An acoustical panel has a multiplicity of short micro-slits, about 10 mm in length each, with each micro-slit having a wedge shaped cross-section in which the opening on the front side of the panel is wider than the opening on the rear side of the panel by a factor of about 2 to effectively absorb sound frequencies in the range of 250-2000 Hz, with the micro-slits greater than 4%. The micro-slits are spaced apart less than 5 mm and several different patterns of micro-slits may be employed including micro-slits that are straight as well as arcuate or some combination of straight and arcuate. The area of the micro-slits on the front surface of the panel exceeds 4%.

A panel with one or more perforations, having a front surface, wherein the contrast Cm between the front surface and the one or more perforations is less than 0.3, a sound absorbing system including a panel and a masking layer, wherein the masking layer is air permeable, and the use of the panel or the sound absorbing system.

An acoustical panel has a multiplicity of short micro-slits, about 10 mm in length each, with each micro-slit having a wedge shaped cross-section in which the opening on the front side of the panel is wider than the opening on the rear side of the panel by a factor of about 2 to effectively absorb sound frequencies in the range of 250-2000 Hz, with the micro-slits greater than 4%. The micro-slits are spaced apart less than 5 mm and several different patterns of micro-slits may be employed including micro-slits that are straight as well as arcuate or some combination of straight and arcuate. The area of the micro-slits on the front surface of the panel exceeds 4%.

An acoustic board having displaced and passably abutted multiple through-holes comprises an outer surface and an inner surface, in which the first through-holes formed from the outer surface toward the inner surface and the second through-holes formed from the inner surface toward the outer surface are displaced and passably abutted thereby conjunctively constituting acoustically absorptive micro-orifices. Herein at least some of the second through-holes have a cross-sectional area of greater than 1 mm.sup.2 and are displaced and passably abutted to at least some of the first through-holes, thereby collectively forming a plurality of acoustically absorptive micro-orifices having a cross-sectional area of smaller than 1 mm.sup.2, and, in comparison with the total area of the acoustic board, the opening rate for the sum of the cross-sectional areas of all such acoustically absorptive micro-orifices is less than 3%.

The present invention provides a sheet material having bi-directionally formed micropores, pertaining to the field of material structures. The sheet material comprises a basic half side and a protrusive half side extending from the basic half side. The basic half side is formed with multiple recesses extending along a first orientation; while the protrusive half side has multiple beams extending along a second orientation. Herein the second orientation extends at an angle with respect to the first orientation, and a bottom edge is respectively formed at the intersection of the beam and the neighboring beam; also, a hole is respectively formed at the crossing position of the bottom edge and the recess.