When planning construction projects, stakeholders are always faced with one problem: The noise predictions cause hassels. Although sound immission forecasts are always part of the planning process, these forecasts often mean nothing to laymen, explains Wölfel engineer Janosch Blaul: “Five decibels louder or quieter, what exactly does that mean? That's a very abstract value that's hard to convey.”

What's more, people perceive noise differently: Sounds that are just a quiet background noise for some are unbearable for others. According to Blaul, expectations are often disappointed, or values underestimated. The result are disputes and protests from those affected.

In the HEAR project, Janosch Blaul, project manager Dr. Andreas Nuber and their team have come up with a very pragmatic solution to this problem: Why not simply simulate the soundscape that residents can expect? The simulation could then be played during public presentations on the construction project, for example. People could then get a much better impression of how the sounds in their environment change. The technical term for such an acoustic simulation is auralization.

Traffic as a complex sound tapestry

What sounds so simple and obvious was a tough nut to crack for the project team. For room acoustics, there are already many auralization tools available. In the HEAR project, however, the focus was explicitly not on interior spaces, but on the urban outdoor space with its sound and noise tapestries of road traffic, people, machines, and factories. The street noise in large cities is a huge stress factor for the inhabitants. Unfortunately, it is also much more complex than room acoustics, even in large rooms such as a concert hall. So Blaul and his team had to think differently and find new approaches to realize their simulation.

“The solution was actually quite simple in the end, but we had to work it out first and sometimes hit dead ends in the process,” reports Blaul. After all, the road noise simulation created by the Wölfel GmbH is one of the first of its kind in the world – and the only one so far that reproduces the soundscape true to level, thus staying within the official calculation regulations for noise immission control.

Janosch Blaul describes the challenges that the team had to overcome when setting up a noise database: “It starts with the fact that you always have background noise when recording outside. And then vehicles are moving objects, so that adds sound effects like the Doppler effect.” The team's initial idea of simply recording road noise at several stationary measurement points and building the simulation on that quickly turned out to be a bottomless pit. “There's so much background noise even in a single measurement that it's almost impossible to process – and you'd have to record an infinite number of situations and locations to create a comprehensive picture,” says Blaul.

Capturing the noise at the source

It quickly became clear that the recordings would have to be made closer to the noise source. So, the HEAR team chose a set of different car models and recorded their motor sounds close to the engine: by varying gears and engine speeds on an idling engine. For tire noise, a microphone was mounted near the wheels and the noise recorded while driving. With these recordings, it was possible to imitate the driving sounds of cars of different sizes and with different noise levels surprisingly well. Supplemented with further sound snippets, partly from the company's own recordings and partly from noise databases available for purchase, they form the basis of the noise simulation.

For the implementation, the project team was able to build on software that Wölfel GmbH has been selling and developing for a long time: The IMMI software is used by construction companies and experts to calculate the noise immissions caused by a construction project. However, the software spits out numbers and values – which, in turn, only experts can make sense of. The new auralization tool is intended to complement the software and, Blaul hopes, will improve communication with customers and laypeople: “If everyone involved knows what kind of noise they're dealing with, they'll also be much better able to formulate what bothers them.”

The finished tool should be available soon

Without the already existing IMMI algorithms, the auralization tool would probably have been an almost unsolvable task, at least for the short project duration of only one and a half years. But now Blaul and his colleagues can report a success at the end of the project: The auralization is almost ready and is currently being optimized. It is expected to be launched for IMMI users within a few months. Blaul reports that customers are showing great interest in this solution. And he is already taking the idea of “trial listening” a step further: At some point, he would like to have an auralization tool that works independently of the IMMI expert software – maybe even as an app? However, the acoustics expert admits that such an app is still a long way off.

For the time being, the new tool should help to make sound immission control less elitist and easier to understand. Auralization cannot, of course, reduce or prevent noise per se, says Blaul – but it should at least be able to help reduce the number of people affected by noise. After all, even the Wölfel engineers gained completely new insights when developing the tool: “We usually only work with numbers and values, even though we're all about sound and noise,” explains Janosch Blaul. “For decades, we have been working with the relevant regulations for noise immission control. And now, for the first time, we were able make the effect of these rules audible!”

The HEAR project is part of the FH-Impuls i_city partnership, in which the Stuttgart University of Applied Sciences (HFT Stuttgart) forms a network with companies and municipalities in the Stuttgart metropolitan region to research the city of the future. In various projects, the partners develop concepts for “smart cities” – from innovative, energy-saving building structures to intelligent energy and noise management to sustainable mobility.