This index is usually required for soundproofing between rooms situated one above the other (dwellings, hotels) and in certain passageway areas (hotel industry). Impact sound insulation is measured by placing a standardised impact machine on the floor of the premises emitting the sound and then taking sound level meter readings of the noise in the next room and in the room below. The performance of floor coverings is characterised by their ΔLw efficiency index measured in the laboratory and expressed in dB. It is equal to the difference between the sound level picked up in a room with a bare floor slab of 140 mm of concrete (78 dB) and the level picked up under the same floor slab covered with the product. The regulation specifies a sound reduction threshold of 60 dB, which means that any carpet of greater than 18 dB is suitable (on a concrete floor at 78 dB). All Balsan carpets are in accord with this threshold. In restoration, the rule consists of replacing worn carpets with high-performance coverings whose effectiveness is at least equal to that of the previous covering. Indeed, the courts have ruled that complaints are admissible with regard to noise resulting from the replacement of carpets by parquet flooring in buildings (civil cassation [cassation civique] of 5/1988) : measures are recommended such as the insulation of floors with carpets, in order to reduce the noise of footsteps. The greater the ΔLw, the better the impact noise insulation of the floor.

Apart from the absorption of impact noise, textile floors possess good aerial noise absorption properties. The “lifespan” of sounds, in a room equipped with a carpet, is reduced by half as compared with bare, smooth-floored rooms.
• In order to avoid the reverberation of noise in buildings, the French regulations require the use of absorbent materials, in such a way as to limit the sound levels in certain passageways. This rating is calculated using a chart of the αSabine absorption coefficients in octave bands (measured in the laboratory). The usual required threshold is 0.25 in shared premises and the hotel business. These materials are characterised by their unique αw absorption index, calculated on the basis of the curve of the αSabine absorption coefficients in octave bands (measured in the laboratory).
• Most materials used in interior decoration (ceilings, walls and floors) are able to reduce sound reverberation. The overall acoustic absorption of the item (αw) will depend on their individual performances.
The choice of textile floors can make a significant contribution to the calculation of this surface area, the absorption performance depending upon its thickness, the production process of the surface area and the back layer of the product. The exceptional sound insulation capacity of carpets is confirmed, in particular, in public spaces, such as open-plan offices, reception halls and libraries. Planning the laying of a carpet at the design stage makes it possible to achieve significant savings in terms of acoustic insulation.