Abstract: A low reverberating room for the entire auditory range. In particular, for ow frequency ranges below 100 Hz, in which the walls and ceiling are covered with sound absorbers. The sound absorbers on a surface of about 70-90% of a room, not including the floor, have a depth of <0.5 m preferably <0.3. The sound absorber also has a closed, plane but acoustically permeable surface, are built up of multiple layers. The sound absorbers are about 20-70% in similarity to composite-plate resonators. They are also provided with inside plates, made of metal or heavy foil, which are designed of varying thickness for absorption in various frequency ranges.

Abstract: A false ceiling for buildings designed to absorb acoustic waves has perfoed plates. One or several suspended plates (1, 6) are provided which are so hard that they cannot vibrate. The plates have a plurality of regularly or irregularly arranged holes (4, 7) with 0.2-3 mm diameter, the surface of the holes being less than 4% of the total surface. The air in the holes (4, 7) forms with the overlying cavities (11) a dampening active mass system of the foil absorber type.