EP1475993A1 - Acoustic system with multiple ribbon type transducers - Google Patents

Abstract

The system has identical transducers for restituting audio signal in low frequency, and a membrane (1) for supporting electricity conducting bands. The transducers comprise a membrane (2) with a structure similar to the membrane (1). A set of transducers is fixed on a baffle plane that is constituted of articulated panels (5-7) folded in a column form.

Description

The present invention relates to loudspeakers, and more particularly those of the ribbon type, dedicated to the reproduction of acoustic signals in the low frequencies of the hearing field.

The majority of sound reproduction systems in the high fidelity field use speakers cone diaphragm electrodynamics for bass reproduction frequencies. The quality level of sound signal reproduction of such systems is, therefore, dependent on the principle of this type of transducer. As stated in US 5,195,143 and EP 166,957, using tape transducers improves quality listening by reducing distortion and increasing dispersion of the sound signal.

In these descriptions, the ribbon constituting the woofer is placed in the immediate vicinity of the magnets generating the magnetic flux in order to benefit from a most homogeneous and intense field optimum. This configuration does not allow movements linear of the driving surface and generates a distortion of the sound, taking into account the decrease in intensity of the magnetic field at the front of the membrane, this phenomenon being described in US 4,001,522.

The magnets behind the membrane are as many obstacles to the propagation of the rear wave and cause signal attenuation and coloring.

The principle of a single or multiple driver, united a flexible membrane stretched on its 4 sides limits the elongations when approaching the membrane fasteners, altering the sound signal and reducing the performance at low frequencies. To improve the sound reproduction in this lower part of the spectrum, FR 2 446 044 describes a membrane allowing pyramidal deformation at more wide travel.

These different types of ribbons do however move not really like pistons. Given the method of attachment membrane, the amplitude of the elongations of the generating element of the sound wave is not homogeneous on all its surface, phenomenon altering the linearity of the response in frequency. In general, the movement of the driving surface remains too weak compared to the amplitude of the signals of the lowest frequencies to reproduce. This observation is increasingly more topical given the improvement of processes which increase the dynamics and to broaden, both bass and treble, the spectrum of sound frequencies to be restored.

For other types of long, narrow ribbons, the fasteners are placed at the ends on the short sides, the long sides remaining free to move along the sides magnets or pole pieces. For such systems we found the same inconveniences described above, as to restrictions on the amplitude of the movement of the membrane. A additional distortion of the sound signal appears, due to the leak air between the long sides of the tape and the faces of the magnets causing air turbulence, as detailed in US 4,580,014.

An additional annoyance appears in these ribbon transducers, when used to reproduce low frequencies, with regard to the robustness of the conductor at the proximity of its fixings. A suspension, described in EP 404 487, reduces the risk of the ribbon conductor breaking. However, for use at very low frequencies, this type of suspension does not accept sufficient travel of the ribbon.

The object of the present invention is a system of sound reproduction restoring the entire audible spectrum. The reproduction of low frequencies is ensured by several identical transducers made of flat membranes rigid rectangular, each with multiple ribbons electrical conductors moving like pistons in a magnetic field free of any obstacle. The piston movement of these membranes is obtained thanks to their non-deformable constitution at which is added a set of elastic fasteners with large travel placed at their ends, now these between the polar faces of a magnetic circuit to guarantee a leak air equivalent to a lateral clearance of less than 1% of the width of the membranes. This air leakage can be minimized by the presence of reinforcement cheeks placed on the edges of the membranes, perpendicular to them, so parallel to the faces polar. Residual air leakage can be eliminated by the addition of a loop-shaped suspension connecting the cheeks reinforcing the magnetic circuit. The set of elastic fasteners long travel gives these transducers a frequency of very low resonance favoring the reproduction of bass sounds and ensuring the tapes of the membranes good resistance to breakage. The reproduction of mid-treble frequencies can be ensured by a single transducer with a structure similar to those previously described, providing the same benefits. However, the cheeks of reinforcement and additional suspensions in the form of loops will not be present on the membrane if the lowest frequency at reproduce by the mid-acute transducer is sufficiently high. The membrane then gains in lightness, this improving its performances for this frequency register. All of these transducers is fixed on a modular flat cabinet in order to minimize the disturbances inherent in any enclosure principle acoustics closed. This system thus reduces the various distortions described above and significantly improves the sound reproduction quality.

The system includes a magnetic circuit made in iron or any other material permeable to magnetism which, according to a first characteristic, in the form of a scale consisting of bars parallel to each other and uprights perpendicular to these last.

Permanent magnets are fixed by one of their faces polar according to a second characteristic on either side of magnetic circuit bars in the form of a ladder, except the first and last bars which have only one row magnets.

A magnetic field is thus created in each air gap formed by the space between the south face of a row of parallelepipedic permanent magnets and the north face of the contiguous row of identical constitution. For all transducers, each rectangular flat membrane produces waves sound by moving in each air gap which according to a third characteristic is free of any obstacle, characteristic obtained by limiting on the one hand the width of the bars to that of the magnets permanent and by placing the other amounts, ensuring the closing of the magnetic circuit, outside the attachment area of the said magnets.

According to a fourth characteristic, the magnetic circuit may have air gaps of different widths in which move membranes of different sizes.

In each air gap is placed according to a fifth characteristic of the invention, a membrane consisting of an element rectangular plan in light material of specific thickness on which are glued parallel in the direction of the largest length, several flat conductive tapes traversed by the electrical current of the audio signal to be reproduced. The rigidity of the membrane ensuring its displacement comparable to that of a piston is obtained by sticking conductive tapes on both sides, the efficiency of this process being proportional to the thickness of the membrane. The conductive tapes are covered with a thin film and light, giving it a second element of rigidity improving the linearity of its frequency response.

According to a sixth characteristic, each membrane is kept centered in the air gap by suspension members made in a thin film, the same width as the membrane, glued on each of its faces in its extension, and on its short sides forming its ends. The tapes as well obtained are folded only once in the shape of a "V", along an axis parallel to the short sides of the membrane and are in opposition two two at each end of the latter. They form respectively a double deformable triangle structure, ensuring the suspension of the membrane and allow a large clearance of this amplitude directly proportional to the length of a side of a triangle, while removing the roll phenomenon from the membrane.

On these strips are also glued the extensions of conductive tapes which are soldered at their ends to a plate of a printed circuit serving as a connector and allowing, according to a seventh characteristic, to ensure the centering of the membrane with side play less than 1% of its total width. The copper on these printed circuit boards is etched spacing electrically separating said conductive tapes glued to the membrane.

According to an eighth characteristic of the invention, the baffle plan consists of two foldable flaps of the height total of the system and are placed on each side of the set of transducers. Each component consists of three panels articulated which can be folded backwards from the transducers to form a column or be gradually deployed to form a flat cabinet to adjust the level of bass reproduction frequencies depending on location, configuration of the local or the wishes of the listener.

• le transducteur ne comportant qu'une membrane voit son circuit magnétique réduit à un cadre rectangulaire, dont deux barreaux parallèles ne comporteront chacun qu'une seule rangée d'aimants.
• deux joues de renfort réalisées dans le même matériau que celui utilisé pour la membrane peuvent être fixées perpendiculairement sur les bords de chacun des deux grands côtés d'une des faces de la membrane, lui conférant un troisième élément de rigidité et limitant le court-circuit acoustique se produisant entre les bords de cette dernière et les faces polaires des aimants.
• un quatrième élément de rigidité peut être obtenu en reliant les joues de renforts entre elles par des nervures également fixées sur la face de la membrane, deux de ces nervures étant situées sur les bords des petits côtés de la dite membrane.
• afin de supprimer le court-circuit acoustique résiduel aux abords des faces polaires des aimants, une suspension réalisée dans un film mince et souple formant une boucle sortant en grande partie de l'entrefer, peut être fixée sur toute la longueur des joues de renfort d'une part, et sur un support collé sur les faces non polaires des aimants ou sur les barreaux du circuit magnétique d'autre part. Ce dispositif est étanche à l'air et n'entrave pas les mouvements de la membrane.
• afin de réduire le court-circuit acoustique aux abords des suspensions, un boítier peut recouvrir chaque suspension à l'arrière de la membrane, une face du dit boítier étant placée le plus près possible de la nervure située sur le bord du petit côté de la membrane.

According to particular embodiments:

• the transducer comprising only one membrane sees its magnetic circuit reduced to a rectangular frame, of which two parallel bars will each comprise only one row of magnets.
• two reinforcing cheeks made of the same material as that used for the membrane can be fixed perpendicularly to the edges of each of the two long sides of one of the faces of the membrane, giving it a third element of rigidity and limiting short-circuit acoustic occurring between the edges of the latter and the pole faces of the magnets.
• a fourth element of rigidity can be obtained by connecting the reinforcement cheeks together by ribs also fixed on the face of the membrane, two of these ribs being located on the edges of the short sides of said membrane.
• in order to eliminate the residual acoustic short-circuit near the pole faces of the magnets, a suspension produced in a thin and flexible film forming a loop coming largely from the air gap, can be fixed over the entire length of the reinforcement cheeks d on the one hand, and on a support bonded to the non-polar faces of the magnets or to the bars of the magnetic circuit on the other hand. This device is airtight and does not obstruct the movement of the membrane.
• in order to reduce the acoustic short circuit around the suspensions, a box can cover each suspension at the rear of the membrane, one side of the said box being placed as close as possible to the rib located on the edge of the short side of the membrane.

La figure 1 représente le système complet dont les panneaux articulés sont entièrement déployés de façon à former un baffle plan autour des transducteurs.

La figure 2 représente une vue arrière partielle du circuit magnétique ainsi que le principe de connexion électrique d'un groupe de quatre transducteurs de grave.

La figure 3 est une vue en coupe de la figure 1 selon l'axe AA.

La figure 4 est une demi-vue en coupe longitudinale de la structure de la membrane d'un transducteur de grave avec sa suspension.

La figure 5 est une vue en coupe transversale de la figure 4 selon l'axe CC, représentant la membrane d'un transducteur de grave en position d'équilibre dans l'entrefer.

La figure 6 est une demi-vue en coupe de la figure 1 selon l'axe BB, représentant un mode de fixation d'une membrane d'un transducteur de grave sur le circuit magnétique.

La figure 7 est une vue arrière de la membrane d'un transducteur de grave après fixation entre les deux rangées d'aimants permanents.

La figure 8 représente un autre mode de fixation de la membrane d'un transducteur de grave.

La figure 9 est une vue partielle en coupe longitudinale de la membrane d'un transducteur médium-aigu.

La figure 10 représente une partie de la membrane d'un transducteur médium-aigu avant formation des pliures de la suspension.

La figure 11 représente la vue arrière du transducteur médium-aigu complet, avant fixation sur le baffle.

La figure 12 est une vue en coupe de la figure 11 selon la l'axe DD.

La figure 13 est une vue en coupe de la figure 11 selon la l'axe EE, représentant le mode de centrage de la membrane du transducteur médium-aigu entre les deux rangées d'aimants permanents.

La figure 14 est une vue en perspective de la cale assurant la fixation et le centrage de la membrane du transducteur médium-aigu dans son circuit magnétique.

The attached figures provide details of the various characteristics of the system:

Figure 1 shows the complete system whose hinged panels are fully deployed so as to form a flat baffle around the transducers.

FIG. 2 represents a partial rear view of the magnetic circuit as well as the principle of electrical connection of a group of four bass transducers.

Figure 3 is a sectional view of Figure 1 along the axis AA.

Figure 4 is a half-view in longitudinal section of the structure of the membrane of a bass transducer with its suspension.

Figure 5 is a cross-sectional view of Figure 4 along the axis CC, showing the membrane of a bass transducer in an equilibrium position in the air gap.

Figure 6 is a half-sectional view of Figure 1 along the axis BB, showing a method of fixing a membrane of a bass transducer on the magnetic circuit.

Figure 7 is a rear view of the membrane of a bass transducer after fixing between the two rows of permanent magnets.

FIG. 8 represents another method of fixing the membrane of a bass transducer.

Figure 9 is a partial view in longitudinal section of the membrane of a medium-acute transducer.

FIG. 10 represents a part of the membrane of a medium-acute transducer before formation of the folds of the suspension.

FIG. 11 represents the rear view of the complete mid-acute transducer, before attachment to the cabinet.

Figure 12 is a sectional view of Figure 11 along the axis DD.

Figure 13 is a sectional view of Figure 11 along the axis EE, showing the centering mode of the membrane of the mid-high transducer between the two rows of permanent magnets.

Figure 14 is a perspective view of the shim ensuring the fixing and centering of the membrane of the mid-acute transducer in its magnetic circuit.

The complete system shown in Figure 1 is consisting of a membrane transducer (2) restoring the spectrum mid-high and several identical transducers with membranes (1) dedicated to the low spectrum. These transducers are fixed on two profiled uprights (4) and are separated by a panel (8), both other panels (8) constituting the vertical termination of the cabinet plan. In the embodiment, the uprights (4) and the panels (8) are made of medium type reconstituted wood. On each side uprights (4), two shutters each consisting of three panels (5) (6) (7) identical, are articulated in relation to all of the transducers along a first vertical axis (11). The two groups three panels (5) (6) (7) are hinged together in two other vertical axes (11). The panel (8) placed above the medium-acute transducer must have a height at least equal to the quarter wavelength of spectrum separation frequency mid-high and low spectrum. In the embodiment, the panel (8) has a height of 20 cm, giving the assembly a total height of 160 cm after stacking the heights of each bass transducer and the two remaining panels (8). The circuit magnetic bass transducers consists of a structure in the form of a ladder comprising bars (3) of square section of soft iron whose side is equal to the width of a permanent magnet. The rows of permanent magnets are located on either side of each bar (3) with the exception of the two bars located at ends of the ladder that have only one row. The rows of permanent magnets are shown in Figure 1 by grid areas.

As presented in more detail in FIG. 2, the magnetic circuit also comprises two vertical bars of soft iron (9) of section smaller than the bars (3), constituting the uprights of the ladder and closing the magnetic circuit. For clarity, the permanent magnets (19) organized in rows are only numbered for the two bars (3) appearing at the top and bottom of Figure 2. The other blocks marked N / S or S / N are also magnets identical to the numbered blocks (19). The two other groups of transducers not shown in FIG. 2 are strictly identical and are placed in the continuity of the magnetic circuit formed by the bars (3) and the two uprights (9). Each bar (3) is fixed to the two profiled uprights (4) by means of two screws (10). Subsequently the two vertical bars (9) closing the magnetic circuit are fixed at the end of each bar (3) by means of two screws (12) as shown in Figure 3. Two rows of four permanent magnets (19) , which are of the ferrite 60x20x15 type in the embodiment, are glued on either side to each bar (3) generating a magnetic field (13) in each space free of any obstacle, between the faces of the permanent magnets (19). The two bars (3) located at the ends of the magnetic circuit forming the scale, comprise only a single row of four permanent magnets (19). In the particular embodiment using the previously described ferrite magnets, the spacing between the rows of magnets (19) was determined to be 35.5mm. The electrical interconnection strands (18), not shown in FIG. 2, make it possible to connect all the tapes in series so as to respect the direction of the current, thus ensuring a displacement in phase. The three groups are interconnected in series and are supplied by the appropriate channel of the frequency separator filter. The interconnection strands (18) are made of copper wire with a cross section of 1.5 mm ² and are kept glued to the uprights (9).

As described in FIGS. 2 and 4, the diaphragm (1) of a bass transducer consists of a flat part (28) (27) (28), corresponding to the driving surface of the piston, and of two rigorously identical suspension positioned at each end of said membrane. In view of this symmetry, for the sake of clarity, FIG. 4 represents only half of the membrane (1). The total width of the membrane (1) is equal to the spacing between two rows of permanent magnets (19) minus the clearance necessary for the displacement of the latter between said rows. The lateral displacement play having to be less than 1% of the total width of the membrane (1), in the embodiment example a width of 35mm is obtained. The structure of the membrane (1) consists of a sheet (27) of expanded polystyrene 2mm thick, on which are glued on each side, four aluminum strips (26) 18µ thick at regular intervals 1mm, as shown in Figure 5. The ends of the ribbons (26) extend longitudinally on either side of the sheet (27) of sufficient length so as to be glued respectively between two strips (25) of polyester , whose function is to keep the fold forming the suspension triangles while protecting the ribbons from breaking, one of these two strips is also glued to the end of the sheet (27). A sheet (28) of 12g / m ² paper of the same width as the sheet (27) is glued to the visible faces of the ribbons (26) in order to give the membrane the rigidity necessary for piston operation ensuring the linearity of its response curve. In the embodiment, the strips (25) sandwiching with the ribbons (26) are made of polyester 50 μ thick. The connector (15), consisting of a rigid printed circuit board of the same width and thickness as the sheet (27), is centered and then bonded according to the same method, between the strips (25) as shown in FIG. 4 A first fold is made along an axis (31) on the bands (25) supporting the ribbons (26), as indicated in FIGS. 4 and 7, forming the first triangle of the suspension. A second fold is made similarly on the other strip (25) in the opposite direction to the first, forming the second triangle of the suspension. This mode of suspension makes it possible to ensure a rectilinear displacement of the flat part of the membrane (1), minimizing the tensions and deformations generating distortions on this driving surface. The eight ribbons (26) are electrically connected by soldering at eight points (29) on the copper tracks (33) of the connector (15), engraved with the separation pitch of the ribbons as described in FIG. 8.

As shown in Figure 5, in order to reduce the effect of the acoustic short circuit, two reinforcement cheeks (30) are pasted on the edges of the back of the sheet (27). The cheeks (30) each consist of a sheet of expanded polystyrene 2mm thick on either side of which are stuck two sheets of paper weighing 12 grams per square meter. With the same objective of reducing this short circuit acoustic, two loops (35) are also cut from polyester strips 50µ thick, eliminating any air leakage on the longitudinal edges of the membrane (1). Each loop is glued over the entire length of the reinforcement cheek (30) and over the entire the length of the row of permanent magnets (19). A rib (34) of the same constitution as the sheet (27) is glued, at each end of the two reinforcement cheeks (30) and on the rear face of the sheet (27). Two other ribs (34) not shown on the Figure 4 are also fixed at regular intervals between those placed at the ends. Reinforcement ribs and cheeks, stiffening the entire membrane (1), reducing mechanical deformations causing distortion phenomena and avoid breaking the ribbons (26). To also minimize deformations of the membrane (1), its length is limited to 220mm in the embodiment, thus determining the number four permanent magnets (19) necessary for forming a row fixed on a bar (3).

According to the representation of Figure 6, in order to remove the effect of the acoustic short circuit around the suspensions, a case (21) tightly fixed on the bars (3) and the uprights (9) covers the suspensions, the rim (22) of said housing flush with the rib (34).

Each membrane (1) thus formed is attached to each of its ends, as shown in figure 6, on the circuit magnetic by means of a set of shims (16) and (17), non-electrically conductive material, blocking the connector (15). In the exemplary embodiment, the shims (16) and (17) are cut out. in a medium type reconstituted wood panel. The modes of attachment to the magnetic circuit, shown in Figures 6, 7 and 8 are identical for each of the two ends of the membranes (1). To make the drawings easier to read, the two cheeks of reinforcement (30) and the ribs (34) of the membrane (1) are not not shown in Figures 7 and 8. The width of the shim (16) is equal to the sum of two thicknesses of permanent magnets (19) plus the spacing between the rows of magnets (19). We obtain in the embodiment, a spacer (16) 65.5mm wide. The thickness of the shim (16) is such that the equilibrium position of the membrane (1) lies in a plane parallel and equidistant from two front and rear faces of the rows of permanent magnets (19). The shims (16) are glued on their two planes of contact with the bars (3). The wedge (17) holds the membrane (1) by blocking the connector (15), by tightening on the shim (16) by means of two screws (20) forming a flange with the shim (17) which spans the connector (15). According to a variant not illustrated, a sheet of absorbent material placed between the contact plane of the connector (15) and the shim (17) may be inserted in order to avoid any residual vibration of the connector (15).

Before final tightening of the four screws (20), the two connectors (15) at the ends of the membrane (1) are placed in support on the N face of the row of permanent magnets (19) by 0.25mm thickness adjustment shims to to adjust the side play to less than 1% of the total width of the membrane (1). All of the bars (3) supporting the magnets permanent (19) can be tightened on the two uprights (4) using screws (10) thanks to the positioning shims (16), before the centering of the membranes (1).

In another exemplary embodiment represented by the Figure 8, the connector (15) has two ears pierced by two holes (32) in which are placed two screws not shown on Figure 8, which allow to attach the membrane (1) to each end on the two shims (16), the shims (17) then no longer utility. In this embodiment of FIG. 8, the part of the connector (15) coming to be placed between the N and S faces of the two rows of permanent magnets (19) is dimensioned to integrate the lateral play of 1% of the total width of the membrane (1) thus avoiding adjustment with shims of thickness.

The rest of Figures 9 to 14 describe the constitution of the medium-acute transducer. Given the relatively frequent separation bass of the two spectra located around 400Hz in the embodiment, the membrane of this transducer must benefit from significant travel. The characteristics of magnetic circuit and the membrane are therefore identical to those described in the present invention relating to bass transducers, and allow you to benefit from the same improvements. However, in order to increase the yield of the medium-acute transducer and to minimize the heating of the ribbons, the magnets will provide a magnetic field of intensity greater than that of the field from the ferrite magnets and the number of ribbons will be increased compared to that defined for the membranes of bass transducers.

The magnetic circuit of the mid-treble transducer is independent of that of the bass transducers, and comprises as shows in Figure 11, two soft iron bars (51) of section square whose width is equal to that of a permanent magnet (50) and two sleepers (52) in soft iron, shown in line dotted, of identical section to the bars (51). Two rows of three permanent magnets (50), which are of the neodymium iron boron type 36x15x10 in the embodiment, are fixed on each bar (51), in the same way as the ferrite type magnets of bass transducers, generating as shown in Figure 12, a homogeneous magnetic field (13) in the free space of everything obstacle, between the faces of the permanent magnets (50). In this particular embodiment, the spacing between the rows magnets (50) has been limited to 12mm to ensure induction constant of 0.75T.

The constitution of the membrane (2) of the mid-acute transducer described in FIG. 9 exploits the same operating principle and the same manufacturing method as those used for the membranes (1) of the bass transducers. As described in FIGS. 9 and 10, the membrane (2) consists of a flat part (38) (37) (38), corresponding to the driving surface of the piston, and two rigorously identical suspensions positioned at each end of the said membrane. The symmetry being comparable to that of the membranes (1), only one half of the membrane (2) is therefore represented. The total width of the membrane (2) is equal to the spacing between two rows of permanent magnets (50) minus the clearance necessary for the movement of the latter between said rows. Given the small width of the membrane (2), the lateral movement clearance is fixed at 0.15 mm in the embodiment, determining a membrane width of 11.7 mm. The structure of the membrane (2) consists of a sheet (37) of light material such as expanded polystyrene 2 mm thick, on which are glued on each side, 6 aluminum tapes (40) thick 18µ at a regular interval of 1mm as shown in Figure 10. The ends of the ribbons (40) extend longitudinally on either side of the sheet (37) of sufficient length so as to be glued respectively between two strips (39 ) of polyester, one of which is also bonded to each end of the sheet (37). In the embodiment, the strips (39) are made of polyester of 50 μ. Two sheets (38) of paper of ²¹ g / m ² of width identical to the sheet (37) are glued to the visible faces of the ribbons (40) in order to provide a second element of rigidity improving the linearity of its frequency response. In the embodiment, the frequency of separation of the mid-high spectrum and the low spectrum having been fixed at 400Hz, the presence of the two reinforcement cheeks (44) proves necessary in order to maintain the same advantages as those described above. for the membranes of the bass transducers. The connector (42), consisting of a printed circuit board of the same width and thickness as the sheet (37), is centered then glued, between the two strips (39) as shown in Figure 10. The 12 ribbons (40) are electrically connected by soldering at 12 points (41) on the copper tracks (43) of the connector (42), engraved with the separation pitch of the ribbons. Two folds along the axes (36) are then performed on the bands (39) to form the suspensions as shown in Figure 9, and in all respects identical to those made on the membranes (1) whose advantages have been previously described in this document. One end of the membrane (2) thus formed is shown in Figure 10 before making the two folds forming the suspension.

The process of centering and fixing the membrane (2) on its magnetic circuit is similar to that already described in this document about membranes (1). The width of the shim (53) is equal to the sum of two thicknesses of permanent magnets (50) plus the spacing separating the rows of magnets (50). We get in the example of embodiment a wedge (53) of width 31.7mm. The thickness of the shim (53) is such that the equilibrium position of the membrane (2) lies in a plane parallel and equidistant from two front and rear sides of the rows of permanent magnets (50) as described in figure 12. The shims (53) are glued on their two contact planes with the bars (51). The centering procedure of the membrane (2) can be carried out according to the same procedure as the one used for the membranes (1), the shims 0.15mm thick replacing those of 0.25mm. In the example of embodiment, the two connectors (42) are bonded to the two shims (53). According to another possibility not illustrated, the connectors (42) may have a constitution similar to that described in FIG. 8 for the connectors (15), facilitating thus the centering procedure and that of a possible replacement. The two crosspieces (52) are subsequently fixed on the bars (51) thanks to four screws (56) and straddle, at the level of connectors (42), the membrane (2) without hindering its movement as shown in figure 13.

The electric strand (55) makes it possible to interconnect the 12 ribbons (40) and is kept glued to the bar (51). The twelve ribbons (40) are connected in series in such a way that the modulation current flows through them in an always identical direction with respect to the magnetic field. This mid-acute transducer is fixed to the cabinet by means of four screws not shown in Figure 11, which are placed in the four mounting holes (54). It is then electrically connected by terminals A and B on the corresponding channel of the filter separating frequencies.

Claims (9)

Sound reproduction system reproducing the entire audible spectrum characterized in that it comprises several identical transducers reproducing the low frequencies, comprising membranes (1) supporting ribbons, and a transducer reproducing the mid-high frequencies comprising a membrane (2) similar in structure to the membrane (1), all of these transducers being fixed to a flat baffle made up of articulated panels (5) (6) (7) which can be folded up in the form of a column. Sound reproduction system according to claim 1 characterized in that the membranes (1) (2) consist of rectangular flat elements (27) of light material of specific thickness on which are glued, parallel in the direction of the greatest length, several flat conductive tapes (26) on both sides of said elements, thus ensuring the membranes their rigidity and their displacement comparable to that of a piston, the efficiency of this process being proportional to the thickness of the rectangular planar elements (27). Sound reproduction system according to claim 2 characterized in that the conductive tapes (26) of the membranes (1) (2) are covered with a thin and light film (28), giving them a second element of rigidity improving the linearity of their frequency response. Sound reproduction system according to Claim 2, characterized in that the membranes (1) (2) are provided with reinforcing cheeks (30) and ribs (34), forming with the planar element (27) a rigid, non-deformable motor structure. reducing the effect of the acoustic short circuit around said membranes. Sound reproduction system according to claim 4 characterized in that the reinforcement cheeks (30) and ribs (34) of the membranes (1) are equipped with additional members consisting of loops (35) and housings (21) (22 ) canceling the effect of the residual acoustic short circuit around said membranes. Sound reproduction system according to any one of the preceding claims, characterized in that the membranes (1) move in air gaps bathed by magnetic fields (13) free of any obstacle, produced by a magnetic circuit in the form of a ladder uprights (9) and bars (3) supporting permanent magnets (19). Sound reproduction system according to Claim 6, characterized in that the magnetic circuit is reduced to a rectangular frame consisting of crosspieces (51) and bars (52) supporting only one row of permanent magnets (50), when the transducer has only one membrane (2). Sound reproduction system according to Claim 2, characterized in that the membranes (1) (2) of the transducers are held in the magnetic fields (13) by suspension members (25) (39) forming a double triangle with large clearance, ensuring a very low resonance frequency and eliminating the phenomena of roll of the membranes (1) (2). Sound reproduction system according to Claim 2, characterized in that the suspension members (25) (39) are fixed on rigid connectors (15) (42) ensuring precise centering of the membranes (1) (2) between the faces of the permanent magnets (19) (50).

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