Impact Noise – What is it and how can we reduce it?

Impact Noise – What is it and how can we reduce it?

Impact noise transfer, also referred to as structure-borne noise, is a form of sound transmission that occurs when an impact or vibration on one surface is transmitted through the structure of a building to other surfaces or spaces. It is the sound produced when an object impacts or interacts with a surface, such as footfall on a floor, falling objects, or mechanical vibrations.

When an impact occurs, the impact’s energy is conveyed to the surrounding structure in the form of vibrations. These vibrations can propagate through the building components, including floors, walls, and ceilings, and emit sound on the other side. The resulting impact noise can be heard in adjacent spaces or rooms as an abrupt, transient sound.

To a certain extent, building regulations in the UK protect adjacent dwellings from impact noise by imposing criteria that needs to be achieved (as required in Approved Document E – see a later blog in this series).

There are numerous variables that can influence impact noise transfer:

Source Characteristics: The force, weight, and surface area of the object causing the impact can affect the generation of impact noise. Heavier objects or those with a larger contact area can generate more intense vibrations and, consequently, impact noise. An example would be the likely sound transfer difference between a grown adult in stilettos and a child in trainers.

Structural Pathways: The path that vibrations travel through a structure plays a significant role in impact noise transfer. Depending on the construction materials, rigidity, and connection points, structural components such as floors, walls, and ceilings can transmit vibrations differently. In general, harder and more rigid materials transmit vibrations more effectively, whereas materials with greater damping properties can help reduce vibrations. We can mitigate this transfer route by the introduction of resilient layers – for example a resilient top layer can be applied above the floor joists or the use of a resilient ‘bar’ to the underside of a structural floor joists. Both of these elements provide a disconnect between the rigid materials, helping to dissipate the sound structural energy.

Below is an image of a resilient bar – this is often used on the underside of floor joists.

Reverberation time / acoustic characteristics of the receiving space: The characteristics of the space in which the impact noise is received also influence its perception. Impact noise transmission and audibility can be affected by the configuration, surface materials, and acoustic properties of the recipient space. A room with firm and reflective surfaces, for instance, can amplify and prolong impact noise, whereas a room with soft and absorbent materials can help reduce its impact.

Several strategies can be implemented to reduce impact noise transfer:

Sound Insulation: Improving the sound insulation properties of the building’s elements can help reduce impact noise transmission. Decoupling the structure and minimising direct transmission can be accomplished by employing resilient underlays or isolating materials between the source and receiving surfaces.

Below is an image of a typical resilient layer, often placed in the floor build-up above the joists.

Carpets / Dampening the impact at source: The incorporation of materials with high damping or absorption properties can aid in the dissipation of impact energy and the reduction of noise. To dampen vibrations, these materials can be applied to the source surface or used in the construction of building elements. The easiest way to do this is by introducing carpets to the floor.

Room Positioning / Arrangement: Considering impact noise mitigation during the building’s design phase can aid in preventing or minimising its transfer. This can be accomplished by separating noisy areas from sensitive areas, utilising partition walls with high sound insulation properties, or instituting structural measures to reduce vibrations.

Below is an image of a cradle and batten solution, which can be used when the floor needs levelling and a high level of impact sound insulation

By addressing impact noise transfer, it is possible to create a more comfortable and tranquil environment, particularly in settings where impact noise sources are prevalent, such as residential buildings, multi-story structures, and high-traffic areas.

We at CSG Acoustics can assist you if you feel you have a structural / impact noise problem at your property, or if you are designing a building to meet Building Regulations and Approved Document E.

Visit the previous blog on Airborne Noise here: Airborne Sound

Stay tuned for next week’s blog Flanking Sound!