Acoustics – Sound-modifying means – Sound absorbing panels
Patent
1996-11-18
1998-05-12
Dang, Khanh
Acoustics
Sound-modifying means
Sound absorbing panels
181286, 181295, E04B 182
Patent
active
057509441
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a foil absorber for sound.
1. Introduction
The use of more or less homogeneous layers of fibrous/porous materials (e.g. synthetic mineral fibers (KMF)) predominate as seen in FIGS. 1A-C: in room acoustics (e.g. wall and ceiling cladding, FIG. 1a), in noise control of loud machines (e.g. cladding and screening) as well as in technological noise control (e.g. by means of sound dampers in flow canals, FIG. 1c). The discussions for many years about possible health risks from the fine dust and fibers (Koster, J.; Grunau, E.B.: Mineralfasern: Eine Gefahrenquelle, Expert-Verlag, Ehningen, 1993) as well as from deposits and germ infestation in such layers have led, on the one hand, to attempts to cover and wrap the porous material with suitable foils and nonwoven fabrics and, on the other hand, to seek alternative sound absorbers obviating the use of porous materials. This search soon led the assignee of the present invention to the development of three totally different absorbers for completely different acoustical applications ("Schallabsorbierendes Bauelement"--German patent document DE 27 58 041; "Schalldampfer Box"--German patent document DE 35 04 208 (corresponding to U.S. Pat. No. 4,787,473); and "schallabsorbierendes Glas--oder Kunstglas-Bauteil"--German patent document DE 43 15 759). These absorbers can, each individually and in combination, as well as as a supplement to enhance the performance of conventional absorbers, cover a broad frequency range of approximately 50 Hz up into the kHz range and a very wide field of applications. Moreover, there are also more or less successful attempts at describing these usually two-dimensionally designed absorbers.
For instance, in Mechel F.; Kiesewetter, N.; Schallabsorber aus Kunststoff-Folie. Acustica 47 (1981), pp. 83-88 shows that a plane plastic foil that is excited to propagate forced bending waves by a diagonally striking soundwave is unable to destroy a substantial part of the sound energy by means of internal friction. In order to, nonetheless, substantially raise the degree of dissipation, it has been proposed to deform the foil in such a manner that rectangular two-dimensional pieces of a few centimeters in length and width, which are bordered by a fold, are created. The fold at the edge of these plates acts like a fastening device and prevents free motion of the foil at this site. By this means, these plates are excited to characteristic vibrations. The wavelengths of these natural vibrations are in the frequency range up to 5000 Hz substantially smaller than the track wavelength of the incident airborne soundwave. The vibration amplitude of the plate is especially great in the case of natural frequencies. Due to the resonance-like co-vibration of the subareas with their characteristic bending vibrations, one thought if there continues to be relatively little internal dampening, but stronger deformation of the foil material, greater dampening of the excited soundwaves could be achieved at least in the vicinity of the natural frequency. In order to obtain a wideband sound absorber despite these profiled foils which are principally limited only functioning in narrow frequency bands, one solution described in "Schallabsorbierendes Baulelement" German patent document DE 29 21 050 (corresponding to U.S. Pat. No. 4,425,981), and "Schallabsorbierendes Bauelement"--German patent document DE 32 33 654 (corresponding to U.S. Pat. No. 4,555,433) tried: surfaces of the foils; and the same plate by preferring oblong instead of square subareas; and small and large deformations plus additional mass inclusions into the swedged foils so that practically all the interesting frequency portions of the to be dampened sound field can be absorbed as fully as possible.
This optimizing of ten or more simultaneously excitable bending vibrations yields a greatly cleaved, rough sound absorber surface.
2. Disadvantage of the conventional foil absorbers
The above-described cupping, molding, structuring, swedgi
REFERENCES:
patent: 4425981 (1984-01-01), Kiesewetter et al.
patent: 4555433 (1985-11-01), Jablonka et al.
patent: 4607466 (1986-08-01), Allred
patent: 4703374 (1987-10-01), Biermeier et al.
patent: 4780777 (1988-10-01), Biermeier et al.
patent: 4832147 (1989-05-01), Dear et al.
Baupraxis & Dokumentation 7, Mineralfasern Eine Gefahrenquelle Mit 35 Biln und 610 Literaturstellan by Johann Koester et al.
Acustica, vol. 47, No. 2, 1981, Schallabsorber aus Kuntststoff-Folie, by von F. Mechel et al.
Dang Khanh
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
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