JPH0477520B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This description describes an annular air gap magnet device for a bass speaker, which includes a moving coil that moves with a large stroke within an operating air gap, a soft iron cylindrical magnetic pole, and an annular permanent magnet. And the outer annular permanent magnet is
disposed between an upper pole plate and a lower pole plate at a distance from the magnetic pole, the upper pole plate limiting the outer circumferential surface of the working gap, and the lower pole plate having a An annular magnet arrangement is provided in which an opening is provided which surrounds the magnetic pole in the lower region, the outer opening being in the axial extension of the operating gap.

In bass speakers, for example, it is required that the diaphragm be suspended extremely flexibly. the result,
After the voice coil passes the main magnetic field of the working air gap of the magnet system, it is moved further inward by internal stray fields and impinges on the lower plate, especially if the loudspeaker is overcontrolled. .

To prevent the voice coil from reaching the lower plates in this manner, it has been necessary in the past to suspend the diaphragm and voice coil more rigidly than is desirable to improve the acoustic quality of the speaker.

It is an object of the invention to provide an annular air-gap magnet arrangement of the type mentioned at the outset with a very flexible suspension of the diaphragm and the voice coil, so that even if the loudspeaker is over-controlled, the voice coil will be suspended in the lower pole plate. The goal is to configure the system so that it does not reach this level.

This object is achieved according to the invention by constructing an annular magnet arrangement as follows. That is, the opening forms a brake gap and has a distance relative to the upper plate, the distance being greater than the thickness of the upper plate, and within the brake gap the lower plate The magnetically permeable cross-section is reduced to form a magnetic reluctance such that the sum of the magnetic flux passing through the braking air gap and the stray flux passing above the braking air gap is the internal stray flux below the working air gap. larger than
This is achieved by configuring the magnetically permeable cross section of the lower plate to be reduced such that both said magnetic fluxes are in opposite directions with respect to the magnetic flux in the working air gap and the stray magnetic flux below the working air gap.

In the present invention, the magnetic flux 10b passing through the working air gap 3
is split due to the reluctance 10e in the lower plate, so that a portion 10a of this magnetic flux passes through the braking air gap. Also, as usual, an additional stray magnetic flux 10c is formed below the working air gap, extending from the pole 5 to the upper plate 7. A corresponding stray magnetic flux 10d extends from the lower plate to the pole.

The stray magnetic flux 10c is the magnetic flux 10b passing through the working air gap.
It acts in the same direction as , and also after the voice coil has already passed below the working gap. Stray magnetic flux 10d acts in the opposite direction to this stray magnetic flux 10c. The main braking magnetic flux is the magnetic flux component 10a of the main magnetic flux.
formed by. In order to form a braking action, it is important that the sum of the magnetic flux 10a passing through the braking air gap and the magnetic flux 10d passing above the braking air gap is greater than the internal stray magnetic flux 10c below the working air gap. Because this internal stray magnetic flux 1
0c because, as mentioned above, even though the voice coil is moved below the working air gap and the magnetic flux through the working air gap has little effect on the coil, it still drives this coil downward. In other words, the opposing magnetic fields formed by the magnetic flux passing through the brake air gap and the stray magnetic flux above the brake air gap are
It must be greater than the magnetic field created by stray magnetic flux passing below the working air gap. Because the direction of magnetic flux through the damping air gap is opposite to the direction of stray magnetic flux below the working air gap, the voice coil is actively damped and prevented from bottoming out on the lower plate.

The magnetic flux in said braking air gap as well as the stray flux above the braking air gap, in the opposite direction to the internal stray flux around the working air gap, provides a magnetic reaction force whose magnitude is easily adjustable, and the loudspeaker Even if the moving coil is over-controlled, the moving coil can be prevented from reaching the lower plate. Moreover, the flexibility of the suspension of the diaphragm is irrelevant in this case.

Magnetoresistiveness can be created by reducing the cross-sectional area of the lower plate. However, it can also be formed by providing a weakly permeable coupling member between the lower pole plate and the magnetic pole.

In order to easily adjust the loudspeaker to the desired acoustic quality, or for reasons of economy, a soft iron ring is provided adjacent to the lower plate, which soft iron ring extends the outer circumference of the damping gap over its axial length. It is preferable to form the soft iron ring over at least a part of the magnet, and to connect the soft iron ring to the inner circumferential surface of the annular permanent magnet in a magnetically conductive manner. The depth of the braking gap and its distance from the upper plate can then be varied by inserting soft iron rings of different heights.

Furthermore, part of the axial length of the brake gap may be formed by an annular permanent magnet. In that case, the permanent magnet is preferably composed of two continuous permanent magnets, of which the inner circumferential surface of the magnet on the side opposite to the working gap forms at least part of the axial length of the outer circumference of the braking gap. It is advantageous to do so.

A detailed explanation of the invention will now be given with reference to preferred embodiments of the invention shown in the drawings.

FIG. 1 shows a bass speaker comprising a magnet device 1 having an annular gap, a conical diaphragm 2 and a frame 2a. A cylindrical body 4b is fixedly connected to the diaphragm, and a voice coil 4a is provided on this cylindrical body. A damper 2b is provided between the lower end of the diaphragm 2 and the frame 2a. frame 2a
is connected to a magnet arrangement in the usual way.

The annular magnet device 1 has a cylindrical magnetic pole 5 made of soft iron.
, and an annular permanent magnet 6 with a thickness D, the permanent magnet is arranged concentrically with respect to the magnetic pole 5, with an annular top plate 7 having a thickness d ₂ and a bottom plate 7. (yoke plate) 8. An operating gap 3 is formed between the magnetic pole 5 and the inner periphery of an upper pole plate 7 provided concentrically with respect to the magnetic pole, and a voice coil 4 is inserted into this operating gap.
A is wearing it.

In FIG. 1, the magnetic pole 5 and the lower pole plate 8 are integrally constructed, similarly to the other figures. However, normally the magnetic pole 5 and the pole plate 8 are two separate parts and are fixedly connected to each other, for example by screws or rivets. This point is indicated in FIG. 1 by the dashed line 5a.

The voice coil 4a moves with a corresponding stroke in the operating gap 3 of the magnet arrangement, for example with a large stroke typical of bass loudspeakers (woofers).

A cylindrical braking gap 9 of depth d ₃ is provided in or at the lower plate 8, which surrounds the magnetic pole 5 in the axial extension of the operating gap 3; The lower end of the voice coil can be inserted into it.

The open end 9a of the braking cavity 9 is located in both embodiments at a distance d ₁ from the underside of the upper plate 7, which distance d ₁ corresponds at least to the thickness d ₂ of the upper plate 7. Therefore, it is advantageous to have a value larger than this.

Braking gap 9 extending below the top surface of the lower plate 8
This reduces the cross-sectional area of the lower plate at the lower end of the braking gap, and this reduced cross-section acts as a magnetoresistive element 10e.

In FIG. 1, the magnetic flux generated through the braking air gap 9 and the magnetic resistance 10e is indicated by a broken line. Lower electrode plate 8
The magnetic flux flowing from to the magnetic pole 5 is generated based on the magnetic resistance 10e to the main magnetic flux 10a passing through the braking air gap 9. And the stray magnetic flux 10d is caused by the braking air gap 9
Flows from the edge and top surface of the lower pole plate 8 to the magnetic pole 5 above the open end 9a of the lower pole plate 8. The main magnetic flux 10a and the stray magnetic flux 10d passing through the braking air gap form the braking magnetic flux, the sum of which is equal to the magnitude of the internal stray magnetic flux 10c (occurring below the working air gap 3) between the magnetic pole 5 and the upper pole plate 7. at least equal to, the larger the better. Once inside the magnet arrangement, the voice coil 4a will eventually come completely out of the magnetic field of the working air gap 3 if properly energized. At this time, the voice coil is driven further inward by the magnetic field of the stray magnetic flux 10c. The sum of braking magnetic fluxes 10a and 10c acts against the driving force due to this stray magnetic flux 10c. As a result, the voice coil 4a is actively braked, so that it is prevented from hitting the lower pole plate.

In other embodiments shown in FIG. 2 and below, only the annular magnet device is shown. Elements that are the same or have the same effect are each given the same symbols as in FIG. 1. Therefore, in the embodiment described below, only features that differ from the embodiment of FIG. 1 will be explained.

In the magnet arrangement of FIG. 2, to the left of the center line of the lower pole plate 8, there is a radially stepped step on the lower surface of the lower pole plate towards the outside of the braking gap 9, in order to save material or reduce weight. An embodiment in which a shaped portion 8a is provided is shown. To the right of the center line, an embodiment is shown in which the lower plate (to provide a step) consists of an annular body 8b and a plate 8c. The magnetic resistance of the plate 8c is determined by its thickness, and the center portion is fixed to the magnetic pole 5.

In the embodiment of FIGS. 1 and 2, the brake air gap 9
is contained within the lower plate 8 over its entire depth d ₃ , whereas in the embodiment of FIG. 3 a the lower plate only forms part of the depth d ₃ of the braking gap. A soft iron ring 12 is provided on the upper surface of the lower pole plate 8, and the outer circumferential surface of the soft iron ring 12 is in magnetic conductive contact with the inner circumferential surface 6a of the permanent magnet 6, and the inner circumferential surface of the soft iron ring is A braking gap is formed over part of its depth.

Similarly, a soft iron ring 12 is provided in the embodiment of _FIG . ing. In this case, the soft iron ring 12 is inserted into a corresponding recess 13 in the lower plate 8.

Unlike the embodiments shown in FIGS. 1, 2, 3a, and 3b, in the embodiments shown in FIGS. 4 and 5, the lower pole plate 8 is formed in an annular shape, and the lower pole plate No soft iron bridge is provided between the
In the embodiment shown in FIG. 4, an annular body 14 having a predetermined height is provided between the inner circumferential surface of the lower pole plate 8 and the outer circumferential surface of the magnetic pole 5, and both members are connected to each other via this annular body. connected. The annular body 14 is made of a non-magnetic material such as brass, aluminum, synthetic resin, etc. In the embodiment shown in FIG. 5, the annular lower pole plate 8 and the magnetic pole 5 are mounted on a plate 15 made of a non-magnetic material, thereby obtaining the same effect as the embodiment shown in FIG.
In the embodiment of FIGS. 4 and 5, there is no soft iron bridge so that all of the magnetic flux passes through the braking air gap.

In the embodiment of FIG. 6, the annular permanent magnet 6 consists of two partial magnet rings 6b and 6c, each having a thickness D ₁ to D ₂ , whose combined thickness is 1.
This corresponds to the thickness D of the permanent magnet 6 in the figure. The upper partial magnet 6b has the same inner diameter as the inner diameter of the permanent magnet 6 in FIG. The inner diameter of the lower partial magnet 6c corresponds to the outer diameter of the brake gap 9. The lower partial magnet 6c therefore forms with its inner circumferential surface the outer circumferential surface of a brake gap 9, which is formed by an annular groove 9 in the lower pole plate 8.
It extends by the distance b. This groove reduces the cross-sectional area of the lower plate, which determines the magnetic resistance. The thickness d ₁ of the partial magnet 6b is determined by the distance from the lower surface of the upper pole plate 7 to the open end 9a of the braking gap 9 equal to the depth of the operating gap, that is, the thickness of the upper pole plate.
d ₂ or more.

The advantage of this embodiment, as well as the embodiment of FIGS. 3a and 3b, is that the thickness of the lower plate can be adjusted in accordance with the embodiment of FIGS. The advantage is that it can be made smaller than in the example case. This reduces the weight of the magnet device.

In FIG. 6, stray magnetic flux is shown to the left of the magnetic pole 5. In this embodiment, the lower region 10d of the stray magnetic flux flowing towards the magnetic poles flows approximately radially through the damping gap 9.

In the annular air-gap magnet arrangement of the embodiment of FIG. 3b, choosing d ₂ =8 mm d ₁ =14 mm d ₃ =10 mm, the total height d ₁ +d ₂ + is measured using an acoustic sensor.
The magnetic flux density B over d ₃ was measured. Since no useful measurement results were obtained at the bottom of the braking gap, measurements were only carried out to a depth of 30 mm. The measurement results are shown in the graph of FIG.

Magnetic flux flows outward from the magnetic poles above the horizontal axis, and toward the magnetic poles below the horizontal axis. As can be seen from the graph, the magnetic flux density is approximately constant over the thickness d ₂ of the upper plate 7, that is, the depth of the working gap 3. At the height d ₁ , ie between the lower surface of the upper plate 7 and the open end 9a of the braking gap 9, the magnetic flux density drops quite sharply due to the stray magnetic flux 10c. The magnetic flux density becomes zero at point Y, that is, at a distance of 9 mm from the bottom surface of the upper pole plate 7. Stray magnetic flux 10d acts from point Y. The magnetic flux density now begins to rise again with the magnetic flux pointing in the opposite direction and reaches its maximum value approximately in the region of the open end 9a of the brake gap 9. This maximum value depends on the magnitude of the reluctance in the lower plate. The magnetic flux density then remains approximately constant over the depth of the measured region of the damping gap. In the graph of FIG. 7, the magnetic flux density is expressed in units of Tesla (T).

As a comparative measurement, magnetic flux density measurements were made with a conventional type of annular air gap magnet arrangement, ie, with a magnet arrangement without a damping air gap. In this case, the magnetic flux density in the working air gap is the same as in a magnet arrangement with a brake air gap. A magnetic flux density corresponding to the dashed curve in the graph was measured below the operating gap. This curve has a gentle slope of decline and lies above the horizontal axis over the entire range. Immediately before the upper surface of the lower plate, ie at point X, the magnetic flux density is still approximately 0.3T. Therefore, conventional magnet systems do not create an opposing magnetic field that would limit the inward movement of the voice coil. Rather, the magnetic field that causes the voice coil to move inward acts even on the upper surface of the lower pole plate 8. This magnetic field causes the voice coil to hit the lower plate during loudspeaker overcontrol.

In contrast, in the annular air gap magnet device of the present invention, the voice coil does not reach the lower plate even if the speaker is overcontrolled. The intrusion motion of the voice coil is
It is limited because it is damped by an opposing magnetic field generated above and within the damping air gap.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway vertical sectional view of a speaker equipped with an annular magnet device having a damping gap according to the present invention, and FIG. 2 is a vertical sectional view of another embodiment of the annular magnet device of the present invention. , 3a and 3b, a soft iron ring is provided to form the outer periphery of the damping gap, 2
FIG. 4 is a longitudinal sectional view of two different embodiments, and FIG. The figure is a longitudinal sectional view of an embodiment in which the magnetic pole and the lower pole plate are fixedly connected to each other by a plate or disk made of non-magnetic material, and FIG. Cross over,
FIG. 7, which is a longitudinal sectional view of an embodiment formed by an annular permanent magnet, is a graph showing the course of the magnetic flux density over the height of the annular gap magnet arrangement of the invention. 3... Operating gap, 5... Magnetic pole, 6, 6b, 6c
...Annular permanent magnet, 7...Upper pole plate, 8...Lower pole plate, 9...Brake gap, 10a...Magnetic flux in brake gap, 10b...Magnetic flux in operating gap, 10c...
Stray magnetic flux below the working air gap, 10d... Stray magnetic flux above the braking air gap, 10e... Magnetic resistance, 12... Soft iron ring.

Claims (1)

[Scope of Claims] 1. An annular air gap magnet device for a bass speaker, comprising: a moving coil 4a that moves with a large stroke within an operating gap 3; a cylindrical magnetic pole 5 made of soft iron; and an annular permanent magnet 6. The annular permanent magnet 6 is arranged between an upper pole plate 7 and a lower pole plate 8 at a distance from the magnetic pole 5, and the upper pole plate 7 limits the operating gap 3. In the annular magnet arrangement, the lower pole plate 8 is provided with an opening 9 surrounding the magnetic pole 5 in its lower region, the opening 9 being on the axial extension of the working gap 3. , the opening 9 forms a braking gap 9 and has a distance d1 with respect to the upper plate 7, the distance d1 is greater than the thickness d2 of the upper plate 7, and the braking gap 9 Inside, the magnetically permeable cross-section of the lower plate 8 is reduced to form a reluctance 10e, namely a magnetic flux 10a passing through the braking air gap 9 and a stray magnetic flux 10 passing above the braking air gap.
d is the internal stray magnetic flux 10 below the working air gap 3.
c, and the two magnetic fluxes 10a and 10d
An annular air gap magnet arrangement characterized in that the magnetically permeable cross section of the lower plate 8 is reduced such that both are in opposite directions with respect to the magnetic flux 10b in the working air gap 3 and the stray magnetic flux 10c below the working air gap. . 2. A soft iron ring 12 is provided on the lower pole plate 8 which limits the braking air gap 9 at least in the upper region of the lower pole plate 8, which soft iron ring on its outer circumferential surface is magnetically conductively connected to the inner circumferential surface of the permanent magnet 6. An annular permanent magnet device according to claim 1 to which it abuts. 3 The outside of the braking gap 9 is in contact with the inner circumferential surface 6 of the permanent magnet 6 over a part of its axial length d3, and the axial length d3 is equal to the height D of the permanent magnet and the upper pole plate. The annular permanent magnet device according to claim 1, wherein the difference is smaller than the difference between the thickness d2 and the thickness d2 of the annular permanent magnet device. 4. The annular permanent magnet 6 is composed of two overlapping annular magnets 6b and 6c, and among these two,
Inner peripheral surface 6 of the permanent magnet 6c on the opposite side from the operating gap 3
4. The annular permanent magnet device according to claim 3, wherein d is in contact with the outside of the braking gap 9.