There is often a trade-off effect in noise control. For example, higher noise levels can be accepted in meeting a specific need; though this usually requires that the occupant is in control.
Many parameters will affect the outdoor noise level at a specific location. Some of these are described here.
4.4.2 Parameters affecting outdoor noise level
The surroundings of a building have a major influence on the expected outdoor noise level. For example, the average outdoor noise level can be 60 dB(A)
in a city centre and 50 dB(A) in a suburban residential area (ÖNORM, 2006).
The distance to the noise source has a decisive influence on the perceived sound level. Doubling the distance from the source reduces the sound level by approximately 3-6 dB. Unobstructed noise from a single source will be reduced more than noise from a linear source, such as traffic.
The presence of noise barriers, and reflections from and absorption in their surfaces, will affect the sound level at a specific location.
The source itself plays a role – traffic generates low frequency noise, birdsong high frequency noise.
Other factors that affect the sound
level – and how it can be redirected – are a building opposite, trees (summer or winter appearance), and the geometry of the noise barrier and its surface absorption properties.
4.4.3 Traffic noise
Traffic noise increases stress levels and the risk of cardiovascular diseases. A conservative estimate is that between 200 and 500 people in Denmark are
dying prematurely from cardiovascular diseases and hypertension every year in Denmark because of traffic noise (Miljøstyrelsen, 2010).
In the first example shown below, a roof window experiences 8 dB lower noise levels than a facade window in the same building. For a roof window facing the back yard, that figure even falls to app-roximately 15 dB lower noise levels.
The second example shows that an opposing building will reflect some of the noise and reduce the diminution in noise level experienced by the roof window by 5 dB (ÖNORM, 2006).