Sound insulation materials

List and explain in brief the materials used for Sound insulation.

ANS:  

            Sound Insulation has to be looked into for two aspects. One is sound insulation for preventing the sound transfer and the other is for acoustic control i. e. for preventing echoes and reverberation. The following materials are, for either of these or for both. And, this has been made explicit in every detail.

1. Cork –

Cork is made from the bark of cork-oak tree. The bark of tree is cleaned, sized, ground to powder and then baked. While it is being baked, it oozes natural resin. This resin binds the powdered cork to form a slab/sheet when pressed or rolled. Cork is a very light material having Sp. gr. 0.25. It is porous and not affected by moisture. It is a good Sound insulator both for sound transfer and for acoustic effects. It is an electric insulator and also a heat insulator for temperatures below 70^o C.

Cork sheets are available in market and can be used for panelling. These can be coated with melamine polish to reduce abrasion damages, but the coating affects acoustic control is marginally.

2. Eel grass tiles:

Eel grass is used for making ceiling or panelling tiles. These tiles are used for both Thermal and sound insulation. Eel grass is a marine plant containing silica and iodine. Silica imparts the property of non-inflammability & iodine makes it termite proof. The grass obviously is a fibrous structure.

These tiles are very light in weight. These are specially recommended for acoustic control and thermal insulation. These have poor abrasion resistance. Hence the use may be restricted to ceiling and panelling above 2.4 meter heights.

3. Quilt -

Quilt is normally referred to some padded material like cotton pad stitched in linen cloth for bed covering or body covering. This cotton quilt can be a good heat & sound insulators. However, it is not moisture & termite proof.

For heat and sound insulation, a material called ‘Cobalt Quilt’ is used. This is created by stitching treated ‘Eel’ grass between very tough craft papers or canvas sheets.

4. Glass wool or Fibre glass

It is made from molten silica glass by forcing the same through apertures under steam or air pressure. A thread like mass is obtained and is known as Fibreglass or Glass wool.

It is fibrous in structure and has a good tensile strength. It is durable. It is a good thermal insulator and is abundantly used for thermally insulated partitions and panelling. It is also a good sound insulator from sound transfer point of view.

These are available in market in blankets form, but the blankets are not firmly built. And the blankets get de-shaped to bulk, if not handled properly. Also, if these blankets or the bulk is handled with bare hands, the skin will irritate. Hence, use of hand-gloves is a must while handling these.

5. Fibre board / Particle board

Fiberboards or particleboard are made from waste wood, grass, crushed sugarcane or similar substances. This raw material is either chipped into particles or crushed to fibres. These fibres or chips are mixed with durable and strong resins like Urea formaldehyde or Phenol formaldehyde. Then these are either hot pressed or cold pressed to from the sheets. These boards can be of interior Grade or of Exterior grade.

These boards are reasonably good heat insulators like plywood or wood. These boards are fairly-good for sound insulation since these are less resilient than plywood. Hence, these boards, when partly perforated, are used in sound insulation for Acoustic purpose. The acoustic effect is enhanced due to half perforated random holes on one side of the board. Due to these random blind holes, echoes and reverberations are reduced to a large level.

These are available in tile forms normally of size 600mm x 600 mm. The normal thickness is 12 mm.

6. Gypsum / POP boards

Gypsum is hydrated Calcium sulphate, i. e. CaSO4.2H2O. This Gypsum; when heated to about 160º C; looses some part of water and we get Plaster of Paris. POP is used for making boards of various sizes. These boards are of 12 to 19 mm thickness. These are reinforced with jute or plastic fibres. These boards are good thermal insulator and are useful for acoustic effects if are with textured surface or with random blunt holes. These boards are more economical compared to particle and fibres boards, and are not combustible. However, these are brittle and are less strong than particle or fibre board.

7. Coir

Coir is a hairy substance grown on Palm trees either on the fruit or on the trunk or under the leaves. This fibrous part is cleaned and used. Coir does not perish or degenerate under normal circumstance or in moist conditions and lasts long. Coir is a good thermal and sound insulator. Coir curtains and coir mats are insulating materials used by people under low income group. Coir quilts were also used earlier for padding and cushioning sofa.

9. Woollen carpets

Woollen carpets are a very good alternative for treating floor for thermal and sound insulation. For acoustic effects, it is the best. Natural wool is best but synthetic wool also gives satisfactory results. It is normally backed by the jute cloth and is laid with an under-layer of PU foam or coir foam or some other synthetic foam. The jute backing cloth and the under-layer, both increase the insulation effect. Cleaning of these carpets is a bit tedious and vacuum cleaner is a must. Removal of stains is more difficult and Petrol-dry-washing process is warranted.

Woollen carpets are available in the market with varying thicknesses ranging from 8 mm to 25 mm. The under-layers are of thickness from 12 mm to 25mm. These carpets are available in roll form of about 1.5m or 1.8m. Both the under-layer and the carpet are laid on the floor with intermittent use of rubber adhesive. The edges of the roll need to be hand-stitched for necessary width adjustments.

10. PVC carpets.

PVC carpets are good thermal insulators. These are fairly good sound insulators from sound transfer point of view but, for acoustic effects do play a marginal role. These are good electrical insulators too.

The thickness available is from 0.6mm to 3mm. But, 1.5 mm or 2mm thick PVC is normally used for flooring. These are available either in tile form or in roll form. The tile sizes vary from 250mm x 250mm till 450mm x 450mm. The roles have widths varying from 1.2m to 1.8m. These are pasted to floor with rubber adhesive. These can be pasted on smooth surfaces and not on rough surfaces like that of ‘rough Shahabad’. These can be easily cleaned by wiping with wet cloth.

11. Wooden flooring.

Wooden flooring done in natural timber is a good thermal insulator and fairly good sound insulator. Wooden flooring done in artificial timber like laminated particle/fibre board; does have thermal insulation properties but their sound insulation properties have some limitations. This is because the lamination on artificial timber, since plastic, reduces the insulation properties from acoustic control point of view. Wooden flooring are normally used for thermal insulation purpose or for places like dance floor, badminton hall etc.

Wooden flooring has a longer life than PVC flooring but it can catch fire. The artificial timber floor is easy to clean with a damp cloth. The natural timber floor, if polished, cannot be cleaned with a damp cloth.

12. Thermocole, Polyurethane foam, Polyurethane beads etc.

Thermocole is a type of plastic and has good thermal insulation properties. It is available in sheet form up to 50mm thickness. It can also be molded to any desired shape in Plastic molding machine. Thermocole is used for sealing gaps in refrigeration chambers or for storing chilled articles. Thermocole tiles are used in false ceiling either as face tiles or as backing tiles. Thermocole is very light and is not adequately strong. It gets abraded with slight friction. Hence for thermally insulated partitions, it is only a filling material and not a surface material. Thermocole has good sound insulation properties from sound transfer point of view and from acoustic effects.

Like Thermocole, PU foam or PU beads are also very good thermal and sound insulators. But these are expensive and are used in expensive refrigeration machinery. In interior jobs, where large quantity is required, Thermocole finds a better alternative.

13. Jute.

This is a vegetable fibre and is produced from ‘Jute plant’. The colour of the fibre varies from white to dark brown. It is bio-degradable. It is extracted from the stem of the plant after soaking it in the running water. The running water loosens the fibre and drives away the non-fibrous vegetable matter. Jute has very low thermal conductivity; it is electric insulator and is a very good sound insulator, both for transfer and acoustics. Jute carpets, Jute curtains, Jute packaging and covering hot water pipes with Jute threads are Insulation applications.

14. Curtains of Natural yarn.

            Cotton or wool curtains are very good Sound insulators from acoustics point of view. Polyester or Nylon curtains are resilient and hence are not useful.

15. Cushion padding.

            Padding the wall/partitions with cushioning materials achieves a very good control in sound insulation. The insulation achieved by these padding is for both the transfer and acoustics. The padding material can be cotton, U foam, coir foam or rubber foam. These padding are draped by cotton or woollen cloths. Use of Natural or foam leather for draping may marginally reduce the acoustic properties.