For panel absorbers, there is a trend towards a design not using fibrous components. For the distributed Helmholtz resonator absorbers, the challenge is to increase the natural losses to increase the absorption bandwidth. This paper presents a new type of distributed resonators. Using a double plate construction, the resonator necks have been laterally elongated, while their widths have been kept small. Thus, the viscous losses in the resonator necks have been increased compared to traditional resonators. Measurements were compared with a theoretical model using analytic solutions for the slit impedances, the end corrections and the resistance of the inner and outer surfaces. For the volume between the plates, a finite difference approach was used. The results were very sensitive to the plate separation. To attain high absorption over a broad frequency range this separation should be in the order of one boundary layer. Absorption bandwidths at least equivalent to those of micro-perforated panels were attained. [References: 12]
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