Flanking Sound – What is it and how can we help reduce it?

flanking sound under a gap in the door

Flanking Sound – What is it and how can we help reduce it?

Flanking noise transmission, is an acoustics phenomenon that occurs when sound energy bypasses or circumvents a primary sound insulation barrier via alternative paths. Sound waves can travel through adjacent structural elements, such as walls, floors, ceilings, ducts, and other interconnected building elements, rather than directly through a partition or barrier. Flanking transmission can result in unintended sound transmission and reduce the effectiveness of sound insulation measures.

The image below shows a sound transfer route through joists and a supporting wall

The term “flank” refers to the margins or borders of a partition where sound can travel via alternative paths. These routes may include:

Structural: Sound can propagate through the structural components of a building, including the floor or ceiling joists, wall studs and building framework. These elements can transmit vibrations from the sound source and emit sound on the other side, circumventing the intended sound insulation barrier.

Airborne: Sound waves can also travel through the air with interconnected spaces, such as gaps, fissures, or penetrations. This can include gaps around doors or windows, electrical receptacles, plumbing fixtures, and any other unsealed areas that enable sound to transfer between spaces.

Shared Services: Sound can travel through shared utilities such as ductwork, pipework, and cable receptacles. These services can transmit acoustic energy from one location to another.

The image below shows some shared services in the CSG Acoustics office. These transfer sound from our neighbouring Chinese restaurant!

Flanking noise transmission can have a significant impact on the efficacy of sound insulation measures, as it permits sound to travel around or through junctions that are intended to impede sound transmission. It can lead to decreased speech privacy, compromised acoustic comfort, and the spread of unwanted sound between various areas within a building.

Several measures can be utilised to reduce flanking transmission:

Sealing and airtightness: Ensuring proper sealing of gaps, fissures, and apertures can aid in preventing sound leakage via airborne flanking paths. This requires the use of acoustic sealants, gaskets, or other suitable sealing materials to reduce air leakage.

Decoupling and Resilient Mounting: Vibrations and sound transmission can be reduced by isolating structural elements or building components from one another. Techniques like resilient mounting, floating floors, and ceiling supports can aid in decoupling structural elements and reducing structural flanking.

The image below shows my son, sandwiched between some pretty hefty resilient matts. These are often used in gyms or heavy industry applications.

Adding Mass: The addition of additional mass or sound-absorbing materials can improve the sound insulation efficacy of the principal barrier. This may involve the installation of sturdier walls, the addition of additional layers of plasterboard or insulation, or the use of specialised soundproofing materials to increase the barrier’s ability to block sound.

Spatial Planning: Careful design of the building’s architecture, taking into account the location of noisy spaces, separating utilities, and minimising potential flanking paths during the design phase can aid in minimising the possibility of flanking transmission.

By addressing flanking transmission paths, it is possible to improve the overall sound insulation performance of a space, thereby enhancing acoustic comfort and minimising the transmission of undesirable noise between different areas within the same building.

If you think you have an issue with flanking noise, please contact a member of the CSG Acoustics team and we will be happy to assist you.

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Visit the previous blog on Impact Sound here:  https://www.csgacoustics.co.uk/impact-noise-what-is-it-and-how-can-we-reduce-it

Stay tuned for next week’s blog Mass Law!