MXPA01000037A - Loudspeakers. - Google Patents

Abstract

A flat panel rectangular or elliptical loudspeaker has one or more anisotropic diaphragms (14, 15), made of double skinned fluted polypropylene copolymer (core flute) or corrugated cardboard, having a longitudinal bending strength greater than the transverse bending strength. The diaphragm is vibrated by a driver unit (16) which comprises a magnet (17) and voice coil (18). In this version the magnet (17) is mounted on the rear diaphragm (15) and the voice coil (18) is mounted on the front diaphragm (14). The two diaphragms (14, 15) are mounted at their edges to a frame (11) with the driver unit (16) mounted in the space enclosed by the frame and the diaphragms.

Description

ALTOPARLANTES FIELD OF THE INVENTION This invention relates to loudspeakers and is particularly applicable, among others, to loudspeakers intended to be hung on a wall in the manner of a frame.

BACKGROUND Flat loudspeakers have been known to many artisans, for example, electrostatic loudspeakers. However, these speakers had to be large and, therefore, so). uncomfortable, to produce a satisfactory sound level. They have been expensive and have had a sound frequency response and a less than desirable sound distribution pattern. So many other types of flat loudspeakers have been devised, to be installed on the wall, but again in various forms they have suffered from lower frequency response or stereophonic performance. DETAILED DESCRIPTION OF THE INVENTION In a first aspect of the present invention, a loudspeaker is provided that includes a first substantially flat diaphragm, which can be vibrated so as to emit sound from at least the front side thereof, and an electro-acoustic motor, operable by a variable electric current to generate variable force in the first diaphragm, the force that varies in a manner related to the variable electric current, characterized in that the electroacoustic motor is connected to the first diaphragm in one or more positions chosen or mounted to a structure that its once it is connected to the diaphragm in one or more chosen positions. Iris preferable that the diaphragm material is anisotropic (with different characteristics in each of its main axes). It is preferable that the material (without openings) have flexural strength in one direction of the material plane, which is significantly greater than the flexural strength along a line in the material plane at right angles to the first direction . I ii your outbound end * > R > "Aunt has a resistance to longitudinal bending, which is close to the double lie of her MiCi-a to i; i transverse bending * which is particularly convenient for panels that are rectangular or elliptical. Preferably the loudspeaker includes a substantially rigid peripheral frame having a front side and a rear side, said first diaphragm extends exactly on the front side and a rear diaphragm extending just on the rear side, so as to enclose substantially the interior space of the loudspeaker.

It is convenient for the electro-acoustic motor to be located within said space distant from the frame. It is an advantage that the electro-acoustic motor is located outside said space, distant from the frame. It would be preferable for the electroacoustic motor to be connected to both diaphragms, so that the electroacoustic motor applies the variable force corresponding to the variable electric current to said diaphragms and causes at least one of said diaphragms to flex and emit an acoustic signal. from the diaphragm side to the outside of the loudspeaker. It is convenient that both diaphragms are flexible and that the electro-acoustic motor operates the diaphragms in a bipolar manner, that is, they move together outwards or inwards. It is preferable that one of said diaphragms be flexible and the other rigid. The electro-acoustic motor is conveniently mounted on the diaphragm in one or more of said chosen positions, these positions being distant from the peripheral edge of the diaphragm. The electroacoustic motor is advantageously mounted on a body, which is mounted on pillars in the diaphragm in said positions. Ready positions are preferably chosen so that the bending of the diaphragm in one or more of its natural modes of vibration is not impeded. Said first diaphragm and / or said rear diaphragm can be double-sided polypropylene copolymer and can be approximately 3mm wide. It is convenient that the or each diaphragm weighs approximately 500 grams or less per square meter and may have a tensile strength of about 28 MPa or more and may have a Shore hardness of 67 or more. It is preferable that the surface of each diaphragm be treated with a corona discharge to aid adhesion of the paint or paper to that or diaphragm to the frame. The or each diaphragm conveniently has longitudinal ribs that form part of its structure, perhaps on one of its sides, although in its preferred form they are internal (this is covered by soft front and back sides). Preferably these ribs have a core of corrugated material or the like and can be square or rectangular and each edge is about 400mm long.

Advantageously the electroacoustic motor includes two coaxial mobile coils, each subject to a diaphragm other than those mentioned, the moving coils act together with a magnet suspended centrally between said moving coils. The or each diaphragm is suitably slightly corrugated or corrugated or slightly curved, so as to provide a modified acoustic performance of the loudspeaker.

The interior of the loudspeaker can constitute a sealed box. Alternatively one or more holes or vents may be provided through the frame or through one or both of said diaphragms. It is preferable that the first diaphragm is made of a sheet of extruded plastic material having a front side and integral faces joined by parallel walls with very little separation, normal to said faces. In another aspect, the invention provides a loudspeaker that includes a substantially planar diaphragm that can be vibrated so as to emit sound from at least the front side thereof, and an electroacoustic motor operable by variable electric current to generate variable force in the diaphragm; the variable force is related in a certain way to the variable electric current, in which the diaphragm is made of sheets of parallel material front and rear, said sheets are separated by a plurality of walls extending between said sheets and these walls which are parallel to each other and extend substantially normal with said sheets or which are generally rhomboidal or sinusoidal in shape. The diaphragm is preferably double-sided polypropylene copolymer and the walls are substantially normal for said parallel sheets, alternatively the diaphragm is made of paper or cardboard, said walls being substantially corrugated in shape and fixed by adhesive to the opposite sides. interiors of the parallel sheets.

It is convenient that the electro-acoustic motor includes a magnet, one of whose poles is in magnetic continuity with a fork and the other pole of which is located from the I. | itil: > r a separation of air through which a moving coil can be operated, the al csi. attached to activate the diaphragm. It is important that the magnet be a permanent cylindrical magnet and the fork be coaxial with said air separation being annular. It is preferable that the magnet be a permanent magnet or resistance as a neodymium magnet. advantageous that the fork is made of pure iron of low oxygen, annealed very lamente in hydrogen.

It would be convenient if the mobile coil had more windings per unit length of that. far from the axial part of the moving coil, which is inside said air gap when no electric current is passed through the windings.

For this purpose, the winding of the moving coil is of a single layer, with the turns separated in the region of said axial part. It is preferable that the moving coil be made of pure copper (although aluminum wire can also be used). Alternatively or in addition, more than said single layer is wound in the regions of the moving coil past said axial part. According to another aspect of the present invention, a loudspeaker is provided that includes a diaphragm that can be vibrated so as to emit sound from at least the front side thereof and an electroacoustic motor operable by means of variable electric current to generate a variable force on the diaphragm, the variable force, in a certain way, is related to the variable electric current, in which a moving coil of the electroacoustic motor is connected to said diaphragm by means of a panel of material, said panel being of a material and having such dimensions that at a range of low audio frequencies, the voice coil and at least that part of the diaphragm adjacent to the panel move substantially at the same amplitude and phase, while at a range of higher audio frequencies at least said part of the diaphragm and a part of the panel adjacent thereto will be moved to a lower amplitude and / or to a different phase of the moving coil, wherein at said frequencies more A substantial part of the sound emitted by the loudspeaker is radiated from one side of the panel adjacent to the voice coil. It is preferable that the diaphragm be a flat diaphragm. It would be convenient for a sheet of cushioning material to be connected from a stationary part of the speaker to said part of the diaphragm adjacent to the panel or panel. I I cushioning material can be fabric or fabric based. It is preferable that the cushioning material is porous or perforated so as to allow air to pass through it. BRIEF DESCRIPTION OF THE DRAWINGS One of the embodiments of the invention is described, given by way of example only, with reference to the accompanying drawings in which: Figure 1 is a front view of a loudspeaker according to the invention, and ') Fineness 2 is a cross section in a vertical plane along line II-ll in fK' and 1.a Figure 3 shows rear and side views of an alternative embodiment. Figure 4 is a partial perspective view of a loudspeaker component, Figure 5 is a cross section of another embodiment, 1. Figure 6 is a first back view of the embodiment shown in Figure 5, and Figure 7 is a second modified rear view of the component shown in the Figure 4. Figure 8 is a cross section through another embodiment.

Figure 9 is a side view of a moving coil shown in the section of Figure 8.

DESCRIPTION KJKMPLO 1 In the drawings, a flat loudspeaker 10 includes a peripheral square frame 1 1 conveniently made of medium density fiber sheet. It is convenient that each outer edge of the frame 1 1 is 400mm long. The frame is suspended by wires or cords 12 attached to rings or other fasteners 13 in the upper part of the frame 1 1. As seen particularly in Figure 2, the front part of the speaker 10 is covered by (iii front diaphragm 1, the which is attached and sealed around the edges thereof to the front face of the frame 1 1, by means of an appropriate adhesive .. Similarly the rear part of the loudspeaker l ü is covered by a rear diaphragm 15 attached and sealed to the rear side of the frame sealed box Normally, the thickness between the front and back sides of the diaphragm 14 is 30 millimeters for a square speaker of 400 millimeters.Your has found that a material suitable for the front and rear diaphragms 14. 15 is a double-sided sheet made of polypropylene copolymer approximately 3 millimeters thick and approximately 500 grams per square meter or less, it is preferable that the sheet be It has a resistance to tension of about 28 MPa as and Shore hardness of 67 or more. The material preferably has a surface with corona discharge to assist the adhesion of the paint or of the wall paper to exterior surfaces of the diaphragms 14, 15 and to assist the adhesion of the Citeriores surfaces of the diaphragms 14, 1 to the frame 1 1. It is preferable that the sheet is laminated and engages a core formed by ribs, tubes or corrugations or the like. One of these aterials is known as "core ilute" material (grooved to the center) by the shape of the longitudinal internal "nails" or corrugations - see Figure 4 (discussed below), or "Practical material is lightweight corrugated cardboard.

The electro-acoustic motor 16 is located adjacent to the center of the diaphragms 14, 15. The electro-acoustic motor is similar to those used in conventional cone-type loudspeakers and includes a magnet 17, which may be a permanent magnet or an electromagnet, and a moving coil joint action 18. The mobile coil 18 carries the usual winding connected by conductors 19 to the terminals 20 on the back of the loudspeaker 10. The magnet 17 is attached, for example, by an adhesive, to the interior surface of the rear diaphragm 15. and the moving coil 18 is attached to the inner surface of the front diaphragm 14. The dimensions of the electroacoustic motor 16 and the spacing between the front and rear diaphragms 1 5 are arranged so that the moving coil 18 is in the correct operating position. with respect to magnet 17 and appropriately centered on that. Depending on the acoustic properties required of the loudspeaker 10, the inside of the loudspeaker 10 may be, at least partially, filled with fibrous material or other sound absorbing material or may be left empty. Similarly, one or more holes or vents can be made in the frame 1 1 or the diaphragms 1, 15. Although the loudspeaker 10 has been shown as a squareIt could be circular, elliptical, rectangular, polygonal and / or other suitable shape. If required, more than one acoustic-electric motor 1 can be provided in suitable locations within the loudspeaker 10. In another embodiment, the front diaphragm 14 or the rear diaphragm 15 can be of substantially rigid material. In addition, the magnet 17 can be fitted to the front diaphragm 1 the moving coil 18 to the rear diaphragm 15. For some purposes it would be preferable to provide two coaxial mobile coils 18. each subject to a different diaphragm 14, 15 and acting in conjunction with a suspended magnet in central form 1 7. Conversely, two magnets 17 can be provided in the diaphragms 1. 15 acting together with a centrally suspended moving coil 18. Either of the surfaces of each diaphragm 14, 15 can be slightly grooved and instead of any of the diaphragms being flat, it could be corrugated or curved, so as to provide a modified acoustic performance of the loudspeaker 10.

EXAMPLE 2 In Figure 3 the frame 1 1 and the rear diaphragm 15 are omitted. The magnet 17 is mounted on a plate 21, which is mounted on the diaphragm 14 on the pillars 22. The pillars 22 are in carefully selected positions on the diaphragm 14, so as not to prevent the diaphragm from being carried in one of its natural modes, for example as shown on line 23. Magnet 17 can be mounted between plate 21 and diaphragm 14, or at the rear of plate 21, as shown. ? alt > The speaker shown in Figure 3 may be suspended from the upper edge of the iafrma 14 or from the plate 21 p of the pillars 22.

Figure 4 shows a preferred construction for the front diaphragm 14. It comprises an integral polyethylene extrusion of about 3-5mm in thickness, the front and rear faces 25, 26 having been joined by longitudinal continuous walls 27 with air spaces around them. By this construction, the material of the diaphragm 14 is anisotropic and has a longitudinal bending strength, which can normally be about twice the resistance to transverse bending. Thus this material is particularly useful in the construction of rectangular loudspeakers, for example for those that have sides of 200mm x lOOmm long. Longer panels or more cones can be made using this type of material.

EXAMPLE 3 Figure 5 shows a loudspeaker having a rigid rear panel 28 of custom-made wood about I 2 mm thick, with the magnet 17 fixed at the center thereof. The frame 1 1 maintains the front diaphragm 14 at a distance of about 3-5mm from the front side of the panel 28. The moving coil 18 is maintained in the gap within the magnet 17, by being fixed in a central hole of the diaphragm 14. The orifice is closed by a concave cap, spherical part 29, attached to the movable coil 18. To allow the desired movement of the diaphragm 14, the panel 28 (shown in Figure 6) has a series of holes or vents 30 through it. he. The sizes and locations of the holes 30 are carefully chosen to achieve a smooth frequency response of the loudspeaker 10. The alternative or additional modification of the frequency response curve is achieved by adhering material that adds mass 31, as shown in FIG. Figure 7. A suitable material is the bituminous sheet loaded with metallic or mineral particles. Further adjustment of the frequency performance can be obtained by adding areas of sound absorbing matter 32 to the diaphragm 14 or to the front side of the panel 28, as shown in Figure 7. The supply of the electrical signal to the moving coil 18 is conveniently performs by gluing strips of copper sheets to one side of the diaphragm 14. EXAMPLE 4 In Figures 8 and 9, a loudspeaker 1 10 includes a diaphragm III, which will be described later. The outer edge of the diaphragm 1 1 1 is gripped by the outer edge of a metal or substantially rigid plastic plate 1 12. For this purpose the plate is provided with a plate 1 13 on which the diaphragm 1 1 1 rests, located the diaphragm 1 1 1 by a substantially vertical wall 1 14 and grasped by a part of the edge 1 IS of the plate 1 12. which bends or winds on the outer edge of the diaphragm 1 1 1. The central part of the plate 1 12 it is formed as a cup 1 16 in which a cylindrical yoke 1 17 is located. In this way, the plate 1 12 serves to center the yoke 1 17 with respect to the diaphragm 1 11, where the yoke 1 19. ieb'u . , that the fork 17 is part of a magnetic circuit, it is preferable to make it pure iron low in oxygen, which has been slowly annealed in hydrogen. A permanent magnet 1 18 is maintained coaxially with the fork 1 17 by means of adhesive. One of the poles of the magnet 1 18 is in magnetic contact with the upper internal surface of the yoke 1 17 and the other pole is adjacent to a disk 135, of the same material and thickness as the rim 120 of the fork 1 17. In this way, an annular magnetic separation 121 is formed between the flange 120 and the upper part of the magnet 1 18. A cylindrical moving spool 122 extends through the separation 121. The fork material serves to maintain the magnetic flux lines within the fork 17, which minimizes undesirable external magnetic fields and also concentrates the flow through the separation 121. In an opening 123 through the diaphragm 1 1 1, there is located and fastened a panel 124 of thin material, usually 0.25mm thick aluminum. The panel 124 has an outwardly turned flange 125 attached to the diaphragm 1 1 1. The moving coil 122 is adhesively secured to a groove 126 formed in the pane! 124, so that the moving coil 122 is concentrically maintained within the separation 121. The movement of the central area of the diaphragm 1 1 1 is cushioned by a damper ring 127 which can be made of cloth or material similar to the fabric, of corrugated preference and is attached by an adhesive to the upper surface of the flange 120 and to the flange 125 and / or to the diaphragm 1 1 1. The plate 1 12 can form an airtight enclosure with the diaphragm 1 1 1 and the panel 124. but if it is preferred, holes or perforations may be provided in the platen 1 12. The blank space within the loudspeaker 1 10 may include fibrous sound absorbing material or plastic foam. The thickness and material of the panel 124 are chosen, so that, for example, at frequencies up to 1000 Hz the panel 124 acts as a substantially rigid member and moves the adjacent area of the diaphragm 1 1 1 when the alternating current passes through the windings 128 in the moving coil 122. At frequencies above 5000 Hz the flexure of the panel 124 is such that the periphery thereof and the adjacent areas of the diaphragm 1 1 1 move much less than the moving coil 122 and the central area of the panel 124 Thus, at these high frequencies the sound is emitted almost completely from the central area of the panel 124. Between those frequencies the sound emission occurs from only a small area of the diaphragm 1 1 1 and from parts of the panel 124.

To modify the frequency response of the loudspeaker i 10 on large excursions of the moving coil 122, the winding 128 may have more turns per unit length towards the ends of the winding 128 than at the center thereof. This can be achieved by spacing the windings in the center or by narrowing the winding of the turns to the full length thereof and adding one or more layers 129 adjacent to the ends thereof. The coils "wind up in a winding template 136 having perforations 137. 1 4 encentrado that a material suitable for the diaphragms 1 1 1 is a sheet of double-sided polypropylene copolymer of approximately 3 millimeters and of approximately 500 grams per square meter or less. It is preferable that the diaphragm I have a tensile strength of about 128 Pa or more and Shore hardness of 67 o .s. The material preferably has a surface treated with corona discharge to aid adhesion of the paint, wallpaper, etc. for the diaphragms I I I. The diaphragm 11 is preferably a sheet having a center of foam, or has ribs, tubes, corrugated sheet or the like. If it has foam center, it is preferable that the foam is not uniform (or the sheets of the cover are molded or reinforced). For example, the foam center could be molded or reinforced in such a way that the flexural stiffness is greater in one direction than in the other. ?? Diaphragm 1 1 1 may comprise an integral polyethylene extrusion of about 3 to 5 in m thick and having front and rear faces 130, 131 joined by continuous longitudinal walls 132 with air spaces therebetween. By this construction, the material of the diaphragm I i I is anisotropic and has a longitudinal bending strength that can normally be close to twice the resistance to transverse bending. In this way, this material is particularly useful in the construction of rectangular loudspeakers, for example, those that have sides of 200mm x 100mm in length. Figure 8 shows the use of a retaining ring 138, of thin aluminum or the like. The ring 138 has a flange 139, which can press down on the external face 130 of the diaphragm 1 1 1. An integral cylindrical portion 140 can be pushed down between the edge of the opening 123 and the outer surface of the cylindrical part. of the panel 124, which has a rib 142 that fits perfectly into a slot 141 in the portion 140 of the ring 138. The rib 142 and the slot 141 can be inverted, if preferred.

ADVANTAGES OF THE PREFERRED EMBODIMENTS: Easy to manufacture. Good acoustics achievable with a low construction cost. Lightweight diaphragm material, particularly suitable for rectangular or elliptical panels. Can be manufactured to scale The loudspeakers or diaphragms can be made in many different shapes or sizes or easily disguised as other objects. This invention is suitable for flat panel speakers of AS or smaller size that are especially suitable for the multimedia market, or for inclusion in vehicles embedded in the panels or in the doors of vehicles. They can-operate in any orientation and, depending on the design, can be provided with or without a frame. ? VCN ES: S '> uci isar one or more electroacoustic motors depending on the size of the diaphragm. The speakers should be ionized by drilling or adding weight. In the drawings we have not, the holes in the back panel (Figures 6 and 7) but sir JS holes can be provided in the diaphragm material. The panels can be tuned by using powdered material such as sugar or similar on the panel when it is horizontal so that nodes can be observed on the panel. The diaphragms can be made in any way (for example, they could have irregular profiles if necessary). It is not necessary to be flat although you prefer it that way. Other materials can be used in addition to corrugated cardboard or "core flute". Preferably, the material should be light and firm but flexible. In the preferred embodiments, exempted "core flute" of 3 mm thickness has been used, but other thicknesses between 2mm and 5mm could be used for most applications. Larger panels may require more electro-acoustic motors and a thicker "core ilute" diaphragm.

The speaker could be disguised as part of a vehicle, a piece of furniture, a box, a painting or almost any object, since they are no longer a restriction of form or size. In one example, we have included flat-panel loudspeakers as part of the vehicle's dashboard and in another application we have made a painting work as a loudspeaker. Finally, various alterations may be made or modifications to the foregoing without departing from the scope of this invention as set forth in the following claims.

Claims (8)

1. CLAIMS 1. A loudspeaker that includes a substantially planar first diaphragm that can vibrate so as to emit sound from at least the front side of it. and an electroacoustic motor operable by a variable electric current to generate a variable force in the first diaphragm, such force varying somewhat in relation to the variable electric current, characterized in that the material of the first planar diaphragm is an isotropic and in that the Electroacoustic moior is connected to the first diaphragm in one or more selected positions or mounted in a structure which, in turn, is connected to the diaphragm in one or more selected positions.
2. 2. A loudspeaker according to claim 1 characterized by a substantially rigid peripheral frame having a front side and a rear side, said first diaphragm extending exactly across the front side and a rear diaphragm extending exactly across the rear side, of so that the interior space of the loudspeaker is substantially enclosed.
3. 3. A loudspeaker according to claim 2 characterized in that the electroacoustic motor is connected to said two diaphragms so that the electroacoustic motor applies a variable force corresponding to the variable electric current to said diaphragms and will cause at least one of said diaphragms to flex and emit an acoustic signal from the diaphragm side to the outside of the loudspeaker.
4. 4. A loudspeaker according to claim 1 characterized in that said first diaphragm and / or said posterior diaphragm is made of double-sided polypropylene copolymer.
5. 5. The loudspeaker according to claim 1, characterized in that the first diaphragm is made of a sheet of extruded plastic material having an integral face and faces joined by parallel walls spaced closely, normal to said faces.
6. 6. A loudspeaker according to any preceding claim characterized in that the or each diaphragm has approximately 500 grams or less per square meter.
7. 7. A loudspeaker according to any preceding claim characterized in that the or each diaphragm has a tensile strength of about 28 MPa or more.
8. 8. A loudspeaker according to any preceding claim characterized in that the or each diaphragm has a Shore hardness of 67 or more. The method according to any preceding claim characterized in that the one or each diaphragm is treated with a corona discharge to aid in the adhesion of paint or paper thereto, or from the diaphragm to the frame. 10. A loudspeaker according to any preceding claim characterized in that the eietro-acoustic motor includes two coaxial mobile coils, each moored to a diaphragm different from those mentioned, the moving coils acting together with a magnet suspended centrally between said movable coils. eleven . A loudspeaker including a substantially planar diaphragm which can be vibrated so as to radiate sound from at least the front side thereof, and an electric-acoustic motor operable by a variable electric current to generate a variable force in the diaphragm, such force varying in some degree. way in relation to the variable electric current, characterized in that the material of the diaphragm is anisotropic and the diaphragm is made of parallel sheets, front and rear, of material, said sheets being spaced and separated by a plurality of walls extending between said sheets, and said walls being parallel to each other and extending substantially normally towards said sheets, or being corrugated in shape generally rhomboidal or sinusoidal. 12. A loudspeaker according to claim 1 characterized in that the diaphragm is of double-sided polypropylene copolymer and the walls are substantially normal for said parallel sheets. 1 . A loudspeaker according to claim 1 characterized in that the diaphragm is made of paper or cardboardsaid walls being substantially corrugated in shape and being fixed by adhesive to the opposite inner sides of the parallel sheets. 14. A loudspeaker according to claim 1 wherein the eietro-acoustic motor includes a magnet, a pole of which is in magnetic continuity with a fork and whose other pole is separated from the fork by an air space through which a motor is operable. mobile coil, the moving coil being connected to activate the diaphragm, characterized in that the fork is made of pure oxygen iron rLv «. * Ho very slowly in hydrogen. alu triante according to claim 14 characterized in that a member. lin! my not material than the fork, it is in magnetic continuity with Ji / t. | Or magnet hair, the air space forming between a portion per! I told her member and an opposite part of the fork. 6- a'10 '!' Iani c according to claim 15, characterized in that said portion "(erk member" and said opposite part of the fork are substantially the same thickness. A loudspeaker according to claim 1 characterized in that the moving coil has more windings per unit of length of that, away from that axial part of the moving coil that is in said air space when no electric current passes Through the windings. A loudspeaker according to claim 17, characterized in that the winding of the movable hollina is of a single layer, with the windings spaced one from the other in the region of said axial part. The loudspeaker according to claim 17, characterized in that more than said single layer is wound in regions of the moving coil beyond said axial part. A loudspeaker according to claim 1 characterized in that the moving coil of the electroacoustic motor is connected to said diaphrby means of a panel of material, said panel being of a material and having dimensions such that at a range of low audio frequencies, the coil mobile and at least that part of the diaphradjacent to the panel move substantially at the same amplitude and phase, while at a range of higher audio frequencies at least said part of the diaphrand a part of the panel adjacent to that move with a smaller amplitude and / or a different phase of the moving coil, whereby at said higher frequencies a substantial part of the sound emitted by the loudspeaker is radiated from one side of the panel adjacent to the moving coil. A loudspeaker according to claim 1 characterized in that a sheet of damping material is connected from a stationary part of the loudspeaker to said part of the diaphradjacent to the panel or to the panel, and in that the damping material is porous or perforated so as to allow the air pass through it. A loudspeaker according to claim 21, characterized in that the damping material is fabric or fabric based.