BLOG 'A chronology of soundproofing systems London'

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London Underground Ltd. studied groundborne noise levels and complaint thresholds following the opening of the Victoria Line. The data has been used to define a complaint threshold of around 40dB L AFmax.

Local authorities have published standards for groundborne noise, usually in response to specific rail projects affecting their jurisdiction. In relation to the Channel Tunnel Rail Link, guidelines indicated that groundborne noise levels, inside dwellings, should not exceed 35dB L AFmax.

Crossrail recognised “the local authorities’ preference for ground-borne noise levels within residential dwellings which are no greater than 35dB L ASmax…”

Mitigating vibration in buildings from railways is challenging. If the issue is recognised before buildings are constructed, the building may be built off carefully designed anti-vibration mounts. However, in an existing building where this is not possible, vibration entering the structure will be readily transmitted throughout the structurally connected components and may be re-radiated as audible noise from, for example, floors, walls and ceilings to rooms. Therefore, it is generally necessary to consider all of these components.

Typical anti-vibration mounts have a natural resonant frequency. At and near this resonant frequency there will be amplification, below it, therefore, will be unity gain (i.e. no benefit) and only significantly above this frequency will there be attenuation of the vibration.

Therefore, anti-vibration measures must ensure the resonant frequency of the system is significantly below the predominant frequency of the forcing vibration. Anti-vibration mounts are often supported with data that provides this information, but other products may not, particularly resilient backed boards and resilient materials that are not primarily intended to be used for the control of vibration at low frequency.

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