The present invention relates to a sound absorbing panel with wedge-shaped cross-section micro-slits. Acousticians have long sought a sound absorbing panel to control reverberation in a room. In some applications, it is preferable for the panel to be fully transparent so that illumination means can be located behind the panel to combine illumination with acoustical treatment. Glazing is a popular building material and has considerable advantages in combining lighting and acoustical function into one panel to save on materials and costs.
The concept of micro-perforation of a panel was first pioneered by D-Y Maa in the 1970s. Maa proposed providing a panel with a multiplicity of small holes to attenuate noise in rooms. The holes contemplated by Maa have diameters less than 1 mm, perhaps as small as 0.1 mm.
Absorbers of this type are Helmholtz resonator type devices but devoid of the usual resistive material. Such devices provide absorption through his viscous losses as air passes through small holes which are only slightly larger than the boundary layer of air. Inherent damping eliminates the need for fiberglass or other porous materials in the air cavity behind the panel.
For high absorption of sound, Maa showed that the panel thickness and hole diameter should be the same. Hence, high frequency absorbing devices are typically foils of polycarbonate or ETFE. The requirement of Maa for small holes restricts the frequency range over which the resonant absorption can be achieved within manufacturing constraints. Thicker materials are useful devices for treating troublesome low to mid frequency noise and reverberance.
U.S. Pat. No. 5,700,527 to Fuchs et al. discloses a sound absorbing glass building component that is provided with micro-perforated holes having a diameter of from 0.1-2.0 mm with the holes being spaced 2-20 mm apart and the panel having a thickness of 0.2-30 mm.
U.S. Pat. No. 6,194,052 to Knipstein discloses a sound absorbing element that includes a plurality of micro-slits that have non-uniform widths along their lengths including extremely narrowed ends. The Knipstein panel enhances sound absorption at extremely low frequencies, typically less than 300 Hz.
Published Application No. U.S. 2001/0050197 to Wood discloses a micro-perforated panel in which the micro-perforations may comprise tapered holes.
U.S. Pat. No. 7,677,359 to Vigran et al. discloses a sound absorbent panel in which a multiplicity of micro-slits is formed therein. The micro-slits are linear and have facing walls lying in parallel planes. The micro-slits in Vigran et al. have a minimum micro-slit width of less than 0.45 mm. The ratio between the length of each micro-slit and its width is at least 50. Moreover, the perforation level of panels made in accordance with the teachings of Vigran et al. is less than 3%.