Sound Transmission Loss
Transmission loss or noise insulation is the reduction of the amount of sound energy passing through a wall, floor, roof, etc., and is a property of the element as a whole. It is expressed in decibels (dB).
Noise may be due to airborne or impact sound, and both must be taken into account where appropriate. Impact sound is a very important factor, for example in intermediate floors, whilst airborne sound would be the predominant factor in separating walls and partitions.
Particular attention should be paid when designing elements to reduce sound transmission, to the ways in which sound may penetrate at the edges of the element, or through doors, windows etc. This 'flanking sound transmission' can be a problem if it is not taken into account at the design stage.