Improved fabric protection element for use in acoustic components of an electronic device, and acoustic component incorporating this element

Abstract

A protective element for a consumer electronic device comprising at least one port (101) and one channel (105) for an audio component (104), wherein the port (101) or the channel (105) has a protective fabric against the intrusion of contaminant particles and water spray. According to the present invention, the fabric (25) has a mesh (11) having a rectangular shape, and the rectangular sides (12, 13) are constituted by respective threads (26, 27). Compared with a prior art square mesh fabric having equivalent air passage characteristics and sound transmission characteristics, the fabric forming the protective element of the present invention provides the advantage of enhancing the protection ability against contaminant particles.

Description

Technical Field

[0001] The present invention relates to a protective element made of a high-performance fabric particularly suitable for use in acoustic components (typically micro speakers) of consumer electronic devices (typically smart phones and tablets) to perform the function of protecting from the spray of particulate matter and water, and to the optimal sound transmission achieved thanks to its specific structure.

Background Art

[0002] In electronic devices with acoustic functions such as smart phones, small openings are provided in their external shells arranged in acoustic components such as speakers and microphones, and sound waves can be transmitted through these openings. However, in almost all cases, these required openings carry the risk that some external contaminating particles penetrate the device and become harmful. This applies to both solid particles that may accumulate on the speaker diaphragm and impede its free movement, and water droplets that may sometimes impair the functionality of the electronic device in the case of spray. Therefore, it is necessary to stop these contaminants at the acoustic ports of the device without them entering the interior of the device.

[0003] For such purposes, in the most common cases, a filter called a "die cut part" is used, which comprises a precise technical filtration medium that is a square mesh monofilament fabric, with the size of a single mesh being uniform in space and time, to have a reasonable certainty of stopping solid particles having a size larger than the characteristic size of the mesh (all equal to each other). For this reason, known square mesh synthetic monofilament precision technical fabrics are ideal media for this type of application.

[0004] Regarding the sizing of such square-mesh industrial fabrics, the requirement is to stop solid particles having the most common sizes. As can be seen below, typical square-mesh monofilament fabrics of the prior art can stop solid particles having sizes greater than their mesh opening values. The latter typically requires lower microns and is valued by manufacturers for good sound transmission and instead requires a fabric that is as open as possible, which ranges from 20 to 100 microns depending on the speaker sensitivity to contamination.

[0005] From all of the above, the limitations of the prior art are already occurring. In fact, at present, there is no optimal design of a fabric that can simultaneously ensure the best protection and sound transmission possible without accompanying problems of distortion.

[0006] Regarding acoustic requirements, there are several factors that impose the use of a fabric that is as open as possible.

[0007] First of all, an overly closed protective fabric reduces sound emission to an unacceptable level. The small speakers of smartphones are very powerful considering their size and reach a sound pressure level (SPL) > 100 dB at a distance of 30 mm. Therefore, manufacturers today will not accept an excessive reduction in performance, and thus there is a need for a very open and "acoustically transparent" fabric, clearly in view of the drawbacks of protection.

[0008] Furthermore, in terms of sound quality, hitherto it has had to be optimal, not only powerful but also with strict requirements involving even minimal distortion. However, due to the need for aesthetic design, the speaker ports of smartphones and tablets are often very small (typically a few holes with a diameter in the range of 1 - 1.5 mm), and thus a very high acoustic velocity (>10 m / s) is generated through such openings, which occurs in the non - linear range and, in the case of either THD (Total Harmonic Distortion), or HOHD (Higher - Order Harmonic Distortion), or R&B (Rub & Buzz), should be said to cause undesirable harmonic distortion of the acoustic signal throughout the fabric. All of these acoustic quantities, which will be better explained below, are indicators of sound quality and must be minimized to meet the common standards of the industry in this field. Typical requirements are THD < 5% and HOHD / R&B < 0.4%.

[0009] In particular, in smartphones, the issue of microphone speaker protection is becoming increasingly important for several reasons as follows.

[0010] 1. There are an increasing number of more powerful micro - speakers, and the movable range of the diaphragm is already considerably higher than 0.5 mm. Therefore, the amount of air set during operation is very high, and a very open mesh is required to ensure accurate sound transmission.

[0011] 2. To achieve the above - mentioned high output, micro - speakers with very powerful magnets. The strongly generated magnetic field has the risk of attracting metal particles existing in the environment into the interior of the speaker. As a result, the protective mesh needs to improve protection from particles compared to the past.

[0012] 3. The increasingly smaller acoustic ports (considering the minimum slots with a total area of several mm² left between the display and the phone shell) generate an increasingly higher acoustic velocity, and thus a fully optimized acoustic fabric is required to keep the acoustic output quality under control. 2

[0013] ​Specific tests are carried out to evaluate the acoustic properties of each mesh that affect the sound emission of the device into which the meshes are inserted. These measurements may be of the hydrodynamic properties carried out on the fabric itself or actual acoustic tests carried out on a test speaker that houses the acoustic fabric under consideration.

[0014] The measured value of the specific airflow resistance, which is a basic parameter quantifying the resistance of the fabric to the passage of sound waves, belongs to the first group. This type of force that resists the airflow generated by sound waves has been found to be the cause of the aforementioned harmonic distortion. The resistance is a concentrated quantity that does not depend on the size of the sample, is proportional to the sound pressure, and is inversely proportional to the airflow velocity through the sample. That quantity is generally expressed by the measurement unit MKSRayls = [Pa / (m / s)].

[0015] As is known, this quantity depends on the airflow velocity through the fabric, and when the latter becomes too high, generally exceeding 1 m / s, the dependence is no longer linear. In most applications of micro speakers in consumer electronic devices (smartphones and tablets), the acoustic mesh is subject to cross-flow that significantly exceeds the linear range of the specific acoustic resistance. Therefore, in order to estimate the acoustic distortion that the mesh can introduce into the device, it is necessary to measure how much the mesh modifies the acoustic signal with respect to high sound velocities.

[0016] Therefore, a dedicated test measures the specific resistance by imposing a high cross-sectional velocity that is extended up to values of up to 30 - 40 m / s, even up to the non-linear range. The curve of the resistance as a function of velocity shows the gradient characteristics of the material being tested. The lower this gradient, the closer the curve is to linearity, and the less distortion is generated by the acoustic mesh with respect to the acoustic signal. Therefore, it is clear that a low resistance value in the non-linear range is preferred and serves as an indicator of the quality of the mesh for use in protecting the acoustic components of electronic devices.

[0017] The above-described tests and parameters are indicators of the acoustic properties of the acoustic mesh that affect the performance of the devices to which they are applied. The evaluation of the device's performance level is instead carried out by other types of tests that are performed directly on the final part, in this case the speaker (or microphone) to which the acoustic protection mesh is assembled.

[0018] Examples of these measurements are the already mentioned SPL, THD, and amounts of HOHD / R&B that are usually measured by a single test performed on a reference model of the microphone and representing the application under consideration comprehensively with the installation of the acoustic mesh.

[0019] Regarding the already mentioned case of very high-performance speakers that generate particularly high air velocities, it is also necessary to analyze how the fabric affects the generation of noise caused by the flow ("flow noise") by the device. In particular, it describes the wide-frequency spectrum noise generated by the air jet discharged at high speed by the external port of the speaker, which can be measured by additional dedicated tests.

[0020] All of the above require the acoustic mesh to have a high aperture area in order to minimize the resistance of the material to the passage of air, which is beneficial for reducing both acoustic insertion loss and acoustic distortion. In parallel, the mesh itself must also ensure appropriate protection for the acoustic components and thus must have an appropriately limited mesh size.

[0021] In conclusion, in order not to degrade the acoustic performance, it is necessary to reduce the mesh opening size while maintaining the void / full ratio, i.e., the opening area of the fabric. In the case of the prior art square mesh, these two conflicting requirements are only partially met, as can be seen here.

[0022] There are two available methods to reduce the mesh size. The first method results in the possibility of inserting an increasing number of threads of the fabric with a fixed diameter. The second method, instead, results in the use of the same number of threads but with a higher thread diameter. In either case, it becomes clear that the void / full ratio decreases and the air passage and acoustic performance of the fabric deteriorate. Therefore, in order to obtain a smaller mesh size while keeping the void / full ratio constant, it is intuitive to think that the only possible way is to use an increasing number of threads while at the same time making the thread diameter smaller and smaller. However, this third method, although clearly ideal, presents the following two limitations.

[0023] 1. Technical limitations in the processing of yarns, where it is impossible to extrude or weave monofilaments below a certain diameter;

[0024] 2. Technical limitations during the weaving process, where it is impossible to increase the number of threads per centimeter beyond a certain threshold. In some cases where high protection requirements are imposed by the application and a mesh with a particularly small size is required, the use of a lower thread diameter may impose a structure with a number of threads that is impossible to achieve.

[0025] Therefore, it is clear that the aforementioned conventional choice, namely the choice to reduce the mesh size, necessarily has the drawback of also reducing the opening area of the mesh itself. As a result, if the conventional square meshes are too narrow, the speed of sound passing through them becomes too high, which has an adverse effect on the performance of the speaker. Even when discussing a new and still uncontaminated fabric, it affects the acoustic insertion loss at the intersection of the fabric itself, as well as the acoustic distortion phenomena: THD (Total Harmonic Distortion), HOHD (Higher Order Harmonic Distortion), and Rub & Buzz. Especially in the case of high-performance speakers, at a high intersection acoustic speed through the mesh, an undesirable "flow noise" effect, i.e., the generation of broad-spectrum noise, may even occur, which further degrades the quality of the acoustic emission. Furthermore, when the conventional square meshes are partially contaminated by their use, the above effects are even more severe and may easily render the entire device unusable.

[0026] From all of the above, it is presumed that the choice of the best conventional square mesh acoustic fabric always constitutes a compromise. A very closed fabric is advantageous for protection but has low performance regarding sound transmission (even when new and uncontaminated), while a more open fabric, in turn, provides an acceptable "acoustic permeability" but exhibits a mesh opening that is too large to effectively stop all particles of contaminants.

[0027] Publication WO 2011 / 132062 discloses a double-layer fabric structure with a laminated continuous film having a waterproof function against the ingress of water into the acoustic components of an electronic device.

[0028] WO 2010 / 124899 relates to a system for manufacturing filters made of composite fabric materials.

[0029] Publication WO 2017 / 134479 relates to a composite multilayer structure that can be used as a sub-component of electronic and acoustic articles.

[0030] WO 2005 / 039234 discloses a protective structure comprising a punched metal foil.

Prior Art Documents

Patent Documents

[0031]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0032] The main object of the present invention is to provide a protective element formed from a high-performance synthetic monofilament fabric or woven mesh to be used as protection for speakers present in electronic devices and smartphones.

[0033] In particular, the object of the present invention is to provide a protective element made of a fabric of the aforementioned type that, unlike fabrics of the prior art, exhibits an improved ability to stop solid particles with the same acoustic performance, or alternatively, improved acoustic characteristics (i.e., lower acoustic insertion loss and lower distortion) with the same ability to protect from particles compared to the prior art.

[0034] These and other objects are achieved by the elements of the present invention according to claim 1. Some preferred embodiments of the present invention result from the remaining claims.

[0035] In relation to a prior art square mesh fabric having equivalent air passage characteristics and sound transmission characteristics, the protective element of the present invention offers the advantage of presenting an improved protective ability from contaminating particles.

[0036] Regarding the prior art fabrics, with respect to the protection ability from solid contaminants, the element of the present invention exhibits improved sound transmission characteristics that improve the acoustic performance of the component in which it is installed.

[0037] Of course, for each respective use of the micro speaker within the electronic device, in both the first range (better protection) and the second range (better sound transmission), in any case, it is possible to select a fabric structure more suitable for the purpose to obtain a partial improvement to a greater extent overall than what is allowed by the prior art.

[0038] The fabric forming the element of the present invention may be manufactured by weaving either a monofilament or a multifilament synthetic material. In its optimal form, the fabric of the present invention is manufactured using a monofilament.

[0039] The material forming the starting monofilament or multifilament may be a synthetic technopolymer belonging to the group consisting of polyester, polyamide, polyaryl ether ketone, polyphenylene sulfide, polypropylene, perfluorocarbon, polyurethane, or polyvinyl chloride. Alternatively, the base monofilament or multifilament material for manufacturing the fabric of the element of the present invention may be an artificial polymer belonging to the group consisting of cellulose or viscose.

[0040] Whenever optimal protection from the scattering of liquids as well as just solid particles is desired, the fabric of the present invention may be implemented with fluorocarbon or silicon properties or other types of hydrophobic and / or water-repellent treatments.

[0041] The monofilaments forming the fabric of the present invention may have a diameter in the range from 10 μm to 90 μm, preferably in the range from 17 μm to 40 μm, in both the warp and weft directions. The fabric of the present invention may be manufactured with a fabric structure that requires a number of yarns per centimeter in the range from 23 to 350.

[0042] The fabric may be manufactured with different fabric architectures and may be manufactured using yarns having different properties or different diameters in the weft and warp. The mesh openings of the fabric of the present invention may have a short side in the range from 5 μm to 150 μm.

[0043] In particular, in the prior art fabric configurations defined as "Tressen", "Reps", or "Dutchweave", the short side / long side dimension ratio of the mesh opening is always lower than 0.25, and it should be noted that this is the condition for saturation, i.e., the contact between the yarns extending parallel to each other.

[0044] Conversely, the present invention, in which the aforementioned dimension ratio is between 0.3 and 0.9, is designed to maximize the cross-sectional area of the air flow (and thus also the sound flow) intersecting orthogonally to the material and to minimize the insertion loss in decibels. In the case of prior art fabrics, especially in filtering applications where the loss of load through the filter is not a problem, it is only necessary to minimize the size of the holes through which the fluid passes.

[0045] Therefore, in prior art fabrics defined as "Tressen", "Reps", or "Dutchweave", one of the two sets of yarns is arranged to be adjacent to each other, thereby reaching so-called "saturation" and leaving only a minimum of cross openings suitable for ensuring extreme filtering capacity, but at the same time resulting in a very high load loss, which is absolutely unacceptable when planning to replace the same fabric configuration in a product for acoustics, which aims to minimize the decibel loss ("insertion loss").

[0046] The above objects, advantages, and features result from the following description of some preferred embodiments of the elements of the present invention, provided as non-limiting examples in the figures of the accompanying drawings.

Brief Description of the Drawings

[0047] In this case,

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 5

Figure 6

Figure 7a

Figure 7b

Figure 6a

Figure 6c

Figure 6b

Figure 6d

Figure 8

Figure 9

Figure 10a

Figure 10b

Figure 11a

Figure 11b

Figure 11c

Figure 11d

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

[0048] In the example of FIG. 1, the smartphone 100 is provided with an acoustic port 102 in an upper speaker called a "receiver", and the upper speaker transmits sound to the user's ear during listening on the smartphone and is adapted to emit stereo sound in the environment when the smartphone also provides this function. A second set of openings 101 enables the sound emission of a lower speaker (a "speaker") for listening with a speakerphone, for audio playback, and for an incoming call tone. Usually, the smartphone also has other openings 103 for a microphone, a pressure sensor, or a vent port to enable equalization of the internal pressure within the waterproof device.

[0049] FIG. 2 shows in cross-section a typical arrangement of components inside the smartphone at the port 101 of the lower speaker or "loudspeaker" 104. The latter communicates with the external environment via a narrow channel 105 that ends at the acoustic port 101.

[0050] The speakers of conventional smartphones are protected from the ingress of contaminant particles 3 and water spray by a shaped element 2 made of a square mesh synthetic monofilament fabric that is inserted between the acoustic port 101 and the channel 105 or, in another embodiment, locked inside the channel itself.

[0051] In use, the fabric forming the element 2 needs to ensure the correct passage of sound waves (a two-way alternating flow F2 in accordance with the characteristics of the acoustic signal) generated by the speaker 104, while at the same time stopping contaminant particles (a flow F1 from outside to inside the smartphone) that pose a risk of reaching the speaker itself.

[0052] In the prior art shown in FIGS. 3, 4a, and 4b, the mesh 4 of the fabric 2 is square and consists of threads 5 that form each side 6 of the square mesh 4.

[0053] The opening area of the prior art mesh 4 itself is calculated as the percentage ratio between the surface of the smaller square 7 (Figure 4a) included between the contours or inner edges of the threads 5 forming the sides 6 of the mesh 4, and the surface of the larger square 8 (Figure 4b) measured up to the center line of the thread 5 itself.

[0054] During the use of an electronic device in a dirty environment, the prior art mesh 4 is exposed to the ingress of contaminants F1, which results in the blocking of contaminant particles 3 typically having a diameter equivalent to the length of the side 6 of the square mesh itself. Consequently, the latter opening becomes clogged, thereby leaving free only a small portion 10 of the surface of the smaller square 7 of the mesh 4 for the passage of sound waves (Figures 5 and 4a).

[0055] As a result of the clogging of the prior art fabric mesh, typically a higher load loss occurs at the intersections of the fabric itself, which leads to a decrease in speaker performance, namely a higher "insertion loss" accompanied by a loss of radiated sound pressure, harmonic distortion (THD) or Rub & Buzz (R&B) phenomena. The final result depends on the severity of the contamination received, but in many cases it is more than a tangible phenomenon and can completely impair the use of the device within 1 - 2 years.

[0056] In addition to all of the above, the selection of the best square mesh acoustic fabric (i.e., of the prior art) is always a compromise, even when considering only the performance of a new, still uncontaminated fabric. The fabric is described by its value of mesh opening and its specific airflow resistance (measured in MKSRayls) as an indicator of its acoustic permeability. These two quantities behave in opposite ways as the thread density per centimeter changes, so it is impossible to minimize both of them. In practice, industrial fabrics that prioritize protection from solid particles and are particularly closed and thus already new but insufficient in terms of sound transmission performance should be selected. Conversely, when selecting a material with a very low specific airflow resistance and thus excellent "acoustic permeability", one is forced to accept a value of mesh opening that does not guarantee adequate protection from solid contaminants.

[0057] To overcome these drawbacks of the prior art, the protective element of the present invention is made of a fabric 25 having a mesh 11 with a rectangular shape having a long side 12 and a short side 13 (FIG. 6). The figure shows a rectangular mesh with the long side arranged in the weft direction, but this is not restrictive and the present invention also provides the opposite configuration with the long side arranged in the warp direction.

[0058] The fabric 25 may be manufactured with different open mesh fabric architectures having the common property of being asymmetric in two directions, the weft and the warp, particularly with respect to the linear density of the yarns per centimeter and / or the diameter of the yarns. Thus, the numerical density of the yarns of the weft is different from that of the warp with respect to the yarn diameter or the nature of the yarn, and / or the weft is different from the warp.

[0059] As a result, it is possible to manufacture the fabric of the present invention having a rectangular mesh, particularly as a function of the structural parameters of the linear density, the diameter of the yarns, and their mutual balance in the asymmetric configuration.

[0060] For this purpose, the ratio between the linear density / cm of the weft and the warp of the mesh 11 in each direction is preferably in the range between 0.4:1 and 2.5:1. Further, preferably, the ratio between the diameter of the warp and the diameter of the weft of the mesh 11 is in the range between 0.5:1 and 2:1.

[0061] FIG. 6a shows a part of a prior art fabric 41 having the same density of yarns per centimeter (N1) with respect to both the warp (vertical in the figure) and the weft (horizontal in the figure). Also, this fabric has the same value of yarn diameter (d1) with respect to the warp and the weft. The open mesh 7 is a square having the same value of mesh opening 6 in two directions (FIG. 6a).

[0062] In FIG. 6b, a possible embodiment of the fabric 25 of the protective element of the present invention is instead proposed, where only the diameters of the warp and the weft are different from each other. As a result,

[0063] - The number of warp threads per centimeter (N1, the vertical threads in Fig. 6b) according to the present invention is the same as that of the prior art in Fig. 6a.

[0064] - The number of weft threads per centimeter (N1, the horizontal threads in Fig. 6b) according to the present invention is the same as that of the prior art in Fig. 6a.

[0065] - The diameter of the warp threads (d1, the vertical threads in Fig. 6b) according to the present invention is the same as that of the prior art in Fig. 6a.

[0066] - The diameter of the weft threads (d2, the weft threads in Fig. 6b) according to the present invention is lower in both directions than both the diameter of the warp threads (d1, Fig. 6b) according to the present invention and the diameter of the threads of the prior art fabric (d1) (Fig. 6a).

[0067] Fig. 6c shows a part of a prior art fabric 41 having the same thread density per centimeter (N1) and the same thread diameter (d1) for both the warp threads (vertical in the figure) and the weft threads (horizontal in the figure). Therefore, the material is completely symmetric.

[0068] In Fig. 6d, a possible embodiment of the fabric 25 for forming the protection element of the present invention is proposed instead, and only the thread density per centimeter for the warp and weft threads differs from each other. As a result,

[0069] - The number of warp threads per centimeter (N1, the vertical threads in Fig. 6d) is the same as that of the conventional fabric in Fig. 6c.

[0070] - The number of weft threads per centimeter (N2, the weft threads in Fig. 6d) according to the present invention is less than the number of threads per centimeter of the warp threads according to the present invention (N1, Fig. 6d) and the number of threads per centimeter of the prior art fabric (N1 in both directions, Fig. 6c).

[0071] - The diameters of the warp and weft threads (d1, both the vertical and horizontal threads in Fig. 6d) according to the present invention are the same as each other and equal to the corresponding values of the prior art in Fig. 6b.

[0072] The opening area of the mesh 11 is calculated as the percentage ratio between the surface of the smaller rectangle 14 (Figure 7a) measured between the contours or edges of the threads 26, 27 that form its respective sides facing the inside of the mesh 11, and the surface of the larger rectangle 15 (Figure 7b) measured up to the centerlines of the aforementioned threads 26, 27. The sides of the rectangular mesh of the fabric of the present invention are such that the ratio of the short side to the long side is within the range between 0.3 and 0.95. This can apply to both the situation where the short side of the mesh is in the weft direction and the situation where it is in the warp direction, and both of these options are covered by the present invention.

[0073] When particles of the contaminant 3 coming from the outside and having a diameter comparable to the length of the short side 13 of the rectangular mesh 11 itself collide with the mesh 11 of the fabric 25, the opening of the rectangular mesh is not completely clogged as in the case of the known mesh 4 having a square shape. Instead, most of the opening area 16 of the mesh 11 itself is left for the passage of the sound flow (Figure 8).

[0074] In this way, the dual purpose of stopping the solid particles 3 on the mesh 11 and leaving the possibility of the sound flow F2 to cross such a mesh 11 through its free portion 16 is achieved. Therefore, the acoustic insertion loss that would have been caused by the presence of contaminants in the prior art is reduced.

[0075] Thanks to the present invention, it is also possible to make the rectangular mesh 11 with the short side 13 even shorter than the side 5 of the square mesh 4 of the fabric 2 of the prior art, thus further enhancing the protection of the fabric 25 of the present invention from the intrusion of particles. Further considerations regarding the stability of the fabric and the shape of the contaminant particles suggest maintaining the ratio between the size of the short side 13 and the size of the long side 12 of the rectangle within the range between the value of 0.3 and the value of 0.95 (this applies when the smaller size is in both the weft direction and the warp direction).

[0076] As can be seen from this specification, by appropriately sizing the ratio between the long and short sides of the rectangular mesh, a larger opening area can be obtained compared to a square mesh, whereby the size of the short side of the rectangle can be fixed equal to that of the square. For example, when the thread diameter is fixed at 24 μm, a square with a side of 85 μm gives an opening area of 60%, and a rectangle with sides of 85×115 μm gives an opening area of 64%. A gain in the opening area is obtained, and thus a better acoustic permeability with a lower specific airflow resistance (MKSRayls) and a lower acoustic insertion loss (dB insertion loss) is obtained, which is equal to the size of the stopped contaminating particles, the size of the short side of the rectangle is lower than that of the square, and the opening areas are equal. For example, when the thread diameter is fixed at 24 μm, a square with an opening area of 60% has a side of 85 μm, and a rectangle with an opening area of 60% has sides of 70×110 μm. At this point, while maintaining the same opening area, and thus the same air passage and the same sound transmission, even protection against smaller particles (70 microns instead of 85) can be obtained, the size of the short side of the rectangle is smaller than that of the square, and furthermore a larger opening area is obtained. For example, when the thread diameter is fixed at 24 μm, a square with an opening area of 60% has a side of 85 μm, and a rectangle with an opening area of 63% has sides of 110×67 μm (in this example, the configuration of the rectangular mesh is further enhanced by the selection of different thread diameters: 24 microns for the warp and 19 microns for the weft). This type of material presents several advantages in both performance areas, offering protection against smaller particles and a lower specific airflow resistance compared to the prior art square mesh, resulting in better sound transmission with lower losses.

[0077] The figures shown in FIGS. 9, 10a, 10b, 11a, 11b, 11c and 11d are described in detail below to show the better performance allowed by the invention introduced in this specification, and represent the results of various tests performed on two variants of a prior art square mesh fabric 2 and a rectangular mesh fabric 25 of the protective element of the invention.

[0078] In this particular case, the materials for comparison are as follows: - The prior art fabric 2, specifically, a monofilament fabric formed by square meshes each having a size equal to 85×85 μm and a mesh opening area equal to 60%; the material has a yarn density equal to 90×90 threads / cm, a specific airflow resistance in the linear range R(0.2) equal to 6 MKS Rayls, and other characteristics as a result of the measurements referred to in the attached figures; - The fabric 25 of the element of the present invention, in its first exemplary variant called "A", is formed in particular by a synthetic monofilament rectangular mesh fabric made of polyester, each rectangular mesh having a size equal to 85×115 μm and a mesh opening area equal to 64%, and the density is equal to 90×70 threads / cm in both the weft and warp directions, while the specific airflow resistance has a nominal value of 5 MKS Rayls in the linear range; - The fabric 25 of the present invention, in its second exemplary variant called "B", is formed by rectangular meshes each having a size equal to 110×70 μm and a mesh opening area equal to 60%; the density is equal to 75×105 threads / cm, and the specific airflow resistance is equal to 6 MKS Rayls in the linear range.

[0079] For comparison, in order to show the advantages of the present invention introduced herein, the foregoing exemplary material measurements of mesh size, airflow resistance in linear and non-linear ranges, and acoustic performance when the fabric itself is attached to the test speaker have been collected. The implementation details of the above tests are shown below.

[0080] The two-directional mesh opening measurements of 12 and 13 in Figure 6 were performed by microscope and image digital processing. The mesh opening usually corresponds to the size of the stopped contaminant particles. In the case of a rectangular mesh, the fabric can stop particles having a size equal to the smaller of the mesh openings of the weft and warp in 12 and 13 respectively. Such an "effective" value of the mesh opening has been selected as an indicator for the two fabrics A and B which are examples of the embodiments of the present invention. For the prior art square mesh fabric N, the value of the mesh 6 opening in Figure 3 has been reported, which is the same in both the warp and weft directions.

[0081] The histogram of FIG. 9 collects the values of this effective mesh opening for the prior art fabric N and two examples A and B of embodiments of the present invention.

[0082] For the evaluation of the specific air flow resistance through the mesh, a continuous air flow (DC flow) measuring device was used instead, whereby the histograms of FIGS. 10a and 10b described below were generated. FIG. 14 shows an aspiration system 303 that passes a predetermined air flow through a fabric sample 301 and accurately checks the air flow rate by a flow meter 304. The device 300 is integrally configured to clamp the fabric sample 301 between two flanges having a known area (typically 10 - 20 cm 2 ). From the flow measurement value and the known area of the intersection, it is possible to calculate the intersection speed of the sample, usually expressed in m / s.

[0083] During the test, the differential pressure sensor 305 detects the pressure difference between the two sides of the fabric sample 301 having a known area, and from the ratio between this pressure drop (expressed in Pa) and the air flow velocity (expressed in m / s), the specific air flow resistance expressed in unit MKSRayls = Pa / (m / s) is derived.

[0084] Within the linear range, i.e., for the evaluation of the specific air flow resistance R(0.2) of the fabric at a speed equal to 0.2 m / s, a first set of data in FIG. 10a was generated with the considerations reported below.

[0085] For the specific air flow resistance in the non-linear range, i.e., in the case of turbulent flow, the device used is the above-mentioned one, and the parameter used instead is the resistance coefficient R(20), which is the specific air flow resistance measured at an intersection speed passing through a mesh equal to 20 m / s. The lower the value of R(20), the more optimized the fabric is from an acoustic point of view, and the distortion of the sound to be transmitted is limited. FIG. 10b shows a comparison between the R(20) of the prior art fabric N and the data of two Examples A and B of the present invention.

[0086] Regarding the measurement of the acoustic performance energy of the speaker, i.e., SPL, THD, and HOHD, the test system schematically described in FIG. 12 is used. The test system includes a reference speaker module 201 arranged in an anechoic environment 200, and a fabric sample 2 to be tested is applied on the acoustic port of the speaker to compare its effect on the acoustic emission of the speaker. The latter is appropriately driven by an amplifier 202, emits a sine wave with a frequency increasing in the audible frequency range of 100 Hz to 20 kHz, is collected by a reference microphone 203 arranged at a predetermined distance of 30 mm from this sine wave speaker, and is then processed / amplified by an amplifier / conditioner for a dedicated microphone 204. Any input and output signals are subjected to analog-digital conversion (or vice versa) by a dedicated sound card 205 before being analyzed and processed by a management PC 206, and the management PC calculates the quantities SPL, THD, and HOHD / R&B described below with respect to the frequency.

[0087] The sound pressure level (SPL), expressed in decibels (dB re 20uPa), is important for evaluating whether the applied fabric reduces the speaker emission in an acceptable or excessive way. A lower value of the SPL reduction (i.e., "insertion loss") is preferred. FIG. 11a shows the SPL values of interest for three fabrics A, B, and N for comparison with respect to a reference speaker operating at an input frequency equal to 620 Hz, and a higher value of SPL is an indicator of better performance.

[0088] The total harmonic distortion rate (THD) is, instead, a ratio expressed as a percentage between the mean square of all the harmonics generated by the distortion and the original signal (or fundamental wave) input to the device. This is an indicator of how much the original signal is impaired in the acoustic transposition of the electrical signal, due in particular to the presence of the acoustic mesh.

[0089] FIG. 11b reports the normalized values of THD detected for Examples A, B, and N shown in this specification under the above conditions.

[0090] Higher order harmonic distortion (HOHD) is a specific case of distortion where the sum of the harmonics generated by the distortion is calculated from the 10th harmonic forward in the cases considered herein. The quantity under discussion focuses on the highest unwantedly generated harmonic, which is typically an indicator of the fact that, from a mechanical point of view, some components generate vibrations, unwanted friction or impacts, adding noise to the emission of the device, and for this reason this quantity is also defined as Rub&Buzz (R&B). When an alternating air flow (sound wave) crosses the fabric, the fabric vibrates and can also affect this type of distortion.

[0091] Figure 11c shows the evaluation of the normalized HOHD in the conditions and cases detailed herein, including prior art example N and two examples A, B of the invention described herein.

[0092] Finally, for the measurement of the flow noise, a dedicated test schematically shown in FIG. 13 is set up. The dedicated test comprises a high-power reference speaker 207 that emits a strong acoustic volume velocity through a dedicated channel 208 with a slot 209 having a very small size (7.8 mm × 1.2 mm). Below it, the fabric 2 to be tested is placed, and the reference microphone 203 is placed outside the main flow 45 mm from the axis and 15 mm above the plane of the fabric. The remaining equipment comprising amplifiers 202, 204, a sound card 205, and a PC 206 is equivalent to that used for the aforementioned measurements schematized in FIG. 12.

[0093] The input signal to the speaker must be filtered to include only frequencies below 2 kHz because the problem of flow noise relates to higher frequencies instead. Here, the input signal is a sine wave with a fixed frequency (620 Hz), which simplifies the estimation of the cross-acoustic velocity within the fabric and enables the clear separation of the influence of harmonic distortion from that of flow noise during the analysis phase. Subsequently, the collected signal is processed to calculate the Power Spectral Density (PSD) as a function of frequency in order to better understand the causes of distortion and noise changing the waveform. If there is high acoustic power related to frequencies outside the input signal, this means there are noise components adding undesirable energy to the system, which clearly also includes the acoustic fabric located on the speaker channel.

[0094] Calculated in the above way, it is found that the PSD is a good indicator of the quality of the emitted acoustic signal, and it is better when the value of the PSD within the target frequency range is low.

[0095] When applied to a speaker, the fabric optimized to minimize flow noise achieves a lower PSD increment value (referred to as the base level of the speaker without the fabric) compared to a fabric not designed for such a purpose.

[0096] Figure 11d shows the measured PSD increases relative to the base level of the speaker without the fabric, for a conventional fabric N and two examples A and B of embodiments of the present invention.

[0097] Therefore, the superiority of each of the two examples of the embodiments of the present invention when compared to the prior art square mesh fabric is clear from the tests conducted.

[0098] Compared to prior art solutions that have to reach a compromise between protection and acoustic performance, each of the two proposed solutions is an improvement in one of the two performance areas considered herein without sacrificing the other, and it can be seen that the latter maintains results that are the same as or slightly better than those of the prior art.

[0099] For ease of reference, the above data is summarized in the following table.

Table 1

[0100] From this table, it results that the fabric with mesh B provides the greatest protection against the crossing of solid particles without impairing the acoustic performance compared to the prior art fabric N.

[0101] Regarding that part, fabric A provides the best acoustic performance together with protection against solid particles comparable to that of the prior art fabric N against solid particles.

[0102] More specifically, the above results show the following.

[0103] - The new fabric A has the same effective mesh opening as the prior art fabric N (Figure 9) and can stop contaminant particles of similar size, so as a result, it is equivalent in terms of protection. However, at the same time, as proven by direct and indirect measurements, the new fabric is far superior from an acoustic perspective, with low air flow resistance in the linear range (Figure 10a) and non-linear range (Figure 10b), which are better indicators of sound transmission, and guarantees a higher emitted sound pressure (Figure 11a) with lower distortion (Figure 11b and Figure 11c) and lower flow noise (Figure 11d).

[0104] - The new fabric B has a significantly lower mesh opening, so it is significantly superior to the prior art N in terms of protection against contaminants. However, this better performance is not achieved at the expense of acoustic performance, but instead fully matches the performance of the prior art fabric. This is proven by the equivalent values of air flow resistance in the linear (Figure 10a) and non-linear (Figure 10b) ranges, the similar emitted sound pressure (Figure 11a), and the emitted power equivalent to the flow noise (Figure 11d). Regarding other measurements of acoustic performance such as the total harmonic distortion THD (Figure 11b) and especially the higher-order harmonic distortion HOHD (Figure 11c), Example B of the present invention is also an improvement in these areas compared to the prior art.

[0105] Naturally, due to the greater freedom provided by the rectangular mesh solution, as an embodiment of the present invention, it is possible to design other products that ensure a more balanced improvement in both the protection characteristics and sound transmission characteristics that are impossible in any case with the prior art square mesh acoustic fabrics.

[0106] The fabric of the protection element of the present invention may also be manufactured from threads of artificial polymers belonging to the group consisting of cellulose or viscose, and is preferably coated with a hydrophobic or hydrophobic / oil-repellent coating.

[0107] Furthermore, the mesh size of the fabric serves to vary in one or both directions of the weft and warp, and it is also possible to provide yarns of different properties and / or different sizes in either the same direction or different weft and warp directions.

Claims

1. A fabric-based protective element against the ingress of contaminant particles and water spray into the acoustic components of an electronic device for consumers, comprising a synthetic monofilament open mesh fabric (25), wherein said mesh (11) has a rectangular shape, and the sides (12, 13) of the rectangle are each composed of respective threads (26, 27), characterized in that it is a protective element.

2. The fabric (25) with the open mesh (11) has an asymmetric structure with respect to the number of threads per centimeter and / or the diameter of the threads in two directions of the weft and warp threads, characterized in that it is the protective element according to Claim 1.

3. The ratio between the linear densities / cm in the respective directions of the weft and warp threads of the fabric is in the range between 0.4:1 and 2.5:1, characterized in that it is the protective element according to Claim 2.

4. The ratio between the diameter of the warp threads and the diameter of the weft threads of the mesh (11) is in the range between 0.5:1 and 2:1, characterized in that it is the protective element according to Claim 2.

5. The mesh (11) has rectangular openings, and the dimension ratio of the short side to the long side is in the range between 0.3 and 0.9 regardless of whether the short side is in the direction of the weft or the warp threads of the fabric, characterized in that it is the protective element according to any one of Claims 1 to 3.

6. The short side of the mesh (11) is in the range from 5 μm to 150 μm, characterized in that it is the protective element according to any one of Claims 1 to 3.

7. The fabric is a monofilament fabric, and the monofilament has a diameter in the range from 10 μm to 90 μm, characterized in that it is the protective element according to any one of Claims 1 to 3.

8. The fabric is made of threads made of a synthetic technopolymer belonging to the group consisting of polyester, polyamide, polyaryletherketone, polyphenylene sulfide, polypropylene, perfluorocarbon, polyurethane, or polyvinyl chloride, characterized in that it is the protective element according to Claim 7.

9. The fabric is made of threads made of an artificial polymer belonging to the group consisting of cellulose or viscose, characterized in that it is the protective element according to Claim 7.

10. The fabric is coated with a hydrophobic or hydrophobic / oil-repellent coating, characterized in that it is the protective element according to Claim 8 or 9.

11. The protective element according to any one of claims 1 to 3, wherein the size of the mesh is variable in one or both of the directions of the weft yarn and the warp yarn.

12. The protective element according to claim 11, characterized in that it provides yarns having different properties and / or different sizes in the same direction or in any of different weft and warp directions.

13. An acoustic component of a consumer electronic device, characterized in that it consists of a microspeaker for a smartphone, a tablet, etc., comprising at least one protective element according to one or more of claims 1 to 12.

14. Use of a fabric (25) having a rectangular shape and an open mesh (11) made of a synthetic monofilament fabric, characterized in that the rectangular sides (12, 13) are each composed of respective yarns (26, 27), for a protective filter of an acoustic component of an electronic device.

15. The use according to claim 14, characterized in that the mesh (11) has an asymmetric structure that is diversified in each direction with respect to the linear density / cm of the weft and warp of the mesh and / or is diversified with respect to the diameter of the warp and the diameter of the weft of the mesh (11) itself.

16. The use according to claim 15, characterized in that the mesh (11) has a rectangular opening, and the dimension ratio of the short side to the long side is in the range between 0.3 and 0.9 regardless of whether the short side is in the direction of the weft or the warp of the fabric.

17. The use according to claim 16, characterized in that the short side of the mesh (11) is in the range from 5 μm to 150 μm.

18. The use according to claim 15, characterized in that the fabric is a monofilament fabric and the monofilament has a diameter in the range from 10 μm to 90 μm.

19. The use according to claim 18, characterized in that the fabric is made of yarns made of a synthetic technopolymer belonging to the group consisting of polyester, polyamide, polyaryletherketone, polyphenylene sulfide, polypropylene, perfluorocarbon, polyurethane, or polyvinyl chloride.

20. The use according to claim 18, characterized in that the fabric is made of yarns made of an artificial polymer belonging to the group consisting of cellulose or viscose.

21. The use according to claim 15, characterized in that the fabric is coated with a hydrophobic or hydrophobic / oil-repellent coating.

22. The use according to claim 15, characterized in that the size of the mesh is variable in one or both of the directions of the weft and the warp.

23. The use according to claim 22, characterized in that yarns having different properties and / or different sizes are provided in the same direction or in any of different weft and warp directions.

24. Use of the fabric according to any one of claims 1 to 23 for the manufacture of an acoustic component of a consumer electronic device for protecting a speaker and acoustic components from the ingress of solid and / or liquid contaminants, wherein a primary or secondary acoustic flow directly crosses the fabric.

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