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  • Most of the common building materials absorb sound to a small extent and hence, for better acoustical requirement, some other materials are to be incorporated on the surface of the room.
  • Such materials are known as sound absorbent materials, and they help a great deal in making the room acoustically good.
  • These materials are used for:
  1. Damping sound in ventilation installations;
  2. Developing special acoustic effects in TV, radio and film shooting studios, etc;
  3. Facing interiors of premises that require a low noise level such as offices, restaurants, commercial centers, banks, etc.
  4. Providing adequate acoustic in theatre halls, auditoriums, etc.
  • 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.
  • Sound absorbent materials can be incorporated either in compressed state or in suspended state or in free state.
  • In compressed state,:- they are provided between the load bearing panels of ceiling and floor.
  • In suspended state,:- they are provided in the form of slabs fastened to ceiling so as to provide an air space.
  • In free state, they are provided in compressed or loose manner.

1) Thermocol

i) Analysis

  • Thermocol offers a non-hydroscopic, odorless, rigid, closed cell expanded polystyrene containing 98% by its volume still
  • Air entrapped in its cell and is the major reason for its excellent insulation properties.
  • Various thickness of thermocol is used for required sound insulation, depends on the enclosure volume.
  • The thickness also depends upon whether wall or ceilings to be sound-proofed.

2) Acoustical tiles


3) Mineral fibre wool

  • It is one of the most commonly used insulation products.
  • It’s made from volcanic rock heated with coke to 1500oc, then spun at high speed these fibers are then bound together in a bat or roll with formaldehyde-based resins.
  • Available in rolls 8.4 m long and width 0.5 m
  • Cost of the above roll of 50 m.M. Thickness is 840 rs

i) Installation

  • The mineral wool roll is first stuck to the walls and then paneling is done with any medium desired.

ii) Analysis

  • It is a replacement of glass wool. It offers a sound insulation of approximately 78%.

4) Wood wool

  • This material is generally used with a thickness of 25mm and it has a density of 0.40 g / cubic centimeter.
  • The average value for coefficient of absorption is 0.20.

i) Acoustic properties

  • Acoustic insulation
  • Resistance of a plastered wall of 5cm wood wool cement boards 36-40db
  • Resistance of a plastered double wall with air space between wwcbs 53-57db
  • Resistance of a permanent shuttered wall with 12cm concrete core 354-56db noise reduction coefficient for 2.5cm board 0.7

ii) Analysis

  • Wood wool is fixed onto the walls by aluminum or wood channel paneling.
  • Then acc. to the finish desired either paint is applied directly onto the wood wool or lamination is done. Joints are concealed.

6) Mineral fibre tiles

  • These 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.
  • However, acoustical tiles are relatively costly than other absorbent materials.

i) Analysis

  • They are most suitable for rooms in which small area is available for acoustical treatment.

ii) Specification


iii) Observations

  • These al the same mineral fiber tiles with a layer of velvet cladding on the mineral fiber tile.
  • This is done to enhance the acoustic ability of the mineral fiber tile.

iv) Analysis

  • Due to the improved sound absorbing quality of the material it is used in larger halls and auditoriums and theatres where the mineral fiber tile would not have been sufficient.
  • The cost of external finishing is also reduced.

7) Acoustic plaster

  • This is also known as fibrous plaster and 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.
  • If quantity of cement is less, the plaster will not have enough strength. Thus the quantity of cement should be carefully decided

i) Analysis

  • For thickness of 20 mm and density of 0.10 g / cubic centimeter, the acoustic plaster possesses an absorbent coefficient of 0.3 at 500 cycles per second.

8) Soft wood/ceiling tiles

  • These are soft which are prepared from compressed wood grains.
  • They are cheaper and can be fixed by ordinary paneling.
  • The average value of coefficient of absorption is 0.17.

i) Analysis

  • It is soft and has air bubbles trapped in the wooden grains and due to this fact it is a sound insulating material, since the tiles are already carved there is no need for external finishing and the carvings make the room acoustically better.

ii) Observations

  • Soft wood/ceiling tiles come in sizes of  2’x2’ and 8’x4’. However the most commonly used is the 2’ x2’ tile. The price of which is 65-70 rupees/tile

iii) Installation

  • The panels of soft wood/ceiling tiles are installed through all or wooden channels or frame and the joints are covered by aluminum t shaped angle.
  • These kind of panels don’t required too much strong frame work because of its light weight.
  • For ceiling work it is installed same as false ceiling is done.

iv) Observations

  • Rockwool mattresses provide excellent acoustical absorption and noise reduction co-efficient.
  • Due to high noise reduction co-efficient, they are used in acoustic insulation work for gensets, auditorium, theatres, public places and industrial areas where noise reduction is required

v) Analysis

  • Attainable value of nrc =0.45 or 45%.
  • Ideal for auditoriums and large conference halls.
  • Standard size: size of mattresses 1.64 m x 1.22 m or 1.52 m X 1.22 m thickness 25 mm to 100 mm. Density (kg/cu.M) 100, 120, 150

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