equivalent to the loss in the intensity of sound expressed in decibels (i.e., dB).

The following facts regarding transmissions loss require special attention:

1. The efficiency of sound insulation of any barrier, such as partition, wall, floor etc. is expressed in terms of the transmission loss of air-borne sound

that occurs while the sound is being transmitted through the barrier.

2. The transmission loss or sound insulation offered by a structure depends upon the materials used and the method of construction employed.

3. Transmission loss varies directly with the frequency of sound.

4. Higher sound insulation of a barrier is indicated by the larger transmission loss.

MAXIMUM ACCEPTABLE NOISE LEVELS

The maximum level of noise which will neither annoy the occupants nor damage the acoustics of the building is termed as acceptable noise level inside the building.

Some maximum Acceptable noise levels:

Hospitals – 40-50 dB.

Class rooms or lecture rooms - 45-50 dB.

Residential buildings – 45-55 dB.

Factories – 60-65dB. etc.

MEANS OF NOISE CONTROL AND SOUND INSULATION

It have been laid by the Indian Standard (Is: 1952-1962) for various types of buildings.

Some example of sound insulation between individual rooms:

Between houses or flats: 40 dB.

Between one room and another in the same house or flat: 30 dB.

Between lecture rooms: 40 dB.

Between 2 wards in hospital: 30 dB . etc.

The study of noise control and sound insulation can be further divided in the following heads:

1. General consideration.

2. Constructional measures of noise control and sound insulation.

3. Practical hints and conclusions.

1. General consideration: The following general considerations should be made for noise control and should insulation in buildings.

1. The 1st and foremost way of insulating against air-borne noise is to isolate it at source. Air tight

rooms for machinery would achieve this purpose to some extent. Working methods, which create less noise, can be adopted.

2. The residential buildings should be properly located in a quite area away from the noisy surroundings. The building should be properly oriented with respect to the road and it should be such that doors and windows do not face the source of noise.

3. The different units of a building should be properly planned.

4. The provision of furnishing material and lining of walls and ceilings by means of air-filled materials, helps to reduce the noise to a great extent.

5. The transmission of noise by vibrations can be prevented by making the walls, floors, partitions very rigid and massive or heavy.

6. The control of impact sound to some extent is possible by either providing resilient materials or to carry the whole floor surface on resilient materials.

7. Structure-borne noise or sounds can be prevented

Constructional Measures of Noise Control and Sound Insulation

by introducing discontinuities in the path of vibrating waves and by using sound absorbing materials.

8. The personal protective devices, such as earplugs, head-phones etc can be used to reduce the noise to the extent of 20 to 30 dB.

1. Walls and partitions.2. Floors and ceilings.

3. Windows and doors.4. Insulating sanitary fillings.5. Machine mounting or insulations of machinery.

1. Walls and partitions: these wall constructions should act as vertical barriers in the transmission of air borne sound or noise. To achieve this objective, the following methods of wall construction can be adopted depending upon the extent of sound insulation required:

i. Rigid and Massive Homogeneous Partitions.ii. Partitions of Porous Materials.

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A composite Construction employing a combination of rigid materials and porous absorbers can be adopted with advantage of better insulation with lesser unit weight of partition.

iii. Hollow and Composite Partition Walls or Double wall Constructions.

2. Floors and Ceilings: The objective of floors and ceilings construction should be to offer adequate insulation against impact sound. The objective can be met by the following constructional measures.

i. Use of Resilient Surface Material on Floors: By this method, insulation against impact noises to an extent of 5 to 10dB over a bare concrete floors can be obtained.

ii. Providing a Floating Floor Construction: The principle underlying the construction of a floating floor is its insulation from any other part of structure.

Floating floor construction can be adopted for both concrete as well as wooden floor.

i. Concrete Floor: It is 5 types.

a. Concrete Floor with Floating Concrete Screed.

b. Concrete Floating Wood Raft.

c. Concrete Floor with Suspended Ceiling and Soft Floor Finish or Covering.

d. Concrete Floor with Light Weight Concrete Screed and Soft Floor Finish or covering.

e. Heavy Concrete Floor With a soft Floor Finish or Covering.

ii. Wooden Floors: It has 2 types.Type 1. when Supporting walls are 10cm thick or

less.Type 2. When Supporting Walls are 20cm thick or

more.We can also use of Suspended-ceiling with Air-

space.3. Windows and Doors: In case of windows,

sound insulations of single windows is improved by making them as air-tight as possible by filling the air space at the edges of such panes with sound absorbing material.

In case of doors, the transmission loss or sound reduction increases with the increase in weight.

4. Insulating Sanitary Fittings: For improved insulation, water-closets should not be fixed above a living room or next to a bed room unless the latter is well-insulated, as for example by cup-boards etc.

5. Machine Mountings or Insulation of Machinery: The machines or mechanical equipments create vibrations is an adjoining building and are transmitted further away as structure-borne sound, the machines should be insulated by resting them

on resilient supports or mountings such as steel springs, rubber, cork etc.

3. Practical Hints and Conclusions:i. From view point of noise control, when

windows of bed or living rooms face a main traffic route or a railway line, they should not be situated less than 30 to 45 m from its near edge.

ii. The increase in transmission loss or sound reduction of a solid massive construction is slow in proportion to the increase in its thickness.

iii. If the material used is of porous and flexible nature, like hair felt, its sound reduction is proportional to its thickness.

iv. In double wall or cavity wall construction, an air-space is generally better than a filling material.

v. A cavity wall with two leaves having thickness of 10cm each, has 80% increase in insulation value as compared to a single brick solid wall of 20cm thickness without any increase in weight but with a little increase in cost.

VI. Smaller and solid glass panes have better insulation property as compared to larger and thicker flexible glass panes.

VII.Double glazing of glass windows improves insulation to a considerable degree.

VIII.Sealed double windows or triple windows of plate glass with an air-space in between can be successfully used where sound-proofing is desired.

IX. A steel plate door is more efficient for sound insulation than a double wall, hollow cold storage

type door.X. The desired sound insulation or sound

reduction can be achieved in any one or more of the following 3 ways:

a. By adopting continuous construction by using homogeneous materials where sound reduction depends upon the weight per square meter.

b. By adopting semi-discontinuous construction where air-cavities are employed with cross-connection between the two partitions. These

cross-connections should be few in number and preferably made of flexible material.

c. By adopting a fully discontinuous construction where there is complete discontinuity in the structure by means of an air cavity or an elastic acoustic materials. This method is considered suitable for meeting the requirements of sound insulation of the highest order within the reasonable weight per square metre.

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