Alternative fibreless absorbers - new tools and materials for noise control and acoustic comfort

A survey is given on Alternative Fibreless Absorber ALFA tools and materials as developed over the past 20 years by an alliance of Fraunhofer scientists with industrial partners. Twelve fairly different reactive and active sound absorption concepts were thoroughly investigated and successfully brought into the market. A case history describes a completely new type of broadband sound attenuator which seems to confirm A. de Saint-Exupery's statement that "perfection is not completed when nothing more may be added but when no more can be deleted". The philosophy and strategy behind these ongoing innovation processes were displayed in a companion paper in this journal [1].