Irritated by noise? This research might help

The technique is called auralisation, a term that is analogous to visualisation. It helps explore the relationship between sound and its impact on people under fully controlled conditions.

“One of my models can simulate the sound of future wind farms and thus make them audible before they are actually built,” says Pieren, who will defend his thesis Auralisation of Environmental Acoustical Sceneries this summer.

‘Auralisation models can be used to inform and involve the public’

The core of the simulation process is a synthesiser that generates sound signals. The simulation shows the effects of different configurations on the noise. “In the case of wind turbines, you can change the angle of the blades for instance, or see what happens if you add so-called trailing edge serrations on them that are intended to reduce noise. These types of models can be useful to policymakers. Equally, spatial planners can use them to determine the required distance of wind parks to houses. Auralisation models can also be used as a tool to inform and involve the public into the planning process”

In an experimental hearing test, participants compared these synthetic sounds to recorded sounds of wind turbines. They often confused the synthetic sounds with real, recorded sounds.

The synthesiser for road vehicles separately produces tyre and propulsion sounds. The generated propulsion sounds depend on the engine type and speed and load. “You can use the model to find out how noise from the road will change if cars use different types of engines but keep the same tyres, for instance. Or if you put sound barriers between roads and houses.”

‘The model can create the typical metallic sound character of railway noise’

The same more or less goes for trains. The model assesses the microstructure of the wheels and rails, as well as the structural resonances of the wheel/rail system, to elicit the typical metallic sound character of railway noise. “Train manufacturers can demonstrate what their trains would sound like on railway tracks in Germany for instance, and also on an ill-conditioned track in India.”

All models simulate sound propagation effects, such as geometrical divergence, the Doppler effect, atmospheric absorption, ground effect and amplitude fluctuations due to atmospheric turbulence, from a virtual point source to a virtual observer location by processing the synthetic source signals with filters.

Not only is the sound energy relevant for comfort level, but also the type of noise. “Outside the scope of my PhD, I was involved in two sleep studies. In line with other published studies, these showed that awakening reactions are not only related to the average sound level, but also to the temporal structure of the noise. Short peaks and fast changes in level increase the probability of arousal and awakening. However, even today, environmental nocturnal noise is commonly assessed by long-term averaged sound levels only, whereby the temporal averaging is performed over several hours. Short-term variations are not considered.”

The research was funded by the Swiss National Science Foundation and largely performed at the Swiss Federal Laboratories for Materials Science and Technology. Pieren did part of his research in Delft under the supervision of Prof. Dick Simons of the Faculty of Aerospace Engineering, who is an expert in aircraft noise and performed similar work on aircraft as Pieren did on trains, cars and wind turbines.