Acoustic resonators, such as Helmholtz resonators or slit resonators, are known as a highly efficient noise control mean for narrow frequency band applications. Their simple passive structure can be built from many different materials. If a noise control treatment is highly restricted by the additional weight, those resonators could be built out of a closed-cell lightweight foam. Because of both, manufacturing reasons and the cellular microstructure of the foam, the surface of such resonators is not perfectly smooth. Especially when openings of the resonators are milled in the foam, the surface roughness inside the opening might be relatively high. This leads to a certain damped behavior of the resonator that cannot be captured by current models. In this contribution, the effect of surface roughness on the airflow resistance and its impact on the acoustic behavior of slit resonators, like the absorption coefficient or the transmission loss for wall integrated means, is studied experimentally.
