If more and more electric vehicles are on our roads, this will not only have a positive impact on the climate and air quality, but also on traffic noise. The extent to which the noise levels of electric vehicles and cars with combustion engines differ has not yet been systematically investigated. Empa and TCS have carried out an extensive research project in close cooperation to find out how the noise levels of comparable cars with different drive systems differ depending on the driving style.

The team found that electric cars are significantly quieter than their combustion engine counterparts, particularly when accelerating. Especially when accelerating below 40 kilometers per hour, for instance, when starting at traffic lights, the noise levels of electric cars are significantly lower on average. Depending on the pair of cars, the difference is more than three decibels, which corresponds to a halving of the sound intensity. The difference between the drive types increases significantly with increasing acceleration: The greater the acceleration and the lower the speed, the louder the combustion engine is compared to the electric car.

The results were different, however, when driving at constant speeds of between 30 and 60 kilometers per hour, i.e. at typical inner-city speed: There were no significant noise differences on average between electric cars and cars with combustion engines, as tire noise dominates and drowns out the engine noise.

For Sascha Grunder, Head of Test & Technology at TCS, the study revealed important findings: "With this detailed study, we have broken new ground and have shown that electric cars are quieter than combustion engines, especially at low speeds and high acceleration. For TCS, it was a privilege to work together with Empa's scientists and provide the Empa acoustics lab with real data for the first time."

Reto Pieren from Empa's Acoustics/Noise Control lab agrees: "The results are an important contribution to noise research and show that e-mobility contributes to noise reduction in urban environments. The collaboration with TCS was enriching, and I look forward to continuing it."

The results of the study will be presented at the international scientific conference Forum Acusticum in Malaga. The study also forms the basis for further research projects. The researchers will continue to evaluate and analyze the measurement data until the end of 2025. In a next step, Empa and TCS want to jointly investigate the influence of the tire type and the road surface properties on the noise level. These investigations will take place in spring 2026, and the results are expected to be published at the end of next year.

In the fight against noise, every centimeter counts in the construction sector. Traditional sound absorbers are usually made of bulky materials such as rock wool or melamine foam, however. In order to effectively dampen even low sound frequencies, thick layers of insulation materials are required – which costs space, restricts design and is often simply not even feasible in outdoor areas. Together with the company de Cavis, Empa researchers have therefore developed ultra-thin sound absorbers made of mineral gypsum or cement foams. These are just as effective as conventional absorbers, but around four times thinner. Further advantages: The foams can be tuned to specific frequency ranges and are easy to cut and install. Made from plaster or cement, they can be fireproof and recyclable, and do not release any harmful particles. Cement foams are also weatherproof and therefore suitable for outdoor use.

In future, the mineral sound absorbers could be retrofitted in driveways, under balconies or on façades in noisy streets. As with all open-pored absorbers, the prerequisite is protection from the weather and from dirt, for example with a perforated top layer. “Ideally, absorbers are already taken into account in the architectural design of new buildings,” explains Van Damme. The elements can also be easily integrated into stairwells or large interior spaces such as offices, canteens or sports halls – also from a design perspective, as the porous mineral foam is made of the same material as the surfaces of the walls.

According to Bart Van Damme, the idea for the absorber originated several years ago. However, the breakthrough only came through the combination of material development and acoustic modeling as part of an Innosuisse project. Thanks to the modeling, the absorber can now be flexibly customized: Should it dampen particularly low tones, such as in large halls? Or should it be more effective in the mid-range, such as in traffic noise, offices or classrooms?

At the moment, production is still complex and partly done by hand. Together with a suitable industrial partner, the material is now to be further developed and produced on a larger scale. The potential is huge – especially for special applications where limited space, fire protection and design requirements have to be taken into account at the same time.