Longitudinal impact level for a raised floor

Professional Definition

The impact sound level resulting from horizontal transmission through a raised floor determined under strictly defined laboratory conditions.

In acoustic engineering, this parameter (commonly denoted as Ln,f) describes how sound from impact (e.g., the tapping of high heels) travels horizontally along the structure of the floor itself, rather than vertically to the room below. It is a key quantity when designing the acoustics of office interiors equipped with technical floors, where the floor panels create a continuous surface that transmits vibrations over long distances.

Acoustics in Simple Words

Imagine a raised floor as a large, taut table set with many cups of water. If you hit the surface at one end of the table, the water in the cups at the other end will start to ripple, even though you haven’t touched them directly. This is similar to how a technical floor works – an impact from a heel on one panel sends vibrations through the metal frame to adjacent panels, causing the sound to "travel" through the office, bypassing partition walls. The longitudinal impact sound level tells us how much a given floor "conducts" this noise – the lower the value, the better it dampens vibrations and prevents them from wandering sideways.

Summary

The longitudinal impact sound level is a measure of how easily footstep sounds spread horizontally through the structure of a technical floor. A low value guarantees that movement in one part of the office will not generate disruptive noise in focused work areas several meters away.