JPH104599A - Loudspeaker device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the destruction of switching element for switching the electric current flowing a driving coil without increasing cost of the device when the driving coil of a loudspeaker such as an electromagnetic coupling loudspeaker is driven by a digital audio signal. SOLUTION: A primary coil of a loudspeaker unit 10 of the electromagnetic coupling loudspeaker consists of 16 coils 1A to 1Q and constant current sources 61A to 61Q are connected to coils 1A to 1Q via switching circuits 63A to 63Q. A snubber circuit 65 consisting of a capacitor and a resistor is connected to the switching element 64 by the switching circuits 63A to 63Q. The electric current to the coils 1A to 1Q are turned on or off by switching the switching element 64 of the switching circuits 63A to 63Q by the signal of each bit of a 16 bit digital audio signal Dp which is a natural binary code from a serial parallel transforming unit 220.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a speaker device such as an electromagnetically coupled speaker.

[0002]

2. Description of the Related Art As a speaker for sound reproduction, a magnet is sandwiched between a center pole yoke and a plate to form a magnetic circuit having an air gap between a center pole portion of the center pole yoke and a plate. A primary coil which is a driving coil is fixed to a center pole portion or a plate in a gap of a circuit, and a secondary coil forming a short coil is fixed in a gap of a magnetic circuit by fixing to a diaphragm so as to face the driving coil. Disposed electromagnetically coupled speakers are known and have been put to practical use.

In this electromagnetically coupled speaker, a secondary current is induced in a secondary coil constituting a short coil by a signal current flowing through a primary coil which is a driving coil, and the secondary current is interacted with a magnetic flux generated in a gap of a magnetic circuit. According to Fleming's left-hand rule, a driving force corresponding to the secondary current is generated in the secondary coil, and the diaphragm to which the secondary coil is fixed is displaced.

[0004] This electromagnetically coupled speaker has advantages in that the primary coil through which a signal current flows is fixed to a center pole portion or a plate made of a magnetic material such as iron, so that it has excellent heat dissipation and can withstand a large input. If the secondary coil constituting the short coil is formed of a one-turn pipe or cylinder made of a non-magnetic conductive material, for example, aluminum, distortion can be reduced.

[0005] Other examples of the speaker include a dynamic speaker in which a voice coil bobbin is fixed to a diaphragm in a gap of a magnetic circuit, and a voice coil serving as a driving coil is wound around the voice coil bobbin. Has been put to practical use.

[0006]

In the above-described electromagnetically coupled speaker, for example, a coil corresponding to the number of bits of a digital audio signal is provided as a primary coil, and each coil corresponds to each bit of the digital audio signal. Then, by driving with the signal of each bit,
Playing audio is conceivable.

FIG. 5 shows a possible digital drive type speaker device. In a serial / parallel converter 220, a digital audio signal of serial data digitized into 16 bits at a sampling frequency of 44.1 kHz or 48 kHz, for example. Ds is converted into a digital audio signal Dp of parallel data. However, in this example,
The 16-bit digital audio signals Ds and Dp are
This is a case where the code is a natural binary code and is linearly quantized.

The speaker unit 10 is an electromagnetically coupled speaker, in which a primary coil as a driving coil is constituted by 16 coils 1A to 1N, 1P and 1Q, and a coil 1A
Correspond to the LSB (least significant bit) of the digital audio signal Dp, and the coils 1B, 1C, 1D, 1E, 1
F, 1G, 1H, 1I, 1J, 1K, 1L, 1M, 1
N, 1P, 1Q are calculated as 15SB, 14SB, 13SB, 1
2SB, 11SB, 10SB, 9SB, 8SB, 7S
B, 6SB, 5SB, 4SB, 3SB, 2SB, MSB
(Most significant bit).

The constant current sources 61A to 61N, 61P, and 6 correspond to the coils 1A to 1N, 1P, and 1Q, respectively.
1Q is connected to each of the switch circuits 62A to 62N, 62
P, 62Q, and switch circuits 62A-62
N, 62P, and 62Q are converted to serial / parallel converters 220.
Of the digital audio signal Dp from the corresponding bit.

In this case, as an example, the coil 1A has 2 turns, the coil 1B has 4 turns, the coil 1C has 8 turns,
Thus, the coils 1A to 1N, 1P, and 1 are respectively associated with the weight of each bit of the digital audio signal Dp.
The number of turns of Q is twice the number of turns of the coil corresponding to the lower bit, and each constant current source 6
Currents Ia-In, I of 1A-61N, 61P, 61Q
p and Iq are made equal to each other. That is, Iq = Ip
= In = ... Ia.

Alternatively, coils 1A to 1N, 1P, 1Q
Are the same number of turns, and the current Ib of the constant current source 61B corresponding to 15SB of the digital audio signal Dp is twice the route of the current Ia of the constant current source 61A corresponding to LSB, that is, Ib = 2 and ^1/2 Ia, below, 14SB, 13SB, 12SB ... to the corresponding constant current source 61C, 61D, 61E ... current Ic, Id, Ie ...
Is twice the route of the currents Ib, Ic, Id.

The driving force F of the vibration system of the electromagnetically coupled speaker is
The product of the secondary current i induced in the secondary coil, the density B of the magnetic flux generated in the air gap of the magnetic circuit, and the length L of the secondary coil in the air gap of the magnetic circuit is represented by F = BLi. Since the magnetic flux density B and the length L are constant, the driving force F of the vibration system is proportional to the secondary current i induced in the secondary coil. The secondary current i induced in the secondary coil is proportional to the product of the square of the signal current flowing through the primary coil and the number of turns (impedance) of the primary coil.

Therefore, in the speaker device of FIG. 5, in the speaker unit 10, as described above, the diaphragm to which the secondary coil is fixed is moved in one direction in each bit of the digital audio signal Dp from the serial / parallel converter 220. Deflected by an amount proportional to the weight, the serial-parallel converter 2
The sound is reproduced faithfully in accordance with the digital sound signal Dp from the digital audio signal 20.

In general, an electromagnetically coupled speaker is excellent in heat dissipation, can withstand a large input, and can reduce distortion. However, an electromagnetic current in which a secondary current is induced in a secondary coil by a signal current flowing in a primary coil. The coupling force is reduced in a low frequency range of several kHz to 1 kHz or less, and it is difficult to reproduce sound up to 20 Hz necessary for reproducing sound. Therefore, the electromagnetically coupled speaker has been conventionally mainly used as a speaker for reproducing high-frequency sound.

However, the serial / parallel converter 2 shown in FIG.
The digital audio signal Dp from the device 20 is, for example, 44.1k
Hz or 48 kHz, and the primary coils 1A to 1Q are driven by digital signals of the same sampling frequency, so that the audio signal before being digitized is several kHz to 1 kHz or less. The low-frequency component also has a high frequency exceeding 20 kHz as a signal current flowing through the primary coils 1A to 1Q.

Therefore, the speaker unit 10 which is an electromagnetically coupled speaker enables reproduction in a low frequency range, thereby realizing a full-range loudspeaker reproducing low to high frequencies.

However, in this case, when the switch circuits 62A to 62Q are switched by the signals of the respective bits of the digital audio signal Dp from the serial / parallel converter 220, back electromotive force is generated in the coils 1A to 1Q, and 1Q and switch circuits 62A to 62Q generate spike noise.

The coil 1A and the switch circuit 62A corresponding to the LSB of the digital audio signal Dp are shown below.
The current flowing through the coil 1A is L of the digital audio signal Dp.
It is turned on and off as shown in the upper part of FIG. 4 according to the value of SB. In accordance with the on / off of the current flowing through the coil 1A, the voltage at the connection point between the coil 1A and the switch circuit 62A is changed to the time t1 when the current flowing through the coil 1A changes from 0 to Ia as shown in the lower part of FIG. At the time point t2 at which the current flowing through the coil 1A changes from Ia to 0, and spike noise occurs at the connection point between the coil 1A and the switch circuit 62A. Here, Vcc is the power supply voltage, R is the resistance of the coil 1A, L is the inductance of the coil 1A, di / dt is the time derivative of the current flowing through the coil 1A, and di / dt is positive at time t1 and di / dt at time t2. dt is negative.

Then, for example, the switch circuits 62A-62
When Q is composed of a MOSFET, the spike voltage may exceed the maximum allowable voltage between the drain and the source of the MOSFET, and the MOSFET may be destroyed. In order to prevent the destruction, M
When an OS / FET having a high withstand voltage is used, the cost of the speaker drive circuit 40 increases. In addition, the reproduced sound quality is degraded by the spike voltage.

Accordingly, the present invention provides a method for driving a driving coil of a speaker such as an electromagnetically coupled speaker by a digital audio signal without destroying a switching element for switching a current flowing through the driving coil without increasing the cost of the apparatus. Can be prevented,
The reproduction sound quality can be improved.

[0021]

According to the present invention, a speaker device includes a speaker unit and a speaker drive circuit, and the speaker drive circuit removes each of the input digital audio signals supplied thereto except for the most significant bit. Bit, or a constant current source corresponding to each bit including the most significant bit, and a signal of each bit except the most significant bit of the input digital audio signal, or a signal of each bit including the most significant bit, from the constant current source. A switch circuit for switching the supply of current to the drive coil of the speaker unit; and a switch circuit for reducing an electromotive voltage generated in the drive coil when switching the supply of current from the constant current source to the drive coil. And a circuit for causing the

In the loudspeaker apparatus according to the present invention having the above-described configuration, the driving of the current from the constant current source is performed by the signal of each bit except the most significant bit or the bit including the most significant bit of the input digital audio signal. When the supply to the coil is switched, the electromotive voltage generated in the drive coil decreases. Therefore, destruction of the switching elements constituting the switch circuit is prevented. Further, since the circuit for reducing the electromotive voltage generated in the driving coil can be constituted by, for example, a capacitor and a resistor, the cost of the device can be reduced as compared with the case where a switching element having a high withstand voltage is used. Further, the reproduction sound quality is improved.

[0023]

FIG. 1 shows an example of a speaker device according to the present invention. In a serial / parallel converter 220, for example, digital data of serial data digitized into 16 bits at a sampling frequency of 44.1 kHz or 48 kHz. The audio signal Ds is converted into a digital audio signal Dp of parallel data.

However, in this example, the 16-bit digital audio signals Ds and Dp are natural binary codes, or the digital audio signal Ds of serial data supplied to the serial / parallel converter 220 is 2 bits. 'Complement code, this is serial-parallel converter 2
At 20, while being converted into parallel data,
It is converted to a natural binary code and converted to a serial / parallel converter 2
The digital audio signal Dp of the parallel data from 20 is a natural binary code. In this example, the digital audio signals Ds and Dp are linearly quantized.

The speaker unit 10 is an electromagnetically coupled speaker. FIG. 2 shows an example of the speaker unit 10. A recess 13 is formed around the tip of a center pole portion 12 of a center pole yoke 11, and the primary coil 1 serving as a driving coil is fitted into the recess 13. To the center pole section 12.

The primary coil 1 is wound as an air-core coil and is press-fitted into the recess 13 so as to be attached to the center pole portion 12 or wound around a magnetic bobbin (not shown). Then, the magnetic bobbin is attached to the center pole portion 12 by being press-fitted and bonded to the concave portion 13, or attached to the center pole portion 12 by being directly wound around the concave portion 13.

An opening 15 is formed in the flange portion 14 of the center pole yoke 11 at a position close to the center pole portion 12.
The terminal plate 16 is attached. Then, a coil lead wire 17 made of, for example, a tinsel wire of the primary coil 1 is adhered to the peripheral surface of the center pole portion 12, inserted into the opening 15, and connected to the input terminal 18 on the terminal plate 16 by soldering.

The coil lead wires 17 are provided at the winding start portion and the winding end portion of the primary coil 1, respectively, and each is connected to a separate input terminal. When the primary coil 1 is composed of a plurality of coils as described later, the coil lead wire 17 of each coil is bonded to the peripheral surface of the center pole portion 12 and inserted into the opening 15,
It is connected to the input terminal 18 on the terminal plate 16.

A magnet 21 is bonded to the front surface of the flange portion 14 of the center pole yoke 11, and a plate 22 is bonded to the front surface of the magnet 21. A magnetic circuit 20 having an air gap 23 between the magnetic circuit 20 and the inner peripheral surface is formed.

The secondary coil 2 constituting a short coil is inserted into the gap 23 of the magnetic circuit 20. The secondary coil 2 is a one-turn cylindrical body made of a nonmagnetic conductive material, for example, aluminum, so that a bobbin around which the secondary coil 2 is wound can be omitted.

The inner peripheral portion of the cone 32 having the edge 31 on the outer peripheral portion, the center cap 33, and the inner peripheral portion of the damper 34 are attached to the secondary coil 2. Also,
A speaker frame 35 is attached to the plate 22, and the outer edge 31 of the cone 32 and the gasket 36 are attached to the speaker frame 35, and the outer periphery of the damper 34 is attached to the speaker frame 35.
Attached to.

However, although not shown, a part of the primary coil may be attached to the peripheral surface of the tip of the center pole portion 12 and the remaining coils may be attached to the inner peripheral surface of the plate 22. In this case, the coil lead wire of the coil attached to the plate 22 is inserted between the plate 22 and the magnet 21, for example.
2 is connected to an input terminal on a terminal plate attached to the outer peripheral surface of the second terminal. Further, all the primary coils may be attached to the inner peripheral surface of the plate 22.

In the example of FIG. 1, the above-described speaker unit 1
0 primary coil 1 has 16 coils 1A to 1N, 1
P, 1Q, and constant current sources 61A to 61N, 61P, 6 for the coils 1A to 1N, 1P, 1Q, respectively.
The switch circuits 63A to 63N, 63
P, 63Q, and switch circuits 63A to 63N, 63P, 63Q according to each bit signal of the digital audio signal Dp from the serial / parallel converter 220.
Is switched.

Further, in this example, the switch circuit 63A
The snubber circuit 65 is connected to each of 63Q.
That is, the switch circuits 63A to 63Q are constituted by a MOS-FET as a switching element 64 and a snubber circuit 65 connected in parallel between the drain and the source, as shown by the switch circuit 63A in FIG. Is done. The snubber circuit 65 includes a capacitor 66 and a resistor 67 connected in series.

Therefore, by selecting the capacitance of the capacitor 66 and the resistance value of the resistor 67, the MO of the switch circuits 63A to 63Q is changed by the signal of each bit of the digital audio signal Dp from the serial / parallel converter 220.
When the S.FET 64 is switched, the coil 1A
~ 1Q, ie, coils 1A ~ 1Q and MOS
The spike voltage generated at the connection point Xa of the FET 64 is M
The value decreases to a value smaller than the maximum allowable voltage between the drain and the source of the OS • FET 64.

Therefore, even if a MOS-FET 64 having a high withstand voltage is not used, the MOS-FET 64 can be used.
Can be prevented from being destroyed. The snubber circuit 65
Can be constituted by the capacitor 66 and the resistor 67, so that the cost of the device can be reduced as compared with the case where a MOS-FET 64 having a high withstand voltage is used. Further, the reproduction sound quality is improved.

The switching element 64 of each of the switch circuits 63A to 63Q can be other than a MOS-FET. Even in this case, the same effect can be obtained by the same operation.

As described above, the driving force F of the vibration system of the speaker unit 10, which is an electromagnetically coupled speaker, is proportional to the secondary current i induced in the secondary coil 2, and the secondary current i
Is proportional to the product of the square of the signal current flowing through the primary coil 1 and the number of turns (impedance) of the primary coil 1.

In the speaker device of the example shown in FIG. 1, for example, the coil 1A has two turns, the coil 1B has four turns, and the coil 1C has eight turns, corresponding to the weight of each bit of the digital audio signal Dp. Then, the number of turns of each of the coils 1A to 1N, 1P, and 1Q is twice the number of turns of the coil corresponding to the next lower bit, and each of the constant current sources 61A to 61N, 61P, and 6
The currents Ia to In, Ip, and Iq of 1Q are made equal to each other. That is, Iq = Ip = In =... = Ia.

Alternatively, the coils 1A to 1N, 1P, 1Q
Are the same number of turns, and the current Ib of the constant current source 61B corresponding to 15SB of the digital audio signal Dp is the current Ia of the constant current source 61A corresponding to LSB.
, Ie, Ib = 2 ^1/2 Ia, and the currents Ic, Id, and Ic of the constant current sources 61C, 61D, 61E... Corresponding to 14SB, 13SB, 12SB.
.. Are made twice the route of the currents Ib, Ic, Id.

Therefore, in the speaker device of the example shown in FIG.
Is shifted in one direction by an amount proportional to the weight of each bit of the digital audio signal Dp from the serial / parallel converter 220, and the audio is faithfully reproduced by the digital audio signal Dp from the serial / parallel converter 220. .

As in the case of a general loudspeaker, the vibration system of the loudspeaker unit 10 is hardly responsive to high frequencies, and hardly reproduces high-frequency components exceeding 20 kHz. Therefore, the primary coil 1 has 44.1 kHz.
Even when driven by a digital signal having a sampling frequency of z or 48 kHz, the sampling frequency component is hardly reproduced. Even if the sound is reproduced with very low sound pressure,
Sounds exceeding 20 kHz can hardly be heard by human ears, so that there is no problem even when listening to music. Further, a mechanical filter having a stop band of 20 kHz or more is intentionally formed, and the speaker unit 10
It is also easy to incorporate into

Moreover, it is possible to realize a speaker device that reproduces sound directly by a digital sound signal without using a D / A converter and a power amplifier, that has a small distortion and a large maximum output.

In the speaker device of the example shown in FIG. 1, since the snubber circuit 65 is connected to the switching elements 64 of the switch circuits 63A to 63Q, a switching element having a high withstand voltage is used as described above. Even if the switching element 64 is not provided, the switching element 64 can be prevented from being destroyed, and the cost of the device can be reduced as compared with the case where a switching element 64 having a high withstand voltage is used.

Incidentally, the snubber circuits may be connected in parallel with the primary coils 1A to 1Q, respectively. Further, in the above-described speaker device, the speaker drive circuit 40 and the speaker unit 10 can be integrated or separated.

In the above example, the digital audio signals Ds and Dp are linearly quantized, and the coils 1A to 1Q
In this case, the number of turns or the current values of the constant current sources 61A to 61Q can be changed in geometric progression. If the digital audio signals Ds and Dp are quantized non-linearly, Coils 1A to 1Q depending on the mode of
Or the current values of the constant current sources 61A to 61Q may be changed.

In the example described above, the primary coil 1 has 16
Although the case where the primary coil 1 is composed of the coils 1A to 1Q, the primary coil 1 may be composed of one coil common to each bit of the digital audio signal Dp from the serial / parallel converter 220. Of course, in that case, the constant current source 61A
It is necessary to change the currents Ia to Iq of .about.61Q as described above.

Further, the primary coil 1 may be constituted by a plurality of coils common to a plurality of bits of a part of the digital audio signal Dp from the serial / parallel converter 220, respectively.

The digital audio signals Ds and Dp
Is the 2's complement code, or
The digital audio signal Ds of the serial data supplied to the serial / parallel converter 220 is a natural binary code, which is converted by the serial / parallel converter 220 into parallel data and converted into a 2's complement code. The digital audio signal Dp of the parallel data from the serial / parallel converter 220 is 2 ′
In the case of the s complement code, the constant current source 61Q and the switch circuit 63Q corresponding to the MSB of the digital audio signal Dp are eliminated, and the lower bit (LS
B to 2SB), as the constant current sources 61A to 61P, according to the value of the MSB of the digital audio signal Dp, when the MSB is 0, the primary coil has a positive direction when the corresponding lower bit is active. When the current is supplied and the MSB is 1, a device that supplies a negative current to the primary coil when the corresponding lower bit is active may be used.

Thus, in the speaker unit 10, the cone 32 is connected to the serial / parallel converter 220.
From the digital audio signal Dp from the serial / parallel converter 220, the audio is reproduced in a direction corresponding to the value of the MSB of the digital audio signal Dp from the serial / parallel converter 220. You.

In the above-described example, the primary coil, which is the driving coil of the electromagnetically coupled speaker, is driven by a digital audio signal. It can also be applied to the case of driving by.

[0052]

As described above, according to the present invention, when a drive coil of a speaker such as an electromagnetically coupled speaker is driven by a digital audio signal, the current flowing through the drive coil can be achieved without increasing the cost of the device. The switching element for switching the switching can be prevented from being destroyed, and the reproduced sound quality can be improved.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating an example of a speaker device according to the present invention.

FIG. 2 is a sectional view showing an example of a speaker unit of the speaker device of FIG.

FIG. 3 is a connection diagram illustrating an example of a switch circuit of the speaker device of FIG. 1;

FIG. 4 is a diagram for explaining a possible operation of the speaker device;

FIG. 5 is a connection diagram showing an example of a possible speaker device.

[Explanation of symbols]

10 Speaker unit, 1, 1A-1N, 1P, 1Q
... Primary coil, 2 ... Secondary coil, 11 ... Center pole and yoke, 12 ... Center pole section, 14 ... Flange section, 16 ... Terminal board, 17 ... Coil lead wire, 18 ... Input terminal, 20 ... Magnetic circuit, 21 ... magnet, 22 ... plate, 23 ... air gap, 32 ... cone, 40 ... speaker drive circuit, 61A to 61N, 61P, 61Q ... constant current source, 63
A to 63N, 63P, 63Q: switch circuit, 64: switching element, 65: snubber circuit, 66: capacitor, 67: resistor, 220: serial-parallel converter

Claims (2)

[Claims] 1. A speaker unit, comprising: a speaker driving circuit, wherein the speaker driving circuit corresponds to each bit excluding the most significant bit of the input digital audio signal supplied thereto, or each bit including the most significant bit. And supplying a current from the constant current source to the drive coil of the speaker unit by a signal of each bit excluding the most significant bit of the input digital audio signal or a bit including the most significant bit of the input digital audio signal. A speaker device, comprising: a switch circuit for switching; and a circuit for reducing an electromotive voltage generated in the drive coil when switching the supply of the current from the constant current source to the drive coil by the switch circuit. 2. The loudspeaker device according to claim 1, wherein the loudspeaker unit has a primary coil fixed as a drive coil in a portion near the air gap of the magnetic circuit having the air gap, and is fixed to a diaphragm. A speaker device which is an electromagnetically coupled speaker in which a secondary coil constituting a short coil is disposed in a gap.