ES2365991T3 - ACOUSTIC PANEL THAT HAS A PANAL STRUCTURE AND PROCEDURE FOR THE MANUFACTURE OF THE SAME. - Google Patents

Abstract

An acoustically absorbent porous panel comprising a layer (8) - constructed from a substantially continuous open cell material - - having interconnected pores therein and - - comprising a cured foam cement material characterized in that - - - which it has a first face (7) with a substantially flat profile and a second face (5) and - - - which is formed from an aerated aqueous foamy grout comprised of cement, water, organic synthetic fibers and surfactant - the foamy grout is comprised of - - from 53 to 68% by weight of cement, - - from 17% to 48% by weight of water - - from 0.05% to 5% by weight of synthetic organic fibers and - - from 0.01% at 10% by weight of surfactant and - the second face (5) has a geometric modeling of depressions (6) formed therein comprising from 50% to 90% of the total volume of the solid form of the layer (8) without depressions

Description

The present invention relates to an acoustically absorbent porous panel according to the preamble of claim 1.

The manufacture of acoustic panels by wet means a wet process that has separate streams diluted in water of fibers, filler and binder which are then mixed to create a grout. The fibers are organic or inorganic. Usually the fibers are inorganic for fire resistance. A typical binder is starch. Fillers may include newsprint (which also acts as a binder), clay and perlite. A typical wetting process of a panel involves the successive stages of depositing the wet slurry onto a conveyor screen, draining the water from the slurry through the screen including the use of suction for the removal of additional water, drained from the Additional water by means of a pressure roller and finally dried by hot air drying the resulting wet panel as molded onto the screen. Once the wet panel enters the dryer it typically has a water content of 60 to 70%.

One of the most important aspects of ceiling plates is their sound absorption function. Specialists have employed many different techniques to increase the sound absorption of acoustic panels, including openings, cracks, and stretch marks. The relative noise reduction capacity is expressed in terms of a Noise Reduction Coefficient (NCR). Historically, wet-processed acoustic panels did not have a very high NCR compared to dry-processed ceiling plates such as those made from fiberglass trays. However, there are many drawbacks associated with the use of fiberglass. The drawbacks include the cost of fiberglass compared to natural fibers, the complexity and costs associated with the manufacture of fiberglass acoustic panels with organic binders, those related to health and the environment associated with the use of solvents. organic and organic binders in the manufacture of fiberglass acoustic panels, and the lack of rigidity associated with acoustic panels that have internal cores that are composed of fiberglass trays.

In the manufacture of wet-processed acoustic panels, it is desirable for sound absorbent compositing materials to achieve an acceptable level of sound absorption. This is usually done by reducing the density of the panel or increasing the thickness of the panel. The competition with the requirements of high sound absorption is the need for a relatively rigid material to provide sufficient structural integrity and sufficient surface hardness to resist punctures and dents that may occur during the manufacture, transport, installation or use of the product. . Additionally, a minimum thickness is also desirable to lower the cost of the material associated with the manufacture of acoustic panels of acoustically absorbent material.

Unfortunately, wet processed materials that exhibit sufficient rigidity and surface hardness are usually quite dense, have small, closed pores, and therefore have no acceptable sound absorption characteristics. In addition, wet-processed materials with highly absorbent acoustic properties are much less dense due to the increase in porosity and therefore do not exhibit stiffness and surface hardness properties required for acoustic panel applications. Additionally, since traditional wet processing techniques require drainage extraction through the cross-section of the wet material to remove water, a significant porosity size gradient is presented across the cross-section of the panel, which further degrades the acoustic attenuation properties and strength of the finished panel.

US 5 824 148 A, which is considered as a prior art of the generic class, discloses a cement composition that improves sound absorption capabilities. The composition has an interconnected open cellular structure so that at least 20% to 100 "of the surface area of the composition is open to provide access to sound waves and has an air drying density in the range of approximately 132 at 1520 Kg / m3 The composition comprises cement, including among other plaster cement, aggregates, including among other polyester fibers, water and a surfactant for the creation of foam.The surfactant is a solution comprised of an ammonium salt and is pre-mixed with water in a dilution ratio in a range of water to surfactant from 40: 1 to 10: 1. Water is mixed with the surfactant to provide a preformed foaming liquid, which is aerated by pumping under pressure with air through a nozzle.The mixture of cement with water is combined with the aerated preformed foamy liquid, after which the aggregate is added and the combination is mixed until it is reaches a required density of the composition. The compression intensity of the produced composition is between 2.07 and 41.4 MPa. The noise reduction coefficient level is acceptable.

It is the object of this invention to create a novel acoustic panel that has a high acoustic absorption by altering the shape of the panel surface to achieve both good sound reduction and maintaining excellent strength properties.

Based on the acoustically absorbent porous panel of the preamble of claim 1, this objective is obtained with the features that characterize claim 1. Claims 2 to 16 refer to preferred embodiments of the invention, while claim 17 refers to a procedure for performing an acoustically absorbent porous panel supplemented by a preferred measure according to claim 18.

The present invention relates to an acoustic panel including at least one layer for use in sound attenuation. This layer can be constructed from a porous, open-cell material. The first layer includes a first face and a second face arranged in opposition defining the first face and a portion of the edge, the periphery of the first and second faces, wherein the edge portion includes a thickness that separates the first and second faces for forming a solid form, typically a substantially rectangular solid form.

The first face has a substantially flat profile and the second face includes a substantially geometric modeling of molded depressions within the second face. Each of the depressions creates an empty volume removed from a rectangular solid where the total volume of the acoustic panel is defined by the volume of the substantially rectangular solid form minus the aggregate volume of the empty volumes within the depressions. The layer inside the acoustic panel resembles an appearance of the honeycomb type. Depressions can be composed in any way. For example, depressions can compose an empty volume that has a hemispherical shape, a cube shape, an inverted pyramid shape, or any solid geometric shape that meets the sound absorption purposes of the acoustic honeycomb.

In one embodiment, the porous open-cell material, which makes up one of the layers within the acoustic panel may comprise a density ranging from 272 to 640 Kg / m3 (from 17 to 40 pounds / ft3). Additionally, the total empty volume of a layer inside the honeycomb may comprise 50% to 90% of the total volume of the solid form of the layer within the acoustic panel. The pore size distribution within the open cell porous material may comprise 45 microns to 200 microns.

In an alternative embodiment of the present invention, a layer within the acoustic panel may include a mesh material adhered to the second surface covering the depressions. The mesh material can be composed of any known fabric, however Applicants have found that a non-woven fiberglass mesh having an air flow of 2.8 to 28.3 m3 / min (100 to 1000 ft3 / 3) is suitable min), as defined by the ASTM D 737 test method. In another embodiment of the present invention, the first flat face of the layer within the acoustic panel may include a support material to further increase the acoustic absorption of the overall panel.

The layer with a series of depressions can be comprised of any number of materials including a foamy cement or a foamy plaster material. Foamy cement material may include Portland cement, Sorrel cement, slag cement, fly ash cement or alumina cement. The foamed plaster material may include calcium calcium sulfate semi-hydrate or calcium calcium sulfate semi-hydrate. Foamy cement or foamed plaster material may also include a surfactant to promote the formation of cement foam during mixing to trap air and to create open-cell pore construction of the layer. Additionally, the foam cement or foam plaster material may also include natural fibers

or synthetic to further strengthen the cement. Such fibers may include inorganic fibers, or synthetic organic fibers composed of, but not limited to: polyolefin, polyamide, or polyester material. Surfactants can be anionic, nonionic, and amphoteric.

In an alternative embodiment, an acoustic panel may comprise two layers of honeycomb material where the two layers are joined together so that the faces having the geometric depressions face each other, such that gaps composed of symmetrical depressions are created to increase the sound absorption of the panel.

These and other features of the present invention will be apparent upon reading the following specification, taken in conjunction with the accompanying drawings.

Figure 1 is a flat top view of a surface of a layer within an acoustic honeycomb according with the present invention. Figure 2 is a cross-sectional view of an acoustic panel in accordance with the present invention, illustrating a mesh and a support material adhered to one or the other side of the honeycomb layer inside the panel. Figure 3 illustrates an alternative embodiment of the present invention, comprising at least two layers of diaper.

Figure 1 illustrates a flat top view of a patterned surface having a multitude of depressions 6 that form a surface of a layer within an acoustic honeycomb 2, in accordance with the present invention. Although the depressions 6 illustrated in Figure 1 have a generally hexagonal cross-section, those skilled in the art will understand that the shape of the depressions can be semi-cylindrical, cubic, or in any other way that effectively improves the sound absorption of the panel constructed in accordance with the present invention.

Figure 2 illustrates an alternative embodiment in which the acoustic panel 2 includes a mesh layer 4 adhered to the surface 5, and a support layer 10 adhered to the surface 7. Layer 8, which includes the depressions 6, is formed from a porous open cell material. An example of a material for use as a layer 8 is foamy plaster, more specifically alpha or beta plaster, or mixtures thereof. The composition may include fibrous materials to add strength. Among the fibrous materials suitable for use in layer 8 are synthetic organic fibers such as polyolefins, polyamides, and polyesters.

It is important that layer 8 be constructed of a foamy material. A surfactant typically facilitates the development of the foamy structure and the matrix around which the cement material solidifies. Surfactants may include anionic, nonionic and amphoteric surfactants.

Another example of material that layer 8 of acoustic panel 2 may comprise is a foamy cement. Examples of cement that can be used include Portland cement, gypsum cement, Sorrel cement, slag cement, fly ash cement, alumina cement and mixtures of any of the cements mentioned above. The cement mixture may also include inorganic fibrous materials such as wollastonite, a fibrous form of calcium silicate. Other fibers include synthetic organic fibers such as polyolefin materials, polyamides, and polyesters. Since foam cement must encapsulate air while it is being mixed before inserting it into a mold, it has been found that anionic, non-ionic and amphoteric surfactants are suitable in the creation of cement foam.

To improve the acoustic absorption of honeycomb 2, a mesh 4 can be adhered to surface 5 to cover depressions or gaps 6. Although any mesh material is acceptable, Applicants have found that one of nonwoven glass fibers of about 0.076 at 0.76 mm (0.003 to 0.03 inches) thick, having an air flow of 2.8 to 28.3 m3 / min (100 to 1000 ft3 / min) is acceptable.

Additionally, Applicants have found that the addition of a support material 10 adhered to the second face 7 of the present invention also improves the acoustic absorption of the invention. The support may be additional foamy material having a thickness of 6.35 to 19 mm (0.25 to 0.75 inches). An additional layer may be comprised of an acoustic material, but Applicants have found that a foamy cement composition works best.

In general, the porous, open-cell material that constitutes layer 8 within the acoustic panel 2 of Figure 2 should have a pore size of 40 to 200 microns. Additionally, where foamy cement is used as a material for layer 8 within acoustic honeycomb 2, the pores should comprise 75 to 95 percent by volume of panel 8. Additionally, the total volume of depressions 6 should comprise 50% at 90% of the total volume of layer 8 without depressions 6. Applicants have also found that an acoustic cell depth of 3.2 to 50.8 mm (1/8 to 2 inches) is acceptable. Additionally, the density of the foam cement or plaster material used for layer 8 should have a density of 272 to 640 kg / m3 (17 to 40 pounds / ft3). Finally, it has been found that a support thickness of 6.35 to 19 mm (0.25 to 0.75 inches) is suitable for the support 10 referenced above within panel 2.

An alternative panel 12 is also provided, shown in Figure 3, comprised of two layers 8 having depressions 6 facing each other to create depressions within the acoustic panel 12. The panel may be composed of foamed plaster material, or Foamy cement including any of the ingredients that are provided in the present invention. Additionally, the layer of support material 10 can be applied to the smooth outer surfaces of the panel 12, if the sound absorption parameters guarantee the addition of such support material.

The following examples below are merely, various experiments used to validate the invention referenced above and are not intended in any way to limit the present invention. The Formulation Table shown below illustrates the various formulations 1 through 7 for the following examples. The Formulation Table below expresses each of the constituents as a percentage by weight. In each of the examples that follow, the density is expressed in kg / m3 and (pounds / ft3).

FORMULATION TABLE

Formulation

 one  2  3  4  5  6  7

Cement

 65.5 63.1 61.8  60.6 58.4  56.4 54.5

Water

32.8 35.4 36.7 37.9  40.1 42.2  44.2

Surfactant

 1.0 0.9 0.9  0.9 0.9  0.8 0.8

Fiber

0.7  0.6 0.6  0.6 0.6  0.6 0.5

Dry density

(50) 800 (48) 768 (40) 640 (30) 480 (25) 400 (20) 320 (17) 272

In the first evaluation of Example 1, Applicants compared panel acoustics that have a

5 single cavity of fixed depth and varied the open area increasing the diameter of the cavity. The amount of open area is reported as a percentage of the total surface area of the layer of plaster or foamy cement. For each of the measurements, the face of the layer that has the various depressions or cavities was enclosed with a fiberglass mesh as previously revealed. A fiberglass mesh of a thickness of 0.51 mm (0.020 inches) was used for this particular example. In Example 1, Applicants measured the Coefficient of

10 Noise Reduction as a function of the increasing percentage of the frontal cavity area. In Examples 1, 2 and 4 through 6 the Applicants determined that the NCR by ASTM specifications E1050-90, C634, C384, and E548 using an impedance tube device. The column titled "Mesh" indicates that the sound was directed to the mesh, and the column titled "Support" indicates that the sound was directed to the flat surface of the panel opposite the mesh.

15 EXAMPLE 1 [Formulation 4]

Percentage of the Front Cavity NCR (Mesh) NCR (Support)

0% 0.66 0.70

20 10% 0.71 0.72 17% 0.67 0.73 26% 0.69 0.69 37% 0.68 0.68 50% 0.66 0.70

25 70% 0.64 0.71

Applicants believe that the data produced from Example 1 reveals a slight variation in acoustic values in relation to the volume diameter of the cavity gap.

30 In Example 2, the applicants evaluated the overall effect of the thickness of the support with respect to the acoustic characteristics. In this example, a layer 8 of 9.5 mm thick (3/8 inch), which has various depressions 6, integrated therein with the foamed cement composition, having a thickness that varied from 0 to 9, 8 mm (0 to 3/8 inch) measured from the bottom of the cell depressions to the first flat surface. A fiberglass mesh was applied over the depressions of the first surface of layer 8. The NCR values

35 in the table below for Example 2 indicate whether the sound was directed to the mesh or flat support of the foamed plaster. The data reveals some dependence of the NCR on the direction from which the sound is focused to the foamy material within layer 8. Applicants have concluded that covering the mesh, the face of the honeycomb is a more effective absorbent than the flat support when Orient towards the incoming sound.

40 EXAMPLE 2 [Formulation 4]

Support Thickness (Mesh) (Support)

0 1.00 1.00

45 1.6 mm (1/16) 0.83 0.84 3.2 mm (1/8) 0.78 0.78 6.4 mm (1/4) 0.79 0.70 9.5 mm (3/8 ) 0.72 0.59

50 Example 3 below illustrates an additional test of the same material of Formulation 4 to confirm that the honeycomb face covered by the mesh is more acoustic than the face of the continuous support. For Example 3, Applicants use a reverberation room test that conforms to the following standards ASTM C423-90a, E 122, E 548, E 795; ANSI S1.6, S1.26, S1.11; and ISO R 354-1963. Applicants also conducted a test air flow that conforms to ASTM D 737. Additionally, Applicants conducted the Sound Transmission Coefficient (STC) tests having results determined by insertion losses as shown in ASTM E 90.

EXAMPLE 3 [Formulation 4]

NCR (reverbe room

ration) Air flow (ohms) STC

Diaper

Mesh    Support Mesh Support Support Mesh

480Kg / m3 (30 pounds / ft3)

0.48  0.38 2 16 3. 4 35

Another important property for the examination was the density of the foamy plaster used for layer 8. In Example 4, Applicants controlled the density to some extent by varying the amount of water added to the mixture. A higher percentage of water weight results in a lower density foam, when the foam dries. All samples in layer 8 were 15.9 mm (5/8 inch) thick, without depression 6. The relationship between density and acoustic properties is more significant as shown in the table for Example 4 lower. The highest sound absorption occurs between the density ranges from 272 to 400 Kg / m3 (from 17 to 25 pounds / ft3)

EXAMPLE 4

NCR Density Formulation

 7 272 kg / m3 (17 pounds / ft3) 1.00 6 320 kg / m3 (20 pounds / ft3) 0.80 5 400 kg / m3 (25 pounds / ft3) 0.48 4 480 kg / m3 (30 pounds / ft3) 0.36 2 768 kg / m3 (48 pounds / ft3) 0.29 1 800 kg / m3 (50 pounds / ft3) 0.24

The table in Example 5 below illustrates yet another example of the effect of density on acoustics. In Example 5, Applicants compared samples of various thicknesses and densities. The Applicants found that the Noise Reduction Coefficient decreased markedly with increasing density.

EXAMPLE 5

NCR Thickness Density

640 kg / m3 (40 pounds / ft3) 12.7 mm (1/2) 0.41 Formulation 3 640 kg / m3 (40 pounds / ft3) 15.9 mm (5/8) 0.43 Formulation 3 800 kg / m3 (50 pounds / ft3) 12.7 mm (1/2) 0.24 Formulation 1 800 kg / m3 (50 pounds / ft3) 15.9 mm (1/2) 0.24

Next, the applicants made three layers 8, which each had a density of 448 kg / m3 (28 pounds / ft3) and measured the Noise Reduction Coefficient with an increase in cell depth within a thickness panel 15, 9 mm (5/8 inch).

EXAMPLE 6

NCR Cell Depth

   3.17 mm (0.125 inches) 0.57 6.34 mm (0.250 inches) 0.75 9.53 mm (0.375 inches) 0.79

The data reveals that cell depth has a significant effect in determining the properties of the structure. The cell width, however, as presented in Example 1 has very little significance.

Finally, the applicants demonstrated a relationship between density and pore size distribution in these structures. The pore size distribution was determined using the Mercury Micromeritics AutoPore II 9220 Pore Meter and is tabulated in Example 7. Pore sizes outside those noted are not measurable with this equipment.

EXAMPLE 7

Density Average pore size Pore size distribution

 272 kg / m3 (17 pounds / ft3) 10 microns 1-10 microns 20%; 42 - 250 microns, Formulation 7 70% 400 kg / m3 (25 pounds / ft3) 8 microns 1-10 microns 20%; 20 - 200 microns, Formulation 5 70% 640 kg / m3 (40 pounds / ft3) 4 microns 1-10 microns 40%; 11 - 42 microns 50% Formulation 3

As illustrated in the table in Example 7, if a plot of the pore size distribution line is made and the results are compared for the table in Example 4, which illustrates the acoustic properties versus density, a greater NCR when the pore size distribution of the foam cement composition is in the range of 45-200 microns. The Applicants therefore concluded from the data referenced above that acoustic properties change as a function of pore size distribution. Applicants believe that control of pore size distribution is the only way to control the acoustic absorption of the foaming material of the invention.

Foamy material is relatively resistant to moisture. This can be quantified as a determined value from a buckling test. The following are approximate intervals of four cycle buckling tests for various embodiments. Each of the cycles consists of submitting a sample of 0.6 mx 0.6 m (2 feet by 2 feet) for 17 hours at 27.8ºC (82ºF) and a relative humidity (RH) of 90% followed by 6 hours at 27.8 ° C (82 ° F) and 35% RH. In a traditional dry fiber panel, with 90% RH there is typically a resulting buckling of less than 3.8 mm (0.15 inches). In one embodiment, at 90% RH there is typically a resulting buckling of 2.5 mm (0.1 inches). In another embodiment, at 90% RH there is typically a resulting buckling of less than 1.3 mm (0.05 inches).

As discussed above, the inventive honeycomb structure can also be comprised of cement or foamy plaster. The formulation of the uncured foamy cement material, in percentages of wet weight may include 53% to 68% cement; from 17% to 48% water; from 0.05% to 5% of fibers; and from 0.01% to 10% surfactant. The fibers may be synthetic organic fibers, such as those formed from polyester. Other formulations for the uncured foamy cement material, in wet weight percentages may include 54% to 61% cement; 32% to 44% water; from 0.1% to 3% of fibers; and from 0.5% to 5% surfactant. Additionally, the uncured foamy cement material, in percentages of wet weight may include 56% to 61% cement; 32% to 42% water, 0.28% to 1.3% fiber; and from 0.7% to 2% surfactant.

In addition, the formulation in weight percentages may include from 54.5% to approximately 65.5% of plaster or cement, from 32.8% to 44.2% of water, from 0.8% to 1.0% of surfactant, and about 0.01% to 0.7% fiber. By performing the aforementioned composition, one method may involve combining all dry ingredients for a uniform dispersion of the polyester fiber (if the fiber is used, since it is not necessary for the present invention, but increases the strength of the panel). In this method the process may involve the preparation of a 40% solution of sodium lauryl sulphosuccinate surfactant and then the addition of the surfactant solution to the dry mixture to moisten it and combine all the ingredients. The process can then include the fiber, cement, and high speed surfactant mixing step with a wire whisk for one to three minutes until the cement / gypsum (fiber) mixture becomes foamy. The process may also include the initiation of a secondary low-cut mixing operation to disperse the fibers (if used) that can be crouched during the high-speed mixing cycle. In the operations of secondary mixing of low cut, the process can use a mixer of vanes of low cut that is similar to those used with the mixture of putty and plaster to disperse the lumps of fiber. The process may involve mixing the spongy cement at low speed until just before the foam begins to fall. The process may then involve applying the foamy material to a honeycomb mold for curing.

The resulting foamy material produces a cement composition with a density between 160 and 640 kg / m3 (between 10 and 40 pounds / ft3). In an alternative embodiment the panel may have a density between 240 and 560 kg / m3 (between 15 and 35 pounds / ft3) or between 320 and 480 kg / m3 (between 20 and 30 pounds / ft3).

A specific stage in the inventive process also includes details in the preparation of the surfactant solution. More specifically, Applicants have found that the maximum foaming of a Portland cement

or gypsum mixture is produced when the surfactant solution is prepared between 20 ° C (68 ° F) and 37.8 ° C (100 ° F), with the preferred temperature of 32.2 ° C (90 ° F). Applicants have also determined that a deviation in water temperature from the optimum temperature range will increase foam density by a factor of 80 kg / m3 (5 pounds / ft3) for each deviation of 5.5 ° C (10 ° F ). In this way it is advantageous to maintain the temperature of the water solution with surfactant at 32.2 ° C (90 ° F).

It is contemplated that the inventive panel core can be composed of many types of materials, as described above. Additionally, the present invention is not limited to ceiling plates, but may include wall structures, exterior decks and punishable surfaces.

Claims (18)

1. An acoustically absorbent porous panel comprising a layer (8) - constructed from a substantially continuous open cell material - - which have interconnected pores in it and - - comprising a cured foam cement material - - - having a first face (7) with a substantially flat profile and a second face (5) and - - - which is formed from an aerated aqueous foamy slurry comprised of cement, water, organic synthetic fibers and surfactant  characterized because

-

 the foamy grout is comprised of

- - from 53 to 68% by weight of cement, - - from 17% to 48% by weight of water - - from 0.05% to 5% by weight of synthetic organic fibers and - - from 0.01% to 10% by weight of surfactant and

-

 The second face (5) has a geometric modeling of depressions (6) formed therein comprising from 50% to 90% of the total volume of the solid form of the layer (8) without depressions.

2.

 The acoustically absorbent porous panel of claim 1, wherein the foamy cement material comprises about 53% to 66% by weight of cement.

3.

 The acoustically absorbent porous panel of claim 1, wherein the foamy cement material is formed from an aerated aqueous foamy grout comprised of

-

 from 54 to 61% by weight of cement,

-

 32% to 44% by weight of water

-

 0.1% to 3% by weight of synthetic organic fibers and

-

 0.5% to 5% by weight of surfactant

Four.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the cement is selected from a group consisting of gypsum cement, Portland cement, Sorrel cement, slag cement, flying ash cement, calcium alumina cement and mixtures of the pampering

5.

 The acoustically absorbent porous panel of claim 4, wherein the gypsum cement is selected from the group consisting of calcium calcium sulfate semi-hydrate and calcium sulfate beta semi-hydrate.

6.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the surfactant is selected from a group consisting of amphoteric, anionic and non-ionic fractions.

7.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the fibers are organic fibers selected from a group consisting of polyester, polyamide, and polyolefin.

8.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the pore interconnection of the substantially continuous open cell porous material of the layer (8) has an average size distribution from 45 μm to 200 μm.

9.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the layer (8) has a density between 160 and 640 kg / m3 (between 10 and 40 pounds / ft3).

10.

 The acoustically absorbent porous panel of claim 9, wherein the layer (8) has a density between 240 and 560 kg / m3 (between 15 and 35 pounds / ft3).

eleven.

 The acoustically absorbent porous panel of one of the preceding claims, wherein the depressions

(6) are at least 3.2 mm (0.125 inches) deep.

12.

 The acoustically absorbent porous panel of one of the preceding claims, further comprising a support material adhered to the first face (7).

13.

 The acoustically absorbent porous panel of one of the preceding claims, comprising two layers

(8) that are fixed together so that faces that have geometric depressions (6) face each other, so that they create gaps composed of symmetrical depressions (6).

14.

 The acoustically absorbent porous panel of one of claims 1 to 12, further including a mesh material (4) fixed to the second face (5).

fifteen.

 The acoustically absorbent porous panel of claim 14, wherein the mesh (4) is formed of a nonwoven fiberglass material having an air flow of 2.8 to 28.3 m3 (100 to 1000 ft3 / min)

16.

 The acoustically absorbent porous panel of claim 15, wherein the nonwoven fiberglass material has a thickness between 0.076 and 0.76 mm (0.003 to 0.03 inches).

17.

 A procedure for making an acoustically absorbent porous panel comprising the steps of:

-

 combine on a wet basis from 53% to 68% by weight of cement, from 17% to 48% by weight of water, from 0.05% to 5% by weight of fiber, and from 0.01% to 10% by weight. surfactant weight to form an uncured aqueous foamy cement material,

-

 form a layer (8) with the uncured aqueous foamy cement material,

-

 forming a geometric modeling of depressions (6) within a surface (5) of the layer (8) of the uncured aqueous foamy cement material and

-

 curing the aqueous foamy cement material so that the depressions (6) formed therein comprise about 50% to about 90% of the layer (8).

18. The process of claim 17, further comprising applying a mesh material (4) to the surface (5) with the depressions (6) of the layer (8) of the cured aqueous foamy cement material.