A well-designed building should incorporate sound insulation to restrain the noise level. High noise conditions result in uncomfortable living conditions, mental strains, fatigue, and may even lead to a nervous breakdown or temporary deafness. Adequate insulation can be achieved by using sound-absorbing or sound repellent materials.
Sound Insulating Materials
Sound Insulating Materials fall into three main categories.
The first type of materials is of a porous nature. They have absorption coefficients which increase approximately with frequency. They reduce sound reflection because the pressure changes due to the sound waves at the surface cause air-flow in and out of the pores, which causes friction between the atoms of air material, thus generating heat and dissipating the energy.
Accordingly, their effectiveness is dependent upon their surface porosity, the proportion of their volume taken up by pores and the extent to which these pores are interconnected.
For this reason, thin porous materials are not usually very good absorbers, and for the same reason foamed rubbers and certain foamed plastics and resins with closed cells do not give good results.
Such sound absorbing materials as acoustic plaster, sprayed asbestos and mineral-wool slabs should therefore not be painted, since paint treatments are likely to seal their surfaces and render them ineffective.
To overcome the decoration problem, they are therefore sometimes provided with grooves or holes in their surface, e.g., acoustic fibreboard tiles, so that they may be decorated without affecting theirs sound-absorbing properties.
On the other hand, wood wool, light-weight concrete blocks and no-fines concrete which have large open surfaces may be decorated without affecting theirs sound-absorbing properties.
The second type of absorber consists of a fairly thin panel mounted in such a fashion as to have an air space between it and room boundary surface. These panels vibrate as a result of the impinging sound energy in a manner determined principally by the stiffness of the panel and the depth of the air space behind.
The third type of the absorber consists essentially of a cavity connected to the air of the room by a long thick neck. Such resonators have very narrow high absorption peaks over a very limited range of frequency. It is possible, by using thick planes drilled with a large number of holes mounted with an air space behind, to create effectively a number of such resonators. The drilled holes form the neck and the air space functions as the cavity.
The commonly used sound insulating materials are cellular concrete, asbestos, rock wool, glass wool, glass silk, mineral wool boards, cane fibre, and porous tiles. Acoustic plastics such as gypsum plaster is very effective in sound insulating.
Properties of Sound Insulating Materials
A good sound insulator should have low density, porous texture, resistance to moisture, and a pleasing look. It should be incombustible, light in weight, and easy to handle and fix, resistant to attacks of vermin, insects termite, and dry hot.
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Joints are too important for the rigid pavements because the joints are responsible for reducing stresses developed due to temperature variations. There are two type of joints-
- Longitudinal Joints
- Transverse Joints
The Transverse joints are subdivided into three categories-
- Expansion Joints
- Contraction Joints
- Construction Joints