Soundproofing is the use of sound-absorbing or sound-insulating materials to achieve a low noise level in one or more rooms. In general, porous materials effectively reduce noise by absorbing generated or reverberated sounds within a room; heavy walls effectively reduce airborne sound transmissions from room to room, and resilient materials effectively reduce sounds stemming from impacts.

Noise Control by Sound-Absorbing Materials

When a sound wave strikes a surface, some of the wave's energy is absorbed and converted to heat, and some of it is reflected. Porous materials absorb sound energy much more effectively than do nonporous materials. How well a porous material absorbs sound energy depends on the pore size and the pore interconnections.

Commercially available sound-absorbing materials include cellulose-fiber tiles and panels, mineral-fiber tiles and panels, granulated minerals consisting of perlite or vermiculate, perforated asbestos-board panels, special acoustical plasters, and such plastics as polyurethane foam.

Noise Control by Sound Insulation

When sound waves travel through the air and strike a room partition (wall, floor, or ceiling), the pressure of the sound waves sets up vibrations in the partition. The partition then acts like a diaphragm and transmits the sounds to an adjoining room. The noise level thus transmitted depends largely on the weight of the partition and the separation between its two sides. The heavier the wall, the greater is the transmission loss. Sheet lead, lead foil, or other lead products can be used to provide an effective sound-transmission barrier. Also, the sound insulation provided by a heavy partition can be increased considerably if the partition is made of two layers, as is a double wall.

A sound originating from a blow on a room partition is called an impact sound. The partition is set into vibration by direct contact, and sounds are radiated from both sides of the partition. Resilient cushioning surfaces, such as a thick carpet with padding underneath, are effective noise-control barriers in such circumstances.

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