FR2521808A1 - Ribbon loudspeaker for HF sounds - has two magnetic poles defining air gap which contains electrically conducting ribbon - Google Patents

Abstract

The loudspeaker (10) has two polar pieces (11,12) preferably of soft iron, mounted on both sides of a magnetic core (13), preferably a cylindrical permanent magnet. The two poles are identical and each has a peripheral annular protuberance (14,15) which faces the other to define an annular airgap (16) containing a perpendicular electrically conducting ribbon (17). The pole pieces may be concave, oval or square. The protuberances are shaped to channel the magnetic flux in the air gap. The ribbon is an aluminium strip slightly folded or corrugated and concentrically disposed w.r.t. the permanent magnet. It is maintained in position by spacers in a nonmagnetic material fixed along the edge of the permanent magnet perpendicular to the pole pieces. The two free ends of the ribbon are connected to two electrical contact elements. The ribbon loudspeaker is suitable for high frequency sounds, producing a uniform frequency spectrum distribution and a constant sound level.

Description

 The present invention relates to a ribbon loudspeaker for high-pitched sounds comprising a magnet comprising two magnetic poles which define an air gap and at least one electrically conductive ribbon disposed in said air gap.

 The tweeter speakers, of the ribbon type, commonly called "ribbon tweeter" comprise a sheet of aluminum stretched in the air gap defined by two magnetic poles, this ribbon being disposed substantially parallel to the lines of force in this air gap , and having its ends respectively connected to two electrical contact terminals.

 Under Laplace's law, this strip, traversed by an electric current, moves in a direction substantially perpendicular to the lines of magnetic force. These loudspeakers known for their very low inertia, however have the disadvantage of being particularly directive. As a result, listening is very good in a perfectly defined direction, and degrades quickly for the listener who is not placed in this axis.

 The present invention proposes to overcome this drawback by providing a loudspeaker as mentioned above, which constitutes a quasi-point and omni-directional sound source. I1 provides a uniform distribution of the frequency spectrum and a constant sound level regardless of the listening position relative to the speakers.

 For this purpose, the loudspeaker according to the invention is characterized in that the magnet comprises two pole pieces arranged opposite one another and each having a substantially planar face, these planar faces being parallel to each other, in that each of these faces is provided with a peripheral annular protuberance and in that at least one annular, electrically conductive strip is disposed between the two protrusions, substantially perpendicular to said planar faces.

 According to a particularly advantageous embodiment, said magnet comprises a cylindrical magnetic core disposed between the two pole pieces made of soft iron.

 Preferably, the magnetic core consists of a permanent magnet of cylindrical shape, the diameter of which is less than the inside diameter of the annular protrusions of the pole pieces.

 According to a preferred embodiment, the electrically conductive strip consists of an aluminum strip arranged concentrically with the magnetic core, and the free ends of which are connected respectively to two electrical contact terminals. To allow the radial extension of the aluminum strip, the latter is preferably slightly folded or wavy, and kept at a substantially constant distance from the magnetic core, for example using rigid spacers arranged at regular intervals and integral with this core.

However according to another embodiment, the distans
cores can consist of a flexible support strip on which
supports the electrically conductive annular tape.

The electrically conductive tape can be formed either by a single strip, or by a series of superimposed strips, separated and con
nected in series. These strips can be placed either on one or on the
two sides of a flexible support. In particular printed by a process which
conch known per se on the flexible support.

The present invention will be better understood with reference to the
description of an exemplary embodiment and the accompanying drawings in which
Figure 1 shows a schematic cross-sectional view
dirty speaker of the invention
Figure 2 shows a schematic view illustrating the mon
tage of electrically conductive tape around the magnetic core, and
Figure 3 shows a sectional view of another embodiment of the tape mounted on a flexible support strip.

Referring to Figure 1, the speaker 10 according to the in
vention essentially consists of two pole pieces 11 and 12 of pref
rence in soft iron, mounted on either side of a magnetic core 13, cons
preferably with a permanent cylindrical magnet. The two magnetic poles 11 and 12 are substantially identical and each comprise a peripheral annular protuberance 14, respectively 15, which face each other and define an annular air gap 16 in which an electrical tape is arranged.
only conductor 17, maintained by means which will be described in more detail below.

Of course, the pole pieces can have any section of concave, oval, square, etc. shape. The periphery protrusions
riques 14 and 15 have any shape well suited to the purpose for which they
are intended, i.e. to channel the magnetic flux in the air gap
16.

Referring to Figure 2, the strip 17, consisting of a slightly pleated or corrugated aluminum strip, is arranged concentrically with respect to the permanent magnet 13 and maintained at a predetermined distance by spacers 18, constituted for example by cylindrical segments
or of any section, made of a non-magnetic material and fixed on
along the periphery of the permanent magnet 13, perpendicular to the workpieces
polar. The two free ends 19 and 20 of the electrically conductive tape
tor 17 are respectively connected to two electrical contact elements
21 and 22.

Figure 3 illustrates another embodiment of the ribbon
electrically conductive. While in FIG. 2, the ribbon 17 is constituted by a single band which makes substantially the complete turn of the magnetic core, in the example of FIG. 3, the electrically conductive ribbon is constituted by a series of bands 23 which can be wound. , glued or printed on one or both sides of a flexible support 24. This flexible support is preferably constituted by a strip of synthetic material having sufficient flexibility to be able to follow the small radial extension which the electrically conductive tape undergoes, traversed by an electric current and placed in the lines of force of the magnetic field generated. in the air gap 16.

The separate and superimposed strips are connected in series either by soldering or by means of microswitches suitably arranged.

 The present invention is not limited to the embodiments described, but can undergo different modifications and be in the form of different variants obvious to those skilled in the art.

 Thanks to this embodiment, the loudspeaker as described or its different variants, makes it possible to produce a substantially point source, omni-directional, which provides a uniform distribution of the frequency spectrum. To increase the power of the device, one can either act on the power of the magnet, or compose several modules connected in series or arranged in parallel on the same vertical axis.

Claims (9)

 1. Ribbon loudspeaker for high-pitched sounds, comprising a magnet comprising two magnetic poles which define an air gap and at least one electrically conductive ribbon disposed in said air gap, characterized in that said magnet comprises two pole pieces arranged opposite the one from the other and each having a substantially planar face, these planar faces being mutually parallel, in that each of these faces is provided with a peripheral annular protuberance and in that at least one annular, electrically conductive strip is disposed between the two protrusions, substantially perpendicular to said planar faces.  2. Speaker according to claim 1, characterized in that said magnet comprises a cylindrical magnetic core disposed between the two circular pole pieces made of soft iron.  3. Loudspeaker according to claim 1, characterized in that said magnetic core comprises a permanent magnet of cylindrical shape, the diameter of which is less than the inside diameter of the annular protrusions of the pole pieces.  4. Loudspeaker according to any one of the preceding claims, characterized in that the electrically conductive strip consists of a strip of light alloy, disposed concentrically with the magnetic core, the free ends of this strip being connected respectively to two terminals of electric contact.  5. Loudspeaker according to claim 4, characterized in that the aluminum strip is pleated so as to allow its radial extension.  6. Loudspeaker according to claim S, characterized in that the ribbon is kept at a substantially constant distance from the magnetic core by means of rigid spacers placed at regular intervals and integral with the magnetic core.  7. Loudspeaker according to claim 5, characterized in that the ribbon is kept at a substantially constant distance from the magnetic core by means of a spacer consisting of a flexible support strip on which the annular electrically conductive ribbon bears.  8. Loudspeaker according to any one of the preceding claims, characterized in that the electrically ashtray annular ribbon consists of a series of separate ribbons, superimposed and connected in series.  9. A loudspeaker according to claim 8, characterized in that the electrically conductive tape comprises a series of separate tapes, superimposed and connected in series, fixed on the two faces of a flexible support concentric with the magnetic core.