The predictions were then used to influence the site
layout and optimise the screening of plant.
An embankment around the project was planned and its screening
effect was included in the model. The construction
of the buildings was optimised, based on the acoustic transmission
loss necessary to meet the far field requirements.
This allowed accurate cost estimates to feed into the bid.
The bid was successful and our client was awarded
the construction contract. The Planning authorities
asked to see predicted noise contours for the whole area
surrounding the development.
Our noise and vibration consultants
built a propagation model using CadnaA software.
This confirmed the validity of the spreadsheet model,
to within 1 dB(A).
Noise contours were predicted, within the site boundary
and out to the nearest residential properties. The
contours within the boundary were useful for confirming
that the contract maximum of 80 dB(A) would not be exceeded,
where items of plant were closely spaced.
The CadnaA model also confirmed that although the earth
bank would provide local screening, it would not justify
lower specification noise treatment to the buildings, because
of the need to maintain limits at the first floor windows
of distant houses.