SOUND ABSORBERS OF A NOVEL MEMBRANE CONSTRUCTION

Porous or fibrous materials are used in a variety of applications to absorb acoustic energy at medium and high frequencies above approximately 200 Hz. There are, however, cases where their open and rough surface entails disadvantages with respect to hygiene and cleaning requirements. The sound absorber presented is of the reactive or resonant type with several different modes of vibration excitable in a complex system of thin, though comparatively stiff, metal or plastic membranes. The absorption of the vibrational energy as stimulated by the sound waves impinging on the new type of acoustic lining or splitters is brought about by frictional forces in bounded shear layers formed between membranes moving against each other and relative to the air volumes adjacent to and between them. When suitably adjusted to the particular noise spectrum, these combined vibrational and damping mechanisms enable the construction of a new generation of sound absorber which no longer requires additional porous material to be incorporated in order to make it effective in a broad band of medium and low frequencies.