Insulation atlas/Impact
Stadium footsteps and a hall’s ball are measured as L'nT,w. A higher figure here is worse.
A heavy slab raises airborne insulation. Impact needs a resilient break and a perimeter strip. Carpet does not replace a floating floor under a gym.
Airborne is not impact
Rw and DnT,w describe sound in air: speech, music, a loudspeaker. Ln,w and L'nT,w under ISO 717-2 describe knocking on the floor heard below. A 200 mm slab can be comfortable for airborne sound and still carry a heel. A floating floor — a resilient layer, then a screed or finish that does not touch the walls — is the break. A perimeter strip stops mortar gluing the screed to the wall. One bridge in the corner brings the knocking back.
Where the line is written
A gym over classrooms: L'nT,w is the line, often asked below 60 for ordinary use and harder for sport. A concourse over locker rooms: impact from the crowd and from kit. A theatre over a foyer or a car park: impact from moving seats and from rain if the lid is a light sheet. A resilient ceiling under the slab is a second path when a floating floor is impossible, and it is drawn with the structural engineer so its hangers are not shorted.
- Carpet improves light impact only.
- A moving stage platform carries vibration if it is tied to the frame without a break.
- Do not mix L'nT,w with reverberation time. The first is between storeys; the second is inside the room.