Noise control and mitigation
Noise emissions from many sources, particularly those associated with industrial processes, can often be reduced by means of noise control measures applied at the source, or very close to the
source. Noise control measures of this kind include acoustic attenuators and acoustic louvres which can be fitted to air handling and ventilation plant, and various types of noise reduction kits which are
available as extras for some items of mechanical plant and equipment.
In some circumstances correctly designed vibration isolation mounts may also be helpful in controlling noise emissions by reducing the amount of acoustic energy which is transmitted to relatively
light structures in the vicinity of the item of plant concerned. Light structures such as lightweight plant enclosures are likely to radiate structure-borne sound more effectively than heavier structures.
New major roads in the UK are increasingly provided with low-noise surfaces and these can be very effective, capable of reducing noise levels by several dB.
Noise from railway is a function of numerous factors including train speed, train weight and the type and condition of track bed and rails.
Poorly maintained tracks generally give rise to higher levels of noise than well maintained tracks.
In cases where new sensitive development is proposed at locations which are affected by existing sources of environmental noise such as road and rail transportation and industrial noise sources
appropriate methods of providing acoustic mitigation include:
the overall layout of the site and the internal layout the proposed buildings (ie placing less sensitive portions of the development closest to the noise source);
the employment of acoustic barriers, which may be either appropriately designed fences, walls or landscaped mounds or bunds, or alternatively buildings which form part of the proposed development
but which are less sensitive than the parts of the development which they protect; and/or
the provision of uprated ventilation and glazing specifications at affected locations on the proposed development.
In cases where a new noise source is proposed in the vicinity of existing sensitive locations it is normally necessary to limit noise impacts to acceptable levels by means of:
noise control measures implemented at source; and/or
the employment of purpose built acoustic barriers, which again may take the form of appropriately designed fences, walls or landscaped mounds or bunds.
In general terms acoustic barriers work best of they are placed close to either the noise source or the receptor. As a rule of thumb, if an acoustic barrier completely removes line of sight
between a noise source and receptor it may be expected to reduce noise levels by around 5 to 10 dB. If it just cuts line
of sight it may be expected to reduce noise levels by around 5 dB. Where lines of sight exists over the top or around
the ends of a barrier the sound reduction is likely to be between 0 and 5 dB.
For levels of attenuation up to around 10 dB the choice of material for the barrier is not particularly critical, although it is important that it does not have significant openings or gaps. The longevity of the barrier should also be considered, as its acoustic performance may reduce with time if it deteriorates, for example because of weathering.
Levels of attenuation in excess of 10 dB can be achieved with well designed barriers, but the acoustic performance of the barrier material itself becomes increasingly important with increased attenuation levels.
Where sensitive-noise buildings are affected by noise from air traffic it is necessary to consider the acoustic performance of the whole of the building, including the roof/ceiling construction as
well as external doors and windows. Some London Boroughs which are affected by noise from aircraft associated with Heathrow Airport specify minimum construction standards for various elements of the building
envelopes of new residential properties.
Noise transmission between adjoining residential properties such as semi-detached houses and flats is also area of critical importance. Approved Document E 2003 of the Building Regulations provides detailed guidance on this topic, including specific requirements for the minimum levels of acoustic isolation which
must be achieved in all new residential properties and conversions. These requirements also include acoustic targets for schools as set out in Building Bulletin 93.
Auracle Acoustics is able to provide advice on most aspects of noise control and noise reduction techniques for most sources of noise, the mitigation of noise impacts using noise barriers and uprated glazing & ventilation specifications and the acoustic performance requirements of Approved Document E 2003 and Building Bulletin 93.