ACOUSTICS

    The word Acoustics is originally derived from the Greek word meaning ‘to hear’. Hence, Acoustics is defined as the science of sound and as such, it discusses the origin, propagation and auditory sensation of sound. When a sound wave sticks, part of its energy is absorbed by friction, part of energy is transmitted and their main part of its energy is reflected.

Acoustics 

    Sound is produced when part of the atmosphere is compressed suddenly. This compression would have retained stationary at that place only in case the air was not elastic. But due to the elasticity of air, the particles originally disturbed in turn disturb the neighbouring particles. Ultimately the compression is propagated or spared away from the source. Sound thus travels in the form of waves and when these waves come near our ear drums, we feel a sensation of hearing. 

Types of Absorbent materials 

    Various types of Absorbent materials are available in the market under different trade names. The value of coefficient of absorption is supplied by the manufacturer. The choice of the absorbent material should be made after carefully considering various factors such as appearance, cost workability, flame resistance, durability, light reflection etc., 

Following are some of the common types of absorbent materials: 

Hair felt: Hair felt was used by Prof. Sabin in his experimental works. If the average value of coefficient of absorption is 25 mm thick, hair felt is 0.60. 

Acoustic plaster: Acoustic plaster is also known as fibrous plaster. It includes granulated insulation material mixed with cement. If quantity of cement is more than required, the plaster will not have sufficient pores to become effective for acoustics. It can be fixed on the wall and their coefficient of abortion varies from 0.15 to 0.30. 

Acoustical tiles: Acoustical tiles are made in factory and sold under different trade names. The absorption of sound is uniform from tile to tile and they can be fixed easily. Because of high cost they are most suitable for rooms in which small area is available for acoustical treatment. 

Strawboards: With a thickness of 13 mm and density of 0.24 g/cm3, it possesses a coefficient of absorption of 0.30 at 500 cycles per second. 

Pulp boards: Pulp boards are soft boards which are prepared from compressed pulp. They are very cheap and can be fixed by ordinary paneling. The average value of coefficient of absorption is 0.17. 

Compressed fire board: Compressed fire board may be perforated or imperforated. The average coefficient of absorption for the former is 0.30 and for the latter is 0.52. It has a density of 0.30 g/cm3. 

Compressed wood particle board: Compressed wood particle board is provided with perforations and it can also be painted. With a thickness of about 13 mm, the average coefficient of absorption is 0.40. 

Perforated plywood: Perforated plywood can be used by forming composite panels with mineral wool and hard board. The average coefficient of absorption is 0.75. 

Quits and mats: Quits and mats are prepared from mineral wool or glass wool and are fixed in the form of acoustic blankets. The coefficient of absorption of depends on thickness and size of Quits and mats. 

By,

Madhumalar.R

Assistant Professor