Patent Description:
As it is known, noise pollution is an increasingly felt problem in many environments, for example in private houses, in the industrial field for insulating offices and production areas, and finally in public environments, such as residential areas crossed by heavy-traffic roads or railways.

In order to avoid or at least reduce noise propagation in all these environments, many types of soundproofing and/or sound-absorbing panels are known, manufactured according to several structures and configurations. These panels are planar structures, i.e. with two lateral dimensions which are much greater than thickness, and they are generally made by overlapping in the thickness direction several layers of different materials, at least one of them being often made of discontinuous materials (fibrous, such as glass wool or rock wool or polymer felts, or polymer foams); it is also common that one of the internal layers is shaped as an air chamber.

Panels of this type are often relatively heavy if consisting of solid or fibrous layers, or otherwise not efficient enough from the point of view of noise absorption and insulation properties. For example, these panels can have good properties of noise insulation (i.e., attenuation on one side of the panel of the noise generated from the other side thereof) but not of noise absorption (i.e. attenuation in the same space where noise is generated), or vice versa.

Document <CIT> relates to a sound insulating panel formed of two exterior walls between which is placed a sheet of metal forming an acoustic insulator. In embodiment, the sound insulating panel is composed of a wooden frame in two parts which block between them an insulating lead sheet whose thickness can range, for example, from <NUM>/<NUM> to <NUM> / <NUM>.

Document <CIT> relates to an acoustical control media including an air impervious septum adjacent which there is positioned a layer of low-density fibrous filler material, on the outside of which there is provided a thin layer of medium-density material formed with perforations.

Document <CIT> relates to a soundproof sandwich panel comprising a plastic sheet having a large number of air chambers disposed in the middle of two sheets of plate materials, arranged in parallel with a predetermined interval, to form two empty volumes.

Document <CIT> relates to an acoustic composite comprises a flow resistive substrate having a solid acoustic barrier material bonded to at least a portion of a major surface of the flow resistive substrate.

An object of the present invention is to provide a soundproofing panel which overcomes prior art problems, being lightweight, with good noise insulation (soundproofing) and absorption features, prominently in the low-frequency field, and which has a modular construction, in order to be assembled at the operative site covering or occupying at best the available surface.

This object and other objects are achieved by the present invention, which in a first aspect thereof relates to a soundproofing element comprising:.

The soundproofing element of the present invention relies on advantages and synergistic effects, to provide soundproofing and sound-absorption.

The first peripheral structure provides sound-absorption for medium-high frequencies. In particular, the first peripheral structure advantageously has an acoustic absorption coefficient greater than <NUM> in the range <NUM>-<NUM>.

The first peripheral structure and the second peripheral structure of the soundproofing element are advantageously juxtaposed to effectively constrain the impervious sheet, which is mechanically interposed.

The impervious sheet together with the perforated sheet defines an acoustic resonator within the first air gap, providing sound-absorbing features for low frequencies, especially in the range <NUM>-<NUM>.

The impervious sheet provides soundproofing, as it is impervious to the acoustic wave that cannot directly pass through the panelling. In addition, the concentrated elements increase soundproofing by providing a resonant behaviour of the system formed by the impervious sheet, acting as resonating plate, and by the concentrated masses. This effect can be tuned appropriately for the desired application, by selecting dimensions, thickness, weight, and distribution of the concentrated elements and by selecting dimensions, thickness, and material of the impervious sheet.

The second peripheral structure further contributes to sound-absorption for medium-high frequencies. At the same time, the second peripheral structure allows the resonant motion within the second air gap of the impervious sheet and of concentrated elements.

The continuous sheet or panel, included or applied to the soundproofing element during installation, represents an element impervious to the acoustic wave, providing further soundproofing features.

In a second aspect thereof, the invention relates to a modular soundproofing panel, i.e. formed by juxtaposing several soundproofing elements of the above-described type along the lateral surfaces thereof.

The invention will be described hereafter with reference to the Figures, in which:.

In the present description, the definition "medium-high frequencies" means frequencies in the range of <NUM>-<NUM>, while "low frequencies" means frequencies in the range of <NUM>-<NUM>.

As shown in the figures, the soundproofing elements of the invention are preferably prism-shaped, in which the two bases can be shaped as an equilateral triangle, a square, a rhombus, a rectangle or a hexagon, while the lateral faces are rectangular.

In the following description, the definition "shape of the soundproofing element" (or of a part thereof) refers to the shape of the base; the definition "thickness", referred to the element or a part thereof refers to a dimension measured in the direction between the two prism bases.

Finally, in the rest of the description it is adopted the convention of regarding as the front part of the element the one comprising the perforated sheet and as the rear part of the element the one comprising the continuous sheet or panel; as a consequence of this conventional choice, the adjective "front", referred to a face or surface of the element or a part thereof, concerns a surface in which there is the perforated sheet or facing it, while the adjective "rear", referred to a face or surface of the element or a part thereof, concerns a surface in which there is the continuous sheet or panel or facing it.

In the figures, the dimensions of the various parts forming the elements or the panels of the invention are not drawn to scale: some parts or some details are shown with enlarged dimensions for clarity of depiction.

<NUM>-<NUM> schematically show the structure of a soundproofing element of the invention, <NUM>. As shown in <FIG>, the element <NUM> consists of a perforated sheet <NUM>, an impervious sheet <NUM> on which there are periodically-arranged concentrated elements <NUM>, <NUM>', <NUM>",. , and a continuous sheet or panel <NUM>.

In some embodiments, as exemplified in Figg. <NUM>-<NUM>, the continuous sheet or panel <NUM> is part of the element <NUM>. In other embodiments, not shown, the continuous sheet or panel is a preexisting planar surface of a structure to which the element <NUM> is applied; for example, the continuous sheet or panel could be a plaster wall, a drywall, a wooden or metal panel.

The perforated sheet <NUM> and the impervious sheet <NUM> are connected respectively to the front surface (or in proximity thereof) 11a and to the rear surface 11b of the first peripheral structure <NUM> and are parallel to each other, defining a first gap <NUM>. The impervious sheet <NUM> is also fixed to the front surface 15a of the second peripheral structure <NUM>; the continuous sheet or panel <NUM> is fixed to the rear surface 15b of the second peripheral structure <NUM>, which is parallel to the impervious sheet <NUM> and defines therewith a second gap, <NUM>.

The definition "periodical arrangement" (and definitions derived therefrom), in the present invention and in the claims means an orderly arrangement of the concentrated elements <NUM>, <NUM>', <NUM>",. , on one or both surfaces of the impervious sheet <NUM>, which depends on the shape of the peripheral structure <NUM> (and/or <NUM>): the concentrated elements are positioned on the nodes of a grid of lines which form therebetween angles corresponding to the geometry of the peripheral structure, i.e. for example a grid of lines with <NUM>° angles (square or rectangular grid) if the peripheral structure is square or rectangular (also comprising the possibility of a square grid in a rectangular peripheral structure and vice versa), a hexagonal grid if the peripheral structure is hexagonal, etc. In this arrangement, it is not necessary that all the nodes of the grid are occupied by the concentrated elements, provided that the arrangement of the latter ones is symmetrical on the surface of the impervious sheet <NUM>, for example with respect to the centre of the sheet surface. The exact positioning of the concentrated elements <NUM>, <NUM>', <NUM>",. , on the nodes of the above-described grid allows a tolerance which is equal to the typical dimension of the concentrated elements, and it is thus not necessary that the centre of the concentrated element exactly coincides with the node of the grid.

In <FIG> the concentrated elements <NUM>, <NUM>', <NUM>",. are shown as protrusions on the front surface of the sheet <NUM>, but they could also be present on the rear surface of the impervious sheet <NUM>, or even, they could protrude with respect to both surfaces.

The perforated sheet <NUM> and the gap <NUM>, together with the peripheral structures <NUM> and <NUM>, form the sound-absorbing sections of the soundproofing element <NUM>, while the impervious sheet <NUM> and the continuous sheet or panel <NUM> give the soundproofing element <NUM> its soundproofing features.

<FIG> shows in a schematic plan view a peripheral structure having a square geometry, <NUM> to which the perforated sheet <NUM> is fixed.

<FIG> shows in a schematic plan view an impervious sheet <NUM>, on which there are the concentrated elements <NUM>, <NUM>', <NUM>",. according to an orderly arrangement; the dotted line in <FIG> represents the print of the peripheral structure <NUM> when the two parts are connected; the portion of the sheet <NUM> enclosed within the area defined by the dotted line <NUM> is thus the part of this sheet which is free to vibrate in the finished element, to give the assembly the soundproofing effect.

<NUM> and <NUM> the elements <NUM>, <NUM>', <NUM>",. are represented as elements differing from the impervious sheet <NUM> and adhering thereto; but the sheet <NUM> and the elements <NUM>, <NUM>', <NUM>",. could be formed as a single part, for example produced by moulding of a polymer material in a suitably shaped mould.

In a preferred embodiment, the elements <NUM>, <NUM>', <NUM>",. , are hollow bodies and have an opening on the front surface facing the sheet <NUM>. Under this condition the elements <NUM>, <NUM>', <NUM>",. , besides being decisive to obtain the soundproofing effect at low frequencies, also contribute to the sound-absorbing effect, moving downwards the frequency of the maximum absorption efficiency.

In a still more preferred embodiment, the elements <NUM>, <NUM>', <NUM>",. , are hollow bodies and comprise internal walls which create a convolute path for the incoming sound wave, thereby maximizing the path thereof. <FIG> shows three different views of a possible element like <NUM> according to the last embodiment. On the left side of the figure a view of the front face of the element <NUM> (i.e. the one facing the sheet <NUM>) is shown; in the central part of the figure a view of the element <NUM> in a section along the line A-A' of the left side of the figure is shown (the same section line A-A' is also reported on the right side of the figure); and on the right side of the figure a view of the element <NUM> in a section along the line B-B' of the central part of the figure is shown.

As shown by the different views in <FIG>, the element <NUM> has a front surface <NUM> on which there is a hole <NUM> which puts the internal recess in communication with the outside (on the right side of the figure the position of the hole <NUM> is indicated by the dotted line); there are walls <NUM>, <NUM>',. , within the recess of the element <NUM> having the same height as the recess (and thus connected both to the front surface <NUM> and to the rear surface <NUM> of the element <NUM>) but a lower length than the side of the recess, and arranged in an alternating manner in the recess so as to form a tortuous path therein. An element <NUM> of this type can have other shapes: for example, the element <NUM> could have a circular shape, the through hole could be in the centre of the front surface thereof, and instead of a series of walls like <NUM>, <NUM>',. , there could be a single wall with a spiral pattern in the recess. Other possible configurations of an element <NUM> of this type will become apparent to the skilled in the art.

Elements <NUM> of this type, if they are positioned on the front face of the sheet <NUM>, can be produced by moulding the lateral walls thereof (including <NUM>, <NUM>',. ) together with the sheet <NUM>, and then letting a perforated flat part, which will be the front surface <NUM>, adhere to the end of these walls opposite the sheet <NUM>; rather, if there are the elements <NUM> on the rear face of the sheet <NUM>, the surface indicated in <FIG> as <NUM> is a portion of the sheet itself, the lateral walls of the element <NUM> can be produced by moulding together with the sheet <NUM>, and the recess can then be closed by adherence of a closing wall <NUM>. Alternatively, elements <NUM> of this type could be produced separately and let then adhere to the sheet <NUM>.

The weight of the concentrated elements <NUM>, <NUM>', <NUM>",. , and the arrangement thereof on the surface of the impervious sheet <NUM>, allow the soundproofing features of the element <NUM> to be modulated as a function of the incident audio-frequency. In particular, the weight of the single element <NUM> can vary between <NUM> and <NUM>, the distance thereof can vary between <NUM> and <NUM> and, within these limits, the range of the maximum insulation efficiency moves towards low frequencies when the weight of the element <NUM>, the distance therebetween and the dimensions of the single element <NUM> increase.

In the case of hollow elements like those shown in <FIG>, which also contribute to sound absorption, the range of the maximum absorption efficiency moves towards low frequencies when the dimensions of the hole on the front surface, the recess volume and the length of the path defined by the internal walls of the element <NUM> increase.

<FIG> shows in a perspective view a soundproofing element of the invention, <NUM>, with a peripheral structure shaped as a square frame. On the left side of the figure the element is shown as a whole: the first peripheral structure <NUM>, the perforated sheet <NUM> supported by the latter, and the second peripheral structure <NUM> are visible; the impervious sheet <NUM>, fixed between the parts <NUM> and <NUM>, is not indicated for simplicity of depiction. On the right side of the figure the element <NUM> is shown in section; in this view, besides the already-mentioned structures <NUM> and <NUM>, the impervious sheet <NUM> with the concentrated elements <NUM>, <NUM>', <NUM>",. arranged according to a periodical order and the continuous sheet or panel <NUM> are shown.

The peripheral structure <NUM>, made of a porous or fibrous material, can be externally covered by a fabric or a perforated plate; the latter possibility is illustrated in <FIG>, in which the perforated plate <NUM> partially surrounding the peripheral structure <NUM> is shown. Moreover, the peripheral structure <NUM> can contain therein structural reinforcement parts (tubes with a square or circular section, metal profiles with a planar, L-shaped, T-shaped, C-shaped, H-shaped,. section) which give a geometric stability to the structure itself; this possibility is exemplified in <FIG>, in which on the right side a frame structural element, <NUM> is shown, within the structural element <NUM>; the element <NUM> is shown in this example as a solid rod. In the case of peripheral structures of reduced dimensions and weight, the geometric stability can also be ensured by the perforated plate <NUM>.

Although the use of a covering of the structural element <NUM> (a fabric or a perforated plate, <NUM>) and of the frame structural element within the latter <NUM> is exemplified only in <FIG>, these further elements can naturally be present in any soundproofing element of the invention.

<FIG> shows in a perspective view a soundproofing element of the invention, <NUM>, with a peripheral structure shaped as a hexagonal frame. In this case too on the left side of the figure the element is shown as a whole and on the right side in section; the details and parts which form the element <NUM> are the same, with the same reference number, as those described above with reference to <FIG>.

Soundproofing elements having a square or hexagonal shape have been exemplified in Figg. <NUM>-<NUM>, but they can have any shape, including circular or elliptical. In particular, it is advantageous that, by the union of several identical elements, it is possible to obtain a continuous planar surface. As it is known, the occupation of a planar surface without leaving voids is defined in a tiling geometry of the plane, and the shapes allowing to obtain it are the equilateral triangle, the square, the rhombus, the rectangle and the hexagon; the peripheral structures can thus preferably but not limiting have any one of these shapes. The choice of a particular geometry of the soundproofing element could not allow a planar surface to be completely covered at the edges thereof; for example, by employing hexagon-shaped soundproofing elements, it is not possible to manufacture a rectangular panel. In these cases, it is possible to provide suitably shaped elements, deriving from the main ones employed in the panel, for example half-hexagon-shaped in the case of hexagon-shaped main elements, as described hereafter with reference to <FIG>. In these potential elements having a "partial" shape the arrangement of the concentrated elements <NUM>, <NUM>', <NUM>",. is still the same as that in the elements having a corresponding complete shape.

The materials which form the soundproofing element of the invention can be chosen among various possibilities.

The materials forming the peripheral structures have a density comprised between <NUM>/m3 and <NUM>/m3 and a modulus of elasticity comprised between <NUM>^<NUM> and <NUM>^<NUM> Pa; these materials are typically porous or fibrous, for example stiff polymer foams. If necessary, these materials can also make up structural elements, and thus be of metal with holes.

The materials forming the perforated sheet <NUM>, the impervious sheet <NUM>, the concentrated elements <NUM>, <NUM>', <NUM>",. and the continuous sheet or panel <NUM> have a density comprised between <NUM>/m3 and <NUM>/m3 and a modulus of elasticity comprised between <NUM>^<NUM> and <NUM>^<NUM> Pa; these materials can be chosen among plastic materials, metals or glass; if it is necessary to allow the visibility through the panelling made of the above-described soundproofing elements, these sheets <NUM>, <NUM> and <NUM> (or panel <NUM>) are made of glass or transparent plastic, for example polymethylmethacrylate.

The soundproofing elements of the invention can have lateral dimensions comprised between <NUM> and <NUM>, and an overall thickness comprised between <NUM> and <NUM>.

The thicknesses of the perforated sheet <NUM>, of the impervious sheet <NUM> (without the concentrated elements <NUM>, <NUM>', <NUM>",. ) and of the continuous sheet or panel <NUM> can vary between <NUM> and <NUM>, while the thicknesses of the two gaps <NUM> and <NUM> can vary between <NUM> and <NUM>.

<FIG> and <FIG> show two possible embodiments of a soundproofing panel of the second aspect of the invention. The two panels <NUM> and <NUM> shown in these two figures are obtained by the juxtaposition along the lateral surfaces thereof of soundproofing elements <NUM> of the above-described type, in particular elements <NUM> being square-shaped in the case of the panel <NUM> and hexagon-shaped in the case of the panel <NUM>. Moreover, the use of elements having a "partial" shape with respect to the main elements of the panel is shown in <FIG>; the elements <NUM> and <NUM>' shown in the figure allow a rectangular panel to be obtained by occupying spaces left by the "complete" elements at the panel edges.

The coupling of the peripheral structure <NUM> with the perforated sheet <NUM> gives the panelling an overall sound absorption curve which is close to or greater than one unit for both low and medium-high frequencies, as reported in <FIG>. The value of the acoustic absorption coefficient alpha can be remarkably in excess of <NUM> due to the combination of soundproofing and/or sound absorption of the various elements above described, at the different frequency ranges.

The assembly of the above-described peripheral structures and sheets (or panel <NUM>) gives the modular panel a high flexural stiffness and load bearing capacity with respect to the wind thrust loads or other horizontal loads such as those linked to the passage of high-speed trains.

Moreover, the lightness of the panel itself makes it particularly suitable for interior applications.

The soundproofing element <NUM> of the present invention provides effective features of sound absorption over a broad frequency band (<NUM> - <NUM>) by synergistically combining effects of its components, in particular the highfrequency adsorption of the first peripheral structure <NUM> is combined with the low-frequency adsorption of the resonator provided by perforated sheet <NUM>, the impervious sheet <NUM> and the first air gap <NUM>.

The soundproofing element of the present invention also provides effective soundproofing features, due to the impervious layer <NUM> and the associated continuous sheet or panel <NUM>.

Claim 1:
Soundproofing element (<NUM>) comprising:
- a first peripheral structure (<NUM>) made of a porous or fibrous material and having a central opening, said first peripheral structure (<NUM>) defined by two frame surfaces (11a, 11b) and a thickness defined by at least one lateral surface, said first peripheral structure (<NUM>) providing sound-absorbing features for medium-high frequencies;
- connected to said first peripheral structure (<NUM>), at a first frame surface (11a) thereof or in proximity thereto and so as to occupy said central opening, a perforated sheet (<NUM>) providing sound-absorbing features for low frequencies;
- connected to the first peripheral structure (<NUM>), at a second frame surface (<NUM>1b) thereof opposite said first frame surface (<NUM>1a), an impervious sheet (<NUM>) which together with the perforated sheet (<NUM>) provides sound-absorbing features for low frequencies, and periodically-arranged concentrated elements (<NUM>, <NUM>', <NUM>", ...) on said impervious sheet (<NUM>) which provide the soundproofing element (<NUM>) with soundproofing features;
- a second peripheral structure (<NUM>) made of a porous or fibrous material and having a shape substantially corresponding to that of the first peripheral structure (<NUM>), connected by a third frame surface (15a) to the impervious sheet (<NUM>) in a position substantially corresponding to the first peripheral structure (<NUM>);
- connected to said second peripheral structure (<NUM>), at a fourth frame surface (15b) thereof opposite said third frame surface (15a), a continuous sheet or panel (<NUM>);
- a first air gap (<NUM>) between said perforated sheet (<NUM>) and said impervious sheet (<NUM>);
- a second air gap (<NUM>) between said impervious sheet (<NUM>) and said continuous sheet or panel (<NUM>).