FR3132403A1 - ISODYNAMIC CROSS-WINDING PLANE LOUDSPEAKER - Google Patents

Abstract

ISODYNAMIC FLAT SPEAKER WITH CROSSED WINDS The loudspeaker comprising a diaphragm (2) of the flat type and a first assembly formed by a flat winding (3) supported on a first face of said diaphragm (2) and at least a bar magnet (6) fixed to a first support (7) facing the first face. The winding is formed of conductive strips (5) parallel to each other and the at least one bar magnet is arranged parallel to the conductive strips and has a North/South magnetic field direction perpendicular to the conductive strips. According to the invention, the loudspeaker comprises a second assembly formed by another flat winding (4) supported on a second face of the membrane and at least one other magnetic bar fixed to another support facing the second face, this second set having a general configuration similar to the first set but being arranged perpendicular to the latter. Fig.1

Description

ISODYNAMIC PLAN LOUDSPEAKER WITH CROSSWINDS

The invention concerns the design of a system capable of reproducing acoustic signals, from very low frequencies to the medium.

It aims more precisely to create an isodynamic planar loudspeaker (also called “planar” or magnetostatic) capable of generating very high quality bass and sub-bass sounds.

Planar, or isodynamic, loudspeakers are part of the family of electromagnetic transducers. They operate on the basis of the electromagnetic force generated by an electric current: the electric current circulating in a conductor placed in a magnetic field generates an electromotive force capable of moving a membrane. The movements of the membrane produce a sound wave which is the image of the electrical signal.

Concretely, such planar speakers include metal ribbons, through which electric current is circulated. They also include magnets (to generate a magnetic field) as well as plastic or paper membranes to reproduce sounds.

The invention concerns this type of so-called “plane”, “planar” or “isodynamic” loudspeakers: they are also well known in the art and they have advantages over electrodynamic loudspeakers with conical membranes. In particular, these planar loudspeakers may have better sound dispersion characteristics, compared to the characteristics of cone-diaphragm loudspeakers, because they emit plane waves rather than a "point" source. When listening, there is no sensation of sound projection.

These speakers also have other advantages: when used in large areas, these speakers operate as a dipole emitting identical sound on both sides, producing immersive and natural listening. These are very fast loudspeakers in their vibrational movements because they have a light moving assembly (comprising a membrane associated with a coil), which makes it possible to avoid dragging problems linked to the inertia of the membrane. These isodynamic speakers also differ from electrostatic speakers by having a stable electrical impedance that does not disturb the audio amplifier in its operation. Additionally, these speakers do not require an external power supply.

The limits of “planar”, “planar” or “isodynamic” loudspeakers appear for the reproduction of low and very low frequencies without distortion. The electromotive forces generated by the conductive ribbons are not exerted uniformly on all the surface of the thin membrane, thus causing deformations of it. The good reproduction of low sound frequencies requires significant mechanical movement and good mechanical control of the movements of the membrane is decisive in the good reproduction of the impacts of bass sounds.

From documents WO02059879, GB2123651, FR2137567, US4480155, US6104825, US7142688, different “planar” or isodynamic type speakers are known. However, none of these documents proposes a relevant solution to guarantee good control of the vibrational behavior of a large flat membrane having to reproduce low frequencies.

In its French patent application FR3054767A1, the inventive entity proposed an isodynamic planar loudspeaker offering improved performance.

However, there is a need for an improved isodynamic planar loudspeaker capable of reproducing bass and sub-bass sounds with very good control of the behavior of the membrane for perfect frequency linearity in the low end of the audible spectrum, and which provides realistic reproduction, without distortion, of the physical impacts of a large orchestra.

The invention relates to an isodynamic planar loudspeaker comprising a planar type membrane, a first flat winding supported on a first face of the membrane and at least one first magnetic bar fixed to a first support facing the first face, the first winding comprising a first series of first conductive ribbons parallel to each other, each first conductive ribbon being connected to at least one other first parallel and adjacent conductive ribbon by at least one end of the conductive ribbon, and the at least one first magnetic bar being arranged parallel to the first conductive ribbons and having a North/South direction of magnetic field perpendicular to the first conductive ribbons. In accordance with the invention, the loudspeaker also comprises a second flat winding supported on a second face of the membrane, electrically isolated from the first winding, and at least one second magnetic bar fixed to a second support facing the second face and arranged perpendicular to said at least one first magnetic bar, the second winding comprising a second series of second conductive strips parallel to each other and perpendicular to the first conductive strips, each second conductive strip being connected to at least one other second conductive strip parallel and adjacent by the at least one end of conductive ribbon, and said at least one second magnetic bar being arranged parallel to the second conductive ribbons and having a North/South direction of magnetic field perpendicular to the second conductive ribbons.

According to a particular characteristic of the loudspeaker of the invention, at least one magnetic bar is bipolar and comprises an adjacent North pole and a South pole.

According to another particular characteristic, at least one magnetic bar is formed of two monopolar magnets which are arranged alternately with a North pole and a South pole located on either side of a conductive ribbon.

According to yet another particular characteristic, at least one magnetic bar has a width corresponding to that of a conductive ribbon.

According to yet another particular characteristic, at least one magnetic bar has a width greater than that of a conductive ribbon.

According to yet another particular characteristic, at least one support is formed from a perforated sheet metal. In other embodiments, the magnet support may be a frame made of chipboard (MDF), plywood, composite materials or plastics.

According to yet another particular characteristic, the membrane is formed of a thin electrically insulating material. Thus, the membrane could be formed from a sheet of paper or a plastic film such as polyester. In other embodiments, the membrane may be formed from a non-ferrous metallic film or a composite material.

Thus produced, the loudspeaker according to the invention vibrates the membrane simultaneously along longitudinal and vertical lines of force. These crossed windings constitute a mesh which guarantees uniform movement of the membrane without deformation even with strong movements.

The loudspeaker according to the invention may have the following characteristics, taken separately or in combination:

- The magnetic assembly is formed of bipolar magnet bars, as mentioned above.

- The magnetized assembly is formed from alternating bars of parallel monopolar magnets, as mentioned above, arranged in front of the empty spaces separating two adjacent conductive ribbons.

- The flat windings placed on either side of the membrane can be identical in pairs.

- The flat windings placed on either side of the membrane can be of different shapes and sizes.

- The windings can be unitary on each side of the membrane.

- There can be multiple windings on each side of the membrane in order to specialize the different zones of it according to the frequency range to be reproduced, for example bass and medium.

The loudspeaker manufacturing procedure is well mastered and is similar to that described in the aforementioned French patent application FR3054767A1 of the inventive entity.

The invention is applicable to the production of loudspeakers for various and varied applications such as:

- The production of high-fidelity speakers.

- The creation of professional sound systems.

- The production of subwoofers.

- The creation of amplification systems for musical instruments.

Other advantages and characteristics of the present invention will appear more clearly on reading the description below of several particular embodiments with reference to the appended drawings, in which:

There is a partial schematic sectional view of a planar loudspeaker conforming to a first embodiment according to the invention.

There is a side representation of the membrane equipped with its two windings of a square speaker according to the invention.

There is a representation of the front face of the membrane equipped with its vertical winding of a square speaker according to the invention.

There is a representation of the rear face of the membrane equipped with its horizontal winding of a square loudspeaker according to the invention.

There is a perspective representation of the membrane equipped with its two windings of a square loudspeaker according to the invention.

There is an exploded side view of all the magnets positioned on either side of the membrane for the production of a square speaker according to the invention.

There is a top view of all the magnets positioned on either side of the membrane for the production of a square speaker according to the invention.

There is a top view of the assembly formed by the membrane, windings and magnets of a square loudspeaker according to the invention.

There is a perspective representation of the assembly formed by the membrane, the windings and the magnets of a square loudspeaker according to the invention.

There is a partial enlargement of a perspective representation of the assembly formed by the membrane, the windings and the magnets of a square loudspeaker according to the invention.

There is a representation of the front face of the membrane equipped with its vertical winding of a rectangular loudspeaker according to the invention.

There is a representation of the rear face of the membrane equipped with its horizontal winding of a rectangular loudspeaker according to the invention.

There is a perspective representation of the membrane equipped with its two windings of a rectangular loudspeaker according to the invention.

There is a side representation of the assembly formed by the membrane, the winding and the magnets of a rectangular loudspeaker according to the invention.

There is a front representation of the assembly formed by the membrane, the windings and the magnets of a rectangular loudspeaker according to the invention.

There is an exploded perspective representation of the assembly formed by the membrane, the winding and the magnets of a rectangular loudspeaker according to the invention.

There is an electrical diagram of a two-way filter combining the two vertical and horizontal windings of the same loudspeaker according to the invention.

In the following description, the terms “vertical”, “horizontal”, “left”, “right” etc. are used. are used in reference to the drawings for greater ease of understanding. They should not be understood as limitations on the scope of the invention.

Reference will initially be made to a first embodiment of a square loudspeaker according to the invention with reference to Figs.1 to 10. Secondly, reference will be made to a second mode of production of a rectangular loudspeaker according to the invention, referring to Figs.11 and 16.

The speakers described in this document must be combined with an amplifier to operate. The association with an amplifier is not described in this document, as this falls within the field known to those skilled in the art.

To make the figures easier to read, the frame used to fix the membrane around its perimeter is not shown.

The first embodiment of a planar loudspeaker in accordance with the invention concerns the elements of a square-shaped loudspeaker which is the simplest solution for producing a planar loudspeaker with dual crossover coils.

The planar loudspeaker according to this first embodiment is illustrated schematically in section at the .

This speaker includes a flexible membrane, which is made with a 12 µm Mylar-type polyester film in the context of this embodiment.

It should be noted that the membrane (2) could be made of a different material without departing from the scope of the invention. It could also be produced by any other plastic film, by a film made of composite materials, of plant material, etc.

The planar loudspeaker presented in Figs.1 to 10 comprises two flat windings (3) and (4) made by circuits of metallic conductive ribbons (5). These two circuits have identical dimensions and form serpentines. They are each glued to one side of the membrane. To comply with this invention, these windings are two by two perpendicular as presented in the , with the vertical winding (3) and the horizontal winding (4).

In our example, the windings (3) and (4) are made by cutting 40 µm adhesive aluminum sheets using a cutting plotter called a “plotter”. They are then deposited and stuck on the membrane using a transfer tape, called transfer tape, following a method commonly used in graphic arts for the application of adhesive letters to a support.

On each winding, the ribbons (5) extend parallel to each other. Each of the ribbons (5) is connected to an adjacent ribbon by at least one of its ends. The ribbons (5) thus form spiral-shaped circuits which constitute the windings (3) and (4).

Opposite each ribbon (5) is placed a magnetic bar (6), whose North/South polarity is perpendicular to the electric current circulating in the ribbon in order to be able to apply Laplace's laws.

We will recall here that Laplace's laws explain the electromagnetic principles used here for the loudspeaker to work: when a magnetic field generated by a magnet is perpendicular to the circulation of an electric current, then a perpendicular driving force is created to the direction of movement of the current and the direction of the magnetic field. It is this force which makes the membrane vibrate and which is responsible for the generation of sound by the speaker.

The enlargement of the shows the alternation of the direction of the magnets in order to obtain an electromotive force in phase on each of the ribbons (5) and obtain a uniform movement of the entire membrane (2).

In the context of this example, bipolar magnetized bars (6) are used. These bars are made of a rubber material impregnated with magnetic particles. They are therefore flexible, resistant and can be cut to the desired length.

By “bipolar” magnets we will understand magnets which have four magnetized poles, namely, two North poles and two South poles, with a North pole which is adjacent to a South pole, as visible in Figs.1 and 10).

It will be noted that the bipolar magnetic bars (6) are all identical and have a width substantially equal to or greater than the width of the conductive ribbons (5) as well as a length substantially equal to the length of the conductive ribbons (5).

It should be understood that the loudspeaker may include different magnetic elements, monopolar for example, and arranged in such a way as to apply Laplace's laws, without departing from the scope of the invention. A multitude of magnets of shorter length and widths different from those provided for in the example of embodiment described here may also be provided. The magnetic bars (6) can be fixed on a perforated metal grid serving as a support (7) and maintaining the magnets (6) at a close distance, between 1 and 10 mm from the membrane assembly (2) plus ribbons (5) .

The two sets of magnetic bars (6) are arranged perpendicularly on either side of the membrane, as shown in Figs.6 to 10. This embodiment ensures so-called “Push-Pull” operation, the membrane being at both repelled and attracted. This technical solution allows perfectly symmetrical sound diffusion, with a constant magnetic field when the membrane moves, thus eliminating non-linear deformations of the membrane and consequently harmonic distortions.

In this embodiment, the windings (3) and (4) each have an electrical resistance of between 2 and 16 Ohms, for example 8 Ohms.

In this first embodiment, the windings (3) and (4) are identical and have the same impedance. The induced electromotive force is thus perfectly symmetrical.

The vertical (3) and horizontal (4) windings can be electrically connected in pairs in parallel to form a circuit with a resistance of 4 Ohms, or in series to form a circuit with a resistance of 16 Ohms.

We will now look at another embodiment of a loudspeaker according to the invention.

In the context of this other example, reference will be made to Figs.11 to 16.

In this embodiment, the membrane is rectangular in shape, which allows other geometries to be considered for a set of large high-fidelity speakers. This geometry brings an additional constraint in the dimensioning of the motor elements, namely, the magnetized bars (6) and the windings (3) and (4).

In order to guarantee symmetrical electromotive forces (Laplace's law) on both faces of the membrane, the vertical winding (3) formed from parallel conductive ribbons (5) and the horizontal winding (4) formed from conductive ribbons (5) must have the same electrical resistance so that the currents circulating in them are of the same value.

In the example presented, the conductive ribbons (5) are doubled in order to increase the electromotive force and adapt the impedance to a value of 8 Ohms.

It should be understood that the number of conductive ribbons (5) may vary depending on the typology and desired impedance of the loudspeaker, without departing from the scope of the invention.

In the example considered here, the conductive ribbons (5) are made of adhesive aluminum sheets with a thickness of 40 µm, a width of 4 mm and a total length of 26 m for each vertical (3) and horizontal (4) winding.

As in the previous example, a bipolar magnetic bar (6) is arranged parallel to the conductive ribbon in order to generate, when an electrical signal passes through the ribbons (5), an electromotive force (Laplace's law).

In order to guarantee symmetrical electromotive forces (Laplace's law) on both faces of the membrane, it is important to respect equality in the total length of the magnet bars (6) for each of the faces of the membrane.

In the context of this invention, specific frequency filtering solutions can be considered.

The presence of two windings (3) and (4) in the same loudspeaker makes it possible to consider different frequency filtering solutions for each winding (3) and (4).

There represents an example of first order electronic filtering used for the mid-bass channel of a set of high-fidelity loudspeakers. In this example, the inductance coil (8), called "self", performs a low pass filter at 200 Hz on the horizontal winding (4) and the inductance coil (9) provides low pass filtering at 1000 Hz for the vertical winding (3). When these two windings (3) and (4) thus filtered are connected to an amplifier, the frequency response curve then shows a gain of 6 dB on the frequency band below 200 Hz.

In this example, the “Push-Pull” operation of the crossover winding only occurs in the bass and sub-bass frequencies which require large mechanical movements of the membrane.

Other passive or active filtering solutions using a digital audio processor, called a “DSP” processor, offer a multitude of possibilities for optimizing the frequency response curve in the bass and sub-bass register, by combining different filtering on the vertical winding (3) and the horizontal winding (4).

Claims (9)

Isodynamic planar loudspeaker comprising a membrane (2) of planar type, a first flat winding (3) supported on a first face of said membrane (2) and at least one first magnetic bar (6) fixed to a first support (7 ) facing said first face, said first winding (3) comprising a first series of first conductive strips (5) parallel to each other, each of said first conductive strips (5) being connected to at least one other first conductive strip (5) parallel and adjacent by at least one end of conductive ribbon (5), and said at least one first magnetic bar (6) being arranged parallel to said first conductive ribbons (5) and having a North/South direction of magnetic field perpendicular to said first ribbons conductors (5), characterized in that it also comprises a second flat winding (4) supported on a second face of said membrane (2), electrically isolated from said first winding (3), and at least one second magnetic bar (6 ) fixed to a second support (7) facing said second face and arranged perpendicular to said at least one first magnetic bar (6), said second winding (4) comprising a second series of second conductive ribbons (5) parallel to each other and perpendicular to said first conductive strips (5), each of said second conductive strips (5) being connected to at least one other second conductive strip (5) parallel and adjacent by at least one end of conductive strip (5), and said at least one second magnetic bar (6) being arranged parallel to said second conductive ribbons (5) and having a North/South direction of magnetic field perpendicular to said second conductive ribbons (5). Loudspeaker according to claim 1, characterized in that at least one said magnetic bar (6) is bipolar and comprises an adjacent North pole and a South pole. Loudspeaker according to claim 1, characterized in that at least one said magnetic bar (6) is formed of two monopolar magnets which are arranged alternately with a North pole and a South pole located on either side of said conductive tape (5). Loudspeaker according to claim 2 or 3, characterized in that at least one said magnetic bar (6) has a width corresponding to that of said conductive ribbon (5). Loudspeaker according to claim 2 or 3, characterized in that at least one said magnetic bar (6) has a width greater than that of said conductive ribbon (5). Loudspeaker according to any one of the preceding claims, characterized in that at least one said support (7) is made of perforated sheet metal. Loudspeaker according to any one of the preceding claims, characterized in that said membrane (2) is formed of a thin electrically insulating material. Loudspeaker according to claim 7, characterized in that said membrane (2) is formed from a sheet of paper. Loudspeaker according to claim 7, characterized in that said membrane (2) is formed of a polyester plastic film.