JPH0439840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speaker unit, and more particularly to a speaker unit including a voice coil whose winding width is larger than the width of a magnetic gap.

A conventional speaker unit of this type is shown in FIG. In FIG. 1, an annular magnet 2 magnetized in the thickness direction is placed on the bottom peripheral edge of a pole yoke 1 having an inverted T-shaped cross section. The plate 3 is placed on the magnet 2 and forms a magnetic gap with the peripheral wall of the center pole 1A of the pole yoke 1. A voice coil 5 wound around a bobbin 4 is inserted into the magnetic gap, and the bobbin 4 is supported by a frame 7 via a damper 6 so as to be able to freely vibrate. A diaphragm 8 is connected to the bobbin 4 through its center hole, and a center cap 9 is further attached to the bobbin 4. The periphery of the opening of the diaphragm 8 is supported by an edge 11 fixed to the frame 7 by a gasket 10. The voice coil 5 is wound around the bobbin 4 so that its winding width is larger than the width of the magnetic gap in order to effectively utilize the magnetic flux in the magnetic gap to improve efficiency.

Next, the operation will be explained. When a current flows through the voice coil 5 in the magnetic gap, an upward or downward driving force acts on the coil 5 depending on the direction of the current. Since the coil 5 is movable, the driving force acting on the coil 5 is transmitted to the diaphragm 8 via the bobbin 4, thereby causing the diaphragm 8 to vibrate and generate sound. The driving force F acting on the coil 5 is expressed as F=Bli, where B is the magnetic flux density interlinking with the coil 5, l is the wire length of the coil 5, and i is the current flowing through the coil 5.

In FIG. 2, a shows a state in which the widthwise center of the coil 5 is located at the center of the magnetic gap, and b shows the distribution of magnetic flux density interlinking with the coil 5 in that state. Also, in Figure 3,
A shows a state in which the center of the coil 5 in the width direction is shifted from the center of the magnetic gap, and b shows the distribution of magnetic flux density interlinking with the coil 5 in that state. In each figure b, the area of the shaded area is the coil 5
It can be seen that the area of the shaded portion in FIG. 3b is smaller than that in FIG. 2b. That is, the value of the force coefficient B·l with respect to the displacement of the coil 5 is not constant within the amplitude of the coil 5, but becomes smaller as the widthwise center of the coil 5 moves away from the center of the magnetic gap, as shown in FIG. Therefore, the driving force F also becomes smaller.

In this way, in the conventional speaker unit, the value of the force coefficient B·l with respect to the displacement of the coil 5 is not constant within the amplitude of the coil 5, so the driving force F does not become a sine wave in response to a sine wave input. This causes third-order harmonic distortion, which is a major cause of distortion in the low frequency range of speakers.

The present invention was made in order to eliminate the drawbacks of the conventional ones as described above, and aims to provide a speaker unit with low distortion by keeping the driving force constant regardless of the displacement of the voice coil. do.

In the speaker unit according to the present invention, a voice coil whose winding width is larger than the width of the magnetic gap is provided, and when the density of magnetic flux that can interlink with this voice coil is B and the wire length of the voice coil is l, the outside of the magnetic gap is By changing the magnetic flux density distribution, that is, the distribution of the leakage magnetic flux density portion, the value of B·l is made constant at least within the amplitude of the voice coil.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 5 is a cross-sectional view showing the first embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals. In FIG. 5, the center pole 1B of the pole yoke 1 has its upper end connected to the voice coil 5.
The center pole 1B has a height that is equal to or higher than the upper limit of the vertical vibration range of the upper end, and on both sides of the facing part 12 with the plate 3 of the center pole 1B, that is, above and below, as the distance from the facing part 12 increases, the center pole 1B
Tapered surfaces 13, 13 are formed such that the outer diameter of the voice coil 5 increases and approaches the voice coil 5 as the distance from the center in the movable direction of the voice coil 5 increases.
The other configurations are the same as in FIG. 1. Tapered surface 13,1 formed on the outer periphery of center pole 1B
3 constitutes a magnetic flux density setting means that makes the value of the force coefficient B·l constant at least within the amplitude of the voice coil 5. Since the magnitude of the magnetic flux density between the center pole 1B and the plate 3 changes depending on the length of the magnetic path, by forming the tapered surfaces 13, 13, the opposing portion 12 of the center pole 1B and the tapered surface 13 , 13 can be made stepwise as shown in FIG. 6b, and the magnetic flux density within the movable range of the annular end face of the voice coil can be made constant. As a result, the voice coil 5
Even if B is displaced from the position shown in FIG. 6a to the position shown in FIG.・When the value of l becomes constant, the driving force F acting on the coil 5 is
(corresponding to the area of the shaded area) is also constant. Therefore,
A sinusoidal driving force F is obtained for the sinusoidal current flowing through the coil 5.

Note that the inclinations of the tapered surfaces 13, 13 do not necessarily have to be straight, but may be curved 13', 13' as shown in FIG. 9, and by appropriately selecting the curvature, the voice The magnetic flux near both ends of the coil 5 can be set to be uniform. In addition, the opposing portion 12 of the center pole 1B
The thickness of the center pole 1B does not have to be the same as the thickness of the plate 3, and the center pole 1B does not need to be integrally molded, but may be constructed by assembling multiple parts as shown in FIG. .

FIG. 11 is a sectional view showing a second embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same symbols. In this embodiment, the center pole 1C of the pole yoke 1 has a height such that its upper end exceeds the upper limit of the vertical vibration range of the upper end of the voice coil 5, and has a height near the center pole 1C on the upper and lower surfaces of the plate 3. is provided with magnetic plates 14, 14 having tapered surfaces whose inner diameters become smaller as they move away from the plate 3, and the magnetic plates 14, 14 maintain the value of the force coefficient B·l at least within the amplitude of the voice coil 5. This constitutes a magnetic flux density setting means that keeps the magnetic flux density constant. According to this configuration, the magnetic plate 14,
14, the distribution of magnetic flux density can be made stepwise as shown in FIG. The area of the shaded portion in FIG. b does not change, and the driving force F acting on the coil 5 remains constant. Therefore, when a sinusoidal current flows through the coil 5, a sinusoidal driving force F is generated in the coil 5, and harmonic distortion can be reduced.

Note that the inclinations of the tapered surfaces of the magnetic plates 14, 14 do not necessarily have to be linear;
As shown in FIG. 13, it may be curved, or it may have a shape as shown in FIGS. 13c and d.

FIG. 14 is a sectional view showing a third embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals. In this embodiment, a magnetic plate 15 having a tapered surface whose outer diameter increases as the distance from the center pole 1A increases on the upper surface of the center pole 1A of the pole yoke 1, and the plate 3
A magnetic plate 16 having a tapered surface whose inner diameter decreases as it moves away from the plate 3 is disposed on the upper surface to face the magnetic plate 15.
5 and 16 constitute magnetic flux density setting means for keeping the value of the force coefficient B·l constant at least within the amplitude of the voice coil 5. According to this configuration, the magnetic flux density distribution shown in FIG. 15b is obtained by the action of the magnetic plates 15 and 16, so that the upward vibration of the voice coil 5
6, the area of the shaded portion in FIG. 15b hardly changes, and the force F acting on the coil 5 remains constant.

In the above embodiment, the magnetic plates 15 and 16 were provided above the voice coil 5, but as shown in FIG. 5 may be provided below, and the same effect as in the above embodiment can be achieved. Furthermore, the inclinations of the tapered surfaces of the magnetic plates 15 and 16 do not necessarily have to be linear, but may be curved as in the case of the second embodiment (see FIG. 13).

FIG. 17 is a sectional view showing a fourth embodiment of the present invention, in which parts equivalent to those in FIG. 11 are designated by the same reference numerals. In this embodiment, the frame 7 is made of a magnetic material, and is formed integrally with the frame 7 inside the plate joint of the frame 7, and has a rising edge having a tapered surface whose inner diameter decreases as it moves away from the upper surface of the plate 3. This rising portion 17 has a force coefficient B·l at least within the amplitude of the voice coil 5.
This constitutes a magnetic flux density setting means for keeping the value constant. According to this configuration, due to the action of the rising portion 17, a distribution of magnetic flux density almost the same as that shown in FIG. When B·l is constant, the driving force F acting on the coil 5 is a function only of the current i, and harmonic distortion can be reduced.

Note that the slope of the tapered surface of the rising portion 17 does not necessarily have to be linear, and may be curved as in each of the above embodiments. Also,
It is also possible to change the thickness of the rising portion 17 between the proximal end and the distal end.

FIG. 18 is a sectional view showing a fifth embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same symbols. In this example, plate 3
A magnetic plate 18 having a tapered surface whose inner diameter becomes smaller as it moves away from the plate 3 is directly disposed on the upper surface, and a magnetic plate 19 having the same configuration as the magnetic plate 18 is disposed on the lower surface of the plate 3. The magnetic plates 18, 1 are arranged via a spacer 20 with a high resistance.
9 and the spacer 20 are at least the voice coil 5
This constitutes a magnetic flux density setting means that keeps the value of the force coefficient B·l constant within the amplitude of . Magnetic plate 19
When the magnet 2 is placed directly on the lower surface of the plate 3, the magnetic flux density on the magnetic plate 19 side is larger than that on the magnetic plate 18 side, and the force coefficient B is・Although the linearity of l will be impaired, as in this example, the spacer 20
By appropriately selecting the thickness and material of the magnetic plates 18 and 19, the magnetic flux densities of the magnetic plates 18 and 19 can be made equal, and the linearity of the force coefficient B·l can be improved.

In addition, as a modification of this embodiment, FIG. 19a,
A configuration shown in b is conceivable.

As explained above, according to the present invention, when a voice coil is provided whose winding width is larger than the width of the magnetic gap, and the density of magnetic flux that can interlink with this voice coil is B, and the line length of the voice coil is l, , the value of B·l is kept constant at least within the amplitude of the voice coil, and a driving force proportional to the current acts on the voice coil, so harmonic distortion can be reduced, and from Fig. 20, As is clear,
Compared to the conventional structure (broken line), distortion especially in the low range can be reduced (solid line in this embodiment), and a speaker unit with excellent sound quality can be obtained.

[Brief explanation of drawings]

Figure 1 is a sectional view showing a conventional example, Figures 2 and 3
Each figure a in the figure is a cross-sectional view of the main part showing the change in position of the voice coil with respect to the magnetic gap, each figure b is a distribution diagram of the magnetic flux density at each position, and Fig. 4 shows the relationship between the displacement of the voice coil and the force coefficient in the conventional example. FIG. 5 is a cross-sectional view showing the first embodiment of the present invention, and each view a of FIG. 6 and FIG. Figure b is a distribution diagram of magnetic flux density at each position,
FIG. 8 is a diagram showing the relationship between the displacement of the voice coil and the force coefficient according to the present invention, and FIGS.
11 is a sectional view showing a second embodiment of the present invention; FIG. 12a is a sectional view showing the position of the voice coil with respect to the magnetic gap; b is a distribution diagram of the magnetic flux density at that position, FIGS. 13a, b, c, and d are sectional views of essential parts showing a modification of the embodiment in FIG. 11, and FIG. 14 is a third embodiment according to the present invention. 15th cross-sectional view showing
Figure a is a cross-sectional view of the main part showing the position of the voice coil with respect to the magnetic gap, b is a distribution diagram of magnetic flux density at that position, Figure 16 is a cross-sectional view showing a modification of the embodiment shown in Figure 14, and Figure 17 is 18 is a cross-sectional view showing a fourth embodiment of the present invention, FIG. 19 is a cross-sectional view showing a fifth embodiment of the present invention, and FIGS. 19 a and b are main parts showing a modification of the embodiment of FIG. 18. The cross-sectional view, FIG. 20, is a diagram showing the distortion characteristics of the speaker according to the present invention (solid line) and the conventional speaker (broken line). Explanation of symbols of main parts, 1...Pole yoke,
2...Magnet, 3...Plate, 5...Voice coil, 7...Frame, 8...Diaphragm, 13
...Tapered surface, 14, 15, 16, 18, 19...
...magnetic plate, 17... rising portion, 20... spacer.

Claims (1)

[Scope of Claims] 1. An annular plate, a pole yoke that is inserted through the center of the ring of the plate and forms a magnetic gap together with the plate, and that is inserted into the magnetic gap and whose winding width is inside the plate. A speaker unit including a voice coil whose height in the center direction is larger than a height in the center direction of a cylindrical end surface, in which at least one of the movable ranges is formed from a side surface of a portion forming an opposing surface of the plate forming the magnetic gap and the pole yoke. 1. A speaker unit comprising: a magnetic flux density setting means having a magnetic body that extends closer to the voice coil as it moves away from the center of the voice coil in a movable direction. 2. The magnetic flux density setting means is a tapered surface formed on at least one side of a portion of the pole yoke facing the plate so that the outer diameter of the pole yoke increases as it moves away from the facing portion. A speaker unit according to claim 1, characterized in that: 3. The magnetic flux density setting means is a magnetic plate disposed on the upper and lower surfaces of the plate so as to face the circumferential wall of the pole yoke, and having a tapered surface whose inner diameter decreases as the distance from the plate increases. A speaker unit according to claim 1, characterized in that: 4. The magnetic flux density setting means comprises a magnetic plate disposed on the upper surface or lower surface of the pole yoke and having a tapered surface whose outer diameter increases as the distance from the pole yoke increases. The speaker unit described in item 1. 5. The magnetic flux density setting means comprises a magnetic plate disposed on the upper surface or lower surface of the plate and having a tapered surface whose inner diameter decreases as the distance from the plate increases. The speaker unit according to item 4. 6. The magnetic flux density setting means is a rising portion formed integrally with the frame inside the plate joint portion of the frame made of a magnetic material, and having a tapered surface whose inner diameter decreases as the distance from the plate increases. A speaker unit according to claim 1.