FR2895201A1 - Loudspeaker for e.g. home theater system, has block positioned ahead of concave membrane along traveling direction and restituting all spectra audible to human ear, where concave membrane restitutes low frequency band - Google Patents

Abstract

The loudspeaker has a concave membrane (341) extending along a direction (351) of an axis (35) and restituting a low frequency band covering certain frequencies comprised between 20 and 200 HZ. A block (364) comprises n-1 convex coaxial membranes extended along another direction (352) of the axis, where n is equal to 4. The block is positioned ahead of the concave membrane along the direction (352) and restitutes all spectra audible to human ear. An absorbent foam layer absorbs sound waves emitted by the concave membrane.

Description

Loudspeaker with n coaxial membranes, n z 3, mounted on the same axis and

  corresponding loudspeaker. FIELD OF THE INVENTION The field of the invention is that of sound and audio, and more specifically the invention relates to loudspeakers and corresponding loudspeakers employing coaxial technologies. invention applies in particular, but not exclusively, in professional listening systems in the studio, in professional systems in the field of cinema, in consumer audio systems in stereophony two channels or multichannel, or in large systems 2. To the prior art To faithfully reproduce a sound field covering the entire frequency band audible by the human ear (which ranges from 20Hz to 20kHz), the most obvious solution is to separate this band of audible frequencies in several subbands (or channels, for example treble, medium and bass) and to implement for each of these sub-band a dedicated speaker.So, as part of the design of an aco speaker In traditional practice, several loudspeakers are used, each comprising a membrane and being dedicated to a sub-band (or channel). Of course, each of the speakers is studied to present the best performance in the frequency subband to which it is dedicated. In the conventional configuration of a multi-speaker speaker, the loudspeakers are superimposed on the front of the loudspeaker so as to reproduce the entire audible frequency band, however this traditional arrangement of the loudspeakers has a disadvantage in terms of radiation, and in particular in the context of the near field (that is to say in the vicinity of 1'entie) given the differences in the market between the sound waves emitted by the different speakers and reviewed by the auditor.

  Indeed, as shown in Figure 1, because the paths 14, 15 and 16 traveled by the sound waves respectively aniseed by the membranes 111, 112 and 113 of the speakers 11, 12, 13 and rect 's by The listener 10 are not identical, the propagation times are different, which results in the appearance of irregularities on the response curve of the speaker by the effect of destructive or constructive interferences. Furthermore, another disadvantage of this arrangement of the speakers on the front of the enclosure is that it causes diffraction phenomena due to breakage on the edges of the enclosure.

  Thus, to overcome these drawbacks, an alternative solution has been proposed. Elie consists in mounting the membranes of the different speakers on the same axis. Such an arrangement is named "coaxial" configuration. A multi-channel loudspeaker is thus obtained, with each of the channels being associated with a transducer (conventionally consisting of a membrane and the electromagnetic device based on a magnet making it possible to actuate the membrane). These co-axial technologies make it possible to obtain a coherent radiation of the different transducers, even in the near field. FIG. 2 illustrates a coaxial three-way loudspeaker, each of the channels being associated with a membrane, respectively 20, 21, 22. In this co-axial assembly of the membranes, the membranes reproducing the treble sounds. 20, the medium high sounds 21, and the low medium sounds 22 have the same emission center 23. The propagation time of the sound waves from the transmitting center 23 to the listener 24 is identical for all these membranes. Thus, unlike conventional loudspeaker speakers, the enclosures comprising coaxial membranes make it possible to obtain coherent radiation from the different transducers, even in the near field. Cabasse has marketed such a three-way coaxial loudspeaker (treble, high medium and low medium) under reference TC22. The three convex membranes (when seen by the auditor) are mounted on the same axis. As a result, the delay to the listener is the same for all the membranes and the loudness response curve of the loudspeaker no longer shows any irregularities as the listener moves into the near field. The sound radiation in the axis, and outside the axis of the enclosure can thus be perfectly controlled.

  However, a disadvantage of this loudspeaker has three coaxial channels is that it does not allow to restore, except by accepting a significant reduction in efficiency, the sounds in the low frequencies of the spectrum of audible frequencies by 1 ' human ear (bass located between 20Hz and a few hundred Hz). 3. OBJECTIVES OF THE INVENTION The invention aims in particular to overcome these drawbacks of anterior art. More specifically, an object of the invention, in at least one of its embodiments, is to provide a coaxial loudspeaker which reproduces the entire spectrum of audible frequencies by the human ear, that is, ie from 20Hz to 20kHz, while having a high efficiency, a low distortion rate and a stable directivity index across the entire audible spectrum. Another object of the invention, in at least one of its embodiments, is to provide such a loudspeaker that maximizes the surface of the membrane restoring the low frequencies.

  Yet another object of the invention, in at least one of its embodiments, is to provide such a technique which makes it possible to reduce the encumbrance of the loudspeaker. The invention also aims to provide such a technique that is simple to implement. 4. Main Features of the Invention These and other objects which will appear later are achieved by means of a loudspeaker with coaxial membranes, n 3, mounted on the same axis, each of the membranes being associated with a separate frequency band. According to the present invention, such a loudspeaker comprises: a concave membrane extending along a first lens of travel of said axis; a block having n-1 convex coaxial membranes extending in a second direction of travel of said axis; and in such a loudspeaker, the block is positioned in front of the concave membrane, in the second direction of travel of said axis.

  The general principle of the invention is based on a particular arrangement in a loudspeaker of a membrane, for example, dedicated to low frequencies and a block of convex coaxial membranes restoring the rest of the band of audible frequencies allowing to maximize the surface of the membrane dedicated to low frequencies.

  Thus, such a coaxial speaker reproduces the entire spectrum of frequencies audible by the human ear while maximizing the surface of the membrane restoring the low frequencies for a given size. Indeed, thanks to this particular arrangement of the concave membrane (advantageously dedicated to the low frequencies of the spectrum) with respect to the block of convex membranes, it can have a large surface area for a given volume compared to a conventional arrangement or the Concave membrane is arranged in a sepal-6 subwoofer of the co-axial loudspeaker; another provision that might be envisaged by a person skilled in the field of loudspeakers who would place this concave membrane on the periphery of the convex membranes. Advantageously, n = 4. Preferably, the loudspeaker according to the invention comprises holding means maintaining said block in front of the concave membrane. According to an advantageous feature of the present invention, the holding means comprises a housing comprising a front face having an opening in its center intended to receive the block, and a rear face facing the concave membrane.

  Advantageously, the loudspeaker according to the invention comprises a box in which the membranes are mounted and to which is fixed a frame supporting the concave membrane, and in that the holding means also comprise at least one connecting arm, secured by a first of its ends, the case and, by a second of its ends, the frame and / or the box.

  According to an advantageous characteristic of 1'invention, the loudspeaker comprises means of diffusion of at least one sound wave emitted by rune at least the membranes of the block, the diffusion means being placed on the front face of the box so that at least part of the front face of the housing has a projecting and / or recessed relief.

  Thus, the diffusion means, which dissymmetrizes the geometry of the front face of the case, make it possible to diffuse the sound waves emitted laterally by the membranes of the block and thus to minimize the energy of the waves diffracted by the edges of the box (or by the connecting arm or by the edges of the cavity formed by the concave membrane or by any other element of the speaker meets by these lateral waves) towards the listener (waves of secondary sources). Preferably, the loudspeaker according to the invention comprises means of absorption of at least one sound wave emitted by said concave membrane, said absorption means being placed between said block and said concave membrane.

  Thus, these absorption means absorb the sound waves emitted by the concave membrane which propagates in the cavity between the concave membrane and the housing. Advantageously, the absorption means are placed on the rear face of the housing.

  According to an advantageous characteristic of the invention, the absorption means comprise at least one of the materials belonging to the group comprising: melamine foam; polyurethane foam; polyethylene foam. Preferentially, the box is of substantially spherical shape.

  According to a first advantageous embodiment of the invention, the holding means hold the block inside a cavity created by the concave membrane. According to a second advantageous embodiment of the invention, the holding means maintain said block above the cavity created by said concave membrane. Advantageously, the box comprises at least one opening practiced close to the block, and forming an event for at least one sound wave emitted by the concave membrane.

  Advantageously, the frequency band associated with the concave membrane corresponds to a bass band covering at least some frequencies between 20 and 200 Hz. Preferably, the loudspeaker according to the invention comprises digital filtering means of a current supplying power. electromagnetic means for actuating at least one of said membranes. These digital filtering means make it possible to obtain a constant spectral response curve and a stable directivity index on the frequency band reproduced by the loudspeaker, even at the level of the spectral transition zones of the membranes (or zones of overlapping membrane responses on the speaker response). The invention also relates to an acoustic enclosure, comprising at least one speaker as previously described. 5. List of Figures Other features and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and non-limiting example, and accompanying drawings, among which: FIG. 1 illustrates the differences in operation of the sound waves emitted by three loudspeakers of a conventional acoustic loudspeaker according to the prior art; FIG. 2 illustrates a three-way coaxial loudspeaker according to prior art; FIG. 3 shows a section of an acoustic loudspeaker comprising a four-way coaxial loudspeaker according to a first embodiment of the invention; FIGS. 4A and 4B show perspective (FIG. 4A) and front view (FIG. 4B) views of the case equipped with the sound wave diffusion system emitted by the convex membranes of the enclosure according to the first embodiment of FIG. invention; FIG. 5 shows a section of the enclosure according to the first embodiment of the invention in which there are arranged means for absorbing sound waves emitted by the concave membrane into the cavity between the concave membrane and the housing; FIG. 6 shows the diagram, in section (FIG. 6A) and seen from the front (FIG. 6B) of an acoustic enclosure comprising a four-way coaxial loudspeaker according to a second embodiment of the invention. 6. Description of an Embodiment of the Invention With reference to FIG. 3, a first embodiment of an acoustic enclosure 30 comprising a coaxial four-way loudspeaker according to the invention is presented.

  Of course, according to variants of this first embodiment, the acoustic chamber 30 comprises any other number (n 3) of coaxial channels. The casing 37 of the chamber 30 of this first embodiment is a hollow sphere (for example made of wood, but it can also be made of any other material), a cap has been cut on the front face leaving room for an opening. Circular 38. In this first embodiment, the enclosure 30 comprises two sets of sound production. A first assembly 34 comprises conventional electromagnetic means 343 actuating a concave membrane 341 extending in a first direction of travel 351 of an axis 35. This concave membrane has an outer diameter of about 55 cm (this diameter being able to differ according to variants of this first embodiment of the invention) and is associated in a flexible manner (by means of an elastic element 3411) to a frame 342. This first sound unit is inserted into the box 37, the frame 342 being fixed around the circular opening 38 of the box. This first set of sound production makes it possible to reproduce a low frequency band covering at least some frequencies between 20 Hz and 200 Hz. In variants of this first embodiment, the first sound production unit covers other frequency ranges. . A second sound production assembly 36 comprises a housing 366 (still called a lens) and a block 364 of coaxial membranes. This second assembly 36 is held inside the cavity created by the concave membrane 341. The housing 366 has a front face having an opening in its center intended to receive the membrane block 364, and a rear face facing the concave membrane 341. The housing 366 is fixed to the casing 37 by means of three connecting arms 39 (holding means), the first end of which is integral with the casing 366 and the second end of the frame 342 which facilitates assembly and operation. disassembly of the frame 342 on the box 37. In a variant of this first embodiment not shown, the second end of the link arm 39 could be fixed directly to the box 37 or simultaneously to the box 37 and the frame 342. Thus, the Membrane block 364 is held inside the cavity created by the concave membrane 341. Of course, any other number of holding arms may be covered under the present invention, on the other hand, any other means of maintenance may be considered. For example, the block of co-axial membranes 364 is the reference module TC22 marketed by the company CABASSE. It is formed in particular of three coaxial membranes 361, 362 and 363 mounted convex on a chassis 342 and extending in a second direction of travel 352 of the axis 35. These three membranes 361, 362 and 363 respectively restore the frequencies acute, high medium, and low medium and are active by electromagnetic means (not shown). Thanks to the second set of sound production 36, the speaker 30 according to the second embodiment of the invention makes it possible to restore all the spectrum audible by the human ear (from 20 Hz to 20 KHz) In addition, the housing 366 supporting block TC22 is equipped with a system 41 for broadcasting sound waves (also called diffusion means) on face 40. FIGS. 4A and 4B show perspective (FIG. 4A) and front (FIG. Case 366 equipped with the diffusion system 41 of sound waves aniseed by the convex membranes of the enclosure according to the first embodiment of the invention. When the membranes 361, 362 and 363 of the block 364 are actuated by the electromagnetic means, they emit sound waves propagating substantially in all directions of space. Thus, these waves propagate along the axis 35 of the coaxial membrane block 364 but also laterally in the plane of the membranes 361, 362 and 363. These lateral sound waves are diffracted notably by the edges of the caisson 37 (but also by the connecting arms 39, by the edges of the cavity formed by the concave membrane 341 or by any other element of the chamber 30 meets by these side waves) especially to the listener. The effect of this diffraction is equivalent to the presence of secondary sound sources placed at the edges of the box 37 which emit towards the listener. The waves of these secondary sources accumulated with the sound waves directly emitted by the membranes 361, 362 and 363 of the membrane block 364 generate accidents on the spectral response curve of the enclosure 30 which correspond to either peaks when it occurs. It acts of constructive interferences (sound waves in phase), or has trolls when it is about destructive interferences (sound waves in opposition of phase). The effect of these secondary sources is all the more important as the environment close to the loudspeaker is symmetrical.

  In order to overcome this diffraction problem, the diffusion system 41 is used. This diffusion system 41 is produced on the front face 40 of the housing 366 by means, for example, of a raised and / or recessed relief, for example, stairs. These projections and / or recesses may for example be arranged randomly to form a heterogeneous and non-uniform relief. This relief 41 can be obtained by bonding material on the case 366, or be provided during molding of the case 366 or by any other suitable technique. Thus, the diffusion system 41, which dissymmetries the geometry of the front face 40 of the housing 364, makes it possible to broadcast the sound waves emitted laterally and thus to minimize the energy of the waves diffracted towards the auditor (secondary source waves). Of course, any relief making it possible to diffuse the sound waves emitted laterally (in the plane of the membranes 361, 362 and 363 of the block 364) can be implemented within the framework of the present invention.

  According to a variant of the first embodiment of the invention, a sound wave diffusion system is not used on the chamber 30. According to this first embodiment of the invention, it is also possible to the absorption means of sound waves emitted by the concave membrane 341 propagating in the cavity between the concave membrane 341 and the housing 366. For example, one can choose absorption means which are particularly effective on the frequency band ranging from 400 Hz to 500 Hz in order to effectively absorb the sound waves emitted by the concave membrane 341.

  As illustrated in FIG. 5, these absorption means can for example be produced by means of an absorbent foam layer 51 of melamine, polyurethane, polyethylene, or any other suitable compound disposed on the rear face. of the lens 366 facing the concave membrane 341.

  This layer of absorbent foam 51 is placed behind the lens 366 and thus makes it possible to dampen and absorb the acoustic waves propagating in the cavity between the concave membrane 341 and the rear of the lens 366. thickness of this layer of absorbent foam 51 is for example 1 cm over the entire surface. According to a variant of this first embodiment of the invention, absorption means are not used. In a traditional speaker or the speakers are superimposed in facade, the sound response spectrum is dependent on the position of the auditor in relation to the speakers, especially in the near field. Thus, on the one hand, the spectral response (in the band from 20 Hz to 20 kHz) of such a speaker with a Dirac peak pulse is deformed with respect to the ideal impulse response (which is a cardinal sinus), this deformation depends on the position of the listener. On the other hand, for such a traditional loudspeaker, the implementation of a digital filtering of the currents supplying the loudspeakers of the loudspeaker leads to the obtaining of a response and a directivity index of the loudspeaker which present irregularities. These irregularities are particularly present at the level of the spectral transition zones of the loudspeakers (or areas of overlapping speaker responses) .Thus, in such a traditional loudspeaker, it is necessary to to adjust the parameters of the filtering for each position of the auditor, which is very restrictive.On the contrary, in the context of an enclosure based on a coaxial diaphragm loudspeaker such as the enclosure 30 according to the first embodiment of the invention, on the one hand, the response to a Dirac peak-type pulse is close to the ideal impulse response (cardinal sinus) on the band from 20 Hz to 20 kHz, and this, whatever the p the hearing of the auditor. On the other hand, for such a chamber 30, it is possible to implement an effective digital filtering that does not require adjustment of the filtering parameters for each position of the listener.

  Thus, in the enclosure 30 according to the first embodiment of the present invention, digital filtering means are used (by means of digital processing means conventionally comprising an electronic card and a DSP for Digital Signal Processor). ) currents supplying the first 34 and second 36 sets of sound production. These digital filtering means make it possible to obtain a constant spectral response curve and a stable directivity index in the frequency band from 20 Hz to 20 kHz, even at the spectral transition regions of the membranes 341, 361, 362 and 363 (or overlapping areas of the membrane responses on the response of the enclosure 30). The digital filtering means make it possible to compensate by digital delays the time delays of the sound waves coming from the different membranes. These time differences result from the fact that the membranes are located on the same axis but not in the same plane. Thus, these digital filtering means optimize the directivity of the coaxial membranes to obtain a response of stable coaxial housing devoid of irregularities which is close to the response of an ideal four-way acoustic system in which the four transducers would be mounted along the same axis and in the same plane. In a variant of the first embodiment of the invention, the enclosure 30 does not include digital filtering means.

  With reference to FIGS. 6A and 6B, the diagram in section (FIG. 6A) and seen from the front (FIG. 6B) of an acoustic loudspeaker 60 comprising a four-way coaxial loudspeaker according to a second embodiment of the invention. Of course, according to variants of this second embodiment, the acoustic chamber 60 comprises any other number (n z 3) of coaxial channels. In this second embodiment, the housing 61 of the enclosure 60 includes a first 610 and a second 611 pieces of sphere. The second piece of sphere 611 is hereinafter referred to as the front cap 611. The front cap 611 comprises two longitudinal openings 65 proximate a block of convex coaxial membranes 644 which is identical to the aforementioned membrane block 364 (the three membranes convexes 361, 362 and 363 of the block 644 extend in a second direction of travel 632 of an axis 63). These two openings 65 constitute side vents 65 for the sound waves emitted by a concave membrane 621. The enclosure 60 comprises two sets of sound production.

  A first assembly 62 comprises conventional electromagnetic means 623 actuating a concave membrane 621 extending in a first direction of travel 631 of the axis 63. This concave membrane has an external diameter of approximately 55 cm (this diameter being able to be different according to variants of this second embodiment of the invention) and is associated in a flexible manner (by means of an elastic element not shown) to a chassis 622. This first sound assembly is fully mounted inside the rear part 610 of the box 61, the frame 622 being fixed on the periphery of the front cap 611. This first set of sound production allows to restore a low frequency band covering at least some frequencies between 20 Hz and 200 Hz. In variants of this second embodiment, the first set of sound production covers other frequency ranges. A second sound production assembly 64 comprises a housing 640 (also called a lens) and a block 644. This second assembly 64 is held above the cavity created by the concave membrane 621 by the fastening of the housing 640 to the front cap 611 of the box 61 by means for example of a bonding or other suitable means of securing. Thus, the membrane block 644 is held above the cavity created by the concave membrane 621. Thanks to the second sound production assembly 64, the chamber 60 according to the second embodiment of the invention makes it possible to restore all the spectrum audible by the human ear (from 20 Hz to 20 KHz) Of course, the chamber 60 according to the second embodiment of the invention can be advantageously provided with diffusion means and / or absorption means and / or digital filtering means as previously described in relation to the enclosure 30 according to the first embodiment of the invention.

  Thus the acoustic speakers 30 and 60 according to the invention previously described, which are optimized from the point of view of the directivity in the transition zones of the different channels (bass / low medium, low-medium / medium, medium / high) s' approach to the ideal acoustic source (without irregularities at the level of the transition bands.) Of course, the invention is not limited to the embodiments mentioned above.On the other hand, the person skilled in the art can combine the first and second embodiment previously described in order to realize an acoustic enclosure according to the present invention.

  In particular, the skilled person can provide any variant in the form and components of the different elements of the speakers 30 and 60 (including the shape of the box, the size of the concave membrane, the membranes of the block, the choice of the absorbent foam, the geometry of the lens). The skilled person may provide any variant in the choice of membranes 361 to 363, 341, 621 and electromagnetic means of activation of these membranes. It will thus be possible to obtain loudspeakers according to these variants of the invention covering different sound spectra (for example the frequency bands from 200 Hz to 20000 Hz, or from 50 Hz to 1000 Hz, or from 50 Hz to 20000 Hz or any other frequency band).

Claims (16)

  1. Loudspeaker with coaxial membranes, n 3, mounted on the same axis (35), each of the membranes being associated with a distinct frequency band, characterized in that it comprises: a concave membrane (341) extending in a first direction of travel (351) of said axis; - a block (364) has n-1 convex coaxial membranes (361, 362, 363) extending in a second direction of travel (352) of said axis; and in that said block (364) is positioned in front of said concave membrane (341) in said second direction of travel of said axis (352).   2. Loudspeaker according to claim 1, characterized in that n = 4.   3. Loudspeaker according to any one of claims 1 and 2, characterized in that it comprises holding means maintaining said block (364) in front of said concave membrane (341). 15   4. Loudspeaker according to claim 3, characterized in that said holding means comprise a housing (366) comprising a front face having an opening in its center intended to receive said block (364), and a rear face facing a said concave membrane (341).   5. Loudspeaker according to claim 4, characterized in that it comprises a box (37) in which are mounted said membranes (341, 361, 362, 363) and which is fixed a frame (342) supporting the membrane concave (341), and in that said holding means also comprise at least one connecting arm (39) secured, by a first of its ends, said housing (366) and, by a second of its ends, said chassis (342) and / or said box (37). 25   6. Loudspeaker according to any one of claims 4 and 5, characterized in that it comprises means for diffusion (41) of at least one sound wave emitted by rune at least said membranes (361, 362, 363) of said block (364), said diffusion means (41) being placed on said front face of said housing (366) so that at least a portion of said front face of the housing (366) has a protruding relief and / or hollow.   7. Loudspeaker according to any one of claims 1 to 6, characterized in that it comprises means for absorbing (51) at least one sound wave emitted by said concave membrane (341), said absorption means (51) being located between said block (364) and said concave membrane (341).   8. Loudspeaker according to claim 7, characterized in that said absorption means (51) are placed on said rear face of said housing (366).   9. The loudspeaker according to any one of claims 7 and 8, characterized in that said absorption means (51) comprise at least one of the materials belonging to the group comprising: melamine foam; polyurethane foam; polyethylene foam.   10. Loudspeaker according to any one of claims 5 to 9, characterized in that said box (37) is of substantially spherical shape.   The loudspeaker of any one of claims 3 to 10, characterized in that said holding means holds said block (364) within a cavity created by said concave membrane (341).   12. A loudspeaker according to any one of claims 3 to 10, characterized in that said holding means hold said block (364) above the cavity created by said concave membrane (341).   13. Loudspeaker according to claim 12, characterized in that said box comprises at least one opening (38) practiced close to said block (364), and forming an event (65) for at least one sound wave emitted by said membrane concave (341).   14. A loudspeaker according to any one of claims 1A 13, characterized in that the frequency band associated with the concave membrane (341) corresponds to a bass band covering at least some frequencies between 20 and 200 Hz.   15. The loudspeaker according to any one of claims 1 to 14, characterized in that it comprises digital filtering means of a current supplying electromagnetic means for actuating at least one of said membranes (341, 361, 362, 363).   16. Acoustic speaker, characterized in that it comprises at least one speaker according to any one of claims 1 to 15.