Simulate future noise
Researchers at Empa have succeeded in simulating road noise by means of "auralization". This should help in road planning to make noise audible and to plan countermeasures.
Auralization is the process of making audible sound events that will only take place in the future. Until a few years ago, it was primarily used by interior designers to optimize room acoustics. In Empa's "TAURA" project, funded by the Swiss National Science Foundation (SNSF), a research group led by Reto Pieren is now working on an auralization model that simulates the sounds of accelerating passenger cars passing an observer. The model thus makes it possible to take noise-reducing precautions into account as early as the planning stage of road construction projects.
Developing such an auralization model is easier said than done. This is because the noise caused by a car speeding past comes from different sources, which are entered into the computer model in the "emission module". On the one hand, there is the engine, which roars in the ears, especially during heavy acceleration. But driving speed, car type and the driving style of the driver also influence the engine or drive noise. Secondly, the tires cause noise by rolling on the road. This depends primarily on the type of road surface and the type of tire. In the future, Pieren and his colleagues want to map even more sound sources in their auralization model, such as the effect of different road surfaces and wind noise.
Complex vehicle sounds
The researchers first had to identify all these influencing variables. To do this, they recorded the driving noises of various car types, for example those of a VW Touran, a Ford Focus 1.8i or a Skoda Fabia. These measurements were made from several microphone positions and at different speeds. The researchers also varied the tire type, engine load and engine speed. They extracted the noise characteristics from the recordings and transferred them as parameters to their auralization model. This resulted in a total of several thousand such parameters, which, depending on their interaction, cause a completely different driving noise.
But that was not enough: Next, propagation phenomena such as the Doppler effect, sound absorption by the air or the attenuation of sound due to the distance between the noise source and the observer had to be taken into account. This is because depending on where an observer is in relation to the noise source and how the two move relative to each other, the observer will perceive the noise differently. The Doppler effect, for example, is well known from everyday life: The siren of an emergency vehicle sounds high when the vehicle is moving toward you, and comparatively low when it moves away from you again.
How annoying are noises perceived?
Finally, the modeled signals must be converted into sound via headphones or a pair of loudspeakers. However, noise only arises in our consciousness, so it is perceived differently from listener to listener and cannot be objectively measured in physical units. Therefore, test persons listen to the simulated driving noises and make statements about their annoyance, the degree of their noise-induced impairment. If several test persons judge different noises according to their annoyance, objectifiable correlations can be determined, although noise is a subjective quantity.
Noise affects people differently depending on the time of day, health status and age. Accordingly, the health consequences range from temporary sleep disturbances to an increased risk of cardiovascular disease. In order to prevent such impairments, noise-reducing measures must be taken into account in the planning of residential and industrial zones as well as traffic routes. For this purpose, urban planners, political decision-makers and the public need information about the expected noise emissions. Standard measures can be calculated today - but auralization can help to evaluate new ideas for noise optimization. This is how Empa researchers contribute to noise reduction with the help of their auralization model.
Also of interest for research
In addition to the practical benefits, there is also a scientific one. Because before Reto Pieren and his colleagues started their research, there was no such detailed auralization model to simulate road noise. In particular, the simulation of accelerating vehicles is new. In this respect, the research group is doing pioneering work in the field of auralization. In the next few weeks, the scientists plan to conduct initial tests with test subjects in the specially set-up listening lab.
Audio samples
Use headphones or a pair of speakers to achieve the highest possible playback quality.
The following three audio samples reproduce the components of the sound of a passenger car accelerating from 20 km/h to 50 km/h with two gear changes.
Total noise (engine and tires together)
Using the next two audio samples, you can compare the driving sounds of a passing passenger car on a road with a normal surface with the sounds of the same car on a road with a "whispering" surface. Both sound samples also simulate the Doppler effect.
(Source: Empa)
