JPH09331594A - Speaker equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in reproduced sound quality by preventing deterioration in an electromagnetic coupling force of an electromagnetic speaker so as to reduce production of an electromagnetic wave due to a harmonic component in the case that a primary coil of the electromagnetic speaker is driven by a digital audio signal. SOLUTION: A primary coil of a speaker unit 10 of an electromagnetic speaker is made up of 16 coils 1A-1Q, and current sources 65A-65Q whose peak currents are Ia-Iq are connected to the coils 1A-1Q via current control circuits 66A-66Q. A chopper 230 is used to set an inactive period for each sampling period to each bit signal of an input digital audio signal Dp being a natural binary code. Each bit being an output of the chipper 230 is fed to a low pass filter 240 and a harmonic component in each bit signal is reduced and each bit signal with a smooth waveform is fed to the current control circuits 66A-66Q.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker device using 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.

In this electromagnetically coupled speaker, since the primary coil through which the signal current flows is fixed to the center pole portion or plate made of a magnetic material such as iron, it has the advantages of excellent heat dissipation and withstanding 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]

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. 7 shows a possible digital drive type speaker device. In the serial-parallel converter 220, for example, a digital audio signal of serial data digitized into 16 bits at a sampling frequency of 44.1 kHz or 48 kHz. 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, and a primary coil, which is a drive coil for the speaker, is composed of 16 coils 1A to 1N, 1P and 1Q.
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 are respectively provided to the coils 1A to 1N, 1P and 1Q.
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.
Switching is performed by the signal of the corresponding bit of the digital audio signal Dp from.

In this case, as an example, the coil 1A has two turns, the coil 1B has four turns, and the coil 1C has eight turns.
In this way, the coils 1A to 1N, 1P, 1 are associated with the weights of the bits 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, 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 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. 7, in the speaker unit 10, the diaphragm to which the secondary coil is fixed as described above is arranged in one direction for each bit of the digital audio signal Dp from the serial / parallel converter 220. The serial-parallel converter 2 is displaced by an amount proportional to the weight.
The sound is reproduced faithfully in accordance with the digital sound signal Dp from the digital audio signal 20.

Generally, an electromagnetically coupled speaker has excellent heat dissipation, can withstand a large input, and can reduce distortion. However, a signal current flowing in the primary coil induces a secondary current in the secondary coil. The coupling force becomes small in a low frequency range of several kHz to 1 kHz or less, and it is difficult to reproduce 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 of 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, can reproduce to a low frequency range, and a full range speaker for reproducing low to high frequencies can be realized.

However, in this case, the signal of a certain bit of the digital audio signal Dp from the serial / parallel converter 220 becomes continuously active during the period of a plurality of consecutive sampling periods, that is, the signal to the corresponding primary coil. It may be a value that allows current to flow.

For example, in FIG. 5, the period Ts is the sampling period of the digital audio signal Dp, and the signal Di (2S
As shown in B), 2SB of the digital audio signal Dp is
In the period Tp of a plurality of consecutive sampling periods, the LSB of the digital audio signal Dp may become 1 in the same period Ta as shown by the signal Di (LSB). In such a case, in the period Tp, The current Ip continuously flows through the primary coil 1P, and the current Ia continuously flows through the primary coil 1A during the period Ta.

In this case, the apparent sampling frequency of the 2SB and LSB signals is lowered, and for example, the periods Tp and T
When a is 1 ms, it becomes 1 kHz. Therefore, the electromagnetic coupling force of the speaker unit 10, which is an electromagnetically coupled speaker, becomes small, and the speaker unit 10 cannot be optimally driven.

Therefore, according to the present invention, when the primary coil of the electromagnetically coupled speaker is driven by the digital audio signal, the electromagnetic coupling force of the electromagnetically coupled speaker is reduced due to the apparent lowering of the sampling frequency of each bit of the digital audio signal. This is intended to prevent the deterioration and to always drive the electromagnetically coupled speaker optimally.

Further, according to the present invention, in the case where the electromagnetic coupling force of the electromagnetically coupled speaker is prevented from lowering due to the apparent lowering of the sampling frequency of each bit of the digital audio signal, the sampling frequency of the digital audio signal is reduced. It is possible to reduce the generation of electromagnetic waves due to the higher harmonic component and to prevent deterioration of reproduced sound quality due to high-speed switching of the signal current flowing through the primary coil.

[0021]

According to a first aspect of the present invention, a speaker device is provided with a speaker unit and a speaker drive circuit, and the speaker unit is provided in the vicinity of the air gap of a magnetic circuit in which the air gap is formed. A primary coil is fixed, and an electromagnetically coupled speaker in which a secondary coil forming a short coil is arranged in the gap by being fixed to a diaphragm is provided, and the speaker driving circuit supplies the input digital audio to the speaker driving circuit. A constant current source corresponding to each bit excluding the most significant bit of the signal or each bit including the most significant bit, and a signal of each bit excluding the most significant bit of the input digital audio signal or each bit including the most significant bit In contrast, a chopper that sets an inactive period for each sampling cycle is provided, and the signal of each bit of the output of this chopper is recorded. Depending on the Le, the controlling switching of the supply to the primary coil of the current from the constant current source, and things.

According to a second aspect of the present invention, the speaker device includes a speaker unit and a speaker drive circuit, and in the speaker unit, a primary coil is fixed in the vicinity of the air gap of the magnetic circuit. , An electromagnetically coupled speaker in which a secondary coil forming a short coil is arranged in the air gap and fixed to a diaphragm, and the speaker drive circuit supplies the most significant bit of an input digital audio signal supplied thereto. Except for each bit, or a current source corresponding to each bit including the most significant bit, and sampling for each bit except the most significant bit of the input digital audio signal or each bit signal including the most significant bit A chopper that sets an inactive period for each cycle, and a filter that reduces the harmonic components in the signal of each bit of the output of this chopper. And a motor, depending on the level of each bit of the signal at the output of the filter, controls the value of current supplied to the primary coil from the current source, and things.

In the speaker device according to the first aspect of the present invention configured as described above, even if a signal of a certain bit of the input digital audio signal is continuously active during a plurality of consecutive sampling periods, The signal of that bit, which is the output of the chopper, is provided with an inactive period for each sampling period in the period of the continuous plurality of sampling periods. Then, the supply of the current from the constant current source to the primary coil is switching-controlled according to the level of the output signal of the chopper.

Therefore, the apparent sampling frequency of the signal of each bit of the digital audio signal does not decrease, the decrease of the electromagnetic coupling force of the electromagnetically coupled speaker due to the decrease of the apparent sampling frequency is prevented, and the speaker unit is It is always driven optimally.

In this case, the signal of each bit of the output of the chopper becomes a rectangular wave signal (binary signal) containing many harmonic components of the sampling frequency of the input digital audio signal, and this rectangular wave signal flows through the primary coil. The signal current is switched at high speed.

In the speaker device of the second aspect of the present invention configured as described above, the signal of each bit of the output of the chopper is extracted through the filter, so that the signal of each bit of the output of the filter has a harmonic component. The signal has a reduced smooth waveform, and the value of the current supplied from the current source to the primary coil is controlled by the signal of each bit of the output of this filter.

Therefore, it is possible to prevent the electromagnetic coupling force of the electromagnetically coupled speaker from being lowered by the apparent lowering of the sampling frequency of each bit of the digital audio signal, and to prevent the electromagnetic wave due to the harmonic component of the sampling frequency of the digital audio signal. Generation is reduced, and deterioration of reproduced sound quality due to high-speed switching of the signal current flowing through the primary coil is prevented.

[0028]

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, when 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. 3 shows an example of the speaker unit 10, in which a recess 13 is formed around the tip of the center pole portion 12 of the center pole yoke 11, and the primary coil 1 as a drive coil is fitted into the recess 13. Attached to the center pole portion 12.

The primary coil 1 is wound as an air-core coil and is press-fitted and adhered to the recess 13 to be attached to the center pole portion 12, or, although not shown, is wound on a magnetic bobbin. Then, the magnetic bobbin is press-fitted and adhered to the recess 13 to be attached to the center pole portion 12, or the magnetic bobbin is directly wound around the recess 13 to be attached to the center pole portion 12.

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, and the rear surface of the flange portion 14 has
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 and winding end of the primary coil 1, respectively, and are connected to separate input terminals. When the primary coil 1 is composed of a plurality of coils as will be described later, the coil lead wires 17 of the respective coils are adhered to the peripheral surface of the center pole portion 12 and inserted into the openings 15, and the terminal plate 16 is connected to an input terminal 18.

A magnet 21 is adhered to the front surface of the flange portion 14 of the center pole yoke 11, and a plate 22 is adhered to the front surface of the magnet 21 so that the outer peripheral surface of the tip portion of the center pole portion 12 and the plate 22 are adhered. The magnetic circuit 20 having a gap 23 between the inner surface and the inner peripheral surface of the magnetic circuit is formed.

The secondary coil 2 forming a short coil is inserted into the space 23 of the magnetic circuit 20. The secondary coil 2 is a one-turn pipe or cylinder made of a non-magnetic conductive material, for example, aluminum, so that a bobbin around which the secondary coil 2 is wound can be omitted.

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

Although not shown, some of the primary coils 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 speaker unit 1 described above is used.
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.
1Q are switch circuits 62A to 62N, 62, respectively.
P, 62Q are connected.

Then, in the serial / parallel converter 220, the sampling clock SCLK is extracted from the digital audio signal Ds of the serial data, and the sampling clock SCLK and the serial / parallel converter 22 are extracted.
The signal of each bit of the digital audio signal Dp from 0,
The chopper 23 is supplied to the chopper 230 described later.
According to the signal of each bit of the output of 0, the switch circuit 62
A to 62N, 62P and 62Q are switched.

FIG. 4 shows an example of the chopper 230. In the chopper 230 of this example, the serial / parallel converter 2 is used.
Sampling clock SC as shown in FIG. 5 from 20
LK and a delay clock DCLK, which is delayed by the delay circuit 81 by a time shorter than the sampling period Ts of the digital audio signal Dp, as shown in the figure, are supplied to the exclusive OR circuit 82, and the exclusive OR circuit 82 is supplied. A signal EX as shown in the same figure is obtained from the Shiv-OR circuit 82, and the signal EX and the sampling clock SCLK are obtained.
Are supplied to the NAND circuit 83, and the NAND circuit 83 obtains a signal NA as shown in FIG.

Then, the output signal N of the NAND circuit 83
A and a signal Di of a certain bit of the digital audio signal Dp
And are supplied to the AND circuit 84. AND circuit 84
4, although only one is shown in FIG. 4, it is provided for each bit of the digital audio signal Dp, and the signal Di of the corresponding bit of the digital audio signal Dp is supplied as one of the respective input signals. The output signal NA of the NAND circuit 83 is supplied as the other input signal of.

Therefore, for example, the digital audio signal Dp
Signals of 2SB and LSB of each of the plurality of consecutive sampling periods Tp and T, as shown as signals Di (2SB) and Di (LSB) in FIG. 5, respectively.
In a, even when the switch circuits 62P and 62A are turned on and the signal currents flow through the coils 1P and 1A, that is, the output signals of the chopper 230 are 2SB and LSB, respectively. As shown as signals Do (2SB) and Do (LSB), for each sampling period Ts, a period Tx that is 0 for a shorter time period, that is, the switch circuits 62P and 62A are turned off, and signals are sent to the coils 1P and 1A. The period during which no current flows is set.

Therefore, the serial / parallel converter 22
Regardless of the content of the digital audio signal Dp from 0, the apparent sampling frequency of the signal of each bit of the digital audio signal Dp does not decrease, and the electromagnetic noise of the speaker unit 10 due to the apparent decrease of the sampling frequency. The decrease in coupling force is prevented, and the speaker unit 10 is always driven optimally.

The period Tx during which the signal current does not flow is preferably as short as possible, but is determined in relation to the characteristics of the element used, and is set to, for example, 1/10 or less of the sampling period Ts.

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 of FIG. 1, as an example, the coil 1A has 2 turns, the coil 1B has 4 turns, and the coil 1C has 8 turns. Then, the number of turns of each of the coils 1A to 1N, 1P, 1Q is set to be twice the number of turns of the coil corresponding to the bit of one lower order, and the constant current sources 61A to 61N, 61P, 6 respectively.
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 of FIG. 1, in the speaker unit 10, the cone 32
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. .

Note that, like a general speaker, the vibration system of the speaker unit 10 is difficult to react in a high frequency range, and in particular, a high frequency component exceeding 20 kHz is hardly reproduced. 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, without using the D / A converter and the power amplifier, it is possible to realize a speaker device which directly reproduces sound by a digital sound signal, has a small distortion, and has a large maximum output.

In the speaker device of the example of FIG. 1, as described above, the electromagnetic coupling force of the speaker unit 10 due to the apparent decrease in the sampling frequency of each bit signal of the digital audio signal Dp from the serial / parallel converter 220. The speaker unit 10 is always driven optimally.

In the speaker device of the example of FIG. 1, the speaker drive circuit 40 and the speaker unit 10 are integrated,
Or it can be a separate body.

In the example of FIG. 1, the signal Do (2SB) of FIG.
And Do (LSB), the signal of each bit of the output of the chopper 230 is provided with the period Tx during which no signal current flows through the corresponding coil, so that the signal of each bit of the output of the chopper 230 becomes serial. Rectangular wave signal (binary signal) containing many harmonic components of the sampling frequency of the digital audio signal Dp from the parallel converter 220
Thus, the signal current flowing through the coils 1A to 1Q is switched at high speed by this rectangular wave signal. . Therefore, the generation of electromagnetic waves due to the harmonic components becomes a problem, and the reproduced sound quality deteriorates due to the distortion of high-speed switching.

In consideration of this point, the example of FIG. 2 can further reduce the generation of electromagnetic waves due to the harmonic components of the sampling frequency of the digital audio signal, and the signal current flowing in the primary coil is switched at high speed. This is a case where deterioration of reproduced sound quality can be prevented.

In the example of FIG. 2 as well, as in the example of FIG. 1, the digital audio signal Dp of the parallel data from the serial / parallel converter 220 is linearly quantized by the natural binary code. This is the case.

In the example of FIG. 2, instead of the constant current sources 61A to 61N, 61P and 61Q of the example of FIG. 1, current sources 65A to 65N, 65P and 65Q as described later are provided, and Switch circuits 62A to 62 of
Instead of N, 62P, 62Q, current control circuits 66A to 66N, 66P, 66Q as described later are provided.

Further, the signal of each bit of the output of the above-mentioned chopper 230 is supplied to the low pass filter 240, and the signal of each bit having a smooth waveform with reduced harmonic components is obtained from the low pass filter 240. The signal of each bit of the output of the low pass filter 240 is
The current values of the current sources 65A to 65Q are controlled by the signals of the respective bits output from the low-pass filter 240, which are supplied to the current control circuits 66A to 66Q.

In this case, the coils 1A to 1N, 1P, 1Q
When the number of turns of the coil is twice as many as the number of turns of the coil corresponding to the lower bit, the current source 65A
~ 65N, 65P, 65Q peak current values Ia ~ In,
Ip and Iq are made equal to each other. Also, coil 1A
When the numbers of turns of 1N, 1P, and 1Q are equal to each other, the peak current values Ia to In, Ip, and Iq of the current sources 65A to 65N, 65P, and 65Q respectively correspond to the one lower bit. Route 2 of peak current value of
Doubled.

FIG. 6 shows the LS in the low pass filter 240.
An example of a portion of a low-pass filter 240A corresponding to B and a current source 65A and a current control circuit 66A corresponding to LSB is shown. The low-pass filters 240B to 240Q (not shown separately in FIG. 2), the current sources 65B to 65Q, and the current control circuits 66B to 66Q corresponding to 2SB to MSB are similarly configured.

In this example, the current source 65A and the current control circuit 66A are integrated as a current source current control circuit 68A having a transistor 67A to form a corresponding coil 1A.
The peak current value Ia is determined by setting the constant of the current source current control circuit 68A.

Then, the LSB signal Do (LSB) output from the chopper 230 is supplied to the low-pass filter 240A to reduce the harmonic components in the signal Do (LSB), thereby smoothing the low-pass filter 240A. A LSB signal Ao (LSB) having a different waveform is obtained, and the signal Ao (LSB) is supplied to the base of the transistor 67A of the current source current control circuit 68A through the capacitor 250A, and the signal Ao (LSB) causes the transistor The current ioa flowing through the collector / emitter of 67A, that is, flowing through the coil 1A can be changed within the range of the peak current value Ia or less.

The smooth waveform LSB signal Ao (LSB) from the low-pass filter 240 A is output by the chopper 230.
Of the rectangular wave signal (binary signal) as shown in FIG.
During the high level period of the signal Do (LSB) of SB, the sine wave has a positive half cycle, and the signal Do (LSB)
In the low level period including the period Tx described above, the sine wave has a negative half cycle.

Therefore, during the high-level period and the low-level period of the signal Do (LSB), the signal Do (LS) is not switched on and off without switching the current supply to the coil 1A.
In the high level period of B), the signal current ioa is applied to the coil 1A.
As a result, a relatively large current flows, and the signal Do (LS
In the low level period including the period Tx of B), a current having a relatively small value flows as the signal current ioa in the coil 1A.

The same applies to 2SB to MSB.
Therefore, in the speaker device of the example of FIG. 2, the generation of electromagnetic waves due to the harmonic components of the sampling frequency of the digital audio signal Dp is reduced, and the reproduction current sound quality is achieved by the high-speed switching of the signal currents flowing through the primary coils 1A to 1Q. Is prevented from deteriorating.

In each of the above examples, the digital audio signals Ds and Dp are linearly quantized, and the coils 1A to 1
The number of turns of Q, the current value of the constant current sources 61A to 61Q, or the peak current value of the current sources 65A to 65Q is
This is a case where the digital audio signals Ds and Dp are non-linearly quantized, which is the case where the digital audio signals Ds and Dp are non-linearly quantized, but the number of turns of the coils 1A to 1Q, or The current values of the constant current sources 61A to 61Q or the peak current values of the current sources 65A to 65Q may be changed.

In each of the above examples, the primary coil 1 is 1
In the case of being composed of six 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 61
Currents Ia to Iq of A to 61Q or current sources 65A to 6A
It is necessary to change the peak current values Ia to Iq of 5Q as described above.

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

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 62Q, or the current source 65Q and the current control circuit 66Q, which correspond to the MSB of the digital audio signal Dp, are eliminated and the lower bit (LSB).
~ 2SB) as the constant current sources 61A to 61P or the current sources 65A to 65P, depending on the value of the MSB of the digital audio signal Dp, when the MSB is 0, when the corresponding lower bit is active. A positive current is supplied to the primary coil, and when the MSB is 1, a negative current is supplied to the primary coil when the corresponding lower bit is active.

As a result, in the speaker unit 10, the cone 32 becomes 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.

[0070]

As described above, according to the first aspect of the invention, when the primary coil of the electromagnetically coupled speaker is driven by the digital audio signal, the apparent sampling frequency of each bit of the digital audio signal can be changed. It is possible to prevent the electromagnetic coupling force of the electromagnetically coupled speaker from decreasing due to
The electromagnetically coupled speaker is always driven optimally.

Further, according to the second aspect of the invention, it is possible to reduce the generation of electromagnetic waves due to the harmonic components of the sampling frequency of the digital audio signal, and the signal current flowing through the primary coil is switched at high speed. It is possible to prevent deterioration of reproduced sound quality.

[Brief description of drawings]

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

FIG. 2 is a connection diagram showing another example of the speaker device of the present invention.

FIG. 3 is a cross-sectional view showing an example of a speaker unit of the speaker device of FIGS. 1 and 2.

FIG. 4 is a connection diagram showing an example of a chopper of the speaker device of FIGS. 1 and 2.

FIG. 5 is a diagram for explaining the operation of the chopper of FIG.

6 is a connection diagram showing an example of a portion of a low-pass filter, a current source, and a current control circuit of the speaker device of FIG.

FIG. 7 is a connection diagram showing an example of a possible speaker device.

[Description of Reference Signs] 10 ... Speaker unit, 1, 1A to 1N, 1P, 1Q
... primary coil, 2 ... secondary coil, 11 ... center pole / yoke, 12 ... center pole part, 14 ... flange part, 16 ... terminal plate, 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, 62
A-62N, 62P, 62Q ... Switch circuit, 65A-
65N, 65P, 65Q ... Current source, 66A to 66N, 6
6P, 66Q ... Current control circuit, 220 ... Serial-parallel converter, 230 ... Chopper, 240, 240A ... Low-pass filter

Claims (2)

[Claims] 1. A loudspeaker unit and a loudspeaker drive circuit, wherein the loudspeaker unit has a primary coil fixed to a portion of a magnetic circuit in which a void is formed in the vicinity of the void and fixed to a diaphragm to form the void. It is an electromagnetically coupled speaker in which a secondary coil forming a short coil is arranged, and the speaker drive circuit outputs each bit except the most significant bit of the input digital audio signal supplied to this speaker, or the most significant bit. A constant current source corresponding to each bit including, each bit except the most significant bit of the input digital audio signal, or each bit signal including the most significant bit, an inactive period for each sampling period, And a chopper for setting the primary chopper of the current from the constant current source according to the signal level of each bit of the output of the chopper. Controlling switching of supply to Le, the speaker device. 2. A speaker unit and a speaker drive circuit are provided, wherein the speaker unit has a primary coil fixed to a portion of the magnetic circuit in which a gap is formed in the vicinity of the gap and is fixed to a diaphragm to form the gap. It is an electromagnetically coupled speaker in which a secondary coil forming a short coil is arranged, and the speaker drive circuit outputs each bit except the most significant bit of the input digital audio signal supplied to this speaker, or the most significant bit. Inactive period is set for each sampling cycle for the current source corresponding to each bit including, each bit except the most significant bit of the input digital audio signal, or each bit signal including the most significant bit. And a filter for reducing the harmonic components in the signal of each bit of the output of this chopper. A speaker device for controlling the value of the current supplied from the current source to the primary coil according to the level of the signal of each bit.