Acoustics and the built environment: Have our Ears Changed?

On an evolutionary scale, it is only recently that we have developed technologies and architecture that allows us to change our immediate environment so significantly that it can have little in common with our original living conditions. This has had an effect on every factor that determines our level of ‘comfort’; however for now I will focus on acoustics, and more specifically, noise.

We can all agree that the natural environment is much quieter than modern man-made environments, and exposure to this increases our daily sound 'intake' to a level much higher than what our ears (and brains) have been designed to.

The US National Parks Service have produced a pair of noise maps that predict sounds levels across the US separately for natural noise and man-made noise (https://www.nps.gov/subjects/sound/soundmap.htm). We can see that the scale of noise level across the map from natural to man-made is increased by up to 27dB, with the noisiest areas predictably in city centres.

Predicted ambient noise levels without man-made noise 

Predicted ambient noise levels with man-made noise

What is most interesting about these noise maps is when we compare these noise levels to standard guidelines for internal living conditions. Predicted noise levels for the natural environment fall below 30-35dB(A) across the US, and when we compare this with good internal noise levels for resting and sleeping, we can see that there is a strong correlation. Does this perhaps mean that as a species our ears have not yet adapted to our new noisier environment? If so, what impact does this have on our health?

BS8233 and WHO guidelines for good internal noise level

Although exposure to extreme noise levels is universally agreed to cause hearing damage, the effect of prolonged levels of medium/high noise has not been fully agreed upon. Multiple studies link high noise levels to hypertension and decreased performance in education (Stansfeld & Matheson, 2003), whereas others have also shown links to ischemic heart disease (Passchier-Vermeer & Passchier, 2000). 

Either way, high noise levels will not have a positive impact on occupant health, and so the impact of this is a serious consideration to make when considering the design of your building.