Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
1996-12-17
2001-02-13
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S290000
Reexamination Certificate
active
06186270
ABSTRACT:
TECHNICAL FIELD
The invention relates to a sound absorber for absorbing acoustic sound waves.
BACKGROUND OF THE INVENTION
It has already been known to prevent sound waves from propagating into the environment right at the site of their occurrence, if possible, so that the environment is not affected too strongly by those acoustic sound waves. In order to form quiet spaces, it is further known to prevent, as far as possible, the sound from penetrating into those spaces from outside. Sound absorbers, which most of the time comprise sound absorbing materials, i.e. so-called “insulating materials” serve this purpose. However, material consumption is relatively high, which not only affects the production costs, but also the disposal of such insulating materials.
From DE 92 15 132 U1, there is known a molded part for use in the engine compartment of motor vehicles, which absorbs air sound and consists of a foil layer and a porous insulating layer. The molded part consists of an open porous PU foam which is sealed off by a PU foil on all sides.
Moreover, there are known sound absorbers (DE-U-92 15 132, DE-C-3 039 651, 4 011 705, 4 317 828 and 4 334 984) which comprise sound absorbing molded parts made of closed cellular PP foam, PE fleece bonded with a binder, polymeric materials or the like; uncovered Helmholtz resonators have also been used.
A sound absorber for absorbing sound from a relatively large frequency spectrum has also been known from U.S. Pat. No. 3,439,774, for instance. Therein, two layers are spaced apart from each other by a honeycombed spacer and provision is made for that the layers comprise micropores. The micropores are to be dimensioned according to a particular selection rule: the porosity of the outer layer, which faces the incident sound, shall comprise a relatively high permeability, i.e. penetrability for sound waves, and the other layer, which faces away from the incident sound, is to comprise a relatively low sound permeability. Such layers consist of stainless steel having a pore size of 50 to 500 &mgr;m, for instance.
Another problem, namely the muffling of body sound, i.e. the muffling of sound generating body portions, is also resolved in that muffling masses like those being spaced apart by spacers are applied onto the body which vibrates and therefore generates sound waves according to U.S. Pat. No. 3,087,571 and 3,087,573 as well as FRP 2 671 899, for instance.
SUMMARY OF THE INVENTION
It is the object underlying the invention to improve a sound absorber of the type specified at the beginning to the effect that as high as possible sound absorption is realized at an as low as possible material expenditure.
The invention is characterized in claim
1
and preferred embodiments are claimed in the subclaims. The following specification also relates to preferred embodiments.
According to the invention, the sound absorbing component consists of a sequence of layers having different densities and degrees of rigidity, which layers may optionally be laterally interrupted or, respectively, separated by webs and spacers. These layers consist of foils, fleeces, foams, other membrane-like materials or fabrics or a gas, which may expediently be air too. It is essential for the acoustic efficiency of the component that the successive layers differ from each other quite clearly, i.e. almost abruptly, in respect of their density and rigidity. At suitable dimensioning, this results in reflections of the sound waves travelling to and fro in the absorber at transition portions, which leads to good sound absorption in specific, preselectable frequency ranges.
Moreover, it is advantageous to laterally limit this layer system by webs or, respectively, pinched-off portions and spacers. This makes it possible to fix the individual materials and to realize different material sequences and, accordingly, different sound absorptions in the corresponding frequency ranges (absorption spectra).
One of said layers may expediently be configured as a carrier layer, i.e. a carrier body having a high mass, in particular.
The carrier body may then be configured as a shell-like or, respectively, tub-like carrier shell while the spacers or the intermediate layers, which keep further thin layers spaced apart from the carrier shell, are configured and arranged such that resonance chambers are formed between the layers and the carrier shell.
In contradistinction to those sound absorbers which are used most frequently and wherein the spaces between the layers are filled with insulating materials, said spaces remain largely material-free in accordance with the invention. Namely, the sound absorbing effect is predominantly achieved by that the gas modules between the layers are made to vibrate by the incident sound waves. The gas modules, which consist of air in particular, have a surface-related rigidity which constitutes a ass-spring system together with the mass coatings of the layers and the surrounding air coupled thereto, which system results in acoustic impedance minima and, accordingly, to sound absorption in the range of the resonance frequencies.
Thus, the absorber may be realized by a successive connection of masses and springs. One acoustic impedance minimum per mass-spring pair appears at the absorber surface, which in its turn results in a resonance in the absorption curve of the component concerned. These resonance frequencies may be varied by varying the material thicknesses and densities and any absorption course may thereby be realized.
It is preferred to select the carrier layer from a material which distinguishes itself by the following properties above all:
It is recommended to produce the carrier layer via deep-drawing or transfer molding or similar non-machining molding processes; press-forming of fibrous structures, in particular, is suitable as well. It is recommended that the carrier layer surfaces, which face away from the resonance chambers, be adapted to those contours which face the visible side of the sound absorber, i.e. the passenger compartment of a motor vehicle, for instance. Thus, the carrier layer may for instance represent the dashboard of the motor vehicle in order to prevent sound waves being generated in the engine compartment from penetrating into the passenger compartment.
Thus, the carrier layer may also be constituted by a component which is necessary anyway, e.g. a partition wall of sheet metal so that the sound absorber does not need a further carrier shell even if it preferably constitutes an integrated assembly which is prefabricated and installed as an integrated assembly at the site of employment.
The layers should comprise a thickness in the range of 10 &mgr;m −5 mm. It is particularly recommended to use a polyurethane elastomer (PU), polypropylene (PP) and/or polyester (PET) for the layers. It is also recommended to produce the layers from carbon, PAN (polyacrylonitrile) or natural fibers and/or from fiber-reinforced thermoplastic or mixtures thereof. More particularly, flax, coir, sisal, jute, hemp or cellulose may be used as natural fiber materials, which may be bonded thermoplastically, pressed more or less strongly or bonded with natural binders, e.g. lignine or starch.
The spacers should be spaced apart from each other between the carrier layer and the further layers such that the resonance chambers are respectively closed by the carrier shell at one end and by one of the layers at the other end or between the layers proper, respectively. It may be expedient for special cases to provide the layers with openings leading towards the resonance chambers; the carrier layer may comprise openings as well.
Very simple spacers are formed by web-shaped or plate-shaped supports extending between the layers and being disposed substantially perpendicularly in respect of these; the spacers may also extend towards these aggregates of the sound absorber under angles deviating therefrom if this is useful for reasons of space, such as for accommodating further components such as electrical components, or for resonance purposes.
The spacers consist
Kock Gerhard
Lahner Stefan
Pfaffelhuber Klaus
Roller Manfred
Dang Khanh
M. Faist GmbH & Co. KG
Wallenstein & Wagner LTD
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