A sound insulation test of a separating partition will be considered as a pass if the airborne sound insulation is equal to or greater than the DnT,w + Ctr value required for the appropriate dwelling and if the impact sound insulation is equal to or less than the L’nT,w value for the appropriate dwelling. The performance criteria are different for new builds and conversions and also differences may occur due to the use of the dwelling type.
DnT,w is an in-situ measured performance parameter which demonstrates the level of resistance to sound transmission between two adjacent spaces. The measurement will include both direct sound transmission and flanking sound transmission of the construction. Flanking transmission is the effect of sound travelling through the building and may be particularly evident where beams and joists bridge a common partition or along poorly isolated lightweight wall constructions. The DnT,w of a separating wall or floor will typically be of the order 5 to 7 dB lower than the manufacturers specified Rw (single figure quantity of sound insulation) for the single element, due principally to the contribution from flanking sound transmission around the element when it is built on site.
Ctr is the spectrum adaption term. It is a correction attributed to the sound insulation quantity to account for urban traffic noise.
L’nT,w is an in-situ measured performance parameter which demonstrates the level of resistance to impact sound transmission between floors. The impact measurement includes both direct sound transmission and flanking sound transmission.
Further information can be obtained by contacting Soundguard Acoustics or by downloading our FREE developers guide to Approved Doc E sound insulation testing