**2.3 Integrated sound and thermal insulation**

Because some of thermal insulating materials have cellular or open matrix construction, they have inherent ability to absorb sound and act as panel dampers. They also reduce noise breakout, from the machinery plant by their ability to be flexible or discontinuous link between an acoustically active surface and the outer cladding. It should be remembered that sound insulation and sound absorption are quite different terms. The function of a sound insulating construction is to reduce sound passing through it. The function of a sound absorbent material is to reduce sound reflected from a surface. Hence, porous materials in general are good sound absorbers. But they are poor sound insulators. On the other hand, hard materials in general are poor sound absorbers. But they are good sound insulators. Further, insulation of sound is measured in an adjoining room while absorption of sound is measured in the room where sound is produced. The simple material which can be used as insulator is a sheet of material placed in the sound transmission pathways. Sound energy reaches the surface in the form of a pressure wave, of which partial energy passes through the partition and the rest is reflected.

Transmission loss: as the air-borne sound passes through any structure, loss of sound-intensity takes place. This is known as transmission loss.

Important facts: (i) transmission loss is numerically equal to the loss of intensity of noise; (ii) the efficiency of sound and thermo-fluid insulation of a wall or a partition is expressed in terms of transmission loss which occurs when air-borne physical agent passes through the wall or the partition; (iii) transmission loss varies directly with the frequency of physical agent. Hence, transmission loss of a structure should be studied over a wide range of frequencies. (iv) Greater insulation of a wall or a partition is indicated by the larger value of transmission loss.

Methods of sound insulation: the method of sound insulation will depend on the type of noise to be treated and the degree of sound insulation required. The methods of sound insulation can thus be classified in three main categories:

	- a.Improvement in working methods: the basic principle of sound insulation is to suppress the noise at the source itself. A working method creating less noise may be adopted. For instance, the machine in the room is enclosed in a box-like structure with sound absorbing on its surfaces.

**107**

*Noise Transmission Losses in Integrated Acoustic and Thermo-Fluid Insulation Panels*

of the room considerably reduces the noise level in the room.

b.Acoustical treatment: the walls, floors and ceilings should be provided with sound absorbing materials. The sound absorbing materials should be mounted on the surfaces near the source of noise. The acoustical treatment

c.Personal protective devices: it is possible to reduce the noise to some extent by using personal protective devices such as ear plugs and headphones.

2.When noise is air-borne: the sounds generated and transmitted in air directly to human ears are known as air-borne sounds. The air-borne noise possesses less power, continues for a long duration and is confined to places near its origin. Following methods of sound insulation may be adopted for the reduction of

a.Solid non-porous homogeneous partitions: provision of solid non-porous homogeneous partitions will reduce air-borne noise. It is found that transmission loss of such partitions depends directly on the weight of partition per unit area. The sound insulation of a partition thus increases with the increase in its thickness. But doubling the thickness of a partition reduces transmission loss by a constant amount. This figure is practically constant and can be used to work out the transmission loss of the partition with different thicknesses. It can thus be seen that sound insulation by solid non-

porous homogeneous partitions is expensive in quantity of material.

b.Partitions of porous materials: the porous materials may be rigid or flexible. For partitions of rigid porous materials such as concrete masonry, the sound insulation increases about 10% due to the absorptive property of the material. But partitions of flexible porous materials such as wool and quilt do not give enough sound insulation. However, the value of transmission loss decreases as further layers of flexible porous materials are added. The general behavior of partitions of flexible porous materials is such that as the thickness of partition is increased in arithmetic progression, the corresponding transmission loss is in geometric progression. A combination of rigid porous materials and flexible porous materials may be used with advantage for the construction of partition wall. It will provide effective sound insulation and

c.Double wall construction: it is found that a double wall construction is better for sound insulation than a solid wall construction. The walls are of plasterboards or fiberboards or plaster on lath. An air space of about 10 to 12 cm is kept between the walls and staggered wooden studs are provided. In order to make the partition more effective, it is necessary to reduce the number of structural ties between the two parts of the partition to a minimum. The

d.Floating floor construction: in this type of construction, a floor is separated from the structural floor by means of a layer of resilient material such as mineral and glass wool quilt. Such a floor is known as a floating floor and it

e. Suspended ceiling construction: if a false independent ceiling is constructed below the structural floor, the sound insulation capacity of the floor increases. This construction is useful especially in case of wood-joist floors.

hollow space may be filled with sound absorbing blankets.

*DOI: http://dx.doi.org/10.5772/intechopen.93296*

air-borne noise:

will have less weight.

results in better sound insulation.

*Noise Transmission Losses in Integrated Acoustic and Thermo-Fluid Insulation Panels DOI: http://dx.doi.org/10.5772/intechopen.93296*

	- a.Solid non-porous homogeneous partitions: provision of solid non-porous homogeneous partitions will reduce air-borne noise. It is found that transmission loss of such partitions depends directly on the weight of partition per unit area. The sound insulation of a partition thus increases with the increase in its thickness. But doubling the thickness of a partition reduces transmission loss by a constant amount. This figure is practically constant and can be used to work out the transmission loss of the partition with different thicknesses. It can thus be seen that sound insulation by solid nonporous homogeneous partitions is expensive in quantity of material.
	- b.Partitions of porous materials: the porous materials may be rigid or flexible. For partitions of rigid porous materials such as concrete masonry, the sound insulation increases about 10% due to the absorptive property of the material. But partitions of flexible porous materials such as wool and quilt do not give enough sound insulation. However, the value of transmission loss decreases as further layers of flexible porous materials are added. The general behavior of partitions of flexible porous materials is such that as the thickness of partition is increased in arithmetic progression, the corresponding transmission loss is in geometric progression. A combination of rigid porous materials and flexible porous materials may be used with advantage for the construction of partition wall. It will provide effective sound insulation and will have less weight.
	- c.Double wall construction: it is found that a double wall construction is better for sound insulation than a solid wall construction. The walls are of plasterboards or fiberboards or plaster on lath. An air space of about 10 to 12 cm is kept between the walls and staggered wooden studs are provided. In order to make the partition more effective, it is necessary to reduce the number of structural ties between the two parts of the partition to a minimum. The hollow space may be filled with sound absorbing blankets.
	- d.Floating floor construction: in this type of construction, a floor is separated from the structural floor by means of a layer of resilient material such as mineral and glass wool quilt. Such a floor is known as a floating floor and it results in better sound insulation.
	- e. Suspended ceiling construction: if a false independent ceiling is constructed below the structural floor, the sound insulation capacity of the floor increases. This construction is useful especially in case of wood-joist floors.

*Noise and Environment*

noise to the receiving room.

noise is thus transmitted to the receiving room.

**2.3 Integrated sound and thermal insulation**

pipes, and cracks and (ii) by forced vibrations set up by the transmitting room to the walls, floors and ceiling of the receiving room. It is found that air-borne noise sets up forced vibrations in the walls, floors and ceiling of the transmitting room and they in turn set up corresponding vibrations in the walls, floors and ceiling of the receiving room. These surfaces of the receiving room create sound waves and

Impact noise or structure-borne noise is developed in solid structures and it is then transmitted as air-borne noise. Closing of doors, vibrations of machines, etc., set up vibrations in solid materials of the structure which result in transmission of

Air-borne noise possesses less power, continues for a long duration and is confined to places near its origin. Impact or structure-borne noise possesses more power, continues for a short duration and is often propagated over long distances.

Because some of thermal insulating materials have cellular or open matrix construction, they have inherent ability to absorb sound and act as panel dampers. They also reduce noise breakout, from the machinery plant by their ability to be flexible or discontinuous link between an acoustically active surface and the outer cladding. It should be remembered that sound insulation and sound absorption are quite different terms. The function of a sound insulating construction is to reduce sound passing through it. The function of a sound absorbent material is to reduce sound reflected from a surface. Hence, porous materials in general are good sound absorbers. But they are poor sound insulators. On the other hand, hard materials in general are poor sound absorbers. But they are good sound insulators. Further, insulation of sound is measured in an adjoining room while absorption of sound is measured in the room where sound is produced. The simple material which can be used as insulator is a sheet of material placed in the sound transmission pathways. Sound energy reaches the surface in the form of a pressure wave, of which partial energy passes through the partition and the rest is

Transmission loss: as the air-borne sound passes through any structure, loss of

Important facts: (i) transmission loss is numerically equal to the loss of intensity

Methods of sound insulation: the method of sound insulation will depend on the type of noise to be treated and the degree of sound insulation required. The meth-

1.When source of noise is in the room itself: following are the methods of sound insulation which are commonly used when the source of noise is situated in the

a.Improvement in working methods: the basic principle of sound insulation is to suppress the noise at the source itself. A working method creating less noise may be adopted. For instance, the machine in the room is enclosed in a

of noise; (ii) the efficiency of sound and thermo-fluid insulation of a wall or a partition is expressed in terms of transmission loss which occurs when air-borne physical agent passes through the wall or the partition; (iii) transmission loss varies directly with the frequency of physical agent. Hence, transmission loss of a structure should be studied over a wide range of frequencies. (iv) Greater insulation of a

wall or a partition is indicated by the larger value of transmission loss.

ods of sound insulation can thus be classified in three main categories:

box-like structure with sound absorbing on its surfaces.

room to be treated for sound insulation:

sound-intensity takes place. This is known as transmission loss.

**106**

reflected.

	- a.Treatment of floors and ceilings: the floors and ceilings may be treated for floating floors and suspended ceilings which help in considerably reducing structure-bore sound.
	- b.Discontinuous construction: this method is similar to box-type construction. The walls of the rooms are constructed on floating floors and the ceilings of the rooms are suspended from the structural floors. The use of structural ties with the main walls is avoided as far as possible or special resilient isolators are employed for this purpose.
	- c.Insulation of machinery: mechanical equipment such as refrigerators, lifts, and fans create vibrations in the structure and hence, if they are isolated properly, structure-borne sound is reduced to a considerable extent. The main principle of insulation of machinery is to rest the mechanical equipment on a flexible support which may be of rubber, cork, felt or metal spring.
	- d.Town planning: vibrations from external sources such as railways, metros, cars, traffic, and factories create structure-borne sound. The most effective method for reducing such type of structure-borne sound is to have a rational town planning. The city is divided into suitable zones and residential zone is placed away from railways, workshops, factories and main streets.
