FR2893646A1 - Sound insulation and absorption screen type device for use in e.g. music room, has felt layer forming free core which has geometry so that portions of surface of free core are not supported on neighboring layers - Google Patents

Abstract

The device has a compressed felt layer (11), followed by a non-compressed felt layer (12), a fabric layer (13) and a perforated rigid wall (14). The rigid wall is maintained on sides by edges. The compressed felt layer (11) is made at a density comprised between 100 and 300 kilogram per cubic meter and has a thickness comprised between 2 and 15 mm. The felt layer (11) forms a free core which presents a geometry such that portions (L) of a surface of the core are not supported on neighboring layers (12, 12b). The layer (12) is made of recycled fibers e.g. cotton. An independent claim is also included for a method for acoustic treatment of a room.

Description

-1- Modular multifrequency acoustic screen

  The present invention relates to a modular sound insulation or multifrequency sound absorption device that can be used in particular to isolate a noisy zone, or to modify or optimize the acoustics of a wall or a room. Acoustical materials or coatings are frequently attached to a wall to modify or improve acoustic properties, such as a partition, floor or ceiling. Such an improvement may include in particular an absorption of the received sound waves, to reduce the transmitted or reflected energy. For example, it involves obtaining good acoustic conditions in a building or a room under construction, or improving the characteristics of a room during a renovation.

  Such materials are also used to make self-supporting acoustic screens arranged around a zone or a sound machine to reduce the nuisance generated around. Such coatings are often made from a material; flexible and ventilated fibers, in particular one or more layers of glass wool or rock wool, fixed on the entire surface of the wall to be treated. To produce a self-supporting screen or to protect the materials, this coating is optionally inserted between two rigid walls fixed on demand by means of intermediate or additional elements, for example on posts implanted along the path of a screen to be produced. . Such coatings or screens are often used to treat problems of an industrial nature, for example machines or exhausts of engines or pipes. Monoblock screens are also manufactured in the form of fibreboard, fixed on a base and making self-stable panels and easily movable. Acoustic performances are, however, often less good, and the dimensions are often unsuited to the particular conditions of certain applications. The premises dedicated to the music are often treated using materials or structures that are very studied and very expensive, for example complex shapes in the thickness of the panels producing traps by multiple reflections.

  The existing solutions, however, have a number of disadvantages, and are often unsuitable for premises where acoustic problems are more particularly in the field of speech. Such problems often arise to reduce the noises of a conversation in a room, or to obtain a good intelligibility of a speaker in teaching or conference rooms. The same types of sounds also cause problems in large rooms with many people who have trouble understanding each other, for example in halls, canteen dining rooms, or offices of the landscape type. An object of the invention is to overcome the disadvantages of known solutions to modify or improve the acoustic characteristics of a room or area. These include providing efficient and economical solutions, effective over a large number of frequencies or frequency ranges and in particular in the field of speech and for a large number of angles with respect to the coating or the 'screen. In many types of collective premises, for example in canteen dining halls, many constraints also exist that go beyond the strict acoustic performance.

  Thus, the invention also seeks to obtain good resistance to shocks and aggression related to the use or maintenance of premises. The invention also seeks to allow a visual appearance easy to integrate into a visual aesthetic or organization. In addition, the invention also seeks to allow a flexible and economical organization of the premises to be treated, while respecting the constraints or safety standards at best. A goal is also to allow a simple manufacturing, economic and limiting the environmental impacts. The term "felt" is defined in certain dictionaries (Robert) as designating a fabric formed by agglutinated fibers. This type of fabric can be obtained in various ways, for example by compressing separate fibers together, or by rubbing fiber strands forming a yarn or fabric. Fiber trades use many specific and different terms, often depending on their specialization and the nature or origin of the fibers used. In the present description, the term "felt" is used in its widest sense, and will thus be used to denote fabrics made from vegetable fibers, or artificial fibers such as polyester, or mineral fibers such as rockwool from glass wool. The invention proposes a device of the multilayer acoustic insulation or sound absorption type whose structure comprises at least one rigid wall covering at least a first layer of a material based on aerated fibers forming a low density felt. This device is characterized in that its structure comprises at least a second layer of a high density felt, called free core, whose geometry is determined so that at least a significant part of its surface is not in support against the neighboring layers.

  The combination of several layers of felt of different densities makes it possible to absorb a wide range of frequencies. The use of a particularly dense core also allows, in addition to the high frequencies treated by the light felts, a better efficiency on the medium frequencies which have a great importance for the speech. The parts of this soul which are not in support on the neighboring layers benefit from a certain freedom of vibration, which enables them on the one hand to better damp some frequencies by absorbing their energy, and on the other hand not to retransmit this energy to neighboring layers and thus limit the reflection of these frequencies.

  The invention also proposes a method of acoustic treatment of a room, comprising the installation of one or more screens of such a type. This structure can be applied as a screen attached to a wall. This structure can also be made on both sides of the free core, to form an effective screen on both sides. Thus, the invention also proposes a device forming a self-supporting rigid screen of a given shape whose free core is covered on both sides by a first layer of felt followed by a layer of fabric and then a perforated rigid wall.

  The invention thus also proposes an acoustic treatment method using at least one such self-supporting screen, the height of which is determined to protrude upwards, with respect to the height of the ears of persons to be isolated, by a distance of between and 40cm.

  According to other features of the invention, which can be combined with one another: the free core has a non-uniform density, or a non-uniform thickness, or a non-planar surface, or a combination of these characteristics; the free core comprises a layer of compressed felt having a density which is at least twice or more than five times that of the felt of the first layer; the free core comprises a layer obtained by compression of a felt layer of the same type as the first layer of felt; the free core comprises a non-uniformly compressed felt; the free core has a non-planar geometry obtained or maintained by fixing said core in at least one edge of the screen; the screen has at least one edge towards which at least one first layer of felt extends closer to said edge than the layer forming the free core; the rigid walls have a geometry determining for the screen a horizontal section wider in the center than at the ends, and more particularly in elongated oval; the screen comprises at least one vertical edge carrying outwardly at least one lip of a compressible material arranged so as to be adjusted or crushed against an obstacle so as to provide some acoustic insulation between said edge and said obstacle; the screen is mounted on at least one base arranged to ensure vertical stability on a horizontal support while allowing it a freedom of inclination determined so as to limit the damage received by the screen in case of horizontal shock ; at least one of the layers of felt is made of plant fibers which have undergone a fireproof treatment; at least one of the felt layers produced comprises recycled cotton fibers; at least one rigid wall is perforated more than 35%; at least one layer of low density felt has a density of between 40 and 80 kg / m 3; at least a portion of the free core has a density of between 100 and 300 kg / m3. Other features and advantages of the invention will emerge from the detailed description of an embodiment which is in no way limitative, and the appended drawings in which: FIG. 1 represents a horizontal sectional view of an acoustic screen according to FIG. invention, in one embodiment using multiple screens for the treatment of the surface of a wall; 2 shows a horizontal sectional view of an acoustic screen according to the invention, in a self-supporting embodiment applied perpendicularly to a wall; FIG. 3 represents a perspective view of an acoustic screen according to the invention, in a self-supporting embodiment; FIG. 4 is a curve of the acoustic performances obtained by a self-supporting screen according to the invention according to the different frequencies of the audible spectrum; Figures 5 and 6 illustrate details of embodiment of some assembly parts of a screen according to the invention in a self-supporting embodiment; Figure 7 illustrates the use of the invention in a self-supporting embodiment used to develop a room refectory type. FIG. 1 shows a screen 1b according to the invention fixed on a wall, for example on a wall M. From the wall, the screen comprises a layer of compressed felt forming a free core 11, followed by a uncompressed layer of felt 12, then a layer of fabric 13, and a perforated rigid wall 14. The rigid wall 14 is placed on a base 21 and held on the sides by edges or uprights 23 (only one shown ). On the outside of this upright 23 is fixed a lip 24 forming acoustic sealing means with the edge 23c of another screen 1c of the same type attached to the first screen lb on the same wall M. In fact, the sealing thus obtained between two screens side by side can make it possible to gain about 5dB compared to a gap of 5mm. This lip 24 is formed more particularly by a ribbon or a bead of flexible or compressible material, fixed in a longitudinal groove 234 of the upright 23 and can be crushed against the lip 24c of the adjacent panel 1c or a perpendicular wall (FIG. 2) . This lip will advantageously be made of a material of good acoustic performance, for example a suitable rubber or felt tape exceeding 5 to 20mm. According to the invention, this free core 11 has a geometry that allows it to be in contact with the adjacent layers 12 and 12b only on certain parts of its surface. This core 11 is thus free, or applied with very little pressure on its neighbor or neighbors, on large portions L of its surface. This geometry can be obtained by creasing or forming, for example by compression. This geometry may comprise in particular a regular or irregular pleating, in one or more directions, or a corrugation for example in the form of a sinusoid. Advantageously, the first layer of felt 12 is made from recycled fibers, originating from fabrics and in particular from cotton. This can allow savings in the manufacturing cost of the device, and limits the ecological impact of the manufacturing process, responding better to certain selection criteria such as the HQE criterion (High Environmental Quality). These fibers are fire-resistant and meet the M1 classification criteria of French standardization. This first layer of felt 12 is produced in a density of between 40 and 80 kg / m 3, preferably 60 kg / m 3. Typically, this first layer of felt 12 has a thickness between 20 and 40mm, for example 30mm.

  The second felt layer 11 constituting the so-called free core is made of a density of between 80 and 400 kg / m 3, preferably between 100 and 300 kg / m 3. This layer has a thickness of between 2 and 15 mm, typically of the order of 3 to 10 mm. In a variant, the felt layer 11 forming the free core 10 has a non-uniform thickness, which can also provide all or part of the free zones L sought. Advantageously, the free core 11 is made of the same type of fibers as the first felt layer 12. More particularly, the free core can be obtained by compression of a low density felt such as that of the first layer 12. This compression can also be used to obtain a non-uniform geometry or a non-uniform thickness or nonuniform density for this free core. The rigid wall 14 advantageously has orifices for better transmission of sound waves towards the inside of the screen. This wall may be made of perforated sheet, for example thermo-lacquered aluminum 2 to 3 mm thick. Good results are observed from 30% perforation, and more particularly from 40% perforation. Advantageously, the perforations are made in a sufficiently small dimension so that children can not pass the finger, for example circles with a diameter of less than 10 mm, or even less than 5 mm. The rigid wall may also be made of woven rushes, for example vegetable such as woven rattan or wicker varnished and treated to marine standards, or artificial like nylon, woven cane wicker chair or like a mosquito net. This rigid wall 14 advantageously has a non-flat shape, convex towards the outside of the screen, preferably in an elongated oval shape, and thus promotes a divergence of sound waves that can be reflected. This non-planar shape, as well as that of the inner layers which are pressed against the wall, makes it possible to standardize the results in space and to obtain good performances for a large number of directions with respect to the screen. The presence of a cloth layer 13 makes it possible to limit the entry of dust, insects, or various objects, and thus allows better safety as well as easier cleaning and better hygiene. The fabric will preferably be of a color close to the perforated rigid wall, so as to avoid creating unpleasant effects of attachment or attraction of the eye due to the perforation patterns.

  As illustrated in FIGS. 1 and 2, the free core 11 does not extend to the edge 23 of the screen 1, 1b, over an area 10 which can be up to 30cm, which makes it possible to limit the transmission of energy absorbed towards these edges. FIG. 2 shows a screen 1 according to the invention, made in the form of a rigid self-supporting screen visible in perspective in FIG. 3. The free core consists of a second layer of compressed felt 11, surrounded on each side by a first layer of uncompressed felt 12 and 12b, then by a layer of fabric 13 and 13b, and protected by a rigid wall 14 and 14b.

  As illustrated in FIG. 3, the different layers and walls of the self-supporting screen 1 are held between a base 21 forming a lower flange and a plate 22 forming an upper flange. The base 21 and the plate 22 are assembled together by two edges 23 and 25, each provided with a sealing lip 24 and 26. For greater safety, these edges advantageously have roundings on their outside corners, for example on the outside. order of 20 to 50mm in diameter, typically 40mm. Advantageously, the core 11 can be fixed on one of the edges of the screen, for example suspended on the lower face of the plate 22. It can also be fixed on several edges, for example on the two inner faces of the plate 22 and the base 21. It is thus possible to obtain that the shape of the soul is kept inside the screen, even when manipulating the screen, and without having to compress too strongly between its neighboring layers. The acoustic performances of the screen according to the invention have been tested and analyzed from the point of view of the noises in general, and more particularly from the point of view of the intelligibility of the speech or of the noises of conversation, and according to the frequency ranges corresponding to the speech domain. Measurements were made by taking eight different positions on both sides of the screen. The overall gain obtained is 12.95dB on average, and higher than 14dB for the most troublesome frequencies. Frequency results are shown in the table below. Hz dB 250 3.61 500 7.72 1000 8, 82 2000 7.40 4000 12.14 8000 20.36 Global total 12.95 Figure 4 represents, as a function of the frequencies from 20 Hz to 20 KHz, results in decibels of transmission attenuation obtained (bottom curve) by interposing a self-supporting screen between a source and a detector, compared to a control situation (top curve). By studying the differences between the two curves, we see that we obtain attenuation over a wide range of frequencies, especially between 50Hz and 10KHz. We also note that we obtain even more efficient results for some specific frequencies that can be very interesting, for example around 750Hz, 2Kz, 3KHz, 4KHz, 8KHz and 10KHz. In the self-supporting embodiment, the screen 1 can be fixed by its base 21 on a low height base, for example two branches in arcs or half-circles 27 and 28 disposed near the two ends of the screen, turned inwards so as to limit their size and the risks of inconvenience in the passage around the screen. These branches 27 and 28 are made to be sufficiently flexible, or even elastic, to be able to accept a certain inclination in case of shock, and thus limit the risk of damage to the body or the walls 14 of the screen. This base is for example made of aluminum with a height of 10 - 4mm, so as to limit the open space under the screen. For the same purpose, the base can be designed so that the base 21 rests directly on the ground, for example by a base recessed or attached to the sides.

  The self-supporting screen 1 according to the invention thus constitutes an effective and easy-to-use modular element that can be used alone or in combination with others, temporarily or permanently. The plate 22 forming the upper flange may comprise upwards, in a fixed or removable manner, a flexible border and / or irregular shape contributing to limiting the diffraction of sound waves above the screen, for example rubber, cardboard or felt, and also serve as decoration. Good results have been obtained by producing elements 21, 22, 23, 25 screen tower water-treated treated wood, covered with two or three layers of marine varnish, for good acoustic and mechanical qualities combined with good resistance to cleaners. More particularly, these elements can be made of agglomerated wood chips, known as medium. As illustrated in FIG. 5, the base 21 and the plate 22 bear on their length two grooves 221 and 221b in which the edge of the rigid walls 14 and 14b is inserted. The layout of these grooves then makes it possible to determine the oval profile of the rigid walls that they receive, and therefore the transverse geometry of the screen. At their ends, the base 21 and the plate 22 comprise blind holes 222 and 222b, receiving pins 232 and 232b of wood for assembly with the edges 23 and 25. As illustrated in FIG. 6, the edges 23 and 25 bore at their end holes 232, 232b corresponding to these pins. On their side of the outer side, these edges carry a groove 234 longitudinal receiving the lip 24 sealing. On their side of the screen side, these edges bear two longitudinal grooves 231, 231b receiving the edges of the rigid walls 14 and 14b. Figure 7 illustrates an example of use of the screen according to the invention, in a large room receiving many people, for example a school canteen refectory. - 11 - Many rooms of this type exist, which have not been particularly studied acoustically during their construction. When many people in this room talk to each other or produce various noises, for example during a meal, the characteristics and the large dimensions of the room often tend to produce a general hubbub of a high noise level, which is both uncomfortable and hinders understanding of individual conversations. The various reflections and reverberations on the walls play a role in this soundscape. By applying an acoustic coating on all or part of the walls of the room, it is possible to reduce this sound environment. Such a coating can then be made simply and without major work by fixing on the walls one or more screens lb, 1c according to the invention. It is also possible to arrange along the walls one or more screens the self-supporting according to the invention, if necessary temporarily in the case of a particular event or a room only rarely used for this purpose. It is also possible to reduce the sound level by separating the entire room into several areas, simply by arranging one or more self-supporting screens 1 according to the invention to create acoustic insulation between these areas, or around a particular area. noisy or particularly protect. By having screens 1 between the tables 30 of such a refectory, we obtain a decrease in the sound level of the entire room, less fatigue for each of those present, and a better understanding of each individual conversation. These screens can be arranged easily without work, and be easily moved in case of reorganization of the interior of the room. In this example, three parallel screens 1 are arranged perpendicular to the wall to separate four tables of eight places 31. These screens are applied by their lip 24 against the same wall so as to obtain a certain acoustic seal between the screen and the wall . Six other self-supporting screens are arranged in groups of two 1, ld joined end to end, so as to separate four groups of two tables -12 - 32, 33. These screens 1, 1c are in contact with each other by their lip 24, 24d in order to obtain a certain acoustic seal between them. These self-supporting screens 1, 1d are made or chosen in dimensions allowing both good efficiency and limited space, as well as storage and easy handling. An example of dimension for the self-supporting screen 1 is about 2m in length, for a thickness at the rigid walls 14 and 14b varying between 45mm at the ends and 90mm in the center, or about half for the embodiment at a only face (Figure 1).

  In the self-supporting embodiment, the height of the screen 1 relative to the ground is of some importance. Indeed, it is appropriate that the height is sufficient to obtain a good efficiency. However, too high a height reduces the visual field, and for example makes it difficult to monitor a person responsible for those present.

  In this context, good results have been obtained with screens whose height is determined to exceed upwards, relative to the height of the ears of people to be isolated, a distance of between 20 and 40 cm, and preferably to around 30cm. In the case of a room designed to accommodate adults sitting, an example of height providing sufficient efficiency to achieve a good compromise was found between 155cm and 135cm, preferably 147cm. In the case of a room for sitting children, a good compromise was found between 115cm and 135cm, preferably 127cm.

  Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

Claims (16)

  A multilayer acoustic insulation or sound absorption screen device (1, 1b) the structure of which comprises at least one rigid wall (14, 14b) covering at least a first layer (12, 12b) of base of aerated fibers forming a low density felt, characterized in that its structure comprises at least a second layer (11) of a high density felt, called free core, whose geometry is determined so that least a significant portion (L) of its surface is not in abutment against the adjacent layer or layers (12, 12b).   2. Device according to claim 1, characterized in that it forms a self-supporting rigid screen (1) of a specific shape whose free core (11) is covered on both sides by a first layer of felt (12, 12b) followed by a fabric layer (13, 13b) followed by a perforated rigid wall (14, 14b).   3. Device according to one of claims 1 or 2, characterized in that the free core (11) has a non-uniform density or a non-uniform thickness or a non-planar surface or a combination of these characteristics.   4. Device according to one of claims 1 to 3, characterized in that the free core (11) comprises a layer of compressed felt having a density at least twice that of the felt of the first layer (12).   5. Device according to one of claims 2 to 4, characterized in that the free core (11) has a non-planar geometry obtained or maintained by fixing said core in at least one edge (22) of the screen ( 1).   6. Device according to one of claims 2 to 5, characterized in that the screen (1, lb) has at least one edge (23, 25) to which at least a first layer of felt (12, 12b) s extends closer to said edge than the layer forming the free core (11).   7. Device according to one of claims 2 to 6, characterized in that the rigid walls (14, 14b) have a geometry determining for the screen (1, lb) a horizontal section wider in the center than at the ends. - 14 -   8. Device according to one of claims 1 to 7, characterized in that the screen (1, lb) comprises at least one edge (23, 25) bearing outwardly at least one lip (24, 26) d a compressible material arranged so that it can be adjusted or crushed against an obstacle so as to provide some acoustic insulation between said edge and said obstacle.   9. Device according to one of claims 2 to 8, characterized in that the screen (1) is mounted on at least one base (27, 28) arranged to provide vertical stability on a horizontal support while allowing it a freedom of inclination determined so as to limit the damage received by said screen in the event of a horizontal shock.   10. Device according to one of claims 1 to 9, characterized in that at least one of the layers of felt (12, 12b,   11) is made of plant fibers which have undergone a fire treatment. 11. Device according to one of claims 1 to 10, characterized in that at least one of the felt layers (12, 12b, 11) comprises recycled cotton fibers.   12. Device according to one of claims 2 to 11, characterized in that at least one rigid wall (14, 14b) is perforated more than 35%.   13. Device according to one of claims 1 to 12, characterized in that at least one layer of felt (12, 12b) of low density has a density between 40 and 80 kg / m3.   14. Device according to one of claims 1 to 13, characterized in that at least a portion of the free core (11) has a density of between 100 and 300 kg / m3. 25   15. Acoustic treatment method of a room comprising the establishment of one or more screens (1, lb, lc, 1d, le) according to one of claims 1 to 14.   16. A method according to claim 15, characterized in that it comprises a use of at least one self-supporting screen (1) whose height is determined to protrude upwards, with respect to the height of the ears of persons to be isolated. , from a distance of between 20 and 40cm.