Firstly, the BS 4142 assessment method requires measurement of the existing background sound level at a development site. The expected noise level from new equipment or activity can then be calculated at a given location. For instance, sound levels from a new development can be calculated at the nearest existing house.
If the new sound is lower than the background sound level, it will have little effect on the existing residential property. However, if the new sound level is greater than or equal to the background sound level, the more annoying that sound might be.
Corrections can also be applied if the new equipment or activity will have ‘annoying features’. These can include switching on or off, or being ‘tonal’. Tonality means that one (or more) frequency stands out among the others. For example, tonality can mean a noise has a ‘hum’, a ‘whine’ or a ‘whistle’ feature.