Improved textile protective element for use in an acoustic component of an electronic device and acoustic component internally

Abstract

A protective element for a consumer electronic device provided with at least one port (101) for an acoustic component (104) and a channel (105), where the port (101) or the channel (105) has a protective fabric against intrusion of contaminant particles and water spray. According to the invention, the fabric (25) has meshes (11) of rectangular shape, the sides (12, 13) of which are made of respective threads (26, 27). The fabric forming the protective element of the present invention provides the advantage of providing an increased protective capability against contamination particles compared to prior art square mesh fabrics having comparable air passage and sound transmission characteristics.

Description

Background of the Invention

[0002] The present invention relates to a protective element made of high-performance textiles which is particularly suitable for use in acoustic components (typically micro-speakers) of consumer electronic devices (typically smartphones and tablets) in order to perform the functions of protection against particulate matter and water spray and to achieve optimal sound transmission due to its specific structure.

[0003] Electronic devices endowed with acoustic functions, such as smartphones, are provided with small openings on their housings, located at acoustic components such as speakers and microphones, through which sound waves can be transmitted. However, these openings, which are required in almost all cases, involve the risk that some external contamination particles may penetrate into the device and be harmful. This is true for both solid particles that may accumulate on the speaker diaphragm and hinder its free movement, and for water droplets generated by sprays that may in some cases impair the functioning of the electronic device. It is therefore necessary to block these contaminants at the acoustic ports of the device without allowing them to enter the interior of the device.

[0004] For this purpose, it is known to use filters known as "die-cut components" which comprise a precision technical filter medium, in the most common case a square mesh monofilament fabric, in which the size of the individual meshes is uniform in space and time, so as to have a reasonable certainty of stopping any solid particles having a size greater than the characteristic size of the meshes (all equal to each other). For this purpose, the known square mesh synthetic monofilament precision technical fabrics are an ideal medium for this application.

[0005] With regard to the size of such square mesh technical fabrics, the requirement is to block solid particles of the most common sizes. As we will see below, a typical square mesh monofilament fabric of the prior art is able to block solid particles of a size greater than or equal to its mesh opening value. The latter usually ranges between 20 microns and 100 microns, depending on the sensitivity of the loudspeaker to contamination (which will require a lower micron value), and the manufacturer's emphasis on good sound transmission (which in turn will require a fabric that is as open as possible).

[0006] From all of the above, the limitations of the existing technology have emerged. In fact, there is currently no optimal design of fabrics that simultaneously ensures the best possible protection and sound transmission without distortion problems.

[0007] With regard to acoustic requirements, there are several factors that will drive the use of fabrics that are as open as possible.

[0008] Firstly, a protective fabric that is too closed reduces the sound emission to unacceptable levels. The small speakers of smartphones, considering their size, are very powerful and they reach sound pressure (SPL) values ​​of >100dB at a distance of 30mm; today, no manufacturer would accept an excessive reduction in performance, so a very open and "acoustically transparent" fabric is required, which is obviously not conducive to protection.

[0009] Furthermore, there are strict requirements on the sound quality, which by far has to be optimal, not only powerful, but even with the lowest distortion. However, it should be said that, for the needs of aesthetic design, the speaker ports of smartphones and tablets are usually very small (a few holes with a diameter that typically ranges between 1 mm and 1.5 mm): very high sound velocities (>10 m / s) are therefore generated through such openings, which occur in the non-linear range and are the cause of undesirable harmonic distortions of the acoustic signal throughout the fabric, in terms of THD (Total Harmonic Distortion), or HOHD (High Order Harmonic Distortion), or R&B (Hot and Buzz). All these acoustic quantities (which will be better described below) are indicators of the sound quality and must be minimized in order to meet the common standards in the industry in this field. Typical requirements are: THD < 5%, HOHD / R&B < 0.4%.

[0010] Among them, in smartphones, micro speaker protection becomes increasingly critical due to the following reasons:

[0011] 1. Increasingly powerful micro-speakers, in which the diaphragm excursion is already significantly higher than 0.5 mm, whereby the air volume set in motion is very high and a very open mesh is required in order to ensure a correct sound transmission.

[0012] 2. The micro speakers are equipped with very strong magnets in order to achieve the above-mentioned high powers. The strong magnetic field generated has the risk of attracting metal particles present in the environment into the interior of the speaker, so a protective mesh is needed to ensure improved protection against particles compared to the past.

[0013] 3. Smaller and smaller acoustic ports (think of the smallest gap left between the display and the phone casing, with a total area of ​​only a few square millimeters), produce higher and higher sound speeds, and therefore this requires perfectly optimized acoustic fabrics in order to keep the sound output quality under control.

[0014] Specific tests are performed in order to evaluate the acoustic properties of each mesh that will affect the sound emission of the device in which the mesh is inserted. These measurements can be those of fluid dynamic properties performed on the fabric itself, or actual acoustic tests performed on a test speaker that contains the acoustic fabric in question inside.

[0015] The measurement of specific airflow resistance belongs to the first group and is the basic parameter that quantifies the resistance of a fabric to the passage of sound waves. This force opposing the airflow generated by the sound waves has proven to be the source of the previously mentioned harmonic distortion. The resistance is an intensive 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. The resistance is usually expressed by the measurement unit MKS Rayleigh = [Pa / (m / s)].

[0016] As is known, this quantity depends on the air velocity through the fabric; when the latter becomes too high, typically exceeding 1 m / s, the dependency is no longer linear. In most applications of microspeakers in consumer electronic devices (smartphones and tablets), the acoustic mesh is subjected to a throughflow significantly above the linear range of the specific acoustic resistance. It is therefore necessary to measure the extent to which the mesh modifies the acoustic signal at high sound speeds in order to estimate the acoustic distortion that the mesh may introduce into the device.

[0017] Therefore, a dedicated test provides for measuring the specific resistance by applying a traversal velocity that is high and extends even into the non-linear range, up to values ​​of 30m / s-40m / s. The curve of the resistance as a function of the velocity shows the slope characteristic of the material tested. The lower this slope, the closer the curve is to linearity, the less distortion of the acoustic signal the acoustic mesh will produce. It is therefore obvious that low resistance values ​​in the non-linear range will be preferred and will be an indicator of the quality of the mesh used to protect the acoustic components of an electronic device.

[0018] The tests and parameters just described are indicators of the acoustic properties of the acoustic mesh that will affect the performance of the device to which it is applied. The evaluation of the performance level of the device is replaced by other types of tests performed directly on the final component, in this case a loudspeaker (or micro-speaker) on which the acoustic and protective meshes are mounted.

[0019] Examples of these measurements are the quantities SPL, THD and HOHD / R&B already mentioned above and they are measured by a single test, usually performed on a reference model of the micro-speaker and representative of the application under consideration, including the installation of the acoustic mesh.

[0020] In relation to the already mentioned case of very high performance loudspeakers generating particularly high air velocities, it is also necessary to analyse how the fabric affects the generation of flow-induced noise ("flow noise") by the device. In particular, we are talking about the broad spectrum noise generated by the air jet emitted at high speed from the external port of the loudspeaker, which can be measured by separate dedicated tests.

[0021] All of this requires that the acoustic mesh has a high open area in order to minimize the material's resistance to the passage of air, which has the advantage of reducing both acoustic insertion losses and sound distortion. At the same time, the mesh itself must also ensure adequate protection of the acoustic components and therefore have an appropriately limited mesh size.

[0022] In summary, there is a need to reduce the mesh opening size while maintaining the void / full ratio, i.e. the open area of ​​the fabric, so as not to compromise the acoustic performance. For the prior art square meshes, these two conflicting requirements are only partially met, as we will now see.

[0023] In order to reduce the mesh size, two possible ways are adopted. The first way offers the possibility of inserting an increasing number of fabric threads, the diameter being fixed. Alternatively, the second way offers the use of the same number of threads, but with a higher thread diameter. It is obvious that in both cases the empty / full ratio will decrease and the air passage and acoustic properties of the fabric will be impaired. Therefore, in order to obtain a mesh of smaller size while keeping the empty / full ratio constant, it is intuitively considered that the only possible way consists in using an increasing number of threads, but at the same time with increasingly smaller thread diameters. This third way is obviously ideal, however, shows two limitations:

[0024] 1. Technical limitations in yarn processing, whereby it is not possible to extrude monofilaments below a certain diameter, or even to weave them;

[0025] 2. Technical limitations during the weaving process, whereby it is not possible to increase the number of threads per cm above a fixed threshold. In some cases, where the application leads to high protection requirements and requires a mesh with particularly small dimensions, the use of threads of smaller diameter may make a construction with many threads impossible to achieve.

[0026] It is therefore obvious that the conventional choice mentioned above, namely the choice of reducing the mesh size, necessarily also involves the disadvantage of reducing the open area of ​​the mesh itself. Therefore, when the square mesh of the prior art is too narrow, the speed of sound passing through the square mesh becomes too high, with such negative effects on the performance of the loudspeaker as acoustic insertion losses through the fabric itself (even if we are talking about a new and not yet contaminated fabric), and acoustic distortion phenomena: THD (Total Harmonic Distortion), HOHD (Higher Order Harmonic Distortion) as well as grating and buzzing. In the case of particularly good loudspeaker performances and high speed of sound through the mesh, even undesirable "flow noise" effects may occur, i.e. the generation of a broad spectrum of noise, which further reduces the quality of the acoustic emission. Moreover, the above-mentioned effects are even more severe when the square mesh of the prior art becomes partially contaminated as a result of its use, and these effects may easily render the entire device unusable.

[0027] In summary, we conclude that the choice of the best square mesh acoustic fabric of the prior art always constitutes a compromise: very closed fabrics are good for protection, but they perform poorly in terms of sound transmission (even if the fabric is new and not contaminated); alternatively, more open fabrics provide acceptable "acoustic transparency", but they exhibit mesh openings that are too large and cannot effectively block all pollutant particles.

[0028] Publication WO 2011 / 132062 A1 discloses a two-layer textile construction in which there is a laminated continuous membrane which has a waterproofing function against the intrusion of water into the acoustic components of an electronic device.

[0029] WO 2010 / 124899 A1 relates to a system for producing a filter consisting of a composite textile material.

[0030] Publication WO 2017 / 134479 A1 relates to composite multilayer structures that can be used as subcomponents in electronic and acoustic articles.

[0031] WO 2005 / 039234 A2 discloses a protective structure comprising a stamped metal foil. SUMMARY OF THE INVENTION

[0033] The main object of the present invention is to provide a protection element made of high performance synthetic monofilament fabric or woven mesh, which serves as protection for speakers present in electronic devices and smartphones.

[0034] In particular, the object of the present invention is to provide a protective element made of a fabric of the type mentioned above, which, unlike the fabrics of the prior art, exhibits an increased ability to block solid particles at the same acoustic performance, or, alternatively, exhibits improved acoustic properties (i.e. lower acoustic insertion loss and lower distortion) at the same particle protection ability as the prior art.

[0035] These and other objects are achieved by the element of the invention according to claim 1. Some preferred embodiments of the invention result from the remaining claims.

[0036] Compared to square mesh fabrics of the prior art having comparable air-passage and sound-transmission properties, the protective element of the invention offers the advantage of exhibiting an increased protection capability against polluting particles.

[0037] The element of the invention exhibits improved sound transmission properties relative to prior art fabrics with regard to protection against solid contaminants, which improves the acoustic performance of the component in which it is installed.

[0038] Naturally, for each application of a micro-speaker inside an electronic device, it is possible to choose a fabric structure better suited to the purpose and to obtain partial improvements both in the first area (better protection) and in the second area (better sound transmission), and in any case overall to a greater extent than the prior art allows.

[0039] The fabric of the element of the present invention can be made by weaving monofilament or multifilament synthetic material.In its best form, the fabric of the present invention is made using monofilament.

[0040] The material from which the starting monofilaments or multifilaments are made may be a synthetic technical polymer belonging to the family consisting of polyesters, polyamides, polyaryletherketones, polyparaphenylene sulphides, polypropylenes, perfluorocarbons, polyurethanes or polyvinyl chlorides. Alternatively, the base monofilament or multifilament material from which the fabric of the element of the invention is made may be a man-made polymer belonging to the family consisting of cellulose or viscose fibers.

[0041] Whenever optimum protection not only against solid particles but also against liquid splashes is desired, the fabrics of the invention may be provided with a hydrophobic and / or hydrophobic-oleophobic treatment of fluorocarbon or silicone nature or other types.

[0042] The monofilaments making up the fabric of the invention may have diameters ranging from 10 to 90 μm, preferably from 17 to 40 μm, in both the warp and weft directions.The fabric of the invention may be made from textile structures requiring a thread count ranging from 23 to 350 threads per cm.

[0043] The fabric can be manufactured with different textile structures and it can be made using threads with different properties or different diameters in the weft and warp.The mesh openings of the fabric of the invention can have a short side in the range from 5 μm to 150 μm.

[0044] It should be particularly noted that in the textile configurations of the prior art defined as "Tressen", "Reps" or "Dutch weave", the short side / long side size ratio of the mesh openings is always below 0.25, which is the condition in which saturation occurs, i.e. contact between threads extending parallel to each other.

[0045] In contrast, the present invention (in which the above-mentioned dimensional ratio is between 0.3 and 0.9) is designed to maximize the cross-section of the airflow (and therefore also the acoustic flow) orthogonal through the material, minimizing the insertion loss in decibels, while with the prior art fabrics it is only necessary to minimize the size of the pores through which the fluid passes, particularly for filtration applications in which load losses through the filter are not a problem.

[0046] Thus, in prior art fabrics defined as "Tressen", "Reps" or "Dutch weave", the threads in one of the two directions are adjacent to each other, reaching a so-called "saturation" leaving only minimal passage openings, suitable for ensuring extreme filtering capabilities, but at the same time generating very high load losses, which are absolutely unacceptable if it is planned to transpose the same textile configuration into an acoustic product with the intention of minimizing decibel losses ("insertion losses"). BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above objects, advantages and features result from the following description of some preferred embodiments of the elements of the invention provided by way of non-limiting examples in the figures of the accompanying drawings.

[0049] in:

[0050] - Figure 1 A typical smartphone is shown with its acoustic port highlighted and the fabric of the present invention positioned at the speaker;

[0051] - Figure 2 By way of example, a cross section of a conventional smartphone equipped with the fabric protection element of the present invention is shown, taken at the acoustic port of the lower speaker;

[0052] - Figure 3 , Figure 4a and Figure 4b The square mesh of the fabric of the prior art is shown;

[0053] - Figure 5 Diagram showing the Figure 3 The mesh;

[0054] - Figure 6 , Figure 7a and Figure 7b The rectangular mesh of the fabric protection element of the present invention is illustrated;

[0055] - Figure 6a and Figure 6c Represents a portion of a prior art filtering open mesh monofilament fabric used as a basis for comparison with a corresponding embodiment of the fabric of the protective element of the present invention;

[0056] - Figure 6b and Figure 6d Two different embodiments of the open mesh monofilament fabric of the present invention are shown as examples and are respectively Figure 6a and Figure 6c The fabrics of the prior art are compared;

[0057] - Figure 8 Diagram showing the Figure 6 The mesh;

[0058] - Fig. 9 A comparison of mesh opening values ​​between a prior art fabric and two possible embodiments of the fabric of the present invention is shown;

[0059] - Fig.10a Shows Fig. 9 Comparison of the specific flow resistance R(0.2) values ​​of the three fabrics under linear conditions (travel velocity = 0.2 m / s);

[0060] - Fig.10b Shows Fig. 9 Comparison of the specific flow resistance R(20) values ​​of the three fabrics under nonlinear conditions (travel velocity = 20 m / s);

[0061] - Fig.11a shows a comparison between the sound pressure (SPL) values ​​emitted by a reference speaker with each of the three aforementioned fabrics inserted;

[0062] - Fig.11b shows a comparison between the total harmonic distortion (THD) values ​​of the transmitted signal relative to the input frequency of the reference loudspeaker, in which each of the three aforementioned fabrics is inserted and normalized relative to a baseline measured without the fabric;

[0063] - Fig.11c shows a comparison between the high-order harmonic distortion (HOHD) values ​​of the transmitted signal relative to the input frequency of the reference loudspeaker, in which each of the three aforementioned fabrics is inserted and normalized relative to a baseline measured without the fabric;

[0064] - Fig.11d shows a comparison of the increase in the values ​​of the power spectral density (power spectral density, PSD) of the undesired sound, relative to a baseline, measured without the fabric, emitted outside the desired frequencies, i.e. as flow noise, measured by a reference loudspeaker with each of the three aforementioned fabrics inserted;

[0065] - Fig.12 Schematically illustrates the Fig.11a , Fig.11b , Fig.11c Components for acoustic testing as mentioned in;

[0066] - Fig.13 Schematically illustrates the Fig.11d Components for acoustic testing as mentioned in;

[0067] - Fig.14 Schematic illustration of the components of a typical apparatus for measurements in a continuous gas flow, for testing Fig.10a and Fig.10b The specific flow resistance mentioned in .

[0068] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] exist Figure 1 In the example of FIG. 1 , the smartphone 100 is provided with an acoustic port 102 at the upper speaker, which is named "receiver" and is used to transmit sound to the user's ear during listening on the phone, and to emit stereo sound in the environment (when the smartphone also provides this function). A second set of openings 101 allows the emission of sound from the lower speaker ("loudspeaker") for listening on the speakerphone, for audio playback and for ringtones. Typically in smartphones, there are also other openings 103 for microphones, pressure sensors or vents to allow internal pressure equalization in waterproof devices.

[0070] Figure 2 A typical arrangement of components inside a smartphone is shown in cross section at the port 101 of a lower speaker or "microphone" 104. The lower speaker or "microphone" 104 communicates with the external environment through a narrow passage 105 terminating in the acoustic port 101.

[0071] In another embodiment, the speaker of a prior art smartphone is protected from the intrusion of polluting particles 3 and water spray by a forming element 2 made of a square mesh synthetic monofilament fabric, which is inserted between the acoustic port 101 and the channel 105, or locked into the channel itself.

[0072] In use, the fabric forming element 2 needs to ensure the correct passage of the sound waves generated by the loudspeaker 104 (flow F2, alternating in two directions according to the characteristics of the acoustic signal), but at the same time the fabric must prevent the risk of contaminant particles reaching the loudspeaker itself (flow F1, from the outside to the inside of the smartphone).

[0073] exist Figure 3 , Figure 4a and Figure 4b In the prior art illustrated in FIG. 1 , the mesh 4 of the fabric 2 is square and is composed of threads 5 forming respective sides 6 of the square mesh 4 .

[0074] The open area of ​​the mesh 4 itself of the prior art is calculated as the percentage between the surface of the smaller square 7 included between the contours or inner edges of the wires 5 forming the sides 6 of the mesh 4 and the surface of the larger square 8 ( Figure 4a ), the surface of the larger square 8 is measured to the center line of the line 5 itself ( Figure 4b ).

[0075] During the use of the electronic device in a dirty environment, the mesh 4 of the prior art is exposed to the intrusion F1 of pollutants, which causes the interception of particles 3 of pollutants, which generally have a diameter comparable to the length of the side 6 of the square mesh itself; therefore, the openings of the square mesh are blocked, leaving only a small part 10 of the surface of the smaller square 7 of the mesh 4 for the passage of sound waves ( Figure 5 and Figure 4a ).

[0076] As a result of the clogging of the mesh of the prior art fabrics, higher load losses usually occur in the traversing fabric itself, leading to a degradation of the loudspeaker performance: higher "insertion losses" and radiated sound pressure losses, harmonic distortion (THD) or hum and buzz (R&B) phenomena. The final result depends on the severity of the contaminants received, but in many cases this is not only a tangible phenomenon, but can also completely impair the use of the device within 1-2 years.

[0077] In addition to all of the above, the choice of the best square mesh acoustic fabric (i.e. the fabric of the state of the art) is always the result of a compromise, even if only the performance of new and not yet contaminated fabrics is considered. A fabric is described by its mesh opening value (in terms of protection) and by a specific flow resistance value (measured in MKS Rayleigh) as an indicator of its acoustic transparency: these two quantities behave in opposite ways with the variation of the linear density per cm, so minimizing both of them would not be possible. In fact, giving priority to protection against solid particles, a particularly closed technical fabric should be chosen, and therefore poorly performing in terms of sound transmission, which is already like new, without contamination; on the contrary, when choosing a material with a very low specific flow resistance and therefore excellent "acoustic transparency", then we are forced to accept mesh opening values ​​that do not guarantee adequate protection against solid contaminants.

[0078] In order to overcome these disadvantages of the prior art, the protective element of the present invention is made of a fabric 25 having a rectangular mesh 11 with a long side 12 and a short side 13 ( Figure 6 ). In the figures a rectangular mesh is shown, in which the long sides are arranged in the weft direction, but this is not restrictive: the invention also provides the opposite configuration, in which the long sides are arranged in the warp direction.

[0079] The fabric 25 can be manufactured with different open mesh textile structures, having the common property of being asymmetric in both the weft and warp directions, in particular with respect to the thread density and / or thread diameter per centimeter. Thus, the number density of the weft threads will differ from the number density of the warp threads and / or the weft threads will differ from the warp threads in terms of thread diameter or yarn properties.

[0080] Thus, it is possible to produce a fabric of the invention having a rectangular mesh, in particular according to the construction parameters of thread density, thread diameter and mutual balancing of the threads in an asymmetric configuration.

[0081] To this end, the ratio between the linear density / cm of the weft and warp of the mesh 11 in the corresponding directions is preferably in the range between 0.4:1 and 2.5:1. In addition, preferably, the ratio between the warp diameter and the weft diameter of the mesh 11 is in the range between 0.5:1 and 2:1.

[0082] Figure 6a The diagram shows a portion of a prior art fabric 41 having the same thread density per cm (N1) for both the warp (vertical in the figure) and the weft (horizontal in the figure). Furthermore, it has the same thread diameter value (d1) for both the warp and weft. The open mesh 7 is square and the mesh openings 6 have the same value in both directions ( Figure 6a ).

[0083] exist Figure 6b In the example of FIG. 1 , a possible embodiment of the fabric 25 of the protective element according to the invention is instead proposed, in which only the diameters of the warp and weft threads differ from one another. Thus:

[0084] - the number of warp threads per cm according to the invention (N1, Figure 6b The vertical line in Figure 6a The warp of the prior art is the same.

[0085] - the number of weft threads per cm according to the invention (N1, Figure 6b The horizontal line in Figure 6a The weft of the prior art is the same.

[0086] - the diameter of the warp threads according to the invention (d1, Figure 6b The vertical line in Figure 6a The warp of the prior art is the same.

[0087] - the diameter of the weft thread according to the invention (d2, Figure 6b The horizontal line in the figure is instead smaller than the diameter of the warp thread according to the invention (d1, Figure 6b )and Figure 6a The diameters (d1) of the threads of the prior art fabric in both directions.

[0088] Figure 6c A portion of a prior art fabric 41 is shown having the same thread density per cm (N1) and the same thread diameter (d1) for both the warp threads (vertical in the figure) and the weft threads (horizontal in the figure). The material is therefore completely symmetrical.

[0089] exist Figure 6dIn , a possible embodiment of a fabric 25 for forming a protective element according to the invention is instead proposed, in which only the densities per cm of the corresponding warp threads and for the weft threads differ from one another. Thus:

[0090] - Number of warp threads per cm (N1, Figure 6d The vertical line in Figure 6c The number of warp threads per cm of the prior art fabrics is the same.

[0091] - the number of weft threads per cm according to the invention (N2, Figure 6d The horizontal line in the middle) is lower than the number of warp threads per cm according to the present invention (N1, Figure 6d ) and is lower than the number of threads per cm of prior art fabrics (N1 in both directions, Figure 6c ).

[0092] - the diameters (d1, Figure 6d The vertical and horizontal lines are identical to each other and equal to Figure 6b The corresponding value of the prior art.

[0093] The open area of ​​the mesh 11 is calculated as the percentage between the surface of the smaller rectangle 14 measured between the outlines or edges of the lines 26, 27 facing the interior of the mesh 11 and forming its respective sides, and the surface of the larger rectangle 15 ( Figure 7a ), the surface of the larger rectangle 15 is measured to the center line of the aforementioned lines 26, 27 ( Figure 7b ). The sides of the rectangular mesh of the fabric of the invention are such that the ratio between the short side and the long side is in the range between 0.3 and 0.95. This applies both to the case where the short side of the mesh is in the weft direction and in the warp direction: these options are covered by the invention.

[0094] When a particle 3 of a pollutant coming from the outside and having a diameter comparable to the length of the short side 13 of the rectangular mesh 11 itself hits the mesh 11 of the fabric 25, the opening of the mesh 11 is not completely blocked as in the case of the known mesh 4 having a square shape, but a large part 16 of the opening area of ​​the mesh 11 itself is left for the passage of the acoustic stream ( Figure 8 ).

[0095] In this way, the dual purpose of retaining the solid particles 3 on the meshes 11 and making it possible for the acoustic flow F2 to pass through such meshes 11 through their free portions 16 is achieved. The acoustic insertion losses are thus reduced, which otherwise would be caused by the presence of polluting substances in the prior art.

[0096] Thanks to the invention, it is also possible to have rectangular meshes 11 with short sides 13 that are even shorter than the sides 5 of the square meshes 4 of the prior art fabric 2, in this way further increasing the protection of the fabric 25 of the invention against particle intrusion. Additional considerations related to the stability of the fabric and the shape of the pollutant particles suggest keeping the ratio between the dimensions of the short sides 13 of the rectangle and the dimensions of the long sides 12 within a range between values ​​0.3 and 0.95 (this applies both when the smaller dimension is in the weft direction and in the warp direction).

[0097] It can be seen from this description that by appropriately determining the ratio between the long side and the short side of the rectangular mesh, it is possible to obtain:

[0098] - A larger open area compared to a square mesh (fixing the size of the short side of the rectangle equal to that of the square). For example, fixing the diameter of the wire equal to 24 μm, an open area of ​​60% is obtained for a square with sides equal to 85 μm, while for a rectangle with sides 85×115 μm, an open area equal to 64%. An increase in the open area is obtained, and therefore a better acoustic transparency, with a lower specific flow resistance (MKS Rayleigh) and a lower acoustic insertion loss (dB insertion loss), equal to the size of the pollutant particles stopped;

[0099] - the size of the short side of the rectangle is smaller than that of the square (opening area is equal). For example, when the diameter of the wire is fixed equal to 24 μm, the side of the square with an opening area equal to 60% is equal to 85 μm, while the side of the rectangle with an opening area equal to 60% is equal to 70×110 μm. In this case, it is possible to obtain protection even against smaller particles (70 microns instead of 85 microns) while maintaining the same opening area and therefore the same air passage and the same sound transmission;

[0100] - The dimensions of the short sides of the rectangle are smaller than those of the square, and the rectangle has even greater open area; for example, when the diameter of the wire is fixed equal to 24 μm, the side of the square with an open area equal to 60% is equal to 85 μm, while the side of the rectangle with an open area equal to 63% is equal to 110×67 μm (in this example, the rectangular configuration of the mesh is further enhanced by the choice of different wire diameters: 24 microns in the warp direction and 19 microns in the weft direction). This material will present some advantages in two performance areas: protection even against smaller particles and lower specific flow resistance compared to the square mesh of the prior art, resulting in better sound transmission and lower losses.

[0101] Fig. 9 , Fig.10a , Fig.10b , Fig.11a , Fig.11b , Fig.11c and Fig.11dThe diagrams shown in represent the results of various tests which are described in detail below and which were carried out on a square mesh fabric 2 of the prior art and on two variants of a rectangular mesh fabric 25 of a protective element according to the invention in order to illustrate the improved performance allowed by the invention presented here.

[0102] In this specific case, the material objects being compared are as follows:

[0103] a fabric 2 of the prior art, in particular a monofilament fabric formed of square meshes, each of which has dimensions equal to 85×85 μm and a mesh opening area equal to 60%; a material having a thread density equal to 90×90 threads / cm, a specific flow resistance R(0.2) in the linear range equal to 6 MKS Rayleigh, and other characteristics resulting from the measurements mentioned in the accompanying drawings;

[0104] - the fabric 25 of the element of the invention, in its first exemplary variant, designated "A", is formed of a synthetic monofilament rectangular mesh fabric, in particular made of polyester, wherein each rectangular mesh has dimensions equal to 85×115 μm and a mesh open area equal to 64%; the density in both the weft and warp directions is equal to 90×70 threads / cm, while the specific flow resistance in the linear range has a nominal value of 5 MKS Rayleigh;

[0105] - The fabric 25 of the invention, in its second exemplary variant, called "B", is formed by rectangular meshes each having dimensions equal to 110×70 μm and a mesh open area equal to 60%; a density equal to 75×105 lines / cm and a specific flow resistance equal to 6 MKS Rayleigh in the linear range.

[0106] By comparison, in order to show the advantages of the invention presented herein, measurements of mesh size, airflow resistance in linear and nonlinear ranges, and acoustic performance when the fabric itself was mounted on a test speaker were collected on the exemplary materials mentioned above. In the following, the execution details of the tests mentioned above are provided.

[0107] exist Figure 6 The measurements of the mesh openings in the two directions 12 and 13 in the have been made by means of a microscope and digital processing of the images. The mesh opening generally corresponds to the size of the pollutant particles that are blocked; in the case of a rectangular mesh, the fabric is able to block particles of a size equal to the smaller of the mesh openings in the weft and warp directions, which are 12 and 13 respectively. Such "effective" values ​​of the mesh openings have been chosen as indicators for two fabrics A and B (examples of embodiments of the invention), whereas for a square mesh fabric N of the prior art, it has been reported Figure 3 The value of the opening of the mesh 6 is the same in both the warp and weft directions.

[0108] Fig. 9 The histogram collects the values ​​of the effective mesh opening for a prior art fabric N and two examples A and B of an embodiment of the present invention.

[0109] To evaluate the specific flow resistance through the mesh, a continuous air flow (DC-flow) measurement device was used instead, which produced the following Fig.10a and Fig.10b Histogram of . Fig.14 The apparatus 300 is generally described as being intended to clamp a fabric sample 301 in a tube having a known area (typically 10 cm) by means of a suction system 303. 2 -20 cm 2 ), the suction system 303 passes a predetermined air flow through the fabric sample 301, the flow rate of which is accurately checked by means of a flow meter 304. Then, from the flow measurement results and the known area of ​​the traversed cross section, the traversal speed of the sample can be calculated, usually expressed in m / s.

[0110] During the test, the differential pressure sensor 305 detects the pressure difference between the two sides of the fabric sample 301 with a known area; from the ratio between this pressure drop (expressed in Pa) and the air flow velocity (measured in m / s), the specific flow resistance is then derived, expressed in units of MKS Rayleigh = Pa / (m / s).

[0111] The first set of evaluations of the fabric's specific flow resistance R(0.2) in the linear range (i.e., at a velocity of 0.2 m / s) yielded Fig.10a The data are reported below.

[0112] For the specific flow resistance in the non-linear range (i.e. turbulent specific flow resistance), the equipment used is that described above and the parameter used is instead the drag coefficient R(20), i.e. the specific flow resistance measured at a traversal velocity through the mesh equal to 20 m / s. The lower the value of R(20), the more optimized the fabric will be from an acoustic point of view and R(20) will limit any distortion of the sound to be transmitted. Fig.10b A comparison between the data of R(20) for a prior art fabric N and two examples A and B of the present invention is shown.

[0113] Regarding the measurement of the acoustic performance of a loudspeaker (i.e. SPL, THD and HOHD), the Fig.12The test system schematically described in . The test system comprises a reference loudspeaker module 201 located in an anechoic environment 200; a fabric sample 2 to be tested is applied to the acoustic port of the loudspeaker in order to compare its effect on the acoustic emission of the loudspeaker. The acoustic emission of the loudspeaker is appropriately driven by an amplifier 202, emitting a sine wave with gradually increasing frequency in the audible sound range 100Hz-20kHz, which is collected by a reference microphone 203 located at a given distance of 30mm from the loudspeaker and then processed / amplified by an amplifier / conditioner of a dedicated microphone 204. Any input and output signal undergoes analog-to-digital conversion (or vice versa) through a dedicated sound card 205 before being analyzed and processed by a management PC 206, which calculates the quantities of SPL, THD and HOHD / R&B with respect to frequency, as described below.

[0114] The Sound Pressure Level (SPL), expressed in decibels (dB re 20uPa), is important for assessing whether the applied fabric reduces the loudspeaker emissions in an acceptable or excessive manner. Lower values ​​of the reduction in SPL (ie "insertion loss") are preferred. Fig.11a The SPL values ​​of three comparative fabrics A, B and N are shown relative to a reference loudspeaker operating at an input frequency equal to 620 Hz: higher SPL values ​​are an indicator of better performance.

[0115] Alternatively, Total Harmonic Distortion (THD) is the ratio expressed as a percentage between the mean square of all harmonics produced by the distortion and the original signal (or fundamental harmonic) input to the device. It is an indicator of the extent to which the original signal has been corrupted in the acoustic transformation of the electrical signal (most importantly due to the insertion of the acoustic mesh).

[0116] Fig.11b Normalized values ​​of THD detected under the above conditions for Examples A, B and N described in this context are reported.

[0117] Higher-order harmonic distortion (HOHD) is a special case of distortion, where in the case studied here the sum of the harmonics produced by the distortion is calculated from the tenth harmonic onwards. The quantity in question focuses attention on the highest harmonics that are not desired to be produced, which is usually an indication of the fact that some parts are vibrating mechanically, undesired friction or impacts adding noise to the emission of the device, which is why this quantity is also defined as rub and buzz (R&B). The fabric may vibrate when it is passed through by an alternating air flow (sound waves) and also influence this distortion.

[0118] Fig.11cEvaluation of normalized HOHD under the conditions and scenarios set forth herein is shown, including an example N of the prior art and two examples A, B of the invention described herein.

[0119] Finally, to measure the flow noise, the Fig.13 The dedicated test schematically shown in FIG. 2 comprises a high power reference loudspeaker 207 emitting a strong sound volume velocity through a dedicated channel 208 provided with a slit 209 of very small dimensions (7.8 mm x 1.2 mm), the fabric 2 to be tested is placed under the slit 209, and the reference microphone 203 is placed outside the primary flow, 45 mm from the axis and 15 mm above the plane of the fabric. The remaining equipment including amplifier 202, amplifier 204, sound card 205 and PC 206 are connected to the primary flow. Fig.12 The apparatus schematically shown in FIG. 1 is equivalent to that used for the aforementioned measurements.

[0120] The input signal to the loudspeaker must be filtered so as to contain only frequencies below 2kHz, since flow noise problems are instead related to high frequencies. Here, the input signal is a sine wave with a fixed frequency (620Hz), which allows to simplify the estimation of the speed of sound passing through the fabric and to clearly separate the harmonic distortion effects from the flow noise effects during the analysis phase. The collected signal is then processed and the acoustic Power Spectral Density (PSD) is calculated as a function of frequency in order to better understand the causes of distortion and noise that change the waveform. If the sound power associated with frequencies other than the input signal is high, this means that there are noise components that add unwanted energy to the system, and obviously the acoustic fabric located on the loudspeaker path also contributes to this.

[0121] Calculated using the above method, PSD proves to be a good indicator of the quality of the transmitted acoustic signal, with the acoustic signal quality being better for lower PSD values ​​in the frequency range of interest.

[0122] If applied to a loudspeaker, a fabric optimized for minimizing flow noise will achieve lower PSD delta values ​​(referenced to the base level of the loudspeaker not including any fabric) than a fabric not designed for such purpose.

[0123] Fig.11d Graphs show the results of measurements of the PSD increase relative to a base level of a loudspeaker comprising no fabric, for a prior art fabric N and two examples A, B of embodiments of the invention.

[0124] Thus, the superiority of each of the two examples of embodiments of the present invention when compared to prior art square mesh fabrics emerged from the tests conducted.

[0125] Compared to prior art solutions where a compromise had to be reached between protection and acoustic performance, each of the two solutions proposed by the present invention proves to be an improvement in one of the two performance areas considered herein without sacrificing the other, but rather maintaining a result similar to or even slightly better than that of the prior art.

[0126] For ease of reference, the above data is summarized in the following table:

[0127] N A B Mesh Square rectangle rectangle Opening 13 (μm) 85 85 70 Opening 12(μm) 85 115 110 Effective opening (μm) 85 85 70 Opening area (%) 60 64 60

[0128] in:

[0129] - The effective opening indicates the size of the solid pollutant particles that are blocked by the mesh. This size must be as low as possible;

[0130] -Opening area is the area of ​​the mesh through which air passes, affecting Figures 11a to 11d The acoustic parameters represented in and the parameters of air passing through ( Figure 10a to Figure 1 0d). The value of the opening area must be as high as possible.

[0131] From the table it can be gathered that the fabric with mesh B provides the greatest protection against the penetration of solid particles compared to the prior art fabric N, without compromising the acoustic performance.

[0132] On its own, fabric A provides the best acoustic performance, as well as protection against solid particles comparable to prior art fabric N.

[0133] More specifically, the results described above indicate that:

[0134] - The new fabric A has the same effective mesh opening as the prior art fabric N ( Fig. 9 ), and is therefore equivalent in terms of protection, since it is able to stop pollutant particles of similar size. However, at the same time, the new fabric A is much better in terms of acoustics, as demonstrated by direct and indirect measurements: the new fabric A is significantly better in terms of linear ( Fig.10a ) and nonlinear ( Fig.10b ) range has lower airflow resistance, which is an indicator of better sound transmission, and the new fabric A guarantees higher emitted sound pressure ( Fig.11a ), with lower distortion ( Fig.11b and Fig.11c ) and lower flow noise ( Fig.11d ).

[0135] - The new fabric B is significantly better than the prior art N in terms of protection against pollutants, since it has significantly reduced mesh openings. However, this better performance is not achieved at the expense of acoustic performance, which is on the contrary completely comparable to that of the prior art fabric. This is explained by the linear ( Fig.10a ) and nonlinear ( Fig.10b ) range, the equivalent value of airflow resistance, similar emission sound pressure ( Fig.11a ) and the equivalent transmission power as flow noise ( Fig.11d ) to prove it. For other measurements of acoustic performance, such as total distortion THD ( Fig.11b ), and especially high-order distortion (HOHD) Fig.11c ), Example B of the present invention is an improvement even in these areas compared to the prior art.

[0136] Naturally, due to the greater freedom offered by the rectangular mesh solution, it will be possible to design other products as embodiments of the invention, ensuring a more balanced improvement of both protection and sound transmission properties, which would in any case not be possible with the square mesh acoustic fabrics of the prior art.

[0137] The fabric of the protective element of the invention can also be made with threads of artificial polymers belonging to the family consisting of cellulose or viscose fibers and is preferably coated with a hydrophobic or hydrophobic / oleophobic coating.

[0138] Furthermore, the mesh size of the fabric may be adapted to vary in one or both of the weft and warp directions, and it may also be possible to provide yarns of different properties and / or different sizes in the same direction or in different weft and warp directions.

Claims

1. A textile-based protective element for preventing the intrusion of pollution particles and water spray into acoustic components of consumer electronic devices, characterized in that The protective element consists of a synthetic monofilament open mesh fabric (25), wherein the mesh (11) has a rectangular shape, the sides (12, 13) of which are made of corresponding threads (26, 27).

2. The protection element according to claim 1, characterized in that: The fabric (25) with an open mesh (11) has an asymmetric structure in terms of the number of threads per cm and / or in terms of the diameter of the threads for both weft and warp directions.

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

1.

4. The protection element according to claim 2, characterized in that: 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.

5. The protection element according to any one of claims 1 to 3, characterized in that: The mesh (11) has a rectangular opening, wherein the short side / long side size ratio is in the range between 0.3 and 0.9, whether the short side is in the weft direction or the warp direction of the fabric.

6. The protection element according to any one of claims 1 to 3, characterized in that: The short side of the mesh (11) is in the range of 5 μm to 150 μm.

7. The protection element according to any one of claims 1 to 3, characterized in that: The fabric is a monofilament fabric, and the diameter of the monofilaments ranges from 10 μm to 90 μm.

8. The protection element according to claim 7, characterized in that: The fabric is manufactured with threads made of synthetic technopolymers belonging to the family consisting of polyesters, polyamides, polyaryletherketones, poly(p-phenylene sulfide), polypropylene, perfluorocarbons, polyurethanes or polyvinyl chloride.

9. The protection element according to claim 7, characterized in that: The fabric is manufactured with threads made of artificial polymers belonging to the family consisting of cellulose or viscose fibers.

10. The protection element according to any one of claims 8 or 9, characterized in that: The fabric is coated with a hydrophobic coating or a hydrophobic / oleophobic coating.

11. A 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 weft and warp directions.

12. The protection element according to claim 11, characterized in that: The protection element provides yarns with different properties and / or different sizes in the same direction or in different weft and warp directions.

13. An acoustic component of a consumer electronic device, characterized in that: The acoustic component consists of a micro-speaker for a smartphone, tablet or the like, which is provided with at least one protective element according to one or more of the preceding claims.

14. Use of a fabric as a protective filter for acoustic components of electronic devices, characterized in that The fabric is a fabric (25) with an open mesh (11) having a rectangular shape and made of a synthetic monofilament fabric, the sides (12, 13) of the mesh (11) being formed by corresponding threads (26, 27).

15. The use according to claim 14, characterized in that The mesh (11) has an asymmetric structure, wherein the linear density / cm of the weft and warp of the mesh in the corresponding directions varies and / or the diameter of the warp and weft of the mesh (11) itself varies.

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

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

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

19. The use according to claim 18, characterized in that The fabric is manufactured with threads made of synthetic technopolymers belonging to the family consisting of polyesters, polyamides, polyaryletherketones, poly(p-phenylene sulfide), polypropylene, perfluorocarbons, polyurethanes or polyvinyl chloride.

20. The use according to claim 18, characterized in that The fabric is manufactured with threads made of artificial polymers belonging to the family consisting of cellulose or viscose fibers.

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

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

23. The use according to claim 22, characterized in that Said use provides yarns having different properties and / or different dimensions in the same direction or in different weft and warp directions.

24. Use of a fabric according to one or more of the preceding claims for the manufacture of acoustic components for consumer electronic devices for protecting loudspeakers and acoustic components from the intrusion of solid and / or liquid contaminants, wherein the primary or secondary sound flow directly passes through the fabric.

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