In practical application it is often required to absorb sound energy in a wide range of frequencies. It is known that a porous material cannot absorb sound energy in a low-frequency range without using a very deep air-space gap. Another option is to use artificial material like acoustic liners, metamaterials and so on but in this case, they act in tight frequency range and they have limitations by the production point of view. In this work, thanks to numerical and experimental investigations, a combination of the latter type of materials has been suitably designed to achieve both a selected frequency sound absorption system (including the low frequencies) and a wide frequency range one. At the same time the design considers limitations imposed by the manufacturer. The optimization by the production point of view (cost, working time, quality, appearance, etc..) together with structural, firer smoke behavior and the other requirement for safety are also considered.
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