Sound absorption and sound absorbers

The property of surface by which sound energy (kinetic energy) is converted into other form of energy, generally heat energy (due to friction) and get absorbed.
There is no royal road for making a particular room acoustically good. It mainly depends on the ideas of the engineer or the Architect. Each case is to be studied separately and after proper thinking and calculations, suitable materials may be specified.

1. SOUND ABSORPTION & ABSORBERS PRESENTED BY: ROHIT BHATT B-ARCH 4 TH SEM K.C.A.D., BAREILLY PRESENTED TO: AR.MALVIKA SRIVASTAVA BUILDING SERVICES

2. SOUND ABSORPTION The property of surface by which sound energy (kinetic energy) is converted into other form of energy, generally heat energy (due to friction) and get absorbed. The degree to which this surface affects the absorption of sound is known as absorption coefficient . There is no royal road for making a particular room acoustically good. It mainly depends on the ideas of the engineer or the Architect. Each case is to be studied separately and after proper thinking and calculations, suitable materials may be specified.

3. REQUIREMENTS OF A GOOD SOUND ABSORBENT: It should be Durable, Vermin-proof, Efficient over wide range of frequencies, Fire-resistant, Non- Hygroscopic and heat insulating, Self- supporting and Easly fixable, Pleasing in appearance, High coefficient of absorption, Sufficient structural strength.

4. TYPES OF SOUND ABSORBING MATERIALS According to their physical composition, POROUS MATERIALS NON- PERFORATED OR MEMBRANE ABSORBERS. CAVITY OR HELMHOLTZ RESONATERS

5. POROUS MATERIALS B asic acoustical characteristic of all porous materials is a cellular network of minute interlocking pores.They convert the incident sound energy into heat energy by the frictional and viscous resistance within these pores and by vibration of their small fibres. Good for high frequency range. Fibreboards , mineral wools , insulation blankets, etc. are some of the examples Glass Wool Rock wool

6. NON PERFORATED PANELS & MEMBRANE ABSORBERS Any impervious material , installed on a solid backing but separated from it by an air space, will be set to vibration when struck by sound waves. Good for low frequency range. Wood and hardboard panelling, gypsum boards , suspended plaster ceilings, furred out plasters, rigid plastic boards, windows, glazing, doors , wood floors and plat-forms, etc Gypsum Boards

7. CAVITY OR HELMHOLTZ RESONATERS They consist of an enclosed body of air confined within rigid walls and connected by a narrow opening(called the neck) with the surrounding space in which the sound waves travel. Cavity resonators can be applied A s individual units A s perforated panel resonators A s slit resonator panels .

8. TYPES OF SOUND ABSORBING MATERIALS According to their trade name and availability in market, HAIRFELT, ACOUSTIC PLASTER, ACOUSTICAL TILES, STRAWBOARD, PULP BOARDS, COMPRESSED FIBREBOARDS, COMPRESSED WOOD PARTICLE BOARDS, PERFORATED PLYWOOD, WOOD WOOL BOARD, QUILTS AND MATS.

9. HAIRFELT: The material was used by prof. Sabin in his experimental works, made up of wool anf fur. The average value of coefficient of absorption of 25mm thick hairfelt is 0.60. It is used at rooms and halls.

10. ACOUSTIC PLASTER Also known as the fibrous plaster and it includes granulated insulation insulation material mixed with cement. The average value of coefficient of absorption of 20mm thick and density of 1kN/m 3 acoustic plaster is 0.30 at 500 cps. For acoustical plaster boards- 0.15-0.30

11. ACOUSTICAL TILES They are factory made, uniform sound absorbers, easily fixable but expensive. Most suitable for rooms in which small area is available for the acoustical treatment.

12. STRAWBOARD Prepared from compressed straw and covered with thick paper or hardboard are used. The average value of coefficient of absorption of 13mm thick and density of 12.4kN/m 3 is 0.3 at 500 cps. It is used at rooms and medium capacity halls.

13. PULPBOARDS These are the softboards prepared from compressed pulps. The average value of coefficient of absorption of 13mm thick, is 0.17 at 500 cps. They are cheap and can be fixed by ordinary panelling.

14. COMPRESSED FIBREBOARD Made up of compressed fibre, may be perforated or unperforated. The average value of coefficient of absorption of perforated one with the density of 3kN/m 3 is 0.30 and of other one is 0.52.

15. COMPRESSED WOOD PARTICLE BOARD Prepared from compressed wood and provided with perforations and it can be painted also. The average value of coefficient of absorption of 13mm thick is 0.40 at 500 cps.

16. PERFORATED PLYWOOD Can be used by forming composite panels with mineral wool and cement asbestos or with mineral wool and hardboard. Generally suspended from trusses. The average value of coefficient of absorption for the former one is as high as 0.95 and for the latter one, it is about 0.20.

17. WOOD WOOL BOARD Prepared from a mixture of portland cement and wood wool or wood shavings . A small quantity of Gypsum is sometimes added. The average value of coefficient of absorption of 25mm thick and density of 4kN/m 3 is 0.20 at 500 cps. It is used at

18. QUILTS AND MATS Prepared from mineral wool or glass wool and are fixed in the form of acoustic blankets The absorption coefficients of such quilts and mats depend on the tickness, density, perforations, mode of fixing, nature of backing and frequency of sound.

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