Normalized longitudinal level difference for raised floor

Professional Definition

The normalized longitudinal level difference for raised floors (denoted as Dn,f or Dn,f,w) is a parameter that defines the acoustic insulation between two adjacent rooms, where the dominant path for sound transmission is the space below the raised floor (lateral transmission).

This value is determined according to standards (e.g. ISO 10848 series) and takes into account the difference in sound pressure levels corrected for the acoustic absorption of the receiving room. This is a key indicator in assessing how much the subfloor void degrades the overall sound insulation of the partition wall built on such a floor.

Acoustics in Simple Words

It can be compared to two linked houses that have separate rooms but share a common open basement extending under the entire building. Even if the walls on the ground floor are thick and solid, noise from a party at the neighbor's can seep into your place “below,” through that shared basement. The normalized longitudinal level difference is an assessment of how well the floor reduces that sound traveling underneath. The higher the value, the better the floor “seals” the escape route for noise under the partition wall.

Summary

This parameter defines the resistance of the raised floor system to lateral sound transmission (subfloor). It is critical when designing rooms that require silence, where partition walls are installed directly on the technical floor slabs, rather than on the structural ceiling.