Broadband electrodynamic transducer for headphones, and associated headphones

Abstract

The invention relates to a broadband electrodynamic transducer for headphones, said transducer comprising: a magnetic motor designed to generate a magnetic field; a coil that is disposed in the air gap of the magnetic motor and can move translationally under the effect of the magnetic field; and a membrane that is connected to the coil in such a way as to convert the translational movement of the coil into an acoustic wave; the transducer comprising a self-supporting coil that is glued to the membrane, the membrane having a Young's modulus of more than 40 GPa.

Claims

1. A broadband electrodynamic transducer for headphones, where said transducer comprises: a magnetic motor configured for generating a magnetic field; a coil arranged in an air gap of said magnetic motor and mobile in translation under the effect of said magnetic field; and a membrane connected to said coil so as to convert the translational movement of said coil into an acoustic wave; characterized in that said transducer comprises a self-supporting coil attached to said membrane by adhering, where said membrane has a Young's modulus over 40 GPa and in that said suspension has a thickness included between 50 and 100 m; and wherein said magnetic motor comprises at least a central recess so as to create a column for air expansion extending from the membrane to a rear of said transducer so that the electrodynamic transducer presents an opening surface of over 35%, said opening surface corresponding to a ratio between an emitting surface of the membrane and a surface of the recess at the rear of said transducer.

2. The electrodynamic transducer according to claim 1, wherein said membrane is implemented of a material chosen from the group comprising beryllium, magnesium and aluminum.

3. The electrodynamic transducer according to claim 1, wherein said coil comprises a single conducting wire wound on itself along the height of said electrodynamic transducer.

4. The electrodynamic transducer according to claim 1, wherein said coil has a diameter (d) included between 20 and 30 mm.

5. The electrodynamic transducer according to claim 1, wherein said coil has a height (h) included between 4 and 5 mm.

6. The electrodynamic transducer according to claim 1, wherein said electrodynamic transducer also comprises a suspension connecting an outer edge of said membrane to a fixed support, where said suspension is made of rubber.

7. The electrodynamic transducer according to claim 1, wherein said electrodynamic transducer has a compliance over 40 mm/N.

8. A headset comprising an electrodynamic transducer according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The way to implement the invention as well as the advantages deriving therefrom will be clearly seen from the description of the following embodiment, supported by the appended figures in which:

(2) FIG. 1 is a rear perspective view of an electrodynamic transducer according to an embodiment of the invention;

(3) FIG. 2 is a front perspective view of the transducer from FIG. 1; and

(4) FIG. 3 is a partial section view of the transducer from FIG. 1.

WAYS TO IMPLEMENT THE INVENTION

(5) FIGS. 1 to 3 are described with reference to an electrodynamic transducer 10 whose front surface has a membrane 14 and whose rear surface has a motor 11. Of course, the orientation of the front and rear surfaces can vary without changing the invention.

(6) The motor 11 is a conventional motor and can take any of the known forms. Preferably, the motor 11 has a shape of revolution extending around a central axis x of the electrodynamic transducer 10. As shown in FIG. 1, the motor 11 can be attached on a fixed support 18 by means of three screws.

(7) Preferably, the motor 11 comprises a central recess 15 so as to create a column for air expansion extending from the membrane 14 to the rear of the electrodynamic transducer 10. Preferably, this column for air expansion has a zero or nearly-zero acoustic impedance so as to limit the slowing of the membrane 14 as much as possible. Thus unlike the devices from the state of the art which require the use of perforations and paper to form low frequencies, a zero or nearly-zero acoustic impedance indicates that the acoustic transducer 10 does not comprise papers arranged behind the membrane 14, in the axis of the motor 11.

(8) Further, the motor 11 has an air gap 13 intended to receive a coil 12. The coil 12 is fixed directly below the membrane 14 by adhering without using a support for coil 12 so as to limit the weight of the mobile part of the electrodynamic transducer 10. To do this, the coil 12 is preferably made with a single conducting wire wound on itself along the height of the electrodynamic transducer 10. The conducting wire can have a circular or square section. The conducting wire can be made of copper or of the CAW type, meaning it is composed of an aluminum core, copper cladding and a protective layer.

(9) By heating the conducting wire, the windings of wire can be securely joined to each other by adhesion of the protective layers with each other, thereby providing the structure of the coil 12. The coil 12 is therefore particularly light.

(10) Further a coil with a very large diameter and height (in the domain of headphones) can be obtained with this embodiment.

(11) For example, a coil 12 with a diameter d included between 20 and 30 mm and a height h included between 4 and 5 mm can be obtained with this embodiment.

(12) The inductance of the coil 12 is included between 150 and 250 H contrary to the state of the art in which the inductance of the coil is generally included between 400 and 500 H. As a variant, the coil 12 can have several series of windings without changing the invention.

(13) The performance of the electrodynamic transducer 10 is also improved by the use of a membrane 14 having a Young's modulus over 40 GPa. Preferably, the membrane 14 is made of aluminum with a Young's modulus substantially equal to 69 GPa, or of beryllium with a Young's modulus substantially equal to 240 GPa. The thickness of the membrane 14 is preferably included between 20 and 30 m for a diameter included between 30 and 32 mm. Thus, the membrane 14 is particularly stiff while also having some lightness compared to titanium or steel. The membrane 14 has a slightly protruding front surface forming a dome at the edges of which the coil 12 is attached. The membrane 14 also extends radially, after the dome, in a substantially straight terminal part 17 extending towards the fixed support 18.

(14) The mobile part of the electrodynamic transducer 10 is completed by a dedicated suspension 16, preferably made of rubber. The suspension 16 extends in the form of a simple arc between the end part 17 of the membrane 14 and a radial edge of the fixed support 18.

(15) Preferably, the suspension 16 has a thickness included between 50 and 100 m. Preferably, the suspension 16 is fixed by adhering on the end part 17 of the membrane 14 and on the radial edge of the fixed support 18. By means of this suspension 16, the compliance of the electrodynamic transducer 10 is particularly improved. In fact, the compliance of the electrodynamic transducer 10 was measured at over 40 mm/N.

(16) A conventional method for measuring the compliance is described in the measurement reference from Klippel GmbH dated Aug. 13, 2012: Linear Parameter Measurement (LPM) S2.

(17) A rear part of the electrodynamic transducer 10 is also open onto a part of the suspension 16 so as to limit slowing of the membrane 14. It follows that the electrodynamic transducer 10 has an opening surface area over 35%. This opening surface corresponds to the ratio between the emitting surface of the membrane 14 and the rear surface of the openings.

(18) The resulting electrodynamic transducer 10 has spectacular performance. For example, for a membrane 14 made of aluminum, the total weight of the mobile part (including the membrane, suspension, coil and adhesive) does not exceed 160 mg. Similarly, for a membrane 14 made of beryllium, the total weight of the mobile part (including the membrane, suspension, coil and adhesive) does not exceed 125 mg. The mass measurements are done with a balance accurate to 0.1 mg.

(19) To finish, two electrodynamic transducers 10 can be used to form a headset, for example an open or semi-open headset.