Patent Description:
Conventionally, there is a speaker that detects the capacitance formed between a centerpole and a voice coil bobbin having a bobbin constituted by an insulator layer and a non-magnetic conductor layer and that outputs the detected capacitance as an electric signal. The detected capacitance is used to eliminate sound distortion in a motional feedback (MFB) circuit (for example, see <CIT>).

Incidentally, a conventional speaker is designed such that the capacitance to be detected is less susceptible to disturbance noise, but change in the capacitance caused by the disturbance noise tends to be larger than the true detection value, which makes it difficult to detect the zero point, and therefore, the accuracy of detecting the position of the voice coil is not high enough to sufficiently eliminate the distortion of the sound in the MFB circuit.

<CIT> discloses a bass reproduction speaker apparatus in which negative stiffness is generated for a vibration system of a speaker unit by using a movable magnet attached to the vibration system of the speaker unit and also a ring-like stationary magnet arranged coaxially at the outer radius thereof in order to increase equivalently internal volume of a cabinet. In addition, an offset in the displacement direction of the vibration system of the speaker unit is detected with a Hall element and fed back to a power amplifier in order to correct the offset in the displacement direction of the vibration system of the speaker unit.

It is a general object of the described embodiment to provide a speaker capable of detecting the position of the voice coil with a high degree of accuracy.

The invention relates to a speaker according to the appended claims. Embodiments are disclosed in the dependent claims.

A speaker according to an aspect of the present disclosure includes a yoke configured to form a magnetic circuit, a first magnet provided in a fixed manner, a voice coil provided in a gap through which a magnetic flux of the magnetic circuit is configured to pass, a diaphragm connected to the voice coil and configured to vibrate with the voice coil, a second magnet provided on a diaphragm unit including the voice coil and the diaphragm, and a magnetic sensor provided at a position through which both of a first magnetic flux generated by the first magnet and a second magnetic flux generated by the second magnet are configured to pass, wherein a direction of the first magnetic flux and a direction of the second magnetic flux are different from each other.

According to the embodiment, the speaker capable of detecting the position of the voice coil with a high degree of accuracy can be provided.

Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:.

In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the specification and drawings, elements having substantially the same functions or configurations are denoted with the same numerals, and duplicate description thereof is omitted.

Hereinafter, an embodiment to which a speaker according to an embodiment of the present disclosure is applied is described.

<FIG> are drawings illustrating a speaker <NUM>. <FIG> illustrates a cross-sectional view taken along line A-A of <FIG> is a plan view illustrating the speaker <NUM> as seen from the top side with a diaphragm and a damper removed. In this specification, a vertical direction is assumed to be defined based on the orientation of <FIG>, and the vertical direction is not intended to mean an absolute direction that is defined with reference to the direction of gravity. The upper surface side is a front side of the speaker <NUM>, and is a side from which sound is output. The lower surface side is a rear side of the speaker <NUM>.

Hereinafter, a term "plan view" is intended to mean a drawing in which an object in question is depicted as seen from the upper surface side or the lower surface side thereof. Also, it is assumed that terms such as perpendicular, orthogonal, vertical, upward, downward, and the like allow for deviation to such a degree that the effects of the embodiment are not impaired.

The speaker <NUM> includes a frame <NUM>, a diaphragm <NUM>, an edge <NUM>, a bobbin <NUM>, a voice coil <NUM>, a damper <NUM>, a yoke <NUM>, a first magnet <NUM>, a top plate <NUM>, a second magnet <NUM>, a magnetic sensor <NUM>, and a base <NUM>. The bobbin <NUM>, the voice coil <NUM>, and the diaphragm <NUM> are an example of a diaphragm unit. The speaker <NUM> is in a circular shape in a plan view, and <FIG> indicate a center axis C of the speaker <NUM>.

The frame <NUM> is a housing of the speaker <NUM>, and is made of metal or resin in a substantially conical shape. The frame <NUM> includes a holding unit 101A on the lower side as illustrated in <FIG>. The holding unit 101A is fixed to the upper surface of the top plate <NUM>. In <FIG>, the holding unit 101A is omitted.

The diaphragm <NUM> is made of paper, resin, or a thin metal plate and is vibrated by vibration of the voice coil <NUM> in the vertical direction to generate sound. The diaphragm <NUM> is in a substantially conical shape as a whole, and in a plan view the diaphragm <NUM> is in a circular shape. The outer circumferential side of the diaphragm <NUM> is connected to the frame <NUM> via the edge <NUM> made of an elastic material such as rubber, and the inner circumferential side of the diaphragm <NUM> is connected to the bobbin <NUM>. The center of the annular shape of the diaphragm <NUM> matches with the center axis C in a plan view.

The bobbin <NUM> is a cylindrical member made of paper, resin, or the like. A top end of the bobbin <NUM> is connected to the inner circumferential side of the diaphragm <NUM> and is connected to the inner circumferential side of the damper <NUM>. The voice coil <NUM> is wound around the outer circumference of the lower portion of the bobbin <NUM>, and the bobbin <NUM> and the voice coil <NUM> are inserted into a gap <NUM>, explained later, from the upper side. The center of the cylindrical shape of the bobbin <NUM> matches with the center axis C in a plan view. The bobbin <NUM> may be integrally formed with the inner circumferential side of the diaphragm <NUM>.

The yoke <NUM> is provided on the rear side of the speaker <NUM>. The yoke <NUM> is in a circular shape in a plan view, and is a member made of a magnetic material having an arm shape as illustrated in a cross-sectional view as illustrated in <FIG>. An end portion 107A of the yoke <NUM> on the outer circumference side holds the first magnet <NUM>. A top end portion 107B on the inner circumferential side of the yoke <NUM> faces the inner circumferential surface of the top plate <NUM> with the gap <NUM> interposed therebetween. Specifically, the gap <NUM> in an annular shape that is a magnetic space is formed between the outer circumference surface of the top end portion 107B of the yoke <NUM> and the inner circumferential surface of the top plate <NUM>. The center of the circular shape of the yoke <NUM> matches with the center axis C in a plan view.

The first magnet <NUM> is a permanent magnet in an annular shape as illustrated in <FIG>. The center of the annular shape of the first magnet <NUM> matches with the center axis C in a plan view. Of the first magnet <NUM>, at least one of the upper surface side and the lower surface side is magnetized with the N pole, and the other is magnetized with the S pole. The magnetic flux generated by the first magnet <NUM> passes through the top plate <NUM>, the gap <NUM>, and the yoke <NUM> and returns to the first magnet <NUM>. At a height position in the vertical direction where the magnetic sensor <NUM> is situated, the direction of the magnetic flux generated by the first magnet is a direction toward the center axis C in a plan view, as illustrated by eight arrows B in a central portion of <FIG>. The magnetic flux generated by the first magnet <NUM> is an example of a first magnetic flux.

The top plate <NUM> is a member made of a magnetic material with an annular shape in a plan view, and is fixed to the top portion of the first magnet <NUM>. The center of the annular shape of the top plate <NUM> matches with the center axis C in a plan view. The top plate <NUM>, the yoke <NUM>, and the first magnet <NUM> constitute a magnetic circuit.

The second magnet <NUM> is attached to a position higher than the voice coil <NUM> on the outer circumference surface of the bobbin <NUM>. The second magnet <NUM> is attached to a single position in a circumferential direction of the bobbin <NUM>, and is situated to face the magnetic sensor <NUM>, explained later, in a plan view, and to overlap with the magnetic sensor <NUM> in the vertical direction. The second magnet <NUM> is a permanent magnet having the N pole and the S pole, and generates magnetic flux in a direction indicated by an arrow D. The magnetic flux of the second magnet <NUM> is an example of a second magnetic flux. The magnetic flux of the second magnet <NUM> is in a tangential direction of a circle formed by the outer circumference surface of the bobbin <NUM> in a plan view. In this case, of the magnetic flux generated by the first magnet <NUM>, a direction of magnetic flux passing through the center of the second magnet <NUM> in a plan view is indicated by an arrow B1. A direction of the magnetic flux of the first magnet <NUM> indicated by the arrow B1 and a direction of the magnetic flux of the second magnet <NUM> indicated by the arrow D are orthogonal to each other in a plan view. The second magnet <NUM> may be smaller than the first magnet <NUM> because it is sufficient for the second magnet <NUM> to be able to provide magnetic flux of a predetermined density (a magnetic field of a predetermined strength) to the magnetic sensor <NUM> in order to detect the position of the voice coil <NUM>.

The magnetic sensor <NUM> is provided on the top plate <NUM> with the base <NUM> interposed therebetween. The base <NUM> is provided to adjust the height of the magnetic sensor <NUM>, and is made of, for example, resin. The magnetic sensor <NUM> is situated on a straight line connecting the center axis C and the center of the second magnet <NUM> in a plan view. Therefore, the position of the magnetic sensor <NUM> is a position where the direction of the magnetic flux of the first magnet <NUM> and the direction of the magnetic flux of the second magnet <NUM> cross each other at a right angle.

The magnetic sensor <NUM> is a sensor capable of detecting the direction of magnetic flux within a plane, and is provided so as to be able to detect the direction of magnetic flux within the plane perpendicular to the center axis C. When a current of an audio signal is passed through the voice coil <NUM>, the bobbin <NUM> and the voice coil <NUM> vibrate in the direction of the center axis C as indicated by a double arrow, and accordingly, the magnetic sensor <NUM> can detect, within the plane perpendicular to the vibration direction of the bobbin <NUM> and the voice coil <NUM>, the direction of a composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM>. The magnetic sensor <NUM> may be a sensor including a magneto resistance (MR) device such as, for example, an anisotropic magneto resistance (AMR) device, a giant magnetic resistance (GMR) device, a tunnel magneto resistance (TMR) device, or the like. In this case, for example, the magnetic sensor <NUM> is assumed to be a sensor including a GMR device.

<FIG> is a drawing illustrating an embodiment of the magnetic sensor <NUM> and the directions of the magnetic fluxes. <FIG> illustrates: a direction B1 of the magnetic flux, located at the position of the magnetic sensor <NUM>, from among the magnetic fluxes of the first magnet <NUM>; and a direction D of the magnetic fluxes of the second magnet <NUM>. <FIG> illustrates XYZ coordinates of the orthogonal coordinate system. The X direction matches with the direction D, and the Y direction matches with the direction B1. The Z direction matches with the direction of the center axis C as illustrated in <FIG>.

The voice coil <NUM> vibrations in the direction of the center axis C (Z direction), and accordingly, when the voice coil <NUM> is driven by an audio signal to vibrate in the Z direction, the second magnet <NUM> also vibrates in the Z direction. In this case, the direction D is assumed to be indicative of a particular magnetic flux generated by the second magnet <NUM>, and when the second magnet <NUM> moves in the Z direction due to the vibration in the Z direction, the position of the particular magnetic flux changes in the Z direction as illustrated by a thick arrow in <FIG>. The density of the magnetic flux of the second magnet <NUM> detected by the magnetic sensor <NUM> decreases as the second magnet <NUM> moves in the Z direction (the upward direction in <FIG>), and therefore, when the second magnet <NUM> moves in the Z direction due to the vibration in the Z direction, the density of the magnetic flux (the strength of the magnetic field) penetrating the magnetic sensor <NUM> in the X direction changes.

Because the magnetic sensor <NUM> is not attached to the diaphragm unit but is attached to the magnetic circuit (a fixed body side), the density of the magnetic flux (the strength of the magnetic field) of the first magnet <NUM> penetrating the magnetic sensor <NUM> in the Y direction is constant. Accordingly, when the density of the magnetic flux penetrating the magnetic sensor <NUM> in the X direction changes, the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> in the XY plane passing through the magnetic sensor <NUM> changes. Therefore, the magnetic sensor <NUM> can detect a change in the direction of the composite magnetic flux due to vibration of the voice coil <NUM> in the Z direction.

The displacement of the voice coil <NUM> in the Z direction represents a displacement of the diaphragm <NUM>, and therefore, the displacement of the diaphragm <NUM>, the bobbin <NUM>, and the voice coil <NUM> in the Z direction can be detected by detecting a change in the direction of the composite magnetic flux with the magnetic sensor <NUM>. A configuration may be such that a relationship between the direction of the composite magnetic flux detected by the magnetic sensor <NUM> and the position or displacement of the voice coil <NUM> in the Z direction is measured in advance and obtained as data that is stored in a memory of a control unit constituted by a microcomputer or the like, and the position or displacement of the voice coil <NUM> in the Z direction corresponding to the direction of the composite magnetic flux detected by the magnetic sensor <NUM> is output. The control unit may be provided in the speaker <NUM>, or may be provided outside of the speaker <NUM> and connected to the speaker from the outside.

The magnetic sensor <NUM> is a sensor that detects the direction of the magnetic flux (magnetic field) in the XY plane, and has such a property that the magnetic resistance changes in response to only the direction of the magnetic field. The magnetic resistance of the magnetic sensor <NUM> does not change in response to the magnitude of the magnetic field. Therefore, the magnetic sensor <NUM> is less susceptible to external noise and the like, and can detect the direction of the magnetic flux with a high degree of accuracy.

Therefore, the speaker <NUM> capable of detecting the position of the voice coil <NUM> with a high degree of accuracy can be provided. The position of the voice coil <NUM> can be detected with a high degree of accuracy, and therefore, when feedback control is performed using an output of a microcomputer indicative of the direction of the composite magnetic flux detected by the magnetic sensor <NUM> (an output indicative of the position or displacement of the voice coil <NUM> in the Z direction) in adaptive signal processing, distortion of sound with respect to an audio signal input to the voice coil <NUM> can be reduced.

The speaker <NUM> is a device that passively outputs audio in response to an audio signal output from the amplifier, and is a device that has a very large distortion and variation in the output in response to an audio signal and that is susceptible to damage due to over-vibration. In the past, a technique for feeding back the amplitude of the voice coil was studied, but a sensor capable of minimizing noise and the burden imposed on speaker was not available, and it was difficult to correct distortion of the output in response to an audio signal with a high degree of accuracy.

Examples of sensors tested in the past include a sensor detecting laser, light, an eddy current, or the like, a differential sensor, a moving coil, and the like, but all of these conventional sensors have problems in that the conventional sensors cannot accurately detect the position of the voice coil, noise is large, the burden imposed on a diaphragm member such as a bobbin or a voice coil is large, the sensors cannot withstand a temperature change, the cost is too high, and the like.

In contrast, the speaker <NUM> using the magnetic sensor <NUM> detecting the direction of the composite magnetic flux as described above has advantages in that the magnetic sensor <NUM> can accurately detect the position of the voice coil <NUM>, noise is small, the burden imposed on the diaphragm member such as the bobbin <NUM> and the voice coil <NUM> is small, the magnetic sensor <NUM> can withstand a temperature change, and the cost is low.

Furthermore, because the first magnet <NUM> is a magnet for forming a magnetic circuit with the yoke <NUM>, the speaker <NUM> capable of detecting the position of the voice coil <NUM> with a high degree of accuracy by using the existing magnet of the speaker <NUM> can be provided.

Furthermore, because the second magnet <NUM> is attached to the bobbin <NUM> around which the voice coil <NUM> is wound, the position of the voice coil <NUM> can be accurately detected by the second magnet <NUM>, and the speaker <NUM> capable of detecting the position of the voice coil <NUM> with a high degree of accuracy can be provided.

Furthermore, because the position where the magnetic sensor <NUM> is provided is on the outer circumference side of the bobbin <NUM>, the magnetic sensor <NUM> can be provided, without difficulty, in proximity to both of the first magnet <NUM> (the magnetic circuit) and the second magnet <NUM>, and the speaker <NUM> capable of detecting the position of the voice coil <NUM> with a high degree of accuracy can be provided.

Because the magnetic sensor <NUM> detects a change in the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> in a plane perpendicular to the vibration direction of the voice coil <NUM>, the composite magnetic flux can be caused to reflect, to the greatest extent, displacement caused by vibration of the voice coil <NUM>, and thus the detection accuracy of the position of the voice coil <NUM> is improved.

Furthermore, because, at the position where the magnetic sensor <NUM> is provided, the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> are orthogonal to each other, the composite magnetic flux can be caused to reflect, to the greatest extent, a change in the density of the magnetic flux of the second magnet <NUM> (a change in the strength of the magnetic field), and the detection accuracy of the position of the voice coil <NUM> is improved.

<FIG> is a drawing illustrating displacement of the voice coil <NUM> of the speaker <NUM> in response to an applied voltage to the voice coil <NUM>. When the absolute value of the applied voltage to the voice coil <NUM> increases, the absolute value of the current of the audio signal that is input to the voice coil <NUM> also increases, although not in a linear manner.

The property denoted with a broken line in <FIG> indicates a property obtained by correcting sound distortion with reference to the applied voltage by applying feedback control with adaptive signal processing on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>. The property denoted with a solid line in <FIG> indicates a property obtained by adjusting sound distortion with adaptive signal processing without applying feedback control on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>.

As illustrated in <FIG>, it is understood that the property denoted with the solid line that is obtained without feedback control on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM> has a large distortion in an operation region in which the absolute value of the applied voltage is large, and the property denoted with the broken line obtained by performing feedback control on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM> is such that the displacement of the voice coil <NUM> linearly changes in response to the applied voltage.

Because the magnetic sensor <NUM> can detect the direction of the composite magnetic flux with a high degree of accuracy, distortion of displacement of the voice coil <NUM> in response to the applied voltage to the voice coil <NUM> can be corrected linearly in this manner. Therefore, the distortion rate of the displacement of the voice coil <NUM> can be improved.

Furthermore, because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, the resonance of the voice coil <NUM> (the voice coil <NUM> and the diaphragm <NUM>) can be controlled, and the vibration of the voice coil <NUM> in a range out of the resonance range can be controlled with a high degree of accuracy.

Furthermore, because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, damage and the like of the diaphragm <NUM>, the edge <NUM>, the bobbin <NUM>, the damper <NUM>, and the like can be detected with a high degree of accuracy. In addition, when these members are damaged, an error can be provided by notification to the source of supply of an audio signal.

Furthermore, because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, buffering of the diaphragm <NUM> may be electrically controlled without using the damper <NUM>.

Furthermore, the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, so that the power that is input to an amplifier for amplifying an audio signal can be optimized, the input power to the amplifier can be reduced, and the size of the amplifier can be reduced.

Furthermore, because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, distortion can be alleviated by feedback control based on position information of the voice coil <NUM>.

Furthermore, because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>, damage to the speaker <NUM> caused by an excessive input can be alleviated, and the margin for the input signal to the speaker <NUM> can be reduced.

Although the second magnet <NUM> is attached to the bobbin <NUM> in the above explanation, the second magnet <NUM> may be attached to the voice coil <NUM>. Also, the second magnet <NUM> may be attached to a portion that vibrates together with the voice coil <NUM>, other than the bobbin <NUM> and the voice coil <NUM>.

Furthermore, although the magnetic sensor <NUM> is provided on the base <NUM> provided on the top plate <NUM> in the above explanation, the magnetic sensor <NUM> may be provided anywhere on the fixed portion side such as the magnetic circuit, the frame <NUM>, and the like so long as the magnetic sensor <NUM> is situated so as to be able to detect the magnetic flux of the second magnet <NUM>.

Furthermore, in the above explanation, the position of the magnetic sensor <NUM> is a position where the direction of the magnetic flux of the first magnet <NUM> and the direction of the magnetic flux of the second magnet <NUM> cross each other at a right angle. However, so long as the magnetic sensor <NUM> can detect the direction of the composite magnetic flux, the direction of the magnetic flux of the first magnet <NUM> and the direction of the magnetic flux of the second magnet <NUM> do not have to cross each other at a right angle. So long as the direction of the magnetic flux of the first magnet <NUM> and the direction of the magnetic flux of the second magnet <NUM> are different, they may cross each other at any angle.

Furthermore, in the above explanation, the magnetic sensor <NUM> detects the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> within the plane perpendicular to the vibration direction of the bobbin <NUM> and the voice coil <NUM>. However, the plane within which the magnetic sensor <NUM> detects the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> does not have to be perpendicular to the vibration direction of the bobbin <NUM> and the voice coil <NUM>, and may cross the vibration direction at any angle. This is because, so long as the plane within which the magnetic sensor <NUM> detects the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> cross the vibration direction at any angle, the magnetic sensor <NUM> can detect a change in the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM> caused by vibration of the bobbin <NUM> and the voice coil <NUM>.

Furthermore, in the above explanation, the magnetic sensor <NUM> detects the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet <NUM> and the magnetic flux of the second magnet <NUM>, and the first magnet <NUM> is fixed, whereas the second magnet <NUM> moves in response to vibration of the bobbin <NUM> and the voice coil <NUM>. However, instead of the first magnet <NUM> as explained above, a magnet may be provided as a first magnet in a fixed manner in the speaker <NUM>, and the magnetic sensor <NUM> may detect the direction of the composite magnetic flux constituted by the magnetic flux of the first magnet and the magnetic flux of the second magnet <NUM>. This is because the displacement of the voice coil <NUM> can be detected with a high degree of accuracy on the basis of the direction of the composite magnetic flux detected by the magnetic sensor <NUM>. Alternatively, the magnetic sensor <NUM> may detect the direction of the composite magnetic flux of the magnetic flux of the magnet provided in a fixed manner in the speaker <NUM>, the magnetic flux of the first magnet <NUM>, and the magnetic flux of the second magnet <NUM>.

Claim 1:
A speaker (<NUM>) comprising:
a yoke (<NUM>) configured to form a magnetic circuit;
a first magnet (<NUM>) provided in a fixed manner;
a voice coil (<NUM>) provided in a gap through which a first magnetic flux of the magnetic circuit is configured to pass;
a diaphragm (<NUM>) connected to the voice coil (<NUM>) and configured to vibrate with the voice coil (<NUM>);
a second magnet (<NUM>) provided on a diaphragm unit (<NUM>, <NUM>, <NUM>) including the voice coil and the diaphragm; and
a magnetic sensor (<NUM>) provided at a position through which both of the first magnetic flux generated by the first magnet (<NUM>) and a second magnetic flux generated by the second magnet (<NUM>) pass,
wherein a direction of the first magnetic flux is different from a direction of the second magnetic flux,
wherein the magnetic sensor (<NUM>) is configured to detect a change in a direction of a composite magnetic flux constituted by the first magnetic flux and the second magnetic flux within a plane that crosses a vibration direction of the diaphragm unit (<NUM>, <NUM>, <NUM>).