Sound absorption & isolation

SOUND ABSORPTION

Acoustic absorption refers to the process by which a material, structure or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into  heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been 'lost'.

When sound waves collides with walls, part of the sound's energy is reflected, part is transmitted, and part is absorbed into the walls. Just as the acoustic energy was transmitted through the air as pressure differentials, the acoustic energy travels through the material which makes up the wall in the same manner. Deformation causes mechanical losses via conversion of part of the sound energy into heat, resulting in acoustic softening

In general, soft, pliable, or porous materials (like cloths) serve as good acoustic insulators - absorbing most sound, whereas dense, hard, impenetrable materials (such as metals) reflect most.

How well a room absorbs sound is quantified by the effective absorption area of the walls, also named total absorption area. This is calculated using its dimensions and the absorptioncoefficients of the walls. The total absorption is expressed in Sabins and is useful in determining the reverberation time of a room.

 

SOUND ISOLATION

Sound insulation or acoustic insulation is the shielding of a room from outside noise. Sometimes also from the inside to the outside (for example a disco).

Sound insulation distinguishes between airborne noise and contact noise. Airborne noise causes the sound to travel through the air. In case of contact noise, the sound spreads through materials.

Because our ear is also a warning organ, soft sound is transmitted well and loud sound is muffled. As a result, the sound perception is not directly proportional to the volume.