Acoustic insulation panel, acoustic insulation system comprising said panel and acoustic insulation method

Abstract

The invention relates to an acoustic insulation panel (1) based on Helmholtz single-cavity resonators, designed to effectively attenuate low-frequency noise generated by industrial equipment. The panel (1) is formed by a front wall (2) and a rear wall (3), both U-shaped, enclosing a hollow space (4) that acts as a resonator cavity. The shorter sides (2', 3') of these walls are folded inwards, forming channels that function as inlets (5) to the resonator. Furthermore, an acoustic insulation system composed of several of these panels (1) is described, in which the panels are arranged so as to allow both ventilation and noise attenuation. The associated acoustic insulation method consists of facing the resonators to maximize noise absorption at specific frequencies, ensuring a laminar air flow that improves the efficiency of the system without the need for large volumes or additional silencers.

Description

[0001] ACOUSTIC INSULATION PANEL, ACOUSTIC INSULATION SYSTEM COMPRISING SAID PANEL AND ACOUSTIC INSULATION PROCEDURE

[0002] DESCRIPTION

[0003] Object of the invention

[0004] The present invention relates, as its name indicates, to the field of acoustics and, more specifically, to the devices and / or installations used to mitigate or reduce airborne noise from sound sources.

[0005] More specifically, the invention relates to both an acoustic panel and a sound insulation system comprised of such panels, intended primarily, though not exclusively, for reducing noise from industrial equipment or machinery located in or near residential areas, offices, or workplaces. These situations are particularly challenging because, on the one hand, space for sound insulation is limited, and on the other hand, noise emission regulations are more restrictive. The invention also relates to a sound insulation method.

[0006] Background of the invention

[0007] Currently, the leading acoustic solution for addressing industrial noise sources is based on the use of enclosures made of acoustic sandwich panels with mineral wool insulation. Specifically, these are cold-formed sandwich-type partition panels where two outer sheets of steel (galvanized or lacquered) or aluminum are bonded to a central insulating core made of mineral wool of varying densities (glass or rock wool).

[0008] In general, the performance of these panels depends on:

[0009] The thickness, with 5, 8 and 10 cm being common, means that the greater the thickness, the higher the overall airborne noise insulation of the panel (due to the greater mass of the assembly) and, specifically, this increase in thickness translates into greater insulation in low frequencies.

[0010] Airtightness is crucial, because any flaw in the installation will result in noise leaks. Just as water escapes from a hose or pipe, or from a tank when there is any kind of crack on the outside, the insulation of an enclosure made of acoustic sandwich panels is compromised when it is poorly installed. Similarly, any opening for ventilation, a window, or a door in an untreated enclosure will lead to a decline in the system's acoustic performance.

[0011] Regarding structural transmission: Any element that generates vibrations, whether from a sudden start or with a high rotational frequency, and that is rigidly anchored to the floor, ceiling, or walls of the enclosure, is likely to transmit this energy to the acoustic panel. On the exterior, both the support structure and the panels themselves could then act as "speakers" (due to the vibration transmitted from the interior), generating new noise outside the building. This indirect structural transmission reduces the theoretical performance of the solution.

[0012] These panels, while fulfilling the function for which they were designed, suffer from a series of defects which, in general, are the following:

[0013] First, these panels can be quite heavy due to the two layers and the insulating material in between, making them difficult to handle, transport, and install. This requires additional equipment and labor for installation, thus increasing overall costs. Furthermore, both fiberglass and rock wool can cause skin, eye, and respiratory irritation if not handled properly, so personal protective equipment is essential during installation. Fine particles of these materials can be released during handling, which are harmful to health if inhaled.

[0014] Another drawback is that fiberglass and rock wool can absorb moisture if not properly protected, which can reduce their insulating effectiveness and cause the panel to swell, leading to detachment and deterioration. In humid environments or when exposed to water, these materials can degrade over time, losing their acoustic and thermal properties. Furthermore, the initial cost of the materials and manufacturing of these panels can be high, especially if high-quality materials are used to ensure durability and acoustic performance. They may also require more frequent maintenance and replacement compared to other types of sound insulation materials, increasing long-term costs. In addition, from an environmental perspective, the production of fiberglass and rock wool is energy-intensive and generates waste that can have a significant environmental impact.Although progress is being made, these materials are not always easy to recycle at the end of their useful life.

[0015] Finally, regarding acoustic performance, while these panels are effective for mid and high frequencies, they are not efficient for very low frequencies (bass), which are precisely those that predominate in the noise generated by industrial machinery. Specifically, for these frequencies (20 Hz - 250 Hz), this type of panel typically offers attenuation results of between 0 and 25 dB, which is clearly insufficient. Thicknesses of up to 40 cm are needed to achieve reductions of around 40 dB at these frequencies.

[0016] Specifically, the present invention is intended to reduce the noise of any type of machinery that, as such, has a series of intrinsic characteristics such as those indicated below.

[0017] High noise levels. The overall A-weighted values ​​(dBA), regardless of their frequency content, are generally high (in many cases, above 85 dBA). Furthermore, production processes often involve the combined use of different types of machinery. This creates an auditory effect, where the individual noise levels combine, thus impacting those nearby.

[0018] Predominance of low frequencies. As mentioned previously, industrial machinery and processes typically employ specific frequencies that are predominantly low (bass sounds). Due to the characteristics of our hearing, these types of sounds are more bothersome. This is due to a biological aspect; these types of noises are not common in nature, so consciously or unconsciously, we find them more annoying.

[0019] Presence of tonal components. Due to the use of elements that rotate at a certain speed (electrical transformers, motors, gears, fans), very specific frequencies can be produced, which predominate within a very small frequency range (e.g., the 50Hz hum of the electrical grid). Similar to low frequencies, these tonal elements are perceived as more annoying.

[0020] Access and ventilation requirements. In most applications, a completely airtight acoustic enclosure for machinery or production processes is not feasible, as these require a certain amount of ventilation air intake and exhaust for proper operation, or quick access to specific areas of the machinery (for safety or maintenance). This makes defining solutions that achieve the correct level of sound insulation more complex (any opening in an acoustic enclosure results in a reduction).

[0021] Regarding the need for ventilation, this is crucial for isolating industrial noise, as the machinery or equipment that generates it must be properly cooled for correct operation and to prevent breakdowns. Therefore, acoustic enclosures made with sandwich panels require the installation of air vents to provide this ventilation. These vents, of course, also represent points through which the noise to be isolated escapes or passes. Consequently, it is essential that these vents incorporate or have the same level of acoustic insulation as the panel that makes up the enclosure, which necessitates the use of dissipative acoustic silencers.

[0022] These dissipative acoustic silencers are devices that include ducts or extensions in the closure, the sound-absorbing material of which reduces the noise escaping through the opening. Specifically, they generally consist of an outer metal casing and equidistant inner baffles attached to the silencer body with screws. The baffles are made of steel and filled with high-performance absorbent fiber panels, with a protective veil on the surface in contact with the air to prevent the entrainment of particles.

[0023] Their performance therefore depends on their dimensions, as they are designed according to the decibels (dB) that need to be attenuated in the installation. The greater the depth of the baffle, the greater the attenuation across all frequency bands. For example, to isolate a generator, the silencers require a minimum space of 2.5m to 3m around the perimeter of the machine.

[0024] Furthermore, another aspect to consider is the airflow rate to be maintained for proper ventilation, since silencers create resistance to the airflow and, therefore, the passages must be sized to maintain this flow rate so that pressure losses are not exceeded.

[0025] Finally, another aspect to consider is the noise generated by them, since the reduction in airflow through the gaps between the drums causes the air to circulate at a higher speed and, at high speeds, can produce sound energy that is not a consequence of the enclosed machine or installation, but of the airflow itself as it passes through the silencer.

[0026] Therefore, in addition to significantly increasing the installation cost and having the problems described above, silencers require even more space for installation.

[0027] Thus, all these important conditions result in the fact that the use of sandwich panels is not the most suitable for eliminating the aforementioned industrial noise, or that, if used, they must be dimensioned with a large size (thickness) or even double panel systems with an intermediate air chamber must be used, which further increase the cost of installation and occupy even more space, and which will still require silencers, thus incurring the main drawbacks mentioned above that this type of insulation presents.

[0028] On the other hand, the use of multiple cavity resonators based on the Helmholtz single cavity resonator to control and absorb certain frequencies in indoor spaces such as auditoriums and theaters is also known in the state of the art.

[0029] In the industrial field, they are also used to reduce or control the noise generated by equipment, especially those frequencies that are particularly annoying or harmful and are usually installed directly on the machinery, for example on the casing itself or at the points where vibrations are generated, or in the ventilation ducts where the noise is generated.

[0030] In some cases, panels with multiple Helmholtz resonators incorporated into their structure have also been used to surround the noise source rather than being installed directly on it. These panels act as acoustic barriers specifically "tuned" to absorb low frequencies around specific work areas, creating quieter zones without directly interfering with machinery operation. Thus, using panels with Helmholtz resonators instead of sandwich panels with fiberglass or rock wool can solve some of the problems mentioned above, such as being lighter, which facilitates handling, or absorbing low frequencies more effectively.

[0031] However, even using this type of panel does not eliminate the problem posed by the need for ventilation in industrial equipment, which, as explained, severely compromises sound insulation or, if silencers are used, increases the space requirements and the final cost of the sound insulation installation.

[0032] In short, there are no known acoustic panels in the state of the art that both solve the aforementioned problems and, on the other hand, constitute effective means of isolating low-frequency noise produced by industrial equipment in an efficient, economical way and without needing to occupy excessive space.

[0033] Description of the invention

[0034] The present invention, as defined in all its claims, addresses and solves the aforementioned problems of sandwich-type acoustic insulation panels in a simple and economical manner, since it describes an acoustic panel with which to form an insulation system that significantly attenuates the low frequencies produced by industrial noise while allowing the passage of air, i.e., the ventilation of the equipment or machinery causing the noise.

[0035] Specifically, the panels of the invention are based on an innovative use of Helmholtz single cavity resonators, which, as already explained, are used for resonance control in concert halls and recording studios to control (absorb) specific frequencies, as acoustic filters in electronic devices and speaker systems to filter out unwanted frequencies, or even in the design of instruments to improve tonal quality.

[0036] A typical Helmholtz resonator consists of a sealed cavity (like a bottle) connected to a narrow neck. The exact geometry may vary, but the operation is always similar and can generally be explained as follows: When sound waves strike the resonator, the air in the neck is compressed and decompressed, acting as a moving mass. Similarly, the internal cavity acts as a volume of compressed air that expands and contracts in response to the movement of the air in the neck. Thus, at a specific frequency, called the resonant frequency, the system efficiently couples with the sound waves, and the oscillation of the air in the neck and cavity reaches its maximum amplitude. At this resonant frequency, the Helmholtz resonator can absorb acoustic energy from the incident sound wave, reducing the sound intensity at that particular frequency.

[0037] The formula for the Resonance Frequency of a Helmholtz resonator follows the following expression: where: c is the speed of sound in air.

[0038] A is the cross-sectional area of ​​the neck.

[0039] V is the volume of the cavity.

[0040] L is the length of the neck.

[0041] And where L is the length of the neck, but adjusted by a correction factor that accounts for the neck opening, so it will be longer than the actual length. Specifically, it is known that when a sound wave propagates through the neck of a Helmholtz resonator, it does not stop abruptly at the edge of the neck, but extends beyond it, creating an additional acoustic mass effect at the ends of the neck. This effect is due to the inertia of the air flowing in and out of the resonator's neck and results in an effective neck length that is greater than the actual physical length.

[0042] As previously mentioned, prior art acoustic insulation panels incorporate numerous single-cavity Helmholtz resonators integrated across their entire surface, such that acoustic waves are absorbed upon impact with the panel rather than reflected (reducing echo or reverberation). Furthermore, as explained earlier, these sandwich panels typically also include insulating elements such as fiberglass or rock wool, with the drawbacks described above. However, the acoustic insulation panel proposed in the present invention comprises a single cavity that also forms the interior of the panel itself.

[0043] More specifically, the sound insulation panel of the invention comprises a front wall and a back wall between which a hollow or empty space is defined, forming the cavity of a Helmholtz resonator. In other words, the sound insulation panel of the invention, with its own structure, forms a single Helmholtz resonator, the "bottle" of which is the entire volume enclosed between said front and back walls.

[0044] The panel, and therefore both front and back walls, will also have a vertical rectangular configuration of variable height and width according to the needs to be covered, for example, 100cm, 150cm, 200cm or more in height and widths of 30cm, 45cm, 90cm, etc., which will give rise to different cavity volumes, which in turn, applying the previous formula, will mean that the behavior of the aforementioned resonance frequency is modified, being lower the larger the volume of said cavity.

[0045] Both the front and back walls are shaped like a letter II, each comprising a longer side and two shorter sides located at the ends of the longer side. The walls are positioned relative to each other so that their shorter sides face each other but do not touch, forming a rectangular hollow space that constitutes the cavity or bottle of Helmholtz single-cavity resonators. This separation between the two walls, in addition to defining the volume of the hollow space, determines the depth of the panel, which, for example, could be 15 cm, 25 cm, 26 cm, or larger dimensions.

[0046] On the other hand, each of the two smaller sides of each wall folds in turn towards the interior of said cavity forming an entrance in the form of a channel when it is faced with the folded smaller side of the other wall, thus forming two channels, one on each side, which constitute the entrances or necks of the resonator.

[0047] Thus, as initially stated, the acoustic insulation panel of the present invention comprises a single cavity formed by the two walls, front and rear, in the shape of a U and facing each other in such a way that the space that remains housed between both walls, in a rectangular prismatic shape, forms a single cavity that is given entry along the entire height of the panel through two entrances or necks along the entire height of said panel and of rectangular cross section located each one on the smaller sides of said rectangular prism.

[0048] Thus, returning to the previous formula for calculating the Resonance Frequency of a Helmholtz resonator, we would have:

[0049] A, which was the cross-sectional area of ​​the neck, will be the cross-sectional area formed by the smaller sides folded inwards from each of the walls, front and back, when they face each other.

[0050] V, which was the volume of the cavity, will be the entire volume contained or enclosed between the front and rear walls.

[0051] L, which was the length of the neck, will be the length of the section of the smaller sides that folds inwards on each of the smaller sides of the walls.

[0052] On the other hand, it was previously mentioned that the panels could be of different dimensions, both in height and width. More specifically, regarding their height, some possibilities were mentioned, such as 100cm, 150cm, 200cm, or more. It so happens that this height, which we can call H, does not affect the calculation of the resonant frequency, because if we review the formula for this frequency again:

[0053] It can be observed that, since the neck is an opening that runs along the entire height H of the panel, the term H used in the formula to calculate the cross-section of the neck A is the same as the H used to calculate the volume of the cavity V, and therefore both cancel each other out when applying the formula.

[0054] It logically follows that the volume V enclosed by the insulation panel, which constitutes the volume V of the resonant cavity, is determined solely by the panel's width—that is, the width of the front and back walls and the separation or distance between them, which forms the panel's bottom. In other words, the panel's performance is independent of its height and, therefore, also independent of the height required to encapsulate or surround the machinery that is the noise source.

[0055] Therefore, the acoustic insulation panel of the invention, as described, will consist of two facing walls, front and back, which house an empty hollow space or cavity of rectangular prismatic shape and on whose shorter sides, along the entire length of its height, are established two lateral entrances that give access to said cavity, thus behaving as a single Helmholtz cavity resonator with two facing entrances or, in other words, as two facing Helmholtz resonators that share the same Helmholtz resonating cavity.

[0056] This structure, which is not described in the state of the art, substantially improves the acoustic attenuation results of traditional sandwich panels at low frequencies, which are precisely those most generated in industrial environments, with significantly lower thicknesses or widths, which save space and therefore allow them to be installed in environments with very little available space.

[0057] Furthermore, this application also relates to a sound insulation system comprised of the aforementioned insulation panels. In other words, the sound insulation system will include as many panels as necessary in each case to isolate the noise source.

[0058] Specifically, the insulation system will comprise at least two insulation panels which, placed side by side, constitute a barrier to industrial noise or, better said, attenuate the noise at the frequency or frequencies determined for which said panels have been calculated, which, as mentioned above, behave as Helmholtz resonant cavities.

[0059] Thus, depending on the area to be isolated / protected from noise, insulation panels of a specific width—which, as mentioned earlier, can be 30cm, 45cm, 90cm, or other widths—are placed one after the other, forming a kind of wall or barrier, with gaps of 3cm, 4cm, 5cm, or other widths between them, depending on ventilation requirements. Furthermore, as already mentioned, when insulating industrial equipment, it is necessary to simultaneously ensure ventilation. Therefore, when using the well-known sandwich panels filled with insulating material, it is necessary to create spaces or openings between them to allow for ventilation. This ventilation results in a loss of insulation and necessitates the installation of bulky acoustic silencers.

[0060] However, with the acoustic insulation panel of the present invention and the insulation system formed with them also of the invention, it is possible to provide adequate ventilation and ensure the necessary airflow without compromising the acoustic insulation for which they have been designed and without the need to install the aforementioned acoustic silencers.

[0061] To this end, the acoustic insulation system of the invention shall comprise a plurality of insulation panels, or at least two of them, in such a way that they are separated from each other and facing each other on their shorter sides, that is, in such a way that the side entrances or necks that each panel comprises on each of its shorter sides and which constitute the entrances to the Helmholtz resonating cavities face each other.

[0062] Thus, on the one hand, the separation between panels will constitute a channel or passage for the air necessary to meet the ventilation requirements of the industrial equipment and, on the other hand, a channel or passage for the acoustic waves produced by the noise of said industrial equipment, in such a way that said acoustic waves are introduced laterally, through the lateral inlets or necks that each panel comprises on each of its smaller sides and that give access to the Helmholtz resonating cavities of each panel.

[0063] In other words, the side entrances or necks of each of the Helmholtz cavities that the panels have are positioned substantially perpendicular to the direction of the acoustic waves of industrial noise.

[0064] This constitutes an absolute novelty with respect to the state of the art which, as explained above, places the resonator inlets always facing the direction of the noise so that it enters the cavities and, in this way, is absorbed and the sound wave does not bounce back generating reverberation or echo.

[0065] Thus, the separation between the insulation panels that form the insulation system will allow, on the one hand, the passage or flow of air necessary for ventilation and, at the same time, this separation constitutes a passage for noise or acoustic waves, which, however, when they reach the side entrances or necks of the insulation panels, will be introduced into the Helmholtz resonant cavities, thus producing attenuation at the resonance frequency for which they are designed according to the application of the formula seen above.

[0066] Finally, this application also relates to a sound insulation procedure based on single-cavity Helmholtz resonators.

[0067] This procedure consists of facing two Helmholtz single cavity resonators in such a way that the entrances of their respective necks are at the same height and facing each other, separated by a distance d in such a way that an air flow can pass between them and in such a way that the acoustic waves R produced by the noise source to be isolated are introduced through each of the entrances in a substantially perpendicular way to the direction of said acoustic waves R emitted by said noise source.

[0068] More specifically, the acoustic insulation procedure of the invention will have, as a preliminary step, the calculation of the dimensions of both resonators, and more specifically, the volume of the cavity of both resonators, which will allow the reduction of the sound intensity at the resonance frequency at which it is desired that the two resonators work.

[0069] This calculation will be performed using the formula for the Resonance Frequency of a Helmholtz resonator described above, so, knowing the device or noise source to be isolated, it will be enough to know at what specific frequency or frequencies you want to reduce that sound intensity.

[0070] On the other hand, the separation distance d between their respective inlets or necks will be determined by the airflow requirements between them, or in other words, by the ventilation requirements. A compromise must be reached between the dimensions d of this air passage (a narrower air passage provides greater attenuation and better low-frequency performance) and the ventilation requirements of the noise source being treated (pressure losses or insufficient airflow for proper operation). Description of the drawings

[0071] To complete the description being made and in order to aid a better understanding of the characteristics of the device according to the present invention, a set of drawings is included with this descriptive document as an integral part thereof, in which the following has been represented for illustrative and non-limiting purposes:

[0072] Figures 1A, 1B and 1C show a schematic representation of the joining of three panels according to the present invention forming an insulation system.

[0073] Figure 2 shows a top plan view of another possible practical embodiment of the insulation system where the panels have angled inlets, as well as a detailed view of the ventilation or air passage zone between two adjacent panels.

[0074] Figures 3A, 3B and 3C show a schematic representation of the joining of three panels according to another possible practical embodiment of the present invention.

[0075] Figure 4 shows a perspective view of the practical realization of the previous figure.

[0076] Figures 5.1 to 5.4 show several graphs showing the behavior of the system of the invention when the airflow speed is varied.

[0077] Figures 6.1 to 6.4 show, respectively, an example of application of the system of the invention and three comparative examples of how the systems of the State of the Art used so far behave under the same conditions.

[0078] Preferred embodiment of the invention

[0079] As can be seen in the figures, which illustrate a possible practical embodiment of the invention, the sound insulation panel (1) proposed in the present invention comprises a front wall (2) and a rear wall (3), between which an empty hollow space (4) is defined, forming the cavity of a Helmholtz resonator. In other words, the sound insulation panel (1) of the invention, with its own structure, forms a single Helmholtz resonator, the "bottle" of which is the entire volume enclosed between said front (2) and rear (3) walls. These walls (2, 3) are preferably identical, according to the preferred embodiment shown in the figures, having the same dimensions and structure, although alternative embodiments where they are not identical are possible.

[0080] The acoustic insulation panel (1) and, therefore, both front (2) and rear (3) walls, will also have a vertical rectangular configuration of variable height and width according to the insulation needs, that is, depending on the resonance frequency for which the panel is to be designed, which, as explained above, will result in different configurations that may have, for example, 100cm, 150cm, 200cm or more in height and 30cm, 45cm, 90cm, etc. of possible widths.

[0081] Furthermore, as can be seen in the figures, the front wall (2) and the back wall (3) are shaped like the letter II, each comprising a longer side and two shorter sides (2') and (3') respectively, located at the ends of the longer side. The walls (2, 3) are positioned relative to each other so that their shorter sides (2', 3') face each other without touching, forming or defining the aforementioned rectangular prismatic hollow space (4). This separation between the two walls (2, 3), in addition to defining the volume of the hollow space (4), will determine the depth of the panel, which, for example, could be 15 cm, 25 cm, 26 cm, or other larger dimensions.

[0082] On the other hand, each of the two smaller sides (2', 3') of each wall (2,3) folds in turn into the interior of said cavity forming an entrance (5) in the form of a channel or neck when it is faced with the folded smaller side of the other wall, thus forming two channels (5), one on each side, which constitute the entrances or necks of the resonator.

[0083] Thus, the acoustic insulation panel (1) of the present invention, which can be seen in the figures, comprises two II-shaped walls, front (2) and rear (3), facing each other in such a way that the empty hollow space (4) that remains between them, in a rectangular prismatic shape, forms a single cavity that is entered through two entrances (5) or necks located along the entire height of said acoustic panel (1) and of rectangular cross-section, each of them located on one of the smaller sides (2', 3').

[0084] Thus, as already stated, the acoustic insulation panel (1) of the invention behaves as a single Helmholtz cavity resonator with two facing entrances (5) or, in other words, as two facing Helmholtz resonators that share the same empty hollow space (4) that makes up the Helmholtz resonating cavity.

[0085] Regarding these entrances (5), the figures show two possible embodiments of them. Specifically, in figure 1C, it can be seen how each of the two shorter sides (2', 3') of each wall (2,3) folds inwards forming a right angle with respect to said shorter sides (2', 3') or, in other words, forming an entrance (5) in the form of a channel or neck that runs towards the empty hollow space (4) parallel to the walls (2,3).

[0086] On the other hand, in figures 2 to 4 another possible practical embodiment is shown in which the two smaller sides (2', 3') of each wall (2,3) are folded inwards forming an acute angle with respect to said smaller sides (2', 3') or, in other words, forming an entrance (5) in the form of a channel or neck that has a larger opening as it runs towards the empty hollow space (4) and, therefore, in an inclined way getting closer and closer to the walls (2,3).

[0087] In this regard, a table of experimentally obtained values ​​is shown below, in which the improvement in noise reduction achieved by the acoustic insulation panel (1) of the invention has been verified for the embodiment in which it has inlets (5) with a certain inclination (measured as the inlet angle a) with respect to the embodiment in which said inlets (5) form a channel without inclination or degree a of opening, i.e., when they form a channel that runs parallel to the walls (2,3). As can be seen, a larger angle α results in a better response or level of noise attenuation. However, there is a twofold limitation to avoid using very large angles α:

[0088] That the shorter sides (2', 3') of each wall (2,3) fold inwards so much that they collide with the longer sides of their respective walls, and

[0089] That the smaller sides (2', 3') of each wall (2,3) fold so far inwards, specifically more than 21°, that the entrance (5) ceases to behave like the neck of a resonator, which implies that the system ceases to behave like a Helmholtz resonator.

[0090] Thus, preferably, an input (5) with an angle a of 15° is considered optimal, since it achieves an attenuation of almost 6dB, which in energy terms represents 2 times more attenuation than with a straight input (5) with an angle a of 0 o On the other hand, as can be seen in the table, from an angle of 15° onwards, a smaller incremental value of noise attenuation is achieved for each 0 a. Opening of the entrance (5).

[0091] In addition to the above and as can be seen in the figures, two possible alternative embodiments are also shown with regard to the morphology of the front and rear walls (2,3) that make up the acoustic insulation panel (1) of the invention.

[0092] Specifically, in figures 1 and 2, a possible embodiment can be seen in which said front and rear walls (2,3) are straight, while in figures 3 and 4, another embodiment is shown in which said front and rear walls (2,3) comprise folded vapors (6) that run along their entire height H.

[0093] These folds (6) fulfill the following functions: a) To achieve the maximum volume of empty hollow space (4), that is, of resonant cavity for the space occupied by a single acoustic insulation panel (1). b) To increase the structural strength of the assembly. c) To reduce the potential noise generated by the vibration of the front and rear walls (2,3) of the acoustic insulation panel (1) by providing greater structural strength. d) To prevent distortions in performance. The enclosed volume of empty hollow space (4) acts as a resistance to the passage of acoustic energy. If the front and rear walls (2,3) of the acoustic insulation panel (1) vibrate too freely due to airflow, parameters of the invention could be modified, altering its performance in an uncontrolled manner.

[0094] From all of the above, the advantages of the acoustic insulation panel (1) of the invention are easily deduced, such as:

[0095] Versatility, as it allows for its particular sizing for each noise source (customized attenuation for the type and level of noise to be reduced) and for each ventilation need (as will be seen later).

[0096] Durability, because its manufacture does not use any type of fibrous absorbent material or adhesives for its joining (which conventional sandwich panels do need), allowing acoustic treatments to be carried out in areas where it is not currently possible due to the presence of high humidity or in corrosive environments (chemical and food industry).

[0097] Economy, economic savings, the system is made up of a single machined material, which reduces costs and manufacturing times, in addition, by avoiding the use of other additional elements to guarantee the attenuation in the ventilation holes such as silencers, the cost of design, manufacture and installation of the overall solution is reduced.

[0098] The high number of manufacturing possibilities in terms of materials, since it can be made in any material without this implying variations in acoustic performance, such as lacquered steel sheet panel, stainless steel, polyester resins and even wood.

[0099] On the other hand, as mentioned, this application also relates to a sound insulation system consisting of the grouping of the sound insulation panels (1) of the invention described above, as shown in the figures. That is, the sound insulation system will comprise as many sound insulation panels (1) as necessary in each case to isolate the noise source. Specifically, the insulation system will comprise at least two sound insulation panels (1) which, placed side by side, constitute a barrier to industrial noise or, more precisely, attenuate the noise at the specific frequency or frequencies for which these panels have been designed, acting as Helmholtz resonant cavities.

[0100] Thus, depending on the space to be isolated / protected from noise, the insulation panels will be placed one after the other, forming a kind of wall or barrier, with a certain width which, as mentioned before, can be 30cm, 45cm, 90cm or others.

[0101] Furthermore, this installation will not require complex setup, as it will suffice to place the panels on guides or rails at both their upper and lower ends. More specifically, according to a possible embodiment of the invention not shown in the figures, it will suffice to have a rail or guide fixed to the floor and place the lower ends of the panels on it, securing them both by means of any conventional system, and, on the other hand, have another rail or guide located above, for example fixed to a ceiling, to which the upper ends of said panels are fixed, also by means of any known system.

[0102] On the other hand, as already explained, when acoustically insulating industrial equipment it is crucial to simultaneously ensure its ventilation, so it is necessary to create spaces that allow for such ventilation.

[0103] Thus, although the insulation at very low frequencies will be higher the narrower the ventilation air passage between panels, thanks to the acoustic insulation system of the present invention, it is possible to provide adequate ventilation ensuring the necessary airflow without compromising the acoustic insulation for which they have been designed.

[0104] To this end, the sound insulation system of the invention comprises a plurality of sound insulation panels (1), for example, two according to a possible embodiment of the invention shown in Figures 3 and 4, or three in the example shown in Figures 1 and 2, wherein the sound insulation panels (1) are placed one after the other, with their shorter sides facing each other and with a distance “d” between two consecutive panels that constitutes the air passage channel. Thus, this distance d between two consecutive sound insulation panels (1) will constitute, on the one hand, a channel or passage for ventilation air, which in the figures has been represented by an arrow V, necessary to meet the ventilation requirements of the industrial equipment.On the other hand, the distance d between two consecutive acoustic insulation panels (1) will constitute a channel or passage for the acoustic waves, which in figure 2 have been represented by arrows R, produced by the noise of said industrial equipment, in such a way that said acoustic waves R are introduced first through the aforementioned channel formed by the distance d between two consecutive panels and, subsequently, through the two entrances (5), one of each panel, which are facing each other and which give access to the empty hollow spaces (4) that make up the Helmholtz resonant cavities of each of said consecutive acoustic insulation panels (1).

[0105] In other words, and as can be seen in the figures, especially in figure 2 and its detailed view, the acoustic waves here referred to as “R” produced by the industrial equipment are introduced through each of the inlets (5) of each of the two consecutive panels in a way that is substantially perpendicular to the direction of said channel and to the direction of the acoustic waves R emitted by the industrial equipment when they are introduced through the channel formed by the separation d.

[0106] On the other hand, from the tests carried out, it has been experimentally observed that the ventilation air velocity V also affects the system's performance, that is, the attenuation (noise) value for the calculated resonance frequency.

[0107] Specifically, in figures 5.1 to 5.4, it can be seen how the attenuation varies in frequency for cases in which the flow of the ventilation air passage V varies between the different acoustic insulation panels (1) that form the acoustic insulation system of the invention.

[0108] More specifically, two curves are shown in Figure 5.1:

[0109] The dashed line shows the behavior of the theoretical acoustic attenuation when there is no airflow, showing a peak centered at the resonance frequency; and the solid line shows the behavior of the theoretical acoustic attenuation when there is a small airflow of 0.5 m / s; and in Figure 5.2, these same curves have been represented for the case where the solid line represents an airflow of 2 m / s.

[0110] Figure 5.3 shows these same curves for the case where the continuous line represents an airflow of 6 m / s.

[0111] Figure 5.4 shows these same curves for the case where the continuous line represents an airflow of 10 m / s.

[0112] As can be seen in Figures 5.1 to 5.4, as the airflow velocity increases from 0.5 m / s to 2 m / s and then to 6 m / s, the low-frequency attenuation (between 10 and 50 Hz) increases. This is because the higher flow velocity causes an increase in air pressure in the empty voids (4) that make up the Helmholtz resonant cavities of each of the acoustic insulation panels (1), and consequently, the resonator mass increases.

[0113] However, this improvement is maintained only when the airflow is laminar, because when it becomes turbulent, as in the case of figure 5.4, which is 10 m / s, the attenuation curve does not follow this progression and behaves unpredictably, with sawtooth distortions appearing.

[0114] Therefore, by maintaining a ventilation airflow (indicated by arrow V in the figures) through the different acoustic insulation panels (1) with speeds that imply a laminar flow, i.e., less than 10 m / sec, an additional acoustic attenuation or insulation of the order of between 4 and 10 dB in low frequency is guaranteed.

[0115] This, evidently, has a fundamental synergistic effect with the aforementioned need for ventilation required by industrial equipment and is the main consequence that, by ensuring adequate ventilation, acoustic insulation is achieved that is even better than that of conventional sandwich panels without holes or a ventilation system.

[0116] As an example of the above, several experimental examples of the application of the system of the invention are described below.

[0117] Example 1 In a first application example, the system of the invention could be used to acoustically insulate water chillers.

[0118] Air-cooled water chillers are a very common solution in industrial, residential, and leisure environments due to their simplicity, reliability, and efficiency of installation, and where the noise-generating elements are:

[0119] Evaporator compressors, located at the bottom of the machine's perimeter, are predominantly low-frequency components in their operation.

[0120] Axial fans typically generate a low-to-mid frequency tonal noise, related to the number of blades and the fan's rotational speed. Due to their operating system, they cannot tolerate pressure drop, therefore conventional dissipative silencers cannot be used.

[0121] The following table presents the data separated by frequency and in this order:

[0122] The noise levels emitted in an actual installation;

[0123] Noise levels measured in front of the facade on the exterior of the nearest dwelling in three different cases: o When no insulation is used. o When a prior art sandwich insulation is used. o When the insulation system of the present invention is used.

[0124] In the context of the table, Lp (dB) indicates the sound pressure levels measured at different frequencies (Hz) for the emission and reception conditions.

[0125] Regarding the second-to-last row of the table, the term or value Global (dBA) represents the overall, or average, A-weighted sound pressure level (dBA) measured across all frequencies specified in the table. A-weighting is used to approximate the human ear's response to different frequencies, giving more weight to those that are more perceptible to people. The global value provides an overall assessment of the sound emission in terms of human perception.

[0126] Regarding the last row of the table, the term or value LKAEQ (dBA) is the A-weighted equivalent continuous sound level, also known as the A-weighted equivalent continuous level (Leq). It represents a constant sound level that, if maintained for the same period of time, would have the same sound energy as the actual fluctuating emission measured. It is an energy measure that provides an idea of ​​the average sound levels over time. The "K" indicates that an A-weighting filter is used.

[0127] In summary, the last two rows provide an overview of the total (global) sound levels and the equivalent continuous sound level (Leq) for both emissions and receptions, adjusted according to A-weighting, which reflects the sensitivity of the human ear. These values ​​are crucial for assessing the overall acoustic impact and compliance with noise regulations.

[0128] On the other hand, in order to evaluate and compare the results of the two insulation systems (ET and invention), it is necessary to consider the regulations, which establish or regulate the following aspects:

[0129] I. Limit values ​​for noise transmission to interior or exterior spaces. These vary depending on the predominant use of the area (residential, industrial, institutional, etc.)

[0130] In the case of the example, the standard establishes that the limit value on the exterior of the dwelling must be 45dBA.

[0131] II. Measurement methods and penalties (tonal, impulsive, and low-frequency). It establishes how to measure and how to compensate (penalties) for the characteristics of our hearing when considering certain types of noise as more annoying.

[0132] In the example given, the standard states that when there is a tonal component—that is, a frequency band that predominates over its neighbors and is perceived as more annoying—an additional penalty of +6 dBA must be added to the measured value. In other words, an additional penalty of +6 dBA must be added to the measured Global (dBA) value to obtain the LKAEQ (dBA).

[0133] In the case of the example considered in the table, that component appears in the 315Hz band, in which it can be observed that there is a significant increase in its value compared to the previous and subsequent bands (250 and 400Hz).

[0134] Analysis of this data shows that, in addition, the noise received in the home comes mainly from the chiller fan (the frequency of 315Hz is related to the rotation frequency and number of blades of the fans).

[0135] Looking at the third column of the table, in the case where there is no insulation, the high levels recorded, exceeding the aforementioned limit of 45dBA, together with the existence of that tonal component which generates (according to the standard) a penalty of +6dBA additional on the measured value of Global (dBA) to obtain the LKAEQ (dBA), this causes the levels received in the nearest dwelling to far exceed the limit values ​​of the regulations.

[0136] Now, analyzing the attenuation based on the type of insulation system used, we have the following.

[0137] In the case shown in 4 aIn the column, where the measured values ​​are reflected when a State of the Art sandwich insulation of a thickness of 8cm has been used, it can be observed that the tonal component of 315 Hz is not eliminated and, therefore, the 6dBA penalty must be added to the Global (dBA) data of 53dBA, which gives an LKAEQ (dBA) of 56dBA, so the noise level is above compliance with the regulations.

[0138] In fact, a conventional sandwich panel would only be able to eliminate this tonal component at the cost of an exceptionally large width, meaning it would be oversized to the point of being economically unfeasible even if space were available for its installation, thus not offering a good solution. The reason for this is that if the sandwich panel provides 56.3 dB of sound insulation at 315 Hz and the tone reaches levels of 73 dB near the house, to avoid this difference with adjacent frequencies and prevent the 315 Hz frequency band from being considered a tone, the noise in that band would need to be reduced by 15 dB, which is not possible except with the aforementioned oversizing.

[0139] However, in the case shown in 5 aThe column, which reflects the values ​​measured using the invention's insulation system, with a thickness of 15 cm, shows that the tonal component is eliminated. Therefore, the Global (dBA) and LKAEQ (dBA) noise levels coincide at 44 dBA, which is below the regulatory compliance level. Furthermore, although the values ​​are not shown to avoid making this text unnecessarily long, if the analysis is extended to the noise levels measured inside the dwelling, starting from the weakest surface in terms of acoustic insulation—in this example, a 4-12-4 type window—the commercial sandwich panel would yield a Global (dBA) value of 23 dBA. This would have to be penalized by +6 dB for not eliminating the tonal component, resulting in an LKAEQ (dBA) of 29 dBA, which is above the permitted level of 25 dB.However, with the isolation system of the present invention, the tonal component is eliminated and, therefore, the noise levels of Global (dBA) and LKAEQ (dBA) coincide and are only 19dBA, which are below the level of compliance with the regulations.

[0140] In other words, by using an acoustic insulation system such as that of the present invention, it is possible to eliminate from the outset the tonal component inherent to the operation of the machine, which occurs at 315Hz, thus improving the final performance and creating a "tailor-made" frequency attenuation system to comply with the standard.

[0141] Example 2 (shown schematically in Figures 6.1 to 6.4)

[0142] In this example, a practical application of the invention is described in comparison with a traditional solution considering sandwich-type acoustic panels combined with acoustic silencers that allow ventilation of the machinery under study.

[0143] Specifically, the noise level generated by a variable refrigerant flow (VRV) chiller located on a rooftop near residential buildings is considered (the regulatory level for these environments, as seen in the previous example, being 45 dBA). The ventilation flow rate required for this machine is 81,000 m³ / h with an air velocity not exceeding 10 m / s.

[0144] The unit considered, although it does not generate an excessively high level (being less than 70dBA in overall level, as can be seen in the table, which is 65.9 dBA), concentrates its energy in the low frequencies, with a marked tonal component at 200Hz.

[0145] Next, in the following table, the first two columns present the noise or sound pressure levels emitted by the installation and measured at different frequencies (Hz) and, in the following 4 columns, the sound pressure levels Lp (dB) measured at different frequencies (Hz) in front of the facade on the outside of the nearest dwelling for four different types of acoustic insulation systems: a) When the insulation system of the invention is used, shown schematically in figure 6.1.

[0146] The insulation system consists of 15 panels, each 45 cm wide, 26 cm deep, and 300 cm high, with a 5 cm gap between each panel for ventilation airflow. b) When using sandwich insulation of the State of the Art ET (1), shown in Figure 6.2, which consists of a standard sandwich panel 8 cm deep, with silencers properly calculated for the ventilation requirements of these machines (81,000 m³ / h) of 120 / 540 cm and a baffle length of 120 cm. c) When using sandwich insulation of the State of the Art ET (2), shown in Figure 6.3, which consists of a standard sandwich panel like the one in the previous example and a similar silencer with a baffle length of 300 cm. d) When using sandwich insulation of the State of the Art ET (3), shown in Figure 6.4, with a standard double-type sandwich panel, that is, with two 8cm panels and an air chamber inside of 10.5cm to which silencers are added as in case c) above with a baffle length of 300cm.

[0147] Regarding the penultimate and last rows of the table shown below, both the overall sound levels (dBA and dBC) and the equivalent continuous sound level (Leq) are provided for the receptions of each of the four cases studied. Frequency Emission Reception Reception Reception Reception

[0148] More specifically, the final global data is expressed in two different values: dBA: A weighting that resembles the sensitivity of the human ear is used and is commonly used to assess the impact of environmental noise on health. dBC: A flatter weighting that includes more low frequencies is used, useful for measuring sounds that have significant components in those frequencies.

[0149] More specifically, the regulations stipulate that, to calculate low-frequency penalties, the overall level must be measured in dBA and dBC. If the difference between these two values ​​is less than 10, no penalty is applied. However, if the difference is between 10 and 15, the overall dBA value is penalized by 3 dB, and if the difference is greater than 15, the overall dBA value is penalized by 6 dB.

[0150] As will be seen later when the results of the example are analyzed, this is fundamental in terms of the advantage that the present invention offers compared to traditional systems of the State of the Art, since in these only the Global dBA level is reduced, but the Global dBC level remains intact, which means that the difference between the two exceeds the limit set by the regulations and that means having to apply a penalty that will leave the LKAEQ (dBA) value, which as seen in the previous example is the equivalent continuous A-weighted sound level, above the admissible value.

[0151] Analysis of the results.

[0152] As can be seen in the corresponding column and in Figure 6.1, applying the invention results in a reduction of noise levels to 41.4 dBA. Furthermore, since no penalties are observed according to the criteria established in the current reference standard (RD 1367 / 2007), the overall assessment value is the observed level of 41.4 dBA, which meets the regulatory requirements for residential environments.

[0153] On the other hand, for case b) ET (1) which is represented in figure 6.2, it can be seen that the attenuation not only does not reach the normative limits of 45dBA, but also tonal penalties (+3 dB) and low frequency penalties (+3 dB) appear, which add 6 dBA to the evaluation level, that is, to 48.4 dBA, resulting in a total LKAEQ (dBA) level of 54.4dBA.

[0154] For case c) ET (2), which is represented in figure 6.3, where the depth of the silencer baffle was increased to 300cm to compensate for the fact that this is the weakest element of the installation in terms of acoustic insulation, it can be seen that although the noise levels are slightly reduced compared to the previous case, it can be seen how the attenuation level is still above the normative value of 45 dBA, since it is 45.6 dBA and, in addition, it does not avoid the penalties for tonal components (+3dB) and for low frequency (+ 3 dB), so its LKAEQ (dBA) is 51.6 dBA.

[0155] Finally, in case d) ET (3), shown in Figure 6.4, where both the panel and the silencer were modified, the resulting overall level is 33.4 dBA, lower than the regulatory value, and the tonal component disappears. However, considering that commercial panels primarily attenuate the system at mid and high frequencies, the difference between the overall levels in dBA and dBC is greater, thus adding the 6 dB penalty for low frequencies, resulting in an LKAEQ (dBA) of 39.4 dBA.

[0156] That is to say, in this latter case, the conventional insulation system with sandwich panels does achieve a similar acoustic insulation performance to that of the present invention; however, it should be noted that, unlike the panel of the invention:

[0157] It occupies more space than the invention due to the silencer. That is, although the depth occupied by the panels is similar to that of the invention, around 26cm, it is necessary to install silencers with a baffle length of +300cm, which obviously implies a much greater space requirement that, in most cases, makes this solution unfeasible.

[0158] It involves a higher cost of materials than the invention because two panels must be installed instead of one, in addition to the cost of the acoustic silencer.

[0159] It involves a higher installation labor cost than the system of the invention (two panels and a large silencer (540x120x300 cm) have to be installed).

[0160] It has a lower durability than the system of the invention due to the use of fibrous absorbent materials (rock wool or glass wool), which are not water-repellent, which usually leads to their deterioration and, furthermore, results in altered noise reduction performance. Example 3

[0161] A final example of the application of the invention that is not limited to the isolation of an industrial piece of equipment as such, or at least not as mentioned in the previous example, is the case of airborne noise insulation on highways.

[0162] In the context of the UNE-EN 1793-3 standard, which refers to road traffic noise reduction devices, the DLR parameter is used to evaluate the traffic noise attenuation capacity of these devices. Specifically, DLR represents the in-situ noise reduction index, that is, the difference between the sound pressure level without the corrective device and the level measured with the device installed. It is expressed in decibels (dB).

[0163] This parameter is crucial for determining the effectiveness of acoustic barriers or noise barriers installed on roads, as it offers a quantitative measure of the noise reduction provided by these devices under real-world conditions. Specifically, it categorizes different types of devices based on their performance, that is, based on their soundproofing capacity, as follows:

[0164] DLR Category (dB)

[0165] B3 > 24

[0166] This European Standard therefore establishes 4 types, ranging from category B3, which would represent the best performance, to B0, which would not be suitable for use as a road screen.

[0167] Without going into the details of the calculation, three prototypes of the system of the invention were tested for cases in which the panels had width / depth measurements of 90 / 25cm, 45 / 26cm and 30 / 15cm respectively and the results obtained were all categorized as B2 or B3 according to said Standard.

[0168] In other words, the improved low-frequency performance makes them suitable for use as roadside barriers. It is also worth noting that, for this type of application, the described panels have the competitive advantage of allowing air to pass through their openings—3 cm in the example—thus reducing the overall wind load compared to similarly sized barriers without any openings.

[0169] Finally, from all of the above, the advantages of the sound insulation system of the invention can now also be easily deduced, such as:

[0170] Allow maximum acoustic insulation in low frequency and / or tonal components, between 10 and 15 times the acoustic insulation of a conventional acoustic panel.

[0171] Allow for proper ventilation without losing acoustic insulation at the sensitive frequencies in each case.

[0172] Doing without acoustic silencers, which in addition to the economic savings represents a significant saving of space in the acoustic treatment of any machine (for informational purposes, to isolate a generator set using conventional systems, silencers need a minimum space around the perimeter of the machine of between 2.5 and 3 m).

[0173] Finally, as already stated, this application also relates to a sound insulation procedure for low-frequency noises comprising:

[0174] For a noise source, define at least one emission frequency for which acoustic attenuation is desired;

[0175] Taking this frequency as the resonant frequency of a simple Helmholtz cavity resonator, according to the formula: Calculate the remaining parameters, where c is the speed of sound in air, A is the cross-sectional area of ​​the resonator neck, V is the volume of the cavity, and L is the length of the neck. With the above values, manufacture or construct at least two single-cavity Helmholtz resonators; and position these at least two single-cavity Helmholtz resonators so that the entrances of their respective necks are at the same height and facing each other, separated by a distance d such that an airflow can flow between them to allow ventilation, and such that the acoustic waves R produced by the noise source to be isolated are introduced through each of the entrances substantially perpendicular to the direction of the acoustic waves R emitted by the noise source.

[0176] On the other hand, according to a preferred embodiment of the invention, each of these at least two single-cavity Helmholtz resonators will be formed by a single acoustic panel (1) comprising a front wall (2) and a rear wall (3) facing each other in such a way that between them an empty hollow space (4) is defined that forms the cavity of the Helmholtz resonator which has the shape of a rectangular prism and where on the shorter sides of said prism are located two shorter sides (2', 3') formed by a separation between the respective walls (2,3) which form two entrances (5) or necks of the resonator located along the entire height of said acoustic panel (1).

[0177] On the other hand, the procedure of the invention consists of placing a plurality of panels (1) as described above, one after the other, with their shorter sides facing each other and with a distance “d” between two adjacent or consecutive panels that constitutes the air passage channel in such a way that the acoustic waves R are introduced first through said channel and, subsequently, substantially perpendicular to the direction of said channel and to that which the acoustic waves R emitted by the industrial equipment carry through the two inlets (5), one of each adjacent panel (1), which are facing each other and which give access to the empty hollow spaces (4) that make up the Helmholtz resonating cavities of each of said adjacent acoustic insulation panels (1).

[0178] On the other hand, in order to obtain an optimal result in the acoustic attenuation values, the airflow must be kept in laminar regime and, more specifically, it must be prevented from exceeding a speed of 10m / sec.

Claims

CLAIMS 1 Acoustic insulation panel (1) characterized in that it comprises a front wall (2) and a rear wall (3) facing each other in such a way that between them an empty hollow space (4) is defined which forms a cavity of a Helmholtz resonator in the form of a rectangular prism and where, in correspondence with the shorter sides of said prism, there are two shorter sides (2', 3') of the respective walls (2,3) which in turn form two entrances (5) or necks of the resonator located along the entire height of said acoustic panel (1).

2. Acoustic insulation panel (1) according to claim 1, characterized in that the front wall (2) and the back wall (3) are II shaped, each comprising a longer side and two shorter sides (2') and (3') respectively, located at the ends of the longer side and where the walls (2, 3) are positioned relative to each other in such a way that their shorter sides (2', 3') face each other without touching, forming the aforementioned empty hollow space (4) inside. 3.- Acoustic insulation panel (1) according to claim 1 or 2, characterized in that each of the two smaller sides (2', 3') of each wall (2,3) is folded into the interior of the empty hollow space (4) forming the entrance (5) as a channel or neck of the resonator when facing the folded smaller side of the other wall. 4.- Acoustic insulation panel (1) according to claim 3, characterized in that each of the two smaller sides (2', 3') of each wall (2,3) is folded inwards forming a right angle with respect to said smaller sides (2', 3'), forming an entrance (5) in the form of a channel or neck that runs towards the empty hollow space (4) parallel to the walls (2,3). 5.- Acoustic insulation panel (1) according to claim 3, characterized in that each of the two smaller sides (2', 3') of each wall (2,3) is folded inwards forming an acute angle with respect to said smaller sides (2', 3'), forming an entrance (5) in the form of a channel or neck that has a larger opening as it runs towards the empty hollow space (4) forming an entrance to.

6. Acoustic insulation panel (1) according to claim 5, characterized in that the entrance angle a is greater than 0 o and less than 15°.

7. Acoustic insulation panel (1) according to any of the preceding claims, characterized in that the front and rear walls (2,3) comprise folded slits (6) running along their entire height in order to increase structural strength and prevent vibrations. 8.- Acoustic insulation panel (1) according to any of the preceding claims, characterized in that the walls (2,3) are identical to each other. 9.- Acoustic insulation system comprising a plurality of acoustic insulation panels as described in any of claims 1 to 8, characterized in that the acoustic insulation panels (1) are positioned adjacent to one another, with their shorter sides facing each other so that their respective inlets (5) are at the same height and facing each other, and wherein between two panels there is a separation “d” that constitutes a channel for the passage of air and acoustic waves R, and such that said acoustic waves R are introduced first through said channel and subsequently substantially perpendicular to the direction of said channel through the inlets (5) of each panel (1) that give access to the empty hollow spaces (4) that form the Helmholtz resonant cavities of each of said adjacent acoustic insulation panels (1). 10.- Acoustic insulation system according to claim 9 or 10, characterized in that the distance d between acoustic insulation panels (1) is calculated based on the airflow that is to be passed from one side to the other of said panels per unit of time and in such a way as to ensure that said flow is laminar. 11.- Acoustic insulation system according to claim 9 or 10, characterized in that it comprises two rails for fixing the upper and lower ends of the acoustic insulation panels (1). 12.- Acoustic insulation procedure for low-frequency noises comprising the following steps: For a noise source, define at least one emission frequency for which acoustic attenuation is desired; Taking this frequency as the resonant frequency of a simple Helmholtz cavity resonator, according to the formula: Calculate the remaining parameters, where c is the speed of sound in air, A is the cross-sectional area of ​​the resonator neck, V is the volume of the cavity, and L is the length of the neck. With the above values, manufacture or construct at least two single-cavity Helmholtz resonators; and position these at least two single-cavity Helmholtz resonators so that the entrances of their respective necks are at the same height and facing each other, separated by a distance d such that an airflow can flow between them to allow ventilation, and such that the acoustic waves R produced by the noise source to be isolated are introduced through each of the entrances substantially perpendicular to the direction of the acoustic waves R emitted by the noise source. 13.- Acoustic insulation method according to claim 12, characterized in that each of these at least two single-cavity Helmholtz resonators shall be formed by a single acoustic panel (1) comprising a front wall (2) and a rear wall (3) facing each other so that between them an empty hollow space (4) is defined which forms the cavity of the Helmholtz resonator which has the shape of a rectangular prism and where on the shorter sides of said prism are located two shorter sides (2', 3') formed by a separation between the respective walls (2,3) which form two entrances (5) or necks of the resonator located along the entire height of said acoustic panel (1).

14. Acoustic insulation method according to claim 13, characterized in that it comprises the placement of a plurality of panels (1) one after the other, with their shorter sides facing each other and with a distance “d” between two adjacent or consecutive panels that constitutes the air passage channel such that the acoustic waves R are introduced first through said channel and, subsequently, substantially perpendicular to the direction of said channel and to that of the acoustic waves R emitted by the industrial equipment through the two inlets (5), one of each adjacent panel (1), which face each other and which give access to the empty hollow spaces (4) that form the Helmholtz resonant cavities of each of said panels adjacent acoustic insulation (1). 15.- Acoustic insulation procedure according to claim 14, characterized in that the airflow is maintained in laminar regime. 16.- Acoustic insulation procedure according to claim 15, characterized in that the airflow is maintained at a speed below 10m / sec.

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