Isolation of Air- and Structure-Borne Sound

Abstract

Sound isolation is the confinement of sound to a space in such a way that transmission to neighboring spaces is totally or partially prevented. Sound isolation is predominantly based on reflection caused by impedance discontinuities in possible transmission paths. Dissipation and absorption may also play a role in sound isolation, but it is usually minor. Another term for sound isolation is sound damming because the sound is, so-to-say, “dammed in”.

Sound isolation must not be confused with sound damping. Damping of sound means that sound energy has been removed from a sound field by means of dissipation and/or absorption. The transmission of sound to another space is one possible method of absorption. Thus, absorption is not necessarily dissipation, the latter being transformation of acoustic/mechanic into thermal energy.

Measures of airborne and structure-born sound isolation are of particular technological relevance. Non-porous leaves or walls are typically inserted into airborne transmission paths to achieve isolation, and isolation of structure-borne sound is accomplished by inserting elastic elements (springs) or layers (resilient materials, air gaps). Sometimes heavy interlocking masses are also used. In every case, the goal is to create impedance discontinuities that result in reflection.