Impact Sound

Impact noise sources produce noise by direct physical excitation of part of a building.

Examples include slamming doors, stamping on the floor and vibrating washing machines.

With impact noise, a relatively small noise source can result in a loud sound being transmitted through the structure, often over long distances.

Impact noise can be controlled by:

• Providing a resilient layer at the point of impact – such as a carpet.

• Structural isolation – such as adding a resilient layer between the floor deck and the floor structure.

Flanking Sound

Flanking sound transmission usually refers to sound that travels through ‘flanking’ structural elements, such as the external wall that flanks a separating wall between two dwellings.

Flanking sound can also include sound that travels along unintended airpaths, such as unsealed gaps in the structure and around service penetrations.

Flanking transmission can be reduced by:

• Extending the separating wall to the underside of the roof.

• Sealing open airpaths.

• Forming a lining backed by a resilient layer to prevent sound energy entering the flanking element.

The rationale for using Mineral Wool for noise control

The sound absorption characteristics of mineral wool make it ideal for use in modern buildings to comply with the Part E Regulations. In addition, the thermal properties of mineral wool provide a secondary benefit of minimising heat loss either between attached dwellings or between attached dwellings or between rooms within a dwelling. A further benefit is that the use of mineral wool in wall constructions can reduce the overall thickness of the wall, increasing useable floor area.

The acoustic performance of both Crown and Rocksilk mineral wool led to their inclusion in many of the constructions tested successfully in the RD programme and these provide many of the Part E solutions recommended by Knauf Insulation.

How mineral wool absorbs sound

Sound waves passing through mineral wool are continually being deflected and broken up by the individual fibres. The fibres vibrate with the sound energy, which is converted to heat.

How mineral wool works in a cavity

In an unfilled stud partition, the plasterboard and cavity alone provide the sound insulation which can result in a hollow sounding partition.

Adding mineral wool improves the sound insulation further by distorting and sound waves and dampening any deflection of the plasterboard (mass spring effect).