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  • Writer's pictureAsad Lalani

Airborne & Structure-Borne Sound!

Sound is a form of energy that has physical characteristics. Sound is caused by vibrations that transmit through a medium and reach the ear or some other form of detecting device. Like any form of energy, sound also has strength or intensity. This strength or intensity is measured in loudness (decibels (dB)) and frequency (Hertz (Hz)).

Airborne sound is sound that is transmitted through the air.

  • Typically, airborne sound might be generated by:

  • People talking.

  • Equipment or devices such as television and radio.

  • Animal sounds such as dogs barking.

  • Transport such as Airplane flying above head, car passing by.

This is as opposed to structure-borne sound that results from an impact on or a continuous vibration against a part of a building fabric resulting in sound being radiated from an adjacent vibrating surface. An example of structure-borne sound is the footsteps of a floor being heard in a room below or furniture being moved above!

Whilst they are sometimes considered to be separate phenomena, airborne and structure-borne sound are related, in that airborne sound can cause structure-borne sound and vice versa. The airborne sound may cause an element of the building fabric to vibrate when it encounters a surface, and structural vibrations may radiate from a surface, generating airborne sound.

Ignoring the aspects of acoustic issues that may cause problems and inferior quality of workmanship can result in airborne sound transmitting directly between spaces, for example through gaps around the edge of doors, and may result in flanking sound, where sound travels around a separating element, even though the element itself might provide exceptionally good acoustic insulation. Even exceedingly small gaps can cause a significant increase in the transmission of airborne sound.

Problems can also occur where doors, windows, or other openings have an orientation towards ‘noisy’ spaces, such as a circulation space, a busy road, or a school playground. If this deters occupants from leaving elements of the building open, this can affect the performance of natural ventilation strategies.

The amount of airborne sound in a space can be reduced by acoustic absorption, which reduces the amount of sound reflecting into the space from the surfaces enclosing it, by acoustic insulation which reduces the amount of sound transmitting into the space from an adjacent space through the building fabric and by the elimination of gaps that might permit direct transmission.

Airborne sound transmission can be tested by placing a sound source in a space to generate sound at a range of frequencies and detecting any resulting sound in an adjacent space with a calibrated microphone. The difference is then calculated, and adjustment made to consider the sound absorption characteristics of the ‘receiving’ space. Tests are typically carried out in the range from 125 Hz to 4000 Hz.

Contact LC Acoustics to conduct acoustic field tests and assessments for your project.

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