JP4760668B2 - Speaker - Google Patents

Description

  The present invention relates to a speaker capable of detecting an electrical signal corresponding to a vibration amount of a coil bobbin or the like of the speaker as an MFB signal.

  Conventionally, a system called an MFB system is known for improving the output quality of a speaker. The MFB system detects an output value from a speaker and feeds back the detected value to the input side as an MFB signal to correct a minute sound distortion generated for each device, or a low frequency that a normal speaker is not good at This is a system that improves the sound reproduction characteristics of the system. In such an MFB system, the detection accuracy of the MFB signal is extremely important.

  Therefore, various MFB signal detection techniques have been proposed. For example, Patent Document 1 discloses a technique for detecting a vibration amount of a speaker vibration system as a change in capacitance. In Patent Document 1, two first electrostatic electrodes are disposed on the outer peripheral surface of the internal magnetic pole of the speaker, and second electrostatic electrodes are disposed on the inner peripheral surface of the bobbin so as to face the two first electrostatic electrodes. Each electrode is provided. In this case, the gap between the first electrostatic electrode and the second electrostatic electrode functions as two capacitors whose values change differentially due to the vibration of the bobbin. In Patent Document 1, the output value (vibration amount) of the speaker is detected based on the change in the capacitance of the capacitor.

JP-A-54-49123

  However, in such a configuration, the first electrostatic electrode and the second electrostatic electrode are interposed between the voice coil and the internal magnetic pole, and the distance between the voice coil and the internal magnetic pole tends to be large. there were. As a result, there is a problem in that the magnetic gap becomes large, leading to a reduction in speaker efficiency and performance.

  Therefore, an object of the present invention is to provide a speaker that can detect an MFB signal with high accuracy without reducing the efficiency and performance of the speaker.

The speaker of the present invention is a substantially cylindrical member that is held so as to be able to vibrate. The speaker has a coil bobbin around which a voice coil is wound, and is disposed inside the coil bobbin so as to face the wound voice coil. a center pole magnetic poles are embedded in the position, a center pole recesses on the upper and lower pole built portions of its outer peripheral surface is formed, is formed in each upper and lower sides of the magnetic pole internal portion A pair of fixed electrodes that are fixedly arranged one by one in the recesses, a movable electrode that is disposed inside the coil bobbin and that partially faces the pair of fixed electrodes, and each fixed electrode that is generated by vibration of the coil bobbin And a detection circuit that detects an electrical signal corresponding to the vibration amount of the coil bobbin as an MFB signal based on a change in capacitance between the movable electrodes. The features.

  In a preferred embodiment, each fixed electrode is fixedly arranged at a position closer to the inner peripheral surface of the coil bobbin than the side surface of the center pole. In another preferred embodiment, a pair of insulators arranged in a gap portion between each fixed electrode and the center pole is further provided.

In another preferred embodiment, the movable electrode is grounded in the detection circuit.

  According to the present invention, since the fixed electrode is not interposed between the magnetic pole and the voice coil, the magnetic gap can be reduced. As a result, the MFB signal can be detected with high accuracy without degrading the efficiency and performance of the speaker.

  Hereinafter, a speaker according to an embodiment of the present invention will be described with reference to the drawings. First, the MFB system 10 in which the speaker 20 of the present embodiment is used will be briefly described. The MFB system 10 is an acoustic reproduction system that controls the motion of the vibration system by negatively feeding back an electrical signal proportional to the motion of the vibration system of the speaker 20 to an amplifier that is a drive system. Many specific configurations of the MFB system 10 have been conventionally proposed. FIG. 1 is a block diagram of an MFB system 10 having the simplest configuration among many conventionally proposed MFB systems.

  An input signal input from the host external device is input to the power amplifier 12 and amplified. The amplified signal is input to the speaker 20 as a drive signal. The vibration system of the speaker 20 vibrates according to the input drive signal and generates sound. The vibration of the vibration system of the speaker 20 at this time is converted into an electric signal by the MFB signal detection device 21 incorporated in the speaker 20 and detected as an MFB signal. The value of the detected MFB signal is adjusted by the feedback circuit 14 and then negatively fed back to the power amplifier 12. As a result, it is possible to correct minute sound distortion caused by individual differences among devices and improve sound reproduction characteristics in a low frequency range, which is not good for general speakers.

  Here, in order to obtain high quality reproduction characteristics in the MFB system 10, the detection accuracy of the MFB signal is extremely important. For this reason, various MFB signal detection methods have been proposed. Among such MFB signal detection methods, there is a method called a capacity detection method. This is because a fixed electrode is provided on the speaker fixed electrode (for example, center pole) and a movable electrode is provided on the vibration system of the speaker. This is a method for detecting. This capacitance detection method has an advantage that it can be easily realized because it can be configured simply by mounting the electrode in the speaker. However, conventionally proposed capacity detection type MFB signal detection devices have problems such as a decrease in efficiency and performance of the speaker and a low detection accuracy of the MFB signal. Therefore, in the present embodiment, the MFB signal detection device 21 having a special aspect is incorporated in the speaker 20 to improve the MFB detection accuracy without reducing the efficiency and performance of the speaker 20.

  Hereinafter, the speaker 20 will be described in detail. FIG. 2 is a schematic longitudinal sectional view of the speaker 20. FIG. 3 is an enlarged view of a portion A in FIG.

  The frame 22 of the speaker 20 is a member that functions as a housing for holding the entire speaker 20 and has a substantially truncated cone shape. Inside the frame 22, a diaphragm 24, a voice coil 30 and a magnetic pole 34 constituting a magnetic circuit are held. The frame 22 is made of a material having a certain rigidity, such as a plated steel plate, and is formed by pressing or the like.

  The diaphragm 24 vibrates according to the drive signal input to the voice coil 30 and radiates sound. The diaphragm 24 has a substantially truncated cone shape that is slightly smaller than the frame 22 and is supported in a floating state by a damper 26.

  A coil bobbin 28 is connected to the lower end of the diaphragm 24. The coil bobbin 28 is a substantially cylindrical member made of a nonmagnetic material such as resin, and a voice coil 30 is wound around the outer periphery thereof. In addition, the coil bobbin 28 incorporates a movable electrode 38 that constitutes an MFB signal detection device to be described later.

  A center pole 32 having a smaller diameter than the inner periphery of the coil bobbin 28 is disposed inside the substantially cylindrical coil bobbin 28. The center pole 32 has a substantially cylindrical shape arranged coaxially with the coil bobbin. A magnetic pole 34 for generating a magnetic field is disposed at the center portion of the center pole 32. The magnetic pole 34 forms a magnetic circuit together with the voice coil 30 wound around the coil bobbin 28. That is, when a current corresponding to the drive signal input from the amplifier flows through the voice coil 30, a Lorentz force is generated between the magnetic field generated by the magnetic pole 34. Then, the voice coil 30, the coil bobbin 28, and the diaphragm 24 vibrate as a whole by this Lorentz force. Thereby, a sound is generated.

  Here, as described above, the MFB signal detection device for detecting the MFB signal is incorporated in the speaker. The MFB signal detection device includes a movable electrode 38 built in the coil bobbin 28, a pair of fixed electrodes 40a and 40b disposed in the gap between the center pole 32 and the coil bobbin 28, and a detection circuit 50 shown in FIG. Composed.

  The first fixed electrode 40a and the second fixed electrode 40b are both plate members made of a conductor, and are arranged in the gap between the center pole 32 and the coil bobbin 28, and their positions are not changed. As described above, the movable electrode 38 is provided inside the coil bobbin 28 at a position facing the pair of fixed electrodes 40a and 40b.

  The gap between the pair of fixed electrodes 40a and 40b and the movable electrode 38 functions as a capacitor. Here, as a matter of course, the movable electrode 38 built in the coil bobbin 28 vibrates integrally with the coil bobbin 28, the diaphragm 24 and the like. With this vibration, the opposing areas of the first fixed electrode 40a and the movable electrode 38, and the second fixed electrode 40b and the movable electrode 38 fluctuate differentially. In other words, the capacitances of the two capacitors formed by the pair of fixed electrodes 40 a and 40 b and the movable electrode 38 fluctuate differentially according to the vibration of the vibration system of the speaker 20.

  The detection circuit 50 illustrated in FIG. 4 is a circuit that detects, as an MFB signal, an electric signal proportional to the vibration amount of the vibration system based on the change in capacitance of the two capacitors 52a and 52b that are differentially varied. It is. Specifically, in this detection circuit 50, the movable electrode 38 is grounded. A capacitor 52a formed by the movable electrode 38 and the first fixed electrode 40a is connected to a DC power source via a first resistor 54a having a predetermined resistance value. Further, the capacitor 52b formed by the movable electrode 38 and the second fixed electrode 40b is also connected to the DC power source via the second resistor 54b having a predetermined resistance value. The differential amplifier 58 detects and amplifies the difference between the voltage values of the capacitors, and outputs the amplified difference to the feedback circuit of the MFB system. The configuration of the detection circuit 50 described here is merely an example, and other configurations may be used as long as the difference between the capacitances of the two capacitors 52a and 52b can be detected.

  As is clear from the above description, the MFB signal detection device of the present embodiment can be said to be a detection device of a capacity detection method. By the way, many of the conventionally proposed capacitive detection type MFB signal detection devices have a configuration in which an electrode for MFB signal detection is interposed between a magnetic pole and a voice coil. For this reason, the distance between the magnetic pole and the voice coil, in other words, the magnetic gap is increased by the thickness of the intervening electrode, and the efficiency and performance of the speaker are reduced.

  Therefore, in the present embodiment, as shown in FIG. 3, the pair of fixed electrodes 40 a and 40 b are arranged at positions avoiding the magnetic pole 34. More specifically, the first fixed electrode 40 a is disposed above the magnetic pole 34, and the second fixed electrode 40 b is disposed below the magnetic pole 34. Further, the outer diameter of the center pole 32 on the upper side and the lower side of the magnetic pole 34 is made smaller than the outer diameter of the portion where the magnetic pole 34 is disposed. In other words, concave portions are formed on the upper side and the lower side of the magnetic pole 34. The recesses are large enough to accommodate the fixed electrodes 40a and 40b and insulators 42a and 42b described later, and the fixed electrodes 40a and 40b are disposed in the recesses. In this case, the fixed electrodes 40 a and 40 b are not interposed between the magnetic pole 34 and the voice coil 30. As a result, the distance between the magnetic pole 34 and the voice coil 30 that has been increased by the thickness of the fixed electrode can be shortened. As a result, the magnetic gap can be reduced, and the efficiency and performance of the speaker 20 can be improved.

  As is apparent from FIG. 4, in this embodiment, the movable electrode 38, which is a common electrode, is grounded instead of the divided fixed electrodes 40a and 40b. Therefore, even if the fixed electrodes 40 a and 40 b and the voice coil 30 are close to each other, the detection circuit 50 is not easily affected by electrostatic induction from the voice coil 30. As a result, the MFB detection accuracy can be further improved.

  On the other hand, since the fixed electrodes 40 a and 40 b are not grounded, a kind of capacitor is formed between the fixed electrodes 40 a and 40 b and the center pole 32. An increase in the capacitance of the capacitor formed by the fixed electrodes 40a and 40b and the center pole 32 causes a decrease in the detection output of the MFB signal. Therefore, in the present embodiment, the fixed electrodes 40a and 40b are arranged as far away from the center pole 32 as possible. More specifically, when the distance from the fixed electrodes 40a, 40b to the coil bobbin 28 is D1, and the distance from the fixed electrodes 40a, 40b to the center pole 32 is D2, the fixed electrodes 40a, 40b are at least at positions where D1 <D2. Is arranged.

  Insulators 42a and 42b are also arranged between the fixed electrodes 40a and 40b and the center pole 32 in order to electrically insulate the fixed electrodes 40a and 40b from the center pole 32. The center pole 32 and the insulators 42a and 42b, and the insulators 42a and 42b and the fixed electrodes 40a and 40b are bonded by, for example, an adhesive. The insulators 42a and 42b are made of a thin material such as paper and a low dielectric constant. By disposing the insulators 42a and 42b between the fixed electrodes 40a and 40b and the center pole 32, it is possible to apply a high voltage to the fixed electrodes 40a and 40b, thereby improving the detection accuracy of the MFB signal. it can.

  As is clear from the above description, according to the present embodiment, it is possible to detect the MFB signal with high accuracy without reducing the efficiency and performance of the speaker.

It is a block diagram which shows the structure of the most basic MFB system. It is a schematic sectional drawing of the speaker which is embodiment of this invention. It is the A section enlarged view in FIG. It is a figure which shows a detection circuit.

Explanation of symbols

  10 MFB system, 12 power amplifier, 14 feedback circuit, 20 speaker, 21 signal detector, 22 frame, 24 diaphragm, 26 damper, 28 coil bobbin, 30 voice coil, 32 center pole, 34 magnetic pole, 38 movable electrode, 40a, 40b fixed electrode, 42a, 42b insulator, 50 detection circuit, 52a, 52b capacitor, 54a, 54b resistor, 58 differential amplifier.

Claims (4)

A substantially cylindrical member held so as to be able to vibrate, a coil bobbin around which a voice coil is wound;
Disposed inside the coil bobbin, a center pole magnetic poles are incorporated in a position facing the wound voice coil, recesses in the upper and lower pole built portions of its outer peripheral surface is formed center With Paul ,
A pair of fixed electrodes fixedly disposed one by one in the recesses formed on each of the upper side and the lower side of the magnetic pole built-in part ;
A movable electrode disposed in a position inside the coil bobbin and partially facing the pair of fixed electrodes;
A detection circuit for detecting an electric signal corresponding to the vibration amount of the coil bobbin as an MFB signal based on a change in capacitance between the fixed electrode and the movable electrode caused by the vibration of the coil bobbin;
A speaker comprising: The speaker according to claim 1,
Each speaker is fixedly arranged at a position closer to the inner peripheral surface of the coil bobbin than the side surface of the center pole. The speaker according to claim 1 or 2, further comprising:
A speaker comprising a pair of insulators arranged in a gap portion between each fixed electrode and a center pole. The speaker according to any one of claims 1 to 3 ,
In the detection circuit, the movable electrode is grounded.

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