JPH06101877B2 - Speaker - Google Patents

Description

The present invention relates to a motional feedback type (hereinafter abbreviated as MFB type) speaker.

[Outline of Invention]

The present invention relates to a speaker, which is composed of a magnet and a pair of oppositely wound coils arranged on both sides in the magnetizing direction of the magnet. One of the magnet and the pair of coils is attached to a diaphragm, and the other is attached to a fixed portion. Since the speaker drive signal is negatively fed back by the signal based on the detection output from the pair of coils of the acceleration sensor, the acceleration sensor affects the leakage magnetic flux from the voice coil. Therefore, the motion of the diaphragm can be accurately detected without phase rotation, the internal impedance of the acceleration sensor is low, and the acceleration sensor can be made small and have a simple structure.

[Conventional technology]

Conventionally, the velocity equivalent signal corresponding to the vibration of the speaker diaphragm is fed back to the speaker drive circuit to improve the output sound pressure frequency characteristics and distortion characteristics near and below the low resonance frequency. System speakers are known. FIG. 6 shows an example thereof.

In the figure, an audio signal S _A from the terminal (41) is equalized by an equalizer amplifier (42), a subtractor (43) and an output amplifier (4
It is supplied to the speaker (45) via (0).

An acceleration equivalent signal Sa corresponding to the vibration of the diaphragm is taken out from the acceleration sensor (46) attached to the diaphragm of the speaker (55), that is, a piezoelectric detecting element such as a bimorph. Supplied to the circuit (47). Then, after being converted into the velocity equivalent signal Sv in this MFB circuit (47), it is supplied to the subtractor (43) as a negative return signal.

By negatively feeding back the velocity equivalent signal Sv, the output sound pressure level decreases in the low range as shown by the solid line a in FIG.
Therefore, if the output sound pressure level in the low frequency range is raised as shown by the dashed line b in FIG. 1 by some method, the output sound pressure level in the low frequency range is generally shown by the broken line c in the figure. So it can be flat. In FIG. 6, an equalizer amplifier (42) is used to increase the output sound pressure level in the low frequency range as shown by the dashed line b in FIG.

In addition to the bimorph, as the acceleration sensor (46),
There are a microphone provided facing the diaphragm, a generator that generates electricity by the magnetic flux created by a voice coil, a moving coil type detector, or a moving magnet type detector.

[Problems to be solved by the invention]

The conventional MFB speaker acceleration sensor has the following drawbacks. In the case of an acceleration sensor composed of a piezoelectric element such as a bimorph, the internal impedance is high, and an impedance converter such as a FET provided in the vicinity of the acceleration sensor is required, which complicates the configuration of the MFB circuit.

In the case of an acceleration sensor consisting of a microphone and a generator, it does not directly detect the movement of the diaphragm, so
There is a phase rotation in the acceleration detection output, and if the speaker drive signal is negatively fed back by the speed detection signal based on the acceleration detection output, the system may become unstable.

In the case of an acceleration sensor composed of a moving coil type detector or a moving magnet type detector, the magnetic flux leaked from the voice coil affects the acceleration sensor and the acceleration of the diaphragm cannot be accurately detected.

In view of such a point, the present invention makes it possible to accurately detect the movement of the diaphragm without phase rotation, because the acceleration sensor is not affected by the leakage magnetic flux from the voice coil, has a low internal impedance of the acceleration sensor, and We are going to propose a MFB type speaker which is compact and simple in construction.

[Means for solving problems]

The speaker according to the present invention comprises a magnet (11) and a pair of coils (14) and (15) which are oppositely wound on both sides of the magnet (11) in the magnetization direction. One of (14) and (15) has an acceleration sensor (10) which is attached to a diaphragm (6) and the other is attached to a fixed portion, and a pair of coils (14) of the acceleration sensor (10) is provided. ), (15) based on the detection output, the speaker drive signal is negatively fed back.

[Action]

According to the present invention, the acceleration detection output of the diaphragm (6) is obtained from the pair of coils (14) and (15), and the speaker drive signal is negatively fed back by the signal based on the acceleration detection output. In this case, a current based on the leakage magnetic flux from the voice coil flows through the pair of coils (14) and (15), but they cancel each other out.

〔Example〕

An embodiment in which the present invention is applied to a speaker having a cone-shaped diaphragm will be described in detail below with reference to FIG.
The magnet (2) is held between the yoke (1) and the plate (3). Center of the yoke (1) (1
A voice coil (5) wound around a bobbin (4) is arranged between the circular hole in the center of (A) and the plate (3). A frame (7) is mounted on the plate (3). A cone-shaped diaphragm (6) is supported between the vicinity of the free end of the bobbin (4) and the peripheral edge of the frame (7) via the edge (8). A cap (9) is attached to the center of the diaphragm (6) so as to close one end of the bobbin (4).

Then, on the cap (9), the acceleration sensor (10)
Is installed. The configuration of this acceleration sensor (10) is the second
It will be described with reference to the drawings. (11) is a magnet, which has a plate shape and is magnetized with N and S in the thickness direction. A rare earth small magnet such as SmCo is used as the magnet (11).
The magnet (11) is magnetized in the vibration direction of the diaphragm (6) and held by the cap (9) so as to be movable with a predetermined stiffness. This magnet (11) is attached to a support piece (13) via a leaf spring (12), and this support piece (13) is fixed to a cap (9) to allow the magnet (1
1) can be elastically moved toward and away from the surface of the cap (9). (14) and (15) are a pair of coils in opposite directions (shape and size are the same)
The magnet (11) is sandwiched in the magnetizing direction, and the coil surfaces of the magnet (11) are arranged substantially parallel to and equidistant from both surfaces of the magnet (11) in the magnetizing direction. The pair of coils (14) and (15) are connected in series (parallel connection is also possible), and the pair of terminals (16) and (17) are led out therefrom.

As shown in FIG. 4, the horizontal component of the magnetic flux from the magnet (11) intersects with the pair of coils (14) and (15), which causes the coils (14) and (15) in opposite directions. An electric current flows, and from the pair of terminals (16) and (17), an acceleration detection signal of the diaphragm (6) composed of the sum of the electric currents is obtained,
This is supplied to the MFB circuit (47) of FIG. 3, and the pair of terminals (16) and (17) of FIG.
8) and (19) are connected respectively. Terminal (18) is a resistor (2
2) Grounded through a low-pass filter consisting of a parallel circuit of a capacitor (48). Terminal (19) is a resistor (3
0) connected to power supply-B.

Then, the terminal (18) is connected to the inverting input terminal of the operational amplifier (21) forming the integrating circuit (20), and the output terminal of this operational amplifier (21) is connected to the inverting input terminal via the capacitor (25). It Then, the terminal (32) from which the speed equivalent signal Sv is obtained is derived from the output terminal of the operational amplifier (21).

Also, a resistor (23) connected between the ground and the terminal (19)
And the connection midpoint P of the Zener diode (24) is connected to the non-inverting input terminal of the operational amplifier (21). In this case, a series circuit of a pair of coils (14), (15), a resistor (22),
A balanced bridge circuit is constituted by (23) and the Zener diode (24).

The output terminal of the operational amplifier (21) is connected via a resistor (26) to the base of a pnp-type transistor (27) forming an integrating circuit (31) for DC servo. The emitter of this transistor (27) is grounded, and the collector is connected to the terminal (19). A capacitor (28) is connected between the base and collector of the transistor (27).

Thus, since the pair of coils (14) and (15) exhibit low impedance, a current signal as an acceleration equivalent signal corresponding to the vibration of the speaker diaphragm from the acceleration sensor (10).
Sai flows almost all through the condenser (25). Therefore, the inter-terminal voltage of the capacitor (25) is the voltage charged by the current signal Sai, that is, the integrated voltage. Since this voltage is the integration of the current signal Sai (acceleration equivalent signal), it becomes the velocity equivalent signal Sv, which is the terminal (3
It is output to 2).

Further, the DC potential of the velocity equivalent signal Sv is amplified by the integrating circuit (31) for DC servo, and the potential of the lower end of the balanced bridge, that is, the terminal (19) is formed. Where the operational amplifier (2
Since the circuit operates so that the potentials of the inverting input terminal and the non-inverting input terminal of 1), that is, the potentials of the terminals (18) and (19) become equal, a zener diode (terminal) is placed between the terminals (18) and (19). Voltage is applied equal to the voltage across 24).

Here, when the DC potential of the speed equivalent signal Sv changes, the potential of the terminal (19) changes, and a difference occurs in the potentials of the terminal (18) and the connection midpoint P. In this case, the potential difference is small,
The value is a pair of coils (14) that form a balanced bridge,
It occurs due to the difference between the impedance of the series circuit of (15) and the operating point impedance of the Zener diode (24). The resistance value of the resistor (23) is, for example, 1 KΩ, whereas the operating point impedance of the Zener diode (24) is extremely low, for example, 100 Ω or less. Therefore, the voltage fluctuation of the terminal (19) and the connection midpoint P The voltage fluctuations of are almost equal. The voltage fluctuation of the terminal (19) is divided into a resistor (22) and a pair of coils (1
The voltage divided by the impedance of the series circuit of 4) and (15) becomes the voltage fluctuation of the terminal (18), which is smaller than the voltage fluctuation of the connection midpoint P. Therefore, as described above, a difference occurs between the potentials of the terminal (18) and the connection midpoint P.

In this case, the potential difference obtained by subtracting the potential of the terminal (18) from the potential of the connection midpoint P is in phase with the potential of the terminal (19) and also with the DC potential of the speed equivalent signal Sv. But,
The potential of the terminal (19) is in anti-phase with the DC potential of the velocity equivalent signal Sv. Therefore, as described above, the operational amplifier (21)
Since the circuit operates so that the potentials of the inverting input terminal and the non-inverting input terminal of the same, that is, the potentials of the terminal (18) and the connection midpoint P become equal, the DC potential of the speed equivalent signal Sv obtained at the terminal (23) is It is controlled to be a constant value, that is, the base potential (-0.6 V) of the transistor (27). For example, when the DC potential of the speed equivalent signal Sv becomes high, the potential of the terminal (19) becomes low, and the potential difference obtained by subtracting the potential of the terminal (18) from the potential at the connection midpoint P becomes negative, and eventually the speed equivalent signal Sv becomes The DC potential is controlled to be low. On the other hand, speed equivalent detection
The reverse operation occurs when the DC potential of Sv becomes low.

Then, as in the case of FIG. 6, the audio signal for driving the speaker of FIG. 1 is supplied to the speaker through the cascade circuit of the equalizer amplifier, the subtractor and the output amplifier, and
The velocity equivalent signal Sv from the output terminal (32) of the MFB circuit (47) in the figure is supplied to the subtractor (43) so that the speaker drive signal is negatively fed back.

Then, the acceleration detection output of the diaphragm (6) is obtained from the pair of coils (14) and (15), and the speaker drive signal is negatively fed back by the equivalent speed signal (speed detection signal) based on the acceleration detection output. At this time, the current based on the leakage magnetic flux from the voice coil (5) is applied to the pair of coils (14), (1
5), but these cancel each other out.

As shown in FIG. 5, in order to emphasize the horizontal component of the magnetic flux from the magnet (11), a pair of U-shaped yokes (light iron core material) (33), () are provided on both sides of the magnet (11). 34) may be arranged.

The present invention can also be applied to other speakers such as a flat speaker. In that case, an acceleration sensor may be attached to the flat diaphragm.

[Advantages of the Invention] According to the present invention described above, the acceleration sensor is not affected by the leakage magnetic flux from the voice coil, and the movement of the diaphragm can be accurately detected without phase rotation, and the internal impedance of the acceleration sensor is reduced. Moreover, it is possible to obtain an MFB type speaker that can be mass-produced at low cost because the acceleration sensor can be made small, lightweight, and have a simple structure.

[Brief description of drawings]

FIG. 1 is an end view of a cutting portion showing an embodiment of the present invention, FIG. 2 is a perspective view of a main portion thereof, FIG. 3 is a circuit diagram showing an MFB circuit of one embodiment, and FIG. 4 is one embodiment. FIG. 5 is a layout view of essential parts of another embodiment of the present invention, FIG. 6 is a configuration diagram of a conventional example, and FIG. 7 is an output sound pressure characteristic curve diagram. (6) a diaphragm, (9) a cap, (10) an acceleration sensor, (11) a magnet, (12) a leaf spring, (14),
(15) are coils respectively.

Claims (1)

[Claims] 1. A magnet and a pair of coils wound in opposite directions to each other on both sides in the magnetizing direction of the magnet,
The magnet and the pair of coils have an acceleration sensor in which one is attached to a diaphragm and the other is attached to a fixed portion, and a speaker drive signal is a signal based on a detection output from the pair of coils of the acceleration sensor. A speaker characterized in that a negative feedback is applied to the speaker.