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NOVA Acoustics

What is Structure Borne Sound? And how can it be reduced?

When considering the installation of sound insulation in new buildings, one factor that must be taken into account is structure-borne sound. So, what is structure-borne sound and what steps can be taken to mitigate its effects?

What is structure-borne sound?

Sound itself is created by pulses that are transferred through a medium to a detection device or to the human ear. In buildings, sound is generally either airborne or structure-borne. According to the British Regulations Approved Document E, structure-borne sound is defined as:‘sound that is carried via the structure of a building’. For example, the noise of footsteps across an upper floor that are audible in the room below or adjacent is classified as structure-borne sound. In technical terms, structure-borne sound can be divided into five distinct processes:

1. Generation: the actual originating source of the oscillation.

2. Transmission: the movement of the oscillation’s energy to the building from its originating source.

3. Propagation: the mechanism that distributes that energy across the entire structure.

4. Attenuation: refers to the reflection of sound waves as they bounce off surfaces within the structure, effectively reducing their energy and diminishing the sound.

5. Radiation: the production of vibrations from an unprotected surface. Airborne and structure-borne sound are intrinsically linked. The vibrations that rebound from a hard structure within a building create airborne sound.

In turn, the airborne sound can cause some constituent of the building to vibrate when it comes into contact with an unprotected surface.

How can structure-borne sound be reduced?

The effects of structure-borne sound can be mitigated in a number of ways:

• Carpets and padding can be installed to absorb sound waves.• In some environments, the use of resilient underlay made from foam, recycled rubber, and rigid fibreglass can provide an effective solution to structure-borne sound.

• Spring ceiling hangers, sound clips, and resilient mounts can be installed where appropriate.

• In areas of the structure such as subflooring, soundproofing compounds can be applied between the two rigid elements. The compound works by disseminating vibrations that are generated by sound saves as they travel around the structure.

• Structure-borne sound can be diminished through the use of a suspended ceiling system, a secondary wall structure, and raised floors.

• High-mass structures that incorporate cavities or offset construction can be utilised in order to prevent the passage of vibrations.

Although structure-borne sound can be mitigated through appropriate building design features, the subject is very complex. The nature of structure-borne sound is dependent on a number of factors, including structural composition, the nature and fabrication of the receiving spaces, and the radiating surface. The design of sensitive buildings may benefit from consultation with a specialist acoustic consultant.

Minimum expected impact sound insulation standard

The Building Regulations Approved Document E (referenced above) defines the lowest acceptable standard for noise insulation. Impact sound transmission should be measured in the structure, using a tapping machine to strike a test surface in order to produce sound in an adjacent area. The structure-borne sound impact is then measured and monitored.

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