FKFS investigates tire-road noise of vehicles not only by far field measurements using microphones at the side of the road. FKFS investigates tire-road noise also by means of a specially developed trailer which provides a housing for the tires to be tested as well as a number of microphones. These microphones record the noise caused by the tested tire-road combination close to its origin in the near-field. Background noise from outside the trailer is suppressed to the greatest possible extent.
The system has considerable advantages over the controlled and statistical pass-by methods. The trailer enables to carry out measurements rapidly and the surrounding traffic has almost no influence on the results. Moreover, compared to corresponding test benches it is more cost effective and the contact patch corresponds to that at the vehicle.
Based on these tire-road noise measurements and by using the tire-road noise test bench developed at FKFS, it is possible to determine the contribution of the air-borne tire-road noise to the interior noise of a vehicle in an isolated way.
To investigate the contribution of tire-road noise to the in-cabin noise, a specific test bench with speakers at the test vehicle's tires is available at FKFS. The speakers reproduce the sound field generated by the tires, which has been recorded previously by means of the tire-road noise trailer. This enables analysis and evaluation of the tire-road noise inside the cabin – without influence from other noise components, such as wind noise or rolling noise (see aeroacoustic wind tunnel and servohydraulic 4-post test bench).