DE19643308A1 - Electrodynamic convertor esp. for active noise control - Google Patents

Abstract

The convertor has a radially symmetrical magnetic circuit (1,2,3,10). An oscillating coil (6) movably extends into the air gap (4) of this magnetic system. The pole core (10) has a low friction sliding layer (8) on which the oscillating coil (6) is guided by at least one sliding bearing (7). The loud speaker membrane (9) is fixedly connected to the oscillating system (5,6, 7a,7b). The oscillating coil (6) may be carried by a radially symmetrical bearing (7). The height of this bearing (7) is such that the oscillating coil (6) does not extend beyond either end of the bearing.

Description

The invention relates to an electrodynamic converter according to the preamble of Claim 1. The electrodynamic transducer is intended for sound conversion, especially in applications for active noise control (ANC: active noise control).

In converters according to the preamble of claim 1, this is usually done Centering of the membrane by the outer membrane clamping (hinge) and that of Voice coil through a centering membrane (spider) that connects directly to the voice coil connected is.

Applications from active noise control (ANC) result in New requirements for the transducers. These are on the one hand in Low frequency range (<100 Hz), on the other hand in the limited radiator area. To generate of the large sound pressures or volume flows required is a large deflection of the Membrane required (with limited membrane area). I.e. do you want this problem with Solving electrodynamic drives requires an extremely long stroke and still linear constructions. In conventional designs, the spider limits the possible deflection due to a strongly non-linear stiffness behavior, that with the deflection increases. A typical deflection is a few mm. Another problem is that Dissipation of temperature from the voice coil, since the required deflections are large Coil currents are required.

From DE 32 45 417 A1, for example, an electromagnetic transducer is known from a centering needle for the exact axial guidance of the moving voice coil is provided, which is guided in a bore through the pole core in the direction of movement. This measure is intended to avoid wobble movements of the voice coil.

The disadvantage of this solution is that obviously an exact radial guidance magnetic liquid between the centering needle and the pole core is necessary. In addition the bore limits the magnetic flux through the core due to the reduced area. This solution is for the expected high loads with regard to acceleration or mechanical force in applications for active noise control.

The object of the invention is to find an electrodynamic converter, the leadership and centering the oscillation system large strokes (a few cm) under linear conditions guaranteed. The temperature problem that occurs with large strokes is said to be caused by a better temperature dissipation than in systems in which the voice coil only from gaseous medium (air) is surrounded, can also be solved.

The above task is in an electrodynamic converter according to the preamble of claim 1 solved by the features shown in the license plate. Refinements preferably result from the subclaims.

For exact axial guidance, a plain bearing is provided, which is fixed to the Voice coil former is connected and in on the pole core of the magnet system Direction of movement is performed. With this arrangement, the voice coil in the Air gap exactly centered, which means further measures for centering (usually a centering membrane or spider) can be omitted and the air gap to achieve high flux densities can be optimally narrow. Continue to be Swinging of the vibrating system is prevented (low distortion factor). The The membrane is suspended with less friction (efficiency!) And softer (lower resonance frequency possible) than with conventional systems with Centering membrane. Due to the positive contact between the bearing bush and the pole core there is a much better dissipation of temperature from the voice coil, resulting in a higher coil current is possible (efficiency!). So be really long stroke and largely linear constructions (a few cm deflection) possible, which are clearly above the go out so far feasible.

The invention is explained in more detail below on the basis of exemplary embodiments. In the Drawings show:

Fig. 1 shows a first variant of an electrodynamic transducer according to the invention (with the coil carrier and with two bearings rings and a fixed to the upper slide bearing ring cone diaphragm)

Fig. 2 shows a second variant with only one (non-continuous) plain bearing ring and a flat membrane attached to the coil carrier

Fig. 3 shows a third variant with a continuous slide bearing, which also acts as a coil carrier.

In Fig. 1 shows an embodiment of an electrodynamic transducer of the invention. A voice coil 6 projects into an annular air gap 4 , which is formed between a pole plate 2 and a pole core 8 . The voice coil 6 is wound on a voice coil former 5 , which in turn is attached to two plain bearing rings 7 a, 7 b. The two plain bearing rings 7 a, 7 b, form a dry-running plain bearing with the pole core 10 , so that the voice coil 6 with the voice coil former 5 is easily displaceable on the pole core 10 . In order to minimize the friction of the pair of plain bearings, the pole core is provided with a sliding layer on its circumferential surface. The friction is further minimized when solid lubricants are stored on the surface of the plain bearing rings 7 a, 7 b.

In this exemplary embodiment, the pole core 10 was provided with a 2 μm thick DLC layer (as protection against tribological stress). The counter bearing is formed by two thermoplastic plastic sliding rings, in which a mixture of solid lubricants (including graphite) is embedded, and which is reinforced by a fiber matrix.

The plain bearing or the positive contact between the plain bearing 7 and the pole core 10 results in a significantly improved temperature dissipation from the voice coil 6 than with voice coils which are surrounded by a gaseous medium. An increased heat dissipation requirement due to the large strokes can thus be better met.

For the transmission of the stroke to the loudspeaker membrane 9 (in this case a conical design), this is rigidly connected directly to the upper slide bearing ring 7b.

In FIG. 2, another embodiment is shown of an electrodynamic transducer of the invention. On the pole core 10 , only a plain bearing ring 7 a is provided here. One end of the voice coil former 5 is connected to the slide bearing ring 7 a and the other end of the voice coil former 5 is connected to the loudspeaker diaphragm 9 . In the embodiment the Lautsprechermenbran 9 is a Flachmenbran so that the voice coil support 5 can be bonded without difficulty with the loudspeaker diaphragm. 9 This variant has the advantage over the first variant that the pole core 10 only has to be made relatively short in order to ensure a large stroke.

The pair of plain bearings is the same as for the first variant.

A third variant results from the illustration according to FIG. 3. As a special feature of this solution, the double function of the slide ring can be regarded as a simultaneous coil carrier.

Reference list

1

Ring magnet - permanent magnet (also works with an electromagnet)

2nd

upper pole plate

3rd

lower pole plate

4th

Air gap

5

Voice coil former

6

Voice coil

7

bearings

8th

low-friction sliding layer

9

Loudspeaker diaphragm (cone, flat diaphragm etc.)

10th

Polkern.

Claims (9)

1. Electrodynamic converter with a radially symmetrical magnetic circuit ( 1 , 2 , 3 , 10 ) and a moving voice coil ( 6 ) projecting into the air gap ( 4 ) of this magnet system, characterized in that the pole core ( 10 ) has a low-friction sliding layer ( 8 ) , on which the voice coil ( 6 ) is guided through at least one slide bearing ( 7 ), and that the loudspeaker membrane ( 9 ) is firmly connected to the vibrating system ( 5 , 6 , 7 a, 7 b). 2. Electrodynamic converter according to claim 1, characterized in that the sliding bearing ( 7 ) is designed as a dry-running bearing. 3. Electrodynamic converter according to claim 1, characterized in that the voice coil ( 6 ) is carried by a radially symmetrical slide bearing ( 7 ), the height of the slide bearing ( 7 ) being dimensioned such that the voice coil ( 6 ) at no end of the slide bearing ( 7 ) survives. 4. Electrodynamic converter according to claim 1, characterized in that the radially symmetrical plain bearing ( 7 ) consists of at least two plain bearing rings ( 7 a, 7 b) which are distributed over the entire length of the voice coil ( 6 ). 5. Electrodynamic converter according to one of the preceding claims, characterized in that the loudspeaker diaphragm ( 9 ) (cone, flat diaphragm, etc.) with the slide bearing ( 7 ) or the upper slide bearing ring ( 7 b) or the voice coil former ( 5 ) is connected , wherein the connection is rigid or elastic. 6. Electrodynamic converter according to one of the preceding claims, characterized in that the pole core ( 10 ) is provided on its peripheral surface with a DLC layer (diamond-like carbon) which has a low coefficient of friction and a long service life compared to the plain bearing material. 7. Electrodynamic converter according to claim 6, characterized in that the slide bearing ( 7 ) is maintenance-free, the preferably made of plastic slide bearing rings ( 7 a, 7 b) having solid lubricants. 8. Electrodynamic converter according to one of the preceding claims, characterized in that a voice coil support ( 5 ) is provided for the voice coil wire. 9. Electrodynamic converter according to one of the preceding claims, characterized in that the voice coil wire without separate voice coil carrier ( 5 ) by baked and / or inserted longitudinally rigid elements, preferably carbon fibers, is itself dimensionally stable.