Noise and/or sound reducing multilayer unit

The invention relates to a noise and/or sound reducing multilayer unitfor reducing noise and/or sound havi ng a frequency from 50 to 15000 Hz, preferably from 100 to 10000 Hz, and most preferably from 100 to 7000 Hz, a method for the preparation of the noise and/or sound- reducing multilayer unit, a noise and/or sound- protect! on wall comprising one or more noise and/or sound- reducing multilayer unit(s) as well as the use of an inorganic powder material as noise and/or sound- reducing material or for the preparation of a noise and/or sound- protect! on wal I .

Noise and/or sound protection wal Is are used i n a great variety of fields where a noise and/or sound reduction or complete noise and/or sound deadening is desired in order to protect human and/or ani mal subjects from the harmful effects of noise and/or sound. T he fields thus cover i ndustrial areas such as noise and/or sound- effecting industrial plants, public areas such as airports, train areas, highways, libraries, sports areas, ki ndergardens, playgrounds and schools as well as private areas such as properties, bed rooms, bathrooms, living rooms, hobby rooms, music rooms, cellars, and garden areas. In this regard, noise and/or sound- protect! on walls build up of individual building units are gaining more and more i nterest. A n individual building unit, which, through stacking and/or juxtaposing several units, enables a quick and easy build-up of a noise and/or sound- protect! on wall which reduces the noise sensation on one side of the wal I. In its ^' basic form, which isthe most commonly widespread one, such an individual building unit consists of a box shaped cage whose bottom, four side walls, and, if appropriate, the lid are made from flat wire mesh pieces fixed respectively to each other, typically using clips, steel wire ties and/or welding. The cage is then filled with crushed stone or, more generally, a similar granular material, whose aggregate is retained within the cage since it cannot pass through the holes in the mesh. Stacked and/or juxtaposed individual building units can be bound together using clips or wire ties in order to build-up a wall.

DE 202006003050 refers to a wire basket having a floor and sidewalls and at least one sound absorbi ng coati ng that is made up of at least one flexi ble contai ner fi I led with sand. T he flexi ble contai ner is i n the form of a sack that consists of a fleece. T he sound absorbing coating lies at a distance behind the visible side of the basket.

FR 2902808 A 1 refers to a wall having courses with modules, whose cage is filled with a filling material e.g. crushed stone, and is formed by a metallic trellis. The courses are arranged one behind the other, and the modules are stacked over each other. A core made of acoustic material is inserted between the courses, and extends along length and height of the wall while acting as a continuous barrier. The acoustic material can be concrete, wood, polystyrene or steel. A layer made of geotextile, geosy ntheti c or acousti c absorbi ng materi al i s i nserted between the core and f i 11 i ng material. The advantage of this solution is to obtain an acoustic insulation core that extends continuously all along the noise barrier and to the full height. However, that solution is especially costly and tricky, especially because it doubles the number of requi red modules and si nee it takes a long ti me to execute.

European patent application EP3214224A1 refers to a gabion comprising a cage basically box-shaped, made up of a bottom, two frontal walls and two side walls.

That bottom, frontal and sidewalls are all formed from meshes respectively that are fixed to each other; two compartmenti ng partitions, that each connect the side walls to one other withi n the i nterior of the cage so that the i nternal volume of the cage is divided into: two frontal compartments that are each filled with a filler material made up of aggregate that cannot pass through the respective meshes of the bottom, the frontal or the side wal Is, nor through the compartmenti ng partitions i n such a way that it is retained within those frontal compartments, and an intermediate

compartment, bounded by the compartmenti ng partitions and which is able to receive a granular acoustic insulation material; and at least one lifting partition, that fixedly connects the frontal walls to each other within the cage extending through each of the frontal compartments and the intermediate compartment, which, opposite the bottom, is provided with at least one grab handle, and which, for the part that is set out in the intermediate compartment, is suited to allowing the acoustic insulation material granules to pass through it in such a way that the acoustic insulation material may spread freely, within the intermediate compartment, on either side of the lifting partition. However, there is still a need in the art for providing noise and/or sound- reducing means that offervery good acoustic properties. Furthermore, it is desired that the noise and/or sound- reducing means are versatile in use and that they can be build-up by private individuals as well as professionals such as civil engineers and workers in a fast, easy and individual manner.

Thus, it is an objective of the present invention to provide a noise and/or sound- reducing unit. In particular, it is thus an objective of the present invention to provide a noise and/or sound- reducing unit which provides very good acoustic properties. It is sti 11 a further objective of the present i nvention to provide a noise and/or sound- reduci ng unit that can be bui Id-up to a noise and/or sound- protect! on wal I by private individuals as well as professionals such as civil engineers and workers in a fast, easy and individual manner. It is another objective of the present invention to provide a noise and/or sound- reduci ng unit that is versati le i n use and can be used i n a great variety of fields.

These and other objectives of the present invention can be solved by a noise and/or sound- reducing multilayer unit, a noise and/or sound- protect! on wall, a method and the uses as described in the present invention and defined in the claims. According to one aspect of the present application, a noise and/or sound- reducing multi layer unit for reduci ng noise and/or sound havi ng a frequency from 50 to 15000 Hz, preferably from 100 to 10000 Hz, and most preferably from 100 to 7000 Hz is provided. The noise and/or sound- reducing multilayer unit comprises at least one solid back layer and at least one solid front layer which are arranged such that one or more space(s) is/are formed between the solid back and front layers, and the one or more space(s) is/are at least partial ly fi lled with an i norganic powder material forming one or more noise and/or sound- reduci ng layerfs), wherei n the one or more i norganic powder material formi ng noise and/or sound- reduci ng layer(s) has/have i n sum an average thickness of 0.1 to 100 cm, wherei n

a) the at least one solid back layer and the at least one solid front layer are configured such that they are suitable for holdi ng the one or more noise and/or sound- reduci ng layer(s) i n position, and

b) the i norganic powder material has

i) a bulk density i n the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2 000 i m, and

iii) a weight median particle size dso i n the range from 0.2 to 1 500 i m, and

iv) a weight particle size dio i n the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50, and vi) a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material.

Accordi ng to one embodi ment, the noise and/or sound-reduci ng multi layer unit further comprises a) one or more i ntermediate layerfs) positioned between the at least one solid front and at least one solid back layer and separati ng two adjacent noise and/or sound- reduci ng layers from each other, and/or b) one or more side layer(s) configured such that the one or more noise and/or sound-reduci ng layerfs) are hold i n position, and/or c) a top layer, and/or d) a bottom layer and e) optional ly at least one layer is of honeycomb shape.

Accordi ng to another embodi ment, the multi layer unit is a three- to twenty-layer unit, preferably a three- to ten-layer unit, and more preferably a three- to five-layer unit.

Accordi ng to yet another embodi ment, the at least one solid back layer and the at least one solid front layer of the noise and/or sound- reduci ng multi layer unit are the same or different, preferably the at least one solid back layer and the at least one solid front layer are made of metal and/or wood and/or concrete and/or brick stone and/or plastic, particularly the at least one solid back layer and the at least one solid front layer are i n plate form and/or wi re form and/or of honeycomb shape oriented vertical ly, horizontal ly or i n any form.

Accordi ng to one embodi ment, each of the at least one solid back layer and at least one solid front layer a) has the same or different stiffness, preferably a stiffness of at least 10 mN m, more preferably of at least 100 mN m, and most preferably of at least 500 mN m, and/or b) has the same or different average thickness, preferably an average thickness i n the range from 1 to 120 cm, more preferably i n the range from 2 to 100 cm, more preferably from 5 to 50 cm.

Accordi ng to another embodi ment, a) the one or more noise and/or sound- reduci ng layer(s) comprise(s) of at least 90 wt.% of the inorganic powder material, and/or b) the i norganic powder material is selected from the group comprisi ng baryt, such as natural or synthetic baryt, talc, mica, clay, kaolin, titanium dioxide, bentonite, magnesite, sati n white, si licates, calcium carbonate-comprisi ng materials, such as natural calcium carbonate, synthetic calcium carbonate, surface modified calcium carbonate and materials comprisi ng calcium carbonate such as dolomite or mixed carbonate based materials of such as mixture, and mixtures thereof; preferably baryt, such as natural baryt or synthetic baryt, talc, mica, clay, bentonite, si licates, calcium carbonate-comprisi ng materials, such as natural calcium carbonate, more preferably marble, li mestone and/or chalk, and materials comprisi ng calcium carbonate such as dolomite, and mixtures thereof.

Accordi ng to yet another embodi ment, the i norganic powder material has i) a bulk density i n the range from 0.6 to 1.8 kg/L , and/or i i) a moisture content of < 5 wt.%, preferably of < 2 wt.-%, based on the total weight of the inorganic powder material, and/or iii) a weight particle size dgo of < 1 500 i m, preferably i n the range from 4 to 1 500 i m, more preferably i n the range from 10 to 1 000 i m, and iv) a weight median particle size dso in the range from 0.2 i m to 1 200 i m, preferably i n the range from 0.2 to 900 i m, more preferably i n the range from 0.2 to 750 i m, most preferably i n the range from 0.2 to 500 i m, and v) a weight particle size dio in the range from 0.1 to 175 i m, preferably i n the range from 0.1 to 150 i m.

Accordi ng to one embodi ment, the i norganic powder material has a steepness factor [(dio/dgo)*100] i n the range from 2.5 to 30. A ccordi ng to another embodi ment, the i norgani c powder materi al has a rati o of steepness factor to bulk density, expressed by a quotient obtai ned by dividi ng the steepness factor [(dio/dgo)*100] to bulk density [steepness factor/bulk density (kg/L)], of 1=130, preferably i n the range from 0.5 to 25, more preferably i n the range from 0.8 to 20 and most preferably i n the range from 1 to 15.

Accordi ng to yet another embodi ment, the noise and/or sound- reduci ng layer formed by the i norgani c powder material has an average layer thickness i n the range from 1 to 100 cm, preferably i n the range from 10 to 80 cm, more preferably i n the range from 12 to 60 cm and most preferably i n the range from 13 to 40 cm.

Accordi ng to one embodi ment, the i norganic powder material comprises a hydrophi lic or hydrophobic treatment layer on the surface of the i norganic powder material. A ccordi ng to a further aspect of the present i nventi on, a method for the preparati on of a noise and/or sound- reducing multi layer unit is provided. T he method comprises at least the steps of:

a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n, c) arrangi ng the back and front layers of step a) such that a space is formed between the back and front layers, and

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers such as to form a noise and/or sound- reduci ng multi layer unit.

Accordi ng to one embodi ment of the i nventive method, the method further comprises i) a step d ), preferably carried out after step c) and/or before step d), of arrangi ng one or more i ntermediate layer(s) such that they are positioned between the at least one sol id front layer and the at I east one sol id back layer, and/or ii) a step c2), preferably carried out after step c) and/or before step d), of arrangi ng one or more side layer(s) such that they are positioned at one or more open sides of the noise and/or sound- reduci ng multi layer unit, and/or iii) a step c3) preferably carried out after step d), of arrangi ng a top layer such that it is positioned on the top of the noise and/or sound- reduci ng multi layer unit, and/or iv) a step c4), preferably carried out before step c), of arrangi ng a bottom layer such that it is positioned at the bottom of the noise and/or sound- reduci ng multi layer unit.

Accordi ng to another aspect of the present i nvention, a noise and/or sound- protect! on wall comprisi ng one or more noise and/or sound- reducing multi layer unit(s) as defi ned herein is provided.

Accordi ng to a further aspect of the present i nvention, the use of an i norganic powder material as defi ned herei n as noise and/or sound- reduci ng material is provided.

Accordi ng to a sti l l further aspect of the present i nvention, the use of an i norganic powder material as defi ned herei n for the preparation of a noise and/or sound- protection wall is provided. Where the term "comprisi ng" is used i n the present description and claims, it does not exclude other elements. For the purposes of the present invention, the term "consist! ng of" is considered to be a preferred embodi ment of the term "comprisi ng of". If herei nafter a group is defined to comprise at least a certai n number of embodiments, this is also to be understood to disclose a group, which preferably consists only of these embodi ments.

Where an indefi nite or defi nite article is used when referring to a si ngular noun, e.g. "a", "an" or "the", this i ncludes a plural of that noun unless somethi ng else is specifically stated.

T erms li ke "obtai nable" or "defi nable" and "obtai ned" or "defined" are used interchangeably. T his e.g. means that, unless the context clearly dictates otherwise, the term "obtai ned" does not mean to i ndicate that, e.g. an embodi ment must be obtained by e.g. the sequence of steps foil owi ng the term "obtai ned" even though such a li mited understandi ng is always i ncluded by the terms "obtai ned" or "defi ned" as a preferred embodi ment.

T he term ^' noise and/or sound refers to any sound and/or noise that is above the heari ng threshold of human bei ngs, i.e. 0 dB (about 20 x 10 ⁶ Pa). It is appreciated that the terms ^' noise and ^' sound are i nterchangeable.

In the meani ng of the present invention, the term ^' thickness , if not i ndicated otherwise, refers to the depths of the corresponding layer or part.

When i n the fol lowi ng reference is made to preferred embodi ments or technical details of the i nventive noise and/or sound- reduci ng multi layer unit, it is to be understood that these preferred embodi ments or technical detai ls also refer to the inventive noise and/or sound- protect! on wall, i nventive method and the i nventive uses as defi ned herein (as far as applicable). As set out above, the inventive noise and/or sound- reducing multilayer unit comprises at least one solid back layer and at least one solid front layer which are arranged such that one or more space(s) is/are formed between the solid back and front layers, and the one or more space(s) is/are at least partially filled with an inorganic powder material forming one or more noise and/or sound- reducing layer(s). In the following, it is referred to further details of the present invention and especially the foregoing components of the inventive noise and/or sound- reducing multi layer unit. T hose ski I led i n the art wi 11 understand that many embodi ments described herein can be combined or applied together.

Noise and/or sound- reducing multilayer unit

A noise and/or sound- reducing multilayer unit for reducing noise having a frequency from 50 to 15000 Hz, preferably from 100 to 10000 Hz, and most preferably from 100 to 7000 Hz is provided, comprising at least one solid back layer and at least one solid front layer which are arranged such that one or more space(s) is/are formed between the solid back and front layers, and the one or more space(s) is/are at least partially filled with an inorganic powder material forming one or more noise and/or sound- reducing layer(s), wherein the one or more inorganic powder material forming noise and/or sound- reduci ng layer(s) has/have i n sum an average thickness of 0.1 to

100 cm, wherein

a) the at least one solid back layer and the at least one solid front layer are configured such that they are suitable for holding the one or more noise and/or sound- reducing layer(s) in position, and

b) the inorganic powder material has

i) a bulk density in the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2000 i m, and

iii) a weight median particle size dso in the range from 0.2 to 1500 i m, and

iv) a weight particle size dio in the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50, and vi) a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material. T hus, the noise and/or sound- reduci ng multi layer unit is suitable for reduci ng noise havi ng a frequency from 50 to 15 000 Hz. Preferably, the noise and/or sound- reduci ng multi layer unit is suitable for reduci ng noise havi ng a frequency from 100 to 10 000 Hz, and most preferably from 100 to 7 000 Hz. It is appreciated that the noise and/or sound- reduci ng multi layer unit at least partial ly reduces the noise and/or sound such that a human or ani mal subject on the other side of the noise and/or sound- reduci ng multi layer unit, or a noise and/or sound- protection wall comprisi ng several noise and/or sound- reduci ng multi layer units, is not negatively affected by the noise and/or sound.

T he noise and/or sound- reduci ng multi layer unit comprises at least one solid back layer and at least one solid front layer which are arranged such that one or more space(s) is/are formed between the solid back and front layers. T he term ^' at I east one_ sol i d back I ayer i n the meani ng of the present i nventi on means that the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, one or more solid back layer(s).

In one embodi ment of the present i nvention, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, one solid back layer. A Iternatively, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, two or more solid back layers. For example, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, two or three solid back layers. Preferably, the noise and/or sound- reducing multi layer unit comprises, preferably consists of, one solid back layer. T he term ^' at I east one_ sol i d front I ayer i n the meani ng of the present i nventi on means that the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, one or more solid front layerfs). In one embodi ment of the present i nvention, the noise and/or sound-reduci ng multi layer unit comprises, preferably consists of, one solid front layer. A Iternatively, the noise and/or sound-reduci ng multi layer unit comprises, preferably consists of, two or more solid front layers. For example, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, two or three solid front layers. Preferably, the noise and/or sound- reducing multi layer unit comprises, preferably consists of, one solid front layer.

In one embodi ment, the noise and/or sound-reduci ng multi layer unit comprises one solid back layer and one solid front layer.

It is appreciated that the at least one solid back layer and at least one solid front layer are arranged such that a space is formed between the solid back and front layers.

T hat is to say, the at least one solid back layer and at least one solid front layer are preferably arranged such that the distance between the back and front layers is almost even at any poi nt. More preferably, the at least one solid back layer and at least one solid front layer are arranged such that the back and front layers are al most paral lel to each other.

It is appreciated that the at least one solid back layer and the at least one solid front layer of the noise and/or sound-reducing multi layer unit are the same or different.

In one embodi ment, the at least one solid back layer and the at least one sol id front layer are made of metal and/or wood and/or concrete and/or brick stone and/or plastic. For example, the at least one solid back layer and the at least one solid front layer are the same and are made of metal. It is to be noted that the at least one sol id back layer and the at least one sol id front layer can be of any form known in the art. For example, the at least one solid back layer and the at least one sol id front layer are i n pi ate form and/or wire form and/or of honeycomb shape oriented vertically, horizontal ly or i n any form. Preferably, the at least one solid back layer and the at least one solid front layer are of honeycomb shape oriented vertical ly, horizontal ly or i n any form.

A Iternatively, the at least one solid back layer and the at least one solid front layer are i n pi ate form.

It is appreciated that the at least one solid back layer and at least one solid front layer are solid. T hat is to say, each of the at least one sol id back layer and at least one solid front layer is of a stiffness that is suitable to hold the one or more noise and/or sound- reduci ng layerfs) i n position, i.e. without relevant deformation of the noise and/or sound- reduci ng multilayer units ^“ shape.

For example, each of the at least one solid back layer and at least one solid front layer has a stiffness of at least 10 mN m. Preferably, each of the at least one solid back layer and at least one solid front layer has a stiffness of at least 100 mN m, more preferably of at least 500 mN m. For example, each of the at least one solid back layer and at least one solid front layer has a stiffness i n the range from 500 to 3 000 mN m.

It is appreciated that the at least one solid back layer and at least one solid front layer have the same or different stiffness. For example, the at least one solid back layer and at least one solid front layer have different stiffness. However, i n view of production and cost efficiency as wel l as stabi lity of the noise and/or sound- reduci ng multi layer unit it is preferred that the at least one solid back layer and at least one solid front layer have the same stiffness. Additional ly or alternatively, the at least one solid back layer and at least one solid front layer have an average thickness i n the range from 1 to 120 cm, more preferably in the range from 2 to 100 cm, more preferably from 5 to 50 cm. It is appreciated that the at least one solid back layer and at least one solid front layer have the same or different average thickness. For example, each of the at least one solid back layer and at least one solid front layer has different average thickness. However, in view of production and cost efficiency as wel l as stabi lity of the noise and/or sound- reduci ng multi layer unit it is preferred that each of the at least one sol id back layer and at least one solid front layer has the same average thickness.

It is requi red that a space is formed between the solid back and front layers which is at least partially fil led with an i norganic powder material formi ng one or more noise and/or sound- reduci ng I ayer(s) .

In one embodi ment of the present i nvention, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, one noise and/or sound- reduci ng layer. A Iternatively, the noise and/or sound- reducing multi layer unit comprises, preferably consists of, two or more noise and/or sound-reducing layers. For example, the noise and/or sound-reduci ng multi layer unit comprises, preferably consists of, two or three or four or five or six noise and/or sound-reduci ng layers. Preferably, the noise and/or sound- reduci ng multi layer unit comprises, preferably consists of, two or more noise and/or sound- reduci ng layers. T hus, the noise and/or sound-reduci ng multi layer unit is i n its si mplest arrangement a three-layer unit. T his embodi ment comprises one solid back layer and one solid front layer and one noise and/or sound-reduci ng layer.

A lternatively, the noise and/or sound-reduci ng multi layer unit comprises one solid back layer and one solid front layer and two or more noise and/or sound-reduci ng layers. T hus, the noise and/or sound- reduci ng multi layer unit forms i n this embodiment at least a four-layer unit.

In one embodi ment, two or more noise and/or sound- reduci ng multi layer units, e.g. a three-layer unit or at least a four-layer unit, are combi ned to bui ld up bigger arrangements.

It is to be noted that the number of units can be adapted to the specific needs and can thus vary i n a great number. However, it is appreciated that the ai m of the present invention is typically achieved if the noise and/or sound- reduci ng multi layer unit is a three- to twenty- layer unit.

In one embodi ment, the multi layer unit is thus a three- to ten-layer unit. Preferably, the noise and/or sound- reduci ng multi layer unit is a three- to five- layer unit, and more preferably a three- or four-layer unit.

If the noise and/or sound- reduci ng multi layer unit comprises two or more noise and/or sound- reduci ng layers, it is preferred that these layers are separated from each other by i ntermediate layerfs).

T hus, if the noise and/or sound- reduci ng multi layer unit comprises five or more layers, the noise and/or sound- reduci ng multi layer unit preferably further comprises one or more i ntermediate layer(s) positioned between the at least one solid front and at least one solid back layer and separati ng two adjacent noise and/or sound-reducing layers from each other.

T hat is to say, the one or more i ntermediate layer(s) are preferably positioned between the at least one solid front and at least one solid back layer such that the intermediate layer(s) are i n parallel to the at least one solid front and at least one solid back layer. In one embodi ment, the i ntermediate layers) are positioned between the at least one solid front and at least one solid back layer such that even spaces between the respective layers are formed such that each noise and/or sound- reduci ng layer is of about the same average thickness. A Iternatively, the i ntermediate layer(s) are positioned between the at least one solid front and at least one solid back layer such that smaller or bigger spaces between the respective layers are formed i.e. each noise and/or sound- reduci ng layers is of a different average thickness. However, it is also possi bl e that the i ntermedi ate I ayer(s) are positi oned between the at I east one sol i d front and at least one solid back layer such that at least three spaces between the respective layers are formed such that two or more noise and/or sound- reduci ng layers are of about the same average thickness and one or more noise and/or sound- reduci ng layerfs) is/are of a different average thickness, i.e. smaller or bigger.

It is to be noted that the one or more i ntermediate layerfs) can be arranged i n the noise and/or sound- reduci ng multi layer unit i n horizontal and/or vertical and/or diagonal alignment as regards the di rection of the noise and/or sound. Preferably, the one or more i ntermediate layer(s) are arranged i n the noise and/or sound- reducing multi layer unit i n vertical and/or diagonal alignment as regards the di rection of the noise and/or sound. For example, the one or more i ntermediate layer(s) are arranged in the noise and/or sound- reduci ng multi layer unit i n vertical and diagonal alignment as regards the di recti on of the noise and/or sound. A Iternatively, the one or more intermediate layer(s) are arranged i n the noise and/or sound-reducing multi layer unit in vertical or diagonal alignment as regards the di rection of the noise and/or sound. In order to hold the one or more noise and/or sound-reducing layer(s) i n position, the noise and/or sound- reduci ng multi layer unit may comprise one or more side layer(s).

In one embodi ment, the noise and/or sound- reduci ng multi layer unit comprises one side layer. T his is preferably the case if the noise and/or sound-reduci ng multi layer unit is a termi nati ng unit of a noise and/or sound- protect! on wal l which is made of several noise and/or sound-reduci ng multi layer units.

A lternatively, the noise and/or sound-reduci ng multi layer unit comprises two side layers. Such a noise and/or sound- reduci ng multi layer unit comprising two side layers may be used as such or as part of a noise and/or sound- protect! on wall.

Furthermore, the noise and/or sound- reduci ng multi layer unit may comprise a top layer and/or a bottom layer.

In one embodi ment, the noise and/or sound- reduci ng multi layer unit comprises a top layer or a bottom layer, preferably a bottom layer. A lternatively, the noise and/or sound- reduci ng multilayer unit may comprise a top layer and a bottom layer. If the noise and/or sound-reduci ng multi layer unit is part of a noise and/or sound- protection wall, it is appreciated that the noise and/or sound-reduci ng multi layer units can be configured such that the units at the top of the wal I comprise a top layer, whereas the units at the bottom of the wal I comprise a bottom layer. A Iternatively, each noise and/or sound- reduci ng multi layer unit being part of a noise and/or sound- protection wall can be configured such that they comprise a top layer and a bottom layer.

It is appreciated that the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer can be made of the same or different material as the at least one solid back layer and the at least one sol id front layer of the noise and/or sound-reducing multi layer unit.

T hus, the one or more i ntermediate layerfs) and/or the one or more side layerfs) and/or the top layer and/or the bottom layer is/are made of metal and/or wood and/or concrete and/or brick stone and/or plastic. For example, the one or more i ntermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer is/are made of metal.

It is to be noted that the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer can be of any form known in the art. For example, the one or more i ntermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer is/are i n plate form and/or wire form and/or of honeycomb shape oriented vertical ly, horizontal ly or i n any form. Preferably, the one or more i ntermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer is/are of honeycomb shape oriented vertical ly, horizontal ly or i n any form.

It is preferred that at least one layer is of honeycomb shape. T hus, it is preferred that the at least one solid back layer and/or the at least one solid front layer, and/or, if present, the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer is/are of honeycomb shape.

It is appreciated the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer is/are solid. T hat is to say, the one or more i ntermedi ate I ayer(s) and/or the one or more si de I ayerfs) and/or the top layer and/or the bottom layer is/are of a stiffness that is suitable to hold the one or more noise and/or sound- reduci ng layer(s) i n position, i.e. without relevant deformation of the noise and/or sound- reduci ng multi layer units ^“ shape. F or exampl e, the one or more i ntermedi ate I ayer(s) and/or the one or more si de layer(s) and/or the top layer and/or the bottom layer has/have a stiffness of at least 10 mN m. Preferably, the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer has/have a stiffness of at least 100 mN m, more preferably of at least 500 mN m. For example, the one or more intermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer has/have a stiffness i n the range from 500 to 3 000 mN m.

It is appreciated that the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer has the same or different stiffness compared to the at least one solid back layer and at least one solid front layer. For example, the one or more i ntermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer and the at least one sol id back layer and at least one solid front layer have different stiffness. H owever, i n view of production and cost efficiency as wel I as stabi lity of the noise and/or sound-reduci ng multi layer unit it is preferred that the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer and the at least one solid back layer and at least one solid front layer have the same stiffness. Additional ly or alternatively, the one or more i ntermediate layerfs) and/or the one or more side layerfs) and/or the top layer and/or the bottom layer has/have an average thickness i n the range from 1 to 120 cm, more preferably i n the range from 2 to 100 cm, more preferably from 5 to 50 cm. It is appreciated that the one or more i ntermediate layerfs) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer has/have the same or different average thickness compared to the at least one solid back layer and at least one solid front layer. For example, that the one or more i ntermediate layerfs) and/or the one or more side layerfs) and/or the top layer and/or the bottom layer has/have a different average thickness than the at least one solid back layer and at least one solid front layer. H owever, i n view of production and cost efficiency as wel l as stability of the noise and/or sound-reduci ng multi layer unit it is preferred that the one or more intermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer and the at least one solid back layer and at least one solid front layer have the same average thickness. In practice, the alignment, both horizontal and vertical, of the one or more intermediate layer(s) and/or the one or more side layer(s) and/or the top layer and/or the bottom layer and/or the at least one solid back layer and/or at least one solid front layer do not have to be strictly precise.

As requi red for the present i nvention, one or more noise and/or sound- reducing layer(s) is/are formed between the at least one solid back layer and at least one solid front layer i n that the formed space between the layers is at least partial ly fi lled with an i norganic powder material.

T he term ^' at least partial ly_ i n the meani ng of the present i nvention refers to a space that is fi I led to at least 10 vol.-%, based on the total volume of the space, with a particulate material. Preferably, a space that is fi l led to at least 30 vol.-%, more preferably at least 50 vol.-% and most preferably at least 70 vol.-%, for example 90 to 95 vol .-% based on the total vol ume of the space, with the i norgani c powder material i n taped, partial ly taped or non-taped form. For example, a space that is fi l led to at least 30 vol.-%, more preferably at least 50 vol.-% and most preferably at least 70 vol.-%, for example 90 to 95 vol.-% based on the total volume of the space, with the i norganic powder material i n non-taped form.

T he advantageous effects of the present i nvention are achieved by usi ng an i norganic powder material which forms the one or more noise and/or sound- reduci ng layer(s).

T hat is to say, the specific i norgani c powder material as set out for the present invention is decisive for achievi ng the very good acoustic properties.

It is especial ly requi red that the i norganic powder material has

i) a bulk density i n the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2 000 i m, and

iii) a weight median particle size dso in the range from 0.2 to 1

500 i m, and iv) a weight particle size dio in the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50 and vi) a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material

T he i norganic material is i n powder form. T he term ^' powder i n the meani ng of the present i nvention refers to a material that is a bulk solid composed of a large number of fi ne particles that may flow freely when shaken or ti lted, i.e. is a non- taped bulk solid.

In particular, the i norganic powder material is characterized by a bulk density i n the range from 0.4 to 2.0 kg/L preferably from 0.6 to 1.8 kg/L .

Additional ly, the very good acoustic properties of the noise and/or sound-reducing multi layer unit is especial ly associated with an i norganic powder material that is characterized by a specific particle size distri bution. In particular, it is requi red that the i norganic powder material has a weight particle size dgo of < 2 000 i m.

Preferably, the i norganic powder material has a weight particle size dgo of

< 1 500 i m, more preferably i n the range from 4 to 1 500 i m, and most preferably i n the range from 10 to 1 000 i m.

Furthermore, the i norganic powder material has a weight median particle size dso i n the range from 0.2 i m to 1 500 i m. Preferably, the i norganic powder material has a weight median particle size dso in the range from 0.2 i m to 1 200 i m, more preferably i n the range from 0.2 i m to 900 i m, even more preferably i n the range from 0.2 to 750 i m, and most preferably i n the range from 0.2 to 500 i m.

Furthermore, the i norganic powder material must have a weight particle size dio i n the range from 0.1 to 200 i m. Preferably, the i norganic powder material has a weight particle size dio in the range from 0.1 to 175 i m, preferably i n the range from 0.1 to 150 i m.

T hus, the i norganic powder material has

i) a weight particle size dgo of < 2 000 i m, preferably, of < 1 500 i m, more preferably i n the range from 4 to 1 500 i m, and most preferably i n the range from 10 to 1 000 i m, and

ii) a weight median particle size dso i n the range from 0.2 to 1 500 i m,

preferably i n the range from 0.2 i m to 1 200 i m, more preferably i n the range from 0.2 to 900 i m, even more preferably i n the range from 0.2 to

750 i m, and most preferably i n the range from 0.2 to 500 i m, and iii) a weight parti cl e size dio i n the range from 0.1 to 200 i m, preferably i n the range from 0.1 to 175 i m, preferably in the range from 0.1 to 150 i m. Additional ly, it is requi red that the i norganic powder material has a very specific ratio of coarse to fi ne particles, which is specified by the steepness factor.

In particular, the i norganic powder material has a steepness factor [(dio/dgo)*100] i n the range from 2 to 50. Preferably, the i norganic powder material has a steepness factor [(dio/dgo)*100] i n the range from 2.5 to 30 and most preferably i n the range from 3 to 25.

It is appreciated that the i norganic powder material has a specific ratio of steepness factor to bulk density.

More precisely, it is preferred that the i norganic powder material has a ratio of steepness factor to bulk density, expressed by a quotient obtai ned by dividi ng the steepness factor [(dio/dgo)*100] to bulk density [steepness factor/bulk density

(kg/L)], of 1=130. Preferably, the i norganic powder material has a ratio of steepness factor to bul k density, expressed by a quoti ent obtai ned by divi di ng the steepness factor [(dio/dgo)*100] to bulk density [steepness factor/bulk density (kg/L)], i n the range from 0.5 to 25, more preferably i n the range from 0.8 to 20 and most preferably i n the range from 1 to 15. Additional ly, it is appreciated that the i norganic powder material has a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material. Preferably, the i norganic powder material has a moisture content i n the range from 0.1 to 12.0 wt.-%, more preferably from 0.1 to 10.0 wt.-% and most preferably from 0.1 to 8.0 wt.-%, based on the total weight of the i norganic powder material.

T he one or more noise and/or sound- reducing layerfs) may comprise any inorganic powder material that has the defi ned characteristics known i n the art.

For example, the i norganic powder material comprises, preferably consists of, one or more i norganic powder material(s), i.e. a mixture of different ki nds of the i norganic powder materials.

In one embodi ment of the present i nvention, the i norganic powder material comprises, preferably consists of, one i norganic powder material. A lternatively, the inorganic powder material comprises, preferably consists of, two or more i norganic powder materials. For example, the i norganic powder material comprises, preferably consists of, two or three i norganic powder materials. Preferably, the i norganic powder material comprises, preferably consists of, one i norganic powder material. For example, the i norganic powder material is selected from the group comprisi ng baryt, such as natural baryt or synthetic baryt, talc, mica, clay, kaoli n, titanium dioxide, bentonite, magnesite, sati n white, si licates, calcium carbonate-comprisi ng materials, such as natural calcium carbonate, synthetic calcium carbonate, surface modified calcium carbonate and materials comprisi ng calcium carbonate such as dolomite or mixed carbonate based materials of such as mixture, and mixtures thereof.

In one embodi ment of the present i nvention, the i norganic powder material is selected from the group comprisi ng baryt, such as natural baryt or synthetic baryt, talc, mica, clay, bentonite, si licates, calcium carbonate-comprisi ng materials.

^' Calcium carbonate-comprising materials refers to a material that comprises calcium carbonate and, eventually may comprise further mi nerals, such as sulfates, si licates such as talc and/or kaoli n clay, quartz and/or mica, carbonates such as magnesium carbonate, dolomite and/or gypsum, and mixtures thereof.

Accordi ng to one embodi ment of the present invention, the amount of calcium carbonate i n the calcium carbonate-comprisi ng material is between 60 and

100 wt.-%, preferably between 70 and 99.95 wt.-%, and most preferably between 95 and 99.5 wt.-%, based on the total dry weight of the calcium carbonate-comprisi ng material.

In view of this, the calcium carbonate-comprisi ng material is preferably selected from a natural calcium carbonate, a material comprisi ng calcium carbonate and mixtures thereof.

^' Natural calcium carbonate i n the meani ng of the present i nvention is a calcium carbonate obtai ned from natural sources, such as l i mestone, marble and/ chalk, and processed through a treatment such as grindi ng, screeni ng and/or fraction! zi ng by wet and/or dry, for example by a cyclone or classifier.

A preferred material comprisi ng calcium carbonate is dolomite. It is to be noted that dolomite is also a natural calcium carbonate. Preferably, the i norganic powder material is selected from the group comprisi ng marble, li mestone, chalk and mixtures thereof.

In one embodi ment, the i norganic powder material comprises a hydrophi l ic and/or hydrophobic treatment layer on the surface of the i norganic powder material.

For example, the i norganic powder material comprises a hydrophi lic and

hydrophobic treatment layer on the surface of the i norganic powder material.

A lternatively, the inorganic powder material comprises a hydrophi lic or hydrophobic treatment layer on the surface of the i norganic powder material. Preferably, the inorganic powder material comprises a hydrophi lic treatment layer on the surface of the i norganic powder material.

If the inorganic powder material comprises a hydrophi l ic and/or hydrophobic treatment I ayer on the surface of the i norgani c powder materi al, the i norgani c powder material has been surface treated with a hydrophilic and/or hydrophobic treatment agent such that on at least a part of the accessi ble surface area of the i norganic powder material a treatment layer is formed. If the inorganic powder material comprises a hydrophobic treatment layer on the surface of the i norganic powder material, the i norganic powder material has been surface treated with a hydrophobic treatment agent selected from an ali phatic carboxylic acid having a total amount of carbon atoms from C4 to C24,

polysi loxanes and mixtures thereof.

T he ali phatic carboxylic acid i n the meani ng of the present i nvention can be selected from one or more straight chai n, branched chai n, saturated, unsaturated and/or alicyclic carboxylic acids. Preferably, the ali phatic carboxylic acid is a

monocarboxyl ic acid, i.e. the ali phatic li near or branched carboxylic acid is characterized i n that a si ngle carboxyl group is present. Said carboxyl group is placed at the end of the carbon skeleton.

In one embodi ment of the present i nvention, the aliphatic carboxylic acid is selected from saturated unbranched carboxylic acids, that is to say the ali phatic carboxylic acid is preferably selected from the group consisti ng of butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, pal mitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid, heneicosanoic acid, behenic acid, tricosanoic acid, lignoceric acid and mixtures thereof.

In another embodi ment of the present i nvention, the ali phatic carboxylic acid is selected from the group consisti ng of octanoic acid, decanoic acid, lauric acid, myristic acid, pal mitic acid, stearic acid, arachidic acid and mixtures thereof.

Preferably, the ali phatic carboxylic acid is selected from the group consisti ng of myristic acid, pal mitic acid, stearic acid and mixtures thereof.

For example, the ali phatic carboxylic acid is stearic acid.

Suitable polysi loxanes are polydialkylsi loxanes as e.g. descri bed i n US

2004/0097616 A 1. Preferred are polydialkylsi loxanes selected from the group consisti ng of polydi methylsiloxane, di methicone, polydiethyl si I oxane,

polymethyl phenylsi loxane and mixtures thereof. M ost preferably, the

polydialkylsi I oxane is polydi methylsi loxane.

Additional ly or alternatively, the i norganic powder material comprises a hydrophi lic treatment layer on the surface of the i norganic powder material. In this case, the inorganic powder material has been surface treated with a hydrophilic treatment agent preferably selected from polyols. Preferred polyols are diols or triols. Most preferably, the polyol is glycerol or monopropylene glycol.

If the inorganic powder material comprises a hydrophi l ic and hydrophobic treatment layer on the surface of the inorganic powder material, the i norganic powder material has been surface treated simultaneously or separately i n any order with the hydrophi lic and hydrophobic treatment agents.

In one embodi ment, the i norganic powder material comprises a hydrophi l ic treatment layer on the surface of the inorganic powder material.

It is to be noted that the noise and/or sound- reduci ng layer can be of any thickness that is typical ly used for the products to be prepared. For example, the noise and/or sound- reduci ng layer formed by the i norganic powder material has an average layer thickness i n the range from 0.2 to 100 cm. Preferably, the noise and/or sound- reduci ng layer formed by the i norganic powder material has an average layer thickness i n the range from 1 cm to 80 cm, more preferably i n the range from 10 to 60 cm and most preferably i n the range from 10 to 40 cm. For example, the noise and/or sound- reduci ng layer formed by the inorganic powder material has an average layer thickness i n the range from 13 cm to 40 cm.

If the noise and/or sound- reduci ng multi layer unit comprises two or more noise and/or sound- reduci ng layers, it is appreciated that the average thickness of the layers may be the same or different. In particular, for production and cost it is preferred that the two or more noise and/or sound-reducing layers have the same average thickness.

It is one requi rement of the present i nvention that the one or more i norganic powder material forming noise and/or sound- reduci ng layer(s) has/have i n sum an average thickness of 0.1 cm to 100 cm, preferably from 1 cm to 80 cm, more preferably from 10 to 60 cm and most preferably from 10 to 40 cm. For example, the one or more inorganic powder material formi ng noise and/or sound- reduci ng layerfs) has/have in sum an average thickness i n the range from 13 cm to 40 cm.

It is to be noted that the di mensions of the noise and/or sound- reduci ng multi layer unit are not limited to a specific size. However, by way of a none li miti ng dimensional example, the height (y-di rection) of the noise and/or sound- reduci ng multi layer unit can be between 0.5 and 10 m, preferably from 1 to 8 m and most preferably from 2 to 5 m. A dditional ly or alternatively, the depth (z-di recti on) of the noise and/or sound- reduci ng multi layer unit can be between 0.5 and 10 m.

Additional ly or alternatively, the length (x-di rection) of the noise and/or sound- reduci ng multi layer unit can be from 0.5 m to several km, e.g. from 0.5 m to 20 km.

Method for the preparation of a noise and/or sound-reducing multi layer unit and uses

T he present i nvention also refers to a method for the preparation of a noise and/or sound- reduci ng multilayer unit, said method comprises the steps of

a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng a i norgani c powder materi al as def i ned herei n,

c) arrangi ng the back and front layers of step a) such that a space is formed between the back and front layers, and

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers such as to form a noise and/or sound- reduci ng multi layer unit.

With regard to the defi nition of the noise and/or sound-reduci ng multi layer unit, the at least one solid back layer and at least one solid front layer, the i norganic powder material and preferred embodi ments thereof, reference is made to the statements provided above when discussi ng the technical detai Is of the noise and/or sound- reduci ng multi layer unit of the present i nvention. Accordi ng to step c) of the method of the present i nvention, the back and front layers of step a) are arranged such that a space is formed between the back and front layers. It is appreciated that the back and front layers of step a) can be arranged i n any known manner that is suitable to achieve the fi nal noise and/or sound- reduci ng multi layer unit.

Accordi ng to step d) of the method of the present i nvention, the i norganic powder material of step b) at least partially fi l led i nto the space formed between the back and front layers such as to form the noise and/or sound- reduci ng multi layer unit. It is appreci ated that the f i 11 i ng of the space formed between the back and front I ayers can be carried out i n any known manner to achieve the fi nal noise and/or sound- reduci ng multi layer unit.

At the end of the step d), that is to say after havi ng fi 11 ed the respective space formed between the back and front layers of the unit, the i norganic powder material of step b) may beneficial ly be compacted. In order to do so, an i mmersion vi brator or a rammer can be applied to the i norganic powder material of step b), via the upper openi ng of the unit. If necessary, at the end of that compaction, additional i norganic powder material of step b) is poured i nto the unit.

In one embodi ment, the noise and/or sound- reduci ng multi layer unit further comprises one or more i ntermediate layer(s).

With regard to the defi nition of the one or more i ntermediate layer(s) and preferred embodi ments thereof, reference i s made to the statements provi ded above when discussi ng the technical detai ls of the noise and/or sound- reduci ng multi layer unit of the present invention.

T hus, the method of the present i nvention preferably comprises a step d ) of arranging one or more i ntermediate layer(s) such that they are positioned between the at least one solid front layer and the at least one solid back layer. It is appreciated that the one or more i ntermediate layer(s) can be positioned between the back and front layers i n any known manner that is suitable to achieve the final noise and/or sound- reduci ng multilayer unit.

In view of this, it is preferred that method step d ) is carried out after method step c). Additional ly or alternatively, method step d ) is carried out before method step d). Preferably, method step d ) is carried out after step c) and before step d).

In one embodi ment, the method of the present i nvention thus comprises the steps of a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c) arrangi ng the back and front layers of step a) such that a space is formed between the back and front layers,

d ) arrangi ng one or more i ntermediate layer(s) such that they are positioned between the at least one solid front layer and the at least one solid back layer, and

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more i ntermediate layer(s) such as to form the noise and/or sound- reducing multi layer unit.

In one embodi ment, the noise and/or sound- reduci ng multi layer unit further comprises one or more side layerfs).

With regard to the defi nition of the one or more side layer(s) and preferred embodiments thereof, reference is made to the statements provided above when discussi ng the technical detai ls of the noise and/or sound- reduci ng multi layer unit of the present invention. T hus, the method of the present i nvention preferably further comprises a step c2) of arranging one or more side layer(s) such that they are positioned at one or more open sides of the noise and/or sound- reduci ng multi layer unit. It is appreciated that the one or more side layerfs) can be positioned at one or more open sides of the noise and/or sound- reduci ng multilayer unit i n any known manner that is suitable to achieve the fi nal noise and/or sound- reducing multi layer unit.

In view of this, it is preferred that method step c2) is carried out after method step c). Additional ly or alternatively, method step c2) is carried out before method step d). Preferably, method step c2) is carried out after step c) and before step d).

In one embodi ment, the method of the present i nvention thus comprises the steps of a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c) arrangi ng the back and front layers of step a) such that a space is formed between the back and front layers,

c2) arrangi ng one or more side layerfs) such that they are positioned at one or more open sides of the noise and/or sound- reduci ng multi layer unit, and d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit.

In one embodi ment, the noise and/or sound- reduci ng multi layer unit further compri ses a top I ayer.

With regard to the defi nition of the top layer and preferred embodi ments thereof, reference is made to the statements provided above when discussi ng the technical details of the noise and/or sound- reduci ng multi layer unit of the present i nvention. T hus, the method of the present i nvention preferably further comprises a step c3) of arranging a top layer such that it is positioned on top of the noise and/or sound- reduci ng multi layer unit. T he top layer is preferably made weather-tight, by any appropriate means. It is appreciated that the top layer can be positioned on top of the noise and/or sound- reduci ng multi layer i n any known manner that is suitable to achieve the final noise and/or sound- reduci ng multi layer unit.

In view of this, it is preferred that method step c3) is carried out after method step d).

In one embodi ment, the method of the present i nvention thus comprises the steps of a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c) arrangi ng the back and front layers of step a) such that a space is formed between the back and front layers,

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit, and

c3) arrangi ng a top layer such that it is positioned on top of the noise and/or sound- reduci ng multi layer unit.

In one embodi ment, the noise and/or sound- reduci ng multi layer unit further comprises a bottom layer.

With regard to the defi nition of the bottom layer and preferred embodi ments thereof, reference is made to the statements provided above when discussi ng the technical details of the noise and/or sound- reduci ng multi layer unit of the present i nvention. T hus, the method of the present i nvention preferably comprises a step c4) of arranging a bottom layer such that it is positioned at the bottom of the noise and/or sound- reduci ng multilayer unit. It is appreciated that the bottom layer can be positioned at the bottom of the noise and/or sound-reduci ng multi layer i n any known manner that is suitable to achieve the final noise and/or sound- reduci ng multi layer unit.

In view of this, it is preferred that method step c4) is carried out before method step c).

In one embodi ment, the method of the present i nvention thus comprises the steps of a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c4) arrangi ng a bottom layer such that it is positioned at the bottom of the noise and/or sound-reduci ng multi layer unit,

c) arrangi ng the back and front layers of step a) on the bottom layer such that a space is formed between the back and front layers, and d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit.

It is preferred that the noise and/or sound- reduci ng multi layer unit comprises a bottom layer and a top layer. In this embodi ment, the method of the present i nvention thus comprises the steps of

a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c4) arrangi ng a bottom layer such that it is positioned at the bottom of the noise and/or sound-reduci ng multi layer unit, c) arrangi ng the back and front layers of step a) on the bottom layer such that a space is formed between the back and front layers,

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit, and

c3) arrangi ng a top layer such that it is positioned on top of the noise and/or sound- reduci ng multi layer unit. Even more preferably, the noise and/or sound- reducing multi layer unit comprises a bottom layer and a top layer and one or more i ntermediate layers. In this

embodiment, the method of the present i nvention thus comprises the steps of

a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c4) arrangi ng, preferably before step c), a bottom layer such that it is positioned at the bottom of the noise and/or sound- reducing multi layer unit, c) arrangi ng the back and front layers of step a) on the bottom layer such that a space is formed between the back and front layers,

d ) arrangi ng, preferably after step c) and before step d), one or more i ntermediate layer(s) such that they are positioned between the at least one solid front layer and the at least one solid back layer,

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit, and

c3) arrangi ng, preferably after step d), a top layer such that it is positioned on top of the noise and/or sound- reduci ng multi layer unit. In one embodi ment, the noise and/or sound- reduci ng multi layer unit comprises a bottom layer and a top layer and one or more i ntermediate layers) and one or more side layer(s). In this embodi ment, the method of the present i nvention thus comprises the steps of

a) providing at least one solid back layer and at least one solid front layer as defined herei n,

b) provi di ng an i norgani c powder materi al as def i ned herei n,

c4) arrangi ng, preferably before step c), a bottom layer such that it is positioned at the bottom of the noise and/or sound- reducing multi layer unit, c) arrangi ng the back and front layers of step a) on the bottom layer such that a space is formed between the back and front layers,

d ) arrangi ng, preferably after step c) and before step d), one or more i ntermediate layer(s) such that they are positioned between the at least one solid front layer and the at least one solid back layer,

c2) arrangi ng, preferably after step c) and/or step d ) and before step d), one or more side layer(s) such that they are positioned at one or more open sides of the noise and/or sound- reduci ng multi layer unit, and

d) f i 11 i ng the i norgani c powder materi al of step b) at I east parti al ly i nto the space formed between the back and front layers and the one or more side layer(s) such as to form the noise and/or sound- reducing multi layer unit, and

c3) arrangi ng, preferably after step d), a top layer such that it is positioned on top of the noise and/or sound- reduci ng multi layer unit. A further aspect of the present i nvention refers to a noise and/or sound- protect! on wall comprisi ng one or more noise and/or sound- reducing multi layer unit(s) as defi ned herein.

Accordi ngly, the noise and/or sound- protect! on wal l comprisi ng one or more noise and/or sound-reduci ng multi layer unit(s) for reduci ng noise havi ng a frequency from 50 to 15 000 Hz, preferably from 100 to 10 000 Hz, and most preferably from 100 to 7 000 Hz, the noise and/or sound- reducing multi layer unit(s) comprise at least one solid back layer and at least one solid front layer which are arranged such that one or more space(s) i s/are formed between the solid back and front layers, and the one or more space(s) is/are at least partial ly fi l led with an i norganic powder material formi ng one or more noise and/or sound- reduci ng layerfs), wherein the one or more inorganic powder material formi ng noise and/or sound- reduci ng layerfs) has/have in sum an average thickness of 0.1 cm to 100 cm, wherei n

a) the at least one solid back layer and the at least one solid front layer are configured such that they are suitable for holdi ng the one or more noise and/or sound- reduci ng layer(s) i n position, and

b) the i norganic powder material has

i) a bulk density i n the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2 000 i m, and

iii) a weight median particle size dso i n the range from 0.2 to 1 500 i m, and

iv) a weight particle size dio in the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50 and a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material.

With regard to the defi nition of the noise and/or sound-reduci ng multi layer unit and preferred embodi ments thereof, reference is made to the statements provided above when discussi ng the technical details of the noise and/or sound- reduci ng multi layer unit of the present i nvention.

It is to be noted that the noise and/or sound- reduci ng multi layer units can be arranged in any known manner i n order to bui ld-up the noise and/or sound- protect! on wal l. T hat is to say, each noise and/or sound- reduci ng multi layer unit can be fixed to an adjacent noise and/or sound- reducing multi layer unit by using any suitable means, such as with cli ps or wi re ties.

T he di mensions of the noise and/or sound- protect! on wall are not li mited to a specific size. However, by way of a none li miti ng di mensional example, the height (y- direction) of the noise and/or sound- protect! on wal l can be between 0.5 and 10 m, preferably from 1 to 8 m and most preferably from 2 to 5 m. Additional ly or alternatively, the depth (z-di rection) of the noise and/or sound- protect! on wall can be between 0.5 and 10 m. A dditional ly or alternatively, the length (x-di recti on) of the noise and/or sound- protect! on wal I can be from 0.5 m to several km, e.g. from 0.5 m to 100 km.

In view of the very good acoustic properties achieved, the present i nvention refers in a further aspect to the use of the i norganic powder material as defined herei n as noise and/or sound- reduci ng material. It is preferred that the noise and/or sound- reduci ng material is suitable for reducing noise havi ng a frequency from 50 to 15 000 Hz, preferably 1 000 to 10 000 Hz, and most preferably from 100 to 7 000 Hz.

More precisely, it is appreciated that the i norganic powder material has

i) a bulk density i n the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2 000 i m, and

iii) a weight median particle size dso i n the range from 0.2 to 1 500 i m, and

iv) a weight particle size dio in the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50, and vi) a moisture content of 1=115.0 wt.-%, based on the total weight of the i norganic powder material.

With regard to the defi nition of the i norganic powder material and preferred embodi ments thereof, reference i s made to the statements provi ded above when discussing the technical details of the noise and/or sound- reducing multilayer unit of the present invention.

According to a further aspect, the use of the inorganic powder material as defined herei n for the preparation of a noise and/or sound- protect! on wal I is provided.

More precisely, it is appreciated that the inorganic powder material has

i) a bulk density in the range from 0.4 to 2.0 kg/L, and

ii) a weight particle size dgo of < 2000 i m, and

iii) a weight median particle size dso in the range from 0.2 to 1500 i m, and

iv) a weight particle size dio in the range from 0.1 to 200 i m, and v) a steepness factor [(dio/dgo)*100] i n the range from 2 to 50, and vi) a moisture content of 1=115.0 wt.-%, based on the total weight of the inorganic powder material.

With regard to the definition of the inorganic powder material and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the noise and/or sound- reducing multilayer unit of the present i nventi on.

Brief description of the Figures

Fig.1 is a schematic sectional front view of the mounting/installation used to conduct the experiments, which is a polystyrene box having a wall thickness of 5 cm.

Fig.2 is a linear extrapolation curve for Polystyrene block as insulator material

Fig.3 is a linear extrapolation curve for American calcined clay as insulator material Fig.4 is a linear extrapolation curve for Sodium activated Bentonite as insulator material

The following examples are meant to illustrate the invention without restricting its scope.

Examples

M easurement M ethods

T he fol I owi ng measurement methods are used to eval uate the parameters given i n the description, examples and claims.

The moisture content

The moisture content is measured in accordance with ISO Norm 11465 moisture content of soi I at 105eC to constant weight.

Specific surface area (SSA)

Throughout the present document, the specific surface area (in m ² /g) of the inorganic powder material is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m ² ) of the material is then obtained by multiplication of the specific surface area and the mass (i n g) of the material prior to treatment.

Particle size distribution (mass % particles with a diameter < X) and weight median diameter (dso) of the particulate material.

The particle size distribution was measured using a Malvern Mastersizer3000 (Malvern Instruments Ltd. Enigma Business Park, Grovewood Road, Malvern, Worcestershire, UK WR141XZ) in combination with Malvern A eroS dry dispersion unit and dry cell was used to determine the particle size distribution of the solid i norgani c powder materi al withi n the fi neness range of dso of from 500 to 0.1 i m by means of laser diffraction. T he methods used are descri bed in the Mastersizer 3000 Basic Guide, Mastersizer 3000 M anual and the M anual for Aero Series D ry dispersion unit avai lable by Malvern Instruments Ltd. A pproxi mately 10 ml of sample was loaded i nto the Aero S through the correspondi ng sieve. T he results are expressed i n V .-% (vol ume %).

T he German Norm DIN 66165 sieve analysis were used to determi ne the particle size distri bution of the solid i norganic powder material withi n the fi neness range of dso of from 2 000 to 45 i m. T he sieve analysis is a procedure used to assess the particle size distri bution of a granular material. A sieve analysis can be performed on any type of granular materials i ncludi ng sands, crushed rock, clays, granite, feldspars, coal, a wide range of manufactured powders, grai n and seeds. T he results are expressed i n V .-% (vol ume %). Bulk Density

T he bulk density of the sol id i norganic powder material withi n the fi neness range of dso of < 45 i m was determi ned i n compl i ance with IS O 60 and fol I owi ng the International standard DIN/ISO 697. T he bulk density of the solid i norganic powder materials withi n the fineness range of dso of from 2 000 to 45 i m was determi ned usi ng a 25 I itre bucket.

Swel ling volume

T he swel I i ng vol ume of activated bentonite was determi ned by pi aci ng 100 ml of disti 11 ed water i nto a 100 ml graduated ( 1 ml steps) gl ass cyl i nder at 23eC . 2 gram of bentonite were added si owly duri ng 10 mi nutes on the top of the water to I et it si nk si owly to the bottom of the cyl i nder. A fter further 10 mi nutes the vol ume of the bentonite on the bottom of the cyl i nder was measured. T he result is reported i n ml/2g (e 1 ml). Equipment

Sound Generator:

DELL PC Model E 6420 / external Logitech Z 200, 5W RSM speakers, using NCH T ongenerator v 3.05 Software by NCH Software, (www.nch.coraauAonegen.de)

Sound Level Meter: Samsung Galaxy S6

using Sound pressure level meter(v 1.6.7) manual by SmartTools Co

http://androidboy1.blogspot.ch/2015/08/sound- meter-v16.html?m=1 The installation

The installation set up to conduct the experiments is a polystyrene cuboid box (PC) is shown in Fig.1, with a width (c) of c = 25 cm, a depth (c) of c = 25 cm, height (d) of d = 60 cm, a height (a) of a = 30 cm and a height (b) of b = 20 cm. The polystyrene cuboid box comprises a bottom and side, front wal Is havi ng a thickness of 5 cm. T he top wall is composed of a wire grid. Another wire grid is placed in the middle height of the polystyrene cuboid box (PC), thus creating 2 chambers; an empty chamber (A) dedicated to receiving the Sound Generator (Q) and another chamber (B) dedicated to receiving the insulating material (i.e. the inorganic powder material) to be tested; i.e. the dry inorganic powder material or polystyrene.

Definitions

Steepness factor f _s = (dio/dgo) *100

10 = basic noise measured in the room

11 = emmited (sent out) noise by the Sound Generator

= i mmited (received) noise measured behi nd the absorbent

f = sound reduction factor

F = F requency at which the experi ments have been conducted

h = height of the insulator material (i.e. the inorganic powder material) used, hex = height at f = 0 (theoretical height of the i nsulator material necessary to extinguished). V alue obtained after the linear extrapolation curve has been generated. Bulk = bulk density i n kg/L of the i nsulator material.

Insulator material = i norganic powder material

E xperi mental protocol

Usi ng the instal lation as shown i n Fig. 1 , a series of experi ments were conducted usi ng various insulati ng material.

Typical ly for each experi ment, the fol lowing steps were conducted:

1 ) Measure of the basic noise measured i n the room (Io)

2) Measure of the noise emitted (sent out) by the sound generator at a specific frequency F at the location M when chamber B is empty; i.e. when h = 0 cm.

3) Fi 11 the chamber B with the chosen i nsulator material I unti I it reaches a height h.

4) W hen appl i cabl e, measure the steepness factor of the i nsul ator materi al I usi ng the fol lowi ng f _s = ( di o/dgo) *100

5) Measure of the noise i mmitted (received) at the location M when chamber B is fi l led with the i nsulator material to be tested; i.e. the dry inorganic powder material or polystyrene.

6) Calculation of the sound reduction factor f usi ng the fol I owing formula; f = I2-I0/I1 -10

7) Repeat the sequence of steps 1 ), 2), 3) and 4) with a different height h of the same i nsulati ng material.

8) M ake a I i near extrapol ati on curve usi ng the measurements above.

9) E xtrapol e the height of the i nsul ator materi al requi red to compl etely

exti nguish the noise hex (when f = 0 Hz)

10) Extrapole the density of the i nsulator material requi red to completely

exti nguish the noise dex (when f = 0 Hz) using the fol lowi ng formula:

1 1 ) Conduct another series of experi ments fol lowing the steps above with a

different frequency. E xample 1 (comparative):

1 ) Insulator material tested: polystyrene block

Bulk density: 0.019 kg/L

2) F requency used to conduct the seri es of ex peri ments: 1 000 H z

T able 1 : results of the noise measurements usi ng the polystyrene block as i nsulator material

T he li near extrapolation curve for the polystyrene block as i nsulator material is shown in Fig. 2.

T he height of polystyrene block requi red necessary to exti nguish completely the noise generated at 1 000 Hz is hex = 13.05 cm (at f = 0) and a density of d = 13.5 L/m ² (at f = 0). T hus, polystyrene is a good candidate as i nsulator material for sound and/or noise reducing. Despite the fact that it gives a good sound i nsulation it is however very flammable. When burni ng, it produces black smoke and toxic styrene oligomers / monomers smoke. E xample 2 (comparative):

1) Insulator material tested: American calcined clay, characteristics of the American calcined clay used:

Moisture content: 0.23 wt.-%

Bulk density: 0.275 kg/L

I dgs = 15.7 i m

I dgo = 10.6 i m

I dso = 3.78 i m

i dio = 1.02 i m

I steepness factor = 9.4

I dso particle volume = 0.00000945 mL

2) F requency used to conduct the seri es of ex peri ments: 250 H z

T able 2: Results of the noise measurements using the American calcined clay as insulator material

The linear extrapolation curve for American calcined clay as insulator material is shown in Fig.3. The height of American calcined clay required necessary to extinguish completely the noise generated at 250 Hz is hex = 1.21 m (at f = 0) and a density of

d = 1210 L/m ² (atf = 0). Thus, an inorganic powder material with the described bulk density in combination with such a particle size distribution and is not a good candidate as i nsulator material for sound and/or noise reduci ng.

E xample 3 (comparative):

1) Insulator material tested: limestone (SwissJ ura), characteristics of the

limestone (SwissJ ura) used:

Moisture content: ~ 0.1 wt.-%

I dgo = 20 mm

I d ₅ o = 15 mm

I dio = 10 mm

I steepness factor = ~ 50

I dso parti cl e volume = ~ 0.375 mL

2) F requency used to conduct the seri es of ex peri ments: 1000 H z

T able3: Results of the noise measurements using the limestone (Swiss J ura) as insulator material

The height of limestone required necessary to extinguish completely the noise generated at 1000 Hz is hex = 65 cm (at f = 0) and a density of d = 650 L/m ² (at f = 0). T hus, an i norganic powder material with the described coarse particle size distri bution is not a good candidate as i nsulator material for sound and/or noise reduci ng.

E xample 4 (comparative):

1 ) Insulator material tested: B lack forest granite (Germany), characteristics of the B lack forest granite used:

Moisture content: ~ 0.2 wt.-%

I dgo = 70 mm

I dso = 45 mm

I dio = 30 mm

I steepness factor = ~ 43

I dso particle volume = ~ 1.125 mL

2) F requency used to conduct the seri es of ex peri ments: 1 000 H z

T able 4: Results of the noise measurements usi ng the B lack forest granite

(Germany) as i nsulator material

T he height of B lack forest granite (Germany) requi red necessary to exti nguish completely the noise generated at 1 000 Hz is hex = 1.8 m (at f = 0) and a density of d = 1 800 L/m ² (at f = 0). T hus, an inorganic powder material with the descri bed very coarse particle size distri bution is not a good candidate as i nsulator material for sound and/or noise reduci ng. E xample 5 (i nvention):

1 ) Insulator material tested: marble (T urkey), characteristics of the marble

(T urkey) used:

Moisture content: 0.05 wt.-%

i dgs = 9.1 i m

i dgo = 5.9 i m

i dso = 1.9 i m

i dio = 0.4 i m

I steepness factor = 6.7

I dso particle volume = 0.00000475 mL

i Bulk density: 0.64 kg/L

I chemical analysis

CaC03 99.7 wt.-%

HC I i nsol. ~ 0.2 wt.-%

2) F requency used to conduct the seri es of ex peri ments: 500 H z

T able 5: Results of the noise measurements usi ng the marble (T urkey) as i nsulator material

The height of T urkish marble required necessary to extinguish completely the noise generated at 500 Hz is h _ex = 39 cm (at f = 0) and a density of d = 390 L/m ² (at f = 0). Thus, an inorganic powder material with the described particle size distribution, moisture content and bulk density is definitely a good candidate as insulator material for sound and/or noise reducing.

Example 6 (invention):

1) Insulator material tested: dolomitic marble /silicate blend (Austria),

characteristics of the dolomitic marble /silicate blend (Austria) used:

Moisture content: 0.3 wt.-%

I dgs = 62.7 i m

I dgo = 7.5 i m

i dso = 2.0 i m

i dio = 0.4 i m l steepness factor = 7

I cho particle volume = 0.00005 mL

l Bulk density: 0.88 kg/L

l B ET specific surface area: 2.1 rrf/g

l chemical analysis

CaC03 94.2 wt.-%

MgCC>3 4.1 wt.-%

HC I i nsol. ~ 1.3 wt.-%, mai nly si licates and little quartz

0.1 wt.-% glycerol, which corresponds to about 0.5 mg/m ² on inorganic powder material

2) F requency used to conduct the series of experi ments: 750 Hz and 1 750 Hz.

T able 6a: Results of the noise measurements usi ng the dolomitic marble (A ustria) as insulator material

T he height of the dolomitic marble (Austria) requi red necessary to exti nguish completely the noise generated at 750 Hz is hex = 37 cm (at f = 0) and a density of d = 370 L/m ² (at f = 0). T hus, an i norganic powder material with the described particle size distri bution and bulk density is defi nitely a good candidate as i nsulator material for sound and/or noise reducing at a frequency of 750 Hz. T able 6b: Results of the noise measurements using the dolomitic marble (Austria) as insulator material

The height of dolomitic marble (Austria) required necessary to extinguish completely the noise generated at 1750 Hz is hex = 35 cm (at f = 0) and a density of d =

350 L/m ² (atf = 0). Thus, an inorganic powder material with the described particle size distribution, moisture content and bulk density is definitely a good candidate as insulator material for sound and/or noise reducing also at a frequency of 1750 Hz.

Example7 (invention):

1) Insulator material tested: Carrara marble (Italy), characteristics of the marble (Italy) used:

Moisture content: 0.95 wt.-%

I dgs = 3000 i m

I dgo = 1100 i m

I dso = 920 i m

I d ₇ o = 600 i m

i dso = 220 i m

i d ₃ o = 90 i m

I d ₂ o = 60 i m

I dio = 35 i m l steepness factor = 3

I cho parti cl e volume = 0.0055 mL

l Bulk density: 1.8 kg/L

l chemical analysis

CaC0 ₃ 99.8 wt.-%

HC I i nsol. ~ 0.15 wt.-%

2) F requency used to conduct the seri es of ex peri ments: 500 Hz.

T able 7: Results of the noise measurements usi ng the Carrara marble (Italy) as insulator material

T he height of the marble (Italy) requi red necessary to exti nguish completely the noise generated at 500 Hz is hex = 31 cm (at f = 0) and a density of d = 310 L/m ² (at f = 0). T hus, an i norganic powder material with the described particle size distri bution, moisture content and bulk density is defi nitely a good candidate as insulator material for sound and/or noise reduci ng. E xample 8 (i nvention):

1 ) Insulator material tested: sodium activated bentonite, characteristics of the sodium activated bentonite used:

Moisture content: 12.1 wt.-%

I dgs = 165.0 i m

I dgo = 83.2 i m

I dso = 25.5 i m

i dio = 6.8 i m

I steepness factor = 8.2

I dso particle volume = 0.00006375 mL

l bulk density: 0.7 kg/L

I Swelli ng volume: 35 ml / 2 g

2) F requency used to conduct the series of experi ments: 100 and 1 000 Hz. T able 8a: Results of the noise measurements usi ng sodium activated bentonite as insulator material

T he li near extrapolation curve for sodium activated bentonite as i nsulator material is shown in Fig. 4.

T he height of the sodi urn activated bentonite requi red necessary to exti nguish completely the noise generated at 1 000 Hz is hex = 17 cm (at f = 0) and a density of d = 170 L/m ² (at f = 0). T hus, an i norganic powder material with the described particle size distri bution, moisture content and bulk density is defi nitely a good candidate as i nsulator material for sound and/or noise reduci ng at a frequency of 1 000 Hz.

T able 8b: Results of the noise measurements usi ng sodium activated bentonite as insulator material

T he height of the sodi urn activated bentonite requi red necessary to exti nguish completely the noise generated at 100 Hz is hex = 28 cm (at f = 0) and a density of d = 280 L/m ² (at f = 0). T hus, an i norganic powder material with the described particle size distri bution, moisture content and bulk density is defi nitely a good candidate as i nsulator material for sound and/or noise reduci ng also at a frequency of 100 Hz. E xample 9 (i nvention):

1 ) Insulator material tested: barium sulfate (baryt), characteristics of the Barium sulfate used:

Moisture content: 0.4 wt.-%

I dgs = 48.2 i m

I dgo = 13 i m

I dso = 3.15 i m

i dio = 0.46 i m

I steepness factor = 3.5

I dso particle volume = 0.00007875 mL

l Bulk density: 1.66 kg/L

2) F requency used to conduct the series of ex peri ments: 1 000 Hz.

T able 9: Results of the noise measurements usi ng barium sulfate as i nsulator material

T he height of the barium sulfate requi red necessary to exti nguish completely the noise generated at 1 000 Hz is hex = 27 cm (at f = 0) and a density of d = 270 L/m ² (at f = 0). T hus, an i norganic powder material with the described particle size distri bution, moisture content and bulk density is defi nitely a good candidate as insulator material for sound and/or noise reduci ng.