If you’re considering installing sound insulation in a new building, you must account for the structure-borne sound. But what exactly is this structure-borne sound and what are the steps you should take to mitigate its effects?
What is structure-borne sound?
This is the sound created by pulses that are usually transferred through a medium to the human ear or a detection device. In buildings, the sound is usually either structure-borne or airborne. According to Document E, approved by the British Regulations, the structure-borne sound can be defined as sound that’s carried through the structure of a building. For instance, the sound of footsteps across the upper floor that’s audible in the adjacent room or the one below is regarded as a structure-borne sound. Technically speaking, structure-borne sound can be categorized into the following:
- Generation: This is the actual source of the oscillation.
- Transmission: The movement of the oscillation energy from the source to the building
- Propagation: The mechanism that distributes the energy throughout the structure
- Attenuation: The reflection or bouncing off sound waves within the structure, which effectively reduces their energy and diminishes the sound.
- Radiation: Production of vibration from an unprotected surface.
Structure-borne and airborne sounds are intrinsically linked. Airborne sound is created when vibrations rebound off a hard structure within a building. In turn, airborne sounds may result in some constituents of the building vibrating when they come into contact with unprotected surfaces.
The following are a number of ways in which the effects of structure-borne sound can be mitigated:
• Padding and carpeting can help absorb sound waves
• Using resilient underlays in some environments can help. These are typically made from recycled rubber, foam, and rigid fiberglass, and they can provide an effective solution to mitigate structure-borne sound.
• Sound clips, spring ceiling hangers, and resilient mounts can be installed where appropriate
• In certain areas of the structure, like the subflooring, certain soundproofing compounds can be applied between two rigid elements. The compound essentially works by disseminating the vibrations that are generated by soundwaves when travelling all around the structure.
• You can diminish structure-borne sound by using secondary wall structures, suspended ceiling systems, and raised floors.
• You can also use structures of high mass that come with cavities or offset construction to prevent vibrations from passing through
While structure-borne sound can be mitigated by using appropriate building design features, the subject is quite complex. Keep in mind that the nature of structure-borne sound will depend on a number of factors, including the nature of the fabrication of the receiving spaces, structural compositions, and the radiating surface. The design of sensitive buildings could benefit from consulting with a specialist acoustic consultant or expert.
The Sound Insulation Standard for Minimum Expected Impact
Document E, which is Approved by the Building Regulations, outlines the lowest allowable standard for noise insulation in buildings. The structure’s impact sound transmission should ideally be measured in the structure, ideally using a tapping machine to strike a test surface to produce sound in an adjacent area. The structure-borne sound impact will then be measured and regularly monitored.
Structure-borne sound is made up of five key processes:
• Generation: This is the source of an oscillation
• Transmission: The transfer of oscillatory energy to the structure from the source
• Propagation: energy distribution throughout the entire structural system
• Attenuation: Waves moving through the structure may encounter material or structural changes causing them to be partially reflected, thereby reducing the energy transmitted and attenuates the sound.
• Radiation: Sound is emitted from an exposed surface
Sometimes, airborne sound and structure-borne sound are considered separate entities, but they are actually closely related. Structural vibration could radiate from surfaces, which could create airborne sound, and this may cause an element of the building fabric to vibrate when it comes into contact with a surface.