Glossary of terms

This glossary contains explanations for commonly quoted measurements involved in noise testing:


This is the weighted standardised level difference. It is a measurement of airborne sound transmission between rooms, including flanking transmission.


Ctr is an adjustment factor used to account for low frequency sound, for example traffic noise. Level difference is usually quoted as DnT,w + Ctr.


RW is weighted sound reduction index. It is a rating of a material’s effectiveness as a soundproofing system. An RW increase of 1 translates to a 1dB increase in sound reduction, so the higher the RW value, the better.


L’nT,w represents Weighted standardised impact sound pressure level, it is a single value used to characterise the impact sound insulation of floors. L’nT,w is based on a field measurement of impact SPL, while LnT,w (without an apostrophe after the L) is based on a lab measurement of impact SPL.