Abstract: An acoustic panel (for absorbing sound) includes a first sheet with spaced microperforations, a second sheet with microperforations more widely spaced than the microperforations of the first sheet, and a first cellular core sandwiched between the first sheet and the second sheet. The panel can be spaced from a surface, such as a wall. A second cellular core can be provided between the second sheet and a third sheet. The third sheet is preferably solid without microperforations but can have microperforations. Noise Reduction Coefficient (NRC) can be 0.8.

Abstract: FIG. 2 shows a microperforated panel absorber 22 comprising: a microperforated facing 24; a non-perforated facing 26; and a cellular core structure 28 therebetween; the core structure 28 provides a number of primary cells 33 and a number of secondary cells 37; the secondary cells 37 each provide a reduced cell depth in comparison to the primary cells 33. FIG. 9 shows that the number of the primary cells 33 and the number of the secondary cells 37 ensures that sound absorption at frequencies up to and including the peak frequency is substantially maintained and that the sound absorption at frequencies higher than peak frequency is substantially increased relative to a comparable panel absorber in which the secondary cells are effectively replaced by primary cells.

Abstract: FIG. 2 shows a microperforated panel absorber 22 comprising: a microperforated facing 24; a non-perforated facing 26; and a cellular core structure 28 therebetween; the core structure 28 provides a number of primary cells 33 and a number of secondary cells 37; the secondary cells 37 each provide a reduced cell depth in comparison to the primary cells 33. FIG. 9 shows that the number of the primary cells 33 and the number of the secondary cells 37 ensures that sound absorption at frequencies up to and including the peak frequency is substantially maintained and that the sound absorption at frequencies higher than peak frequency is substantially increased relative to a comparable panel absorber in which the secondary cells are effectively replaced by primary cells.