Noise diffraction

In recent years, various solutions for the reduction of tyre-road noise have been proposed. These include single en double layer porous asphalt concrete (ZOAB), silent surface dressings and noise barriers. We propose a novel, additional solution contributing to the reduction of tyre-road noise: diffraction by means of side-resonators1.


The solution encompasses placement of cavities (resonators) alongside the road which diffract the sound emitted from the tyre. The diffraction is in upward direction and therefore a quiet zone is induced behind the resonators, as is shown in Figure 1

Figure 1. Resonators along the road. The size of the resonators has been exaggerated for clarity.

Figure 2. Simulated SPLs near resonators.

Computer simulation

Computer simulations confirm the quiet zone behind the resonators. In Figure 2 the calculated sound pressure level (SPL) near the resonators for a simple point source is shown for one specific frequency. These computer simulations can be used to optimize the resonator dimensions.

Figure 3. The tested resonator configuration.

Figure 4. SPL versus frequency with and without resonators.

Experimental validation

To prove the concept, experiments have been performed near the city of Enschede, the Netherlands. The tested configuration is shown in Figure 3. The SPL as a function of frequency has been measured at 7.5 m distance from the center of the lane and 1.2 m above ground level, as is shown in Figure 4. For this simple prototype, already an overall SPL reduction of about 3dB has been observed.


The support of the technology foundation STW, the local authority of Enschede and Vredestein is gratefully acknowledged.



Wijnant. Y.H. "Weg met geluid-diffractoren". Patent: NL 2003697.

For more information regarding this project, contact dr. Y. Wijnant