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Low frequency impact sound: problems with timber floors

At the 2015 Institute of Acoustics conference in Harrogate, Jack Harvie-Clark presented the investigation of low frequency impact sound that can occur with timber (and composite) joist floors.  There was strong support from the audience for the acoustic industry to “do something about it” and that is exactly what we are now doing.  This work attracted a “Highly Commended” accolade in the Association of Noise Consultants Awards 2016.

Most members of the audience had come across the same problem: occupiers complain that the impact sound from normal footfall is very intrusive or intolerable, but when tested according to the Building Regulations, the floor is found to meet the minimum impact sound standards required by the law.  This happens far too often, and is a result of the very poor correlation between the assessment of impact sound under the Building Regulations, and people’s response to noise from footfall.  Crucially, the Building Regulations assess impact sound down to 100 Hz, but it is impact sound transmission the lower frequencies that are strongly correlated with occupant dissatisfaction.  The low-frequency noise from footfall can be very significant for timber floors.

It is embarrassing for the acoustics profession that the assessment method that is relied upon by the Building Regulations does not protect people from significant intrusive noise.  In the conference paper, Jack describes how the problem has been characterised in different ways by separate researchers, working independently, on different continents.  There are different assessments of test measurements proposed as solutions to this problem.  You can download the paper below.

Jack is now forming an industry-led task force that will determine its scope, and may include the following:

  • review any other relevant scientific literature
  • adopt a suitable metric to describe the problem
  • review the current performance of typical timber frame constructions in the UK
  • determine construction details that increase the risk of a low-frequency noise problem
  • determine methods to avoid or mitigate the problem

The intention is to help the timber frame industry avoid getting a poor reputation for impact sound unnecessarily.  This initiative is being conducted through the Association of Noise Consultants’ (ANC) Good Practice Committee, for which Jack is the ANC Board liaison member.  If you have knowledge of this issue and would like to contribute to the task force please contact either Jack Harvie-Clark or the Association of Noise Consultants.

Download the full conference paper below:

Low frequency impact sound_Apex Acoustics Proc. IOA_2015.pdf

Read more about our other research here.

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