JPH1051884A - Speaker system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust sound volume without deteriorating sound quality in a speaker system in which an electromagnetic coupling speaker unit is current- driven by a digital audio signal. SOLUTION: A primary coil is composed of a plurality of coils 1A-1P in the electromagnetic coupling speaker 10. Each of impedance circuits 42A-42P, each of the primary coils 1A-1P, and each of switch circuits 41A-41P are connected in series with respect to a switching power supply circuit 15. A clock P53 whose frequency is an integer multiple of a sampling frequency of a digital audio signal SD is fed to the switching power supply circuit 51 as a switching clock. The switch circuits 41A-41P are on/off-controlled respectively by each bit of a digital audio signal SD. Number of pulses with a pulse voltage V51 from the switching power supply circuit 51 is changed by data denoting a sound volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digitally driven speaker device.

[0002]

2. Description of the Related Art Generally, a speaker device is driven by an analog audio signal. However, a speaker device that can be directly driven by a digital audio signal has been considered.

FIG. 2 shows an example of a speaker unit 10 used in such a digitally driven speaker device. The speaker unit 10 is of an electromagnetic coupling type, and in this example, a pole piece 11
A concave portion or groove 13 is formed around the tip of the center pole portion 12, and a primary coil 1 described later is attached to the groove 13.

In this case, the primary coil 1 is mounted by being wound as an air-core coil and adhered to the groove 13, or is mounted by being wound directly on the groove 13, or not shown. Is wound around a bobbin made of a magnetic material, and the bobbin is fitted into the groove 13 and adhered thereto.

Further, the flange portion 1 of the pole piece 11
4 has a through hole or opening 15 formed at a position continuously adjacent to the center pole portion 12, and a terminal plate 16 is attached to the rear surface of the flange portion 14. Then, the lead wire 17 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 terminal 18 of the terminal plate 16 by soldering or the like.

Also, the flange portion 14 of the pole piece 11
A permanent magnet 21 is bonded to the front surface of the permanent magnet 2.
The plate 22 is bonded to the front surface of the plate 1 to form a magnetic circuit 20 having a gap 23 between the outer peripheral surface of the tip of the center pole portion 12 and the inner peripheral surface of the plate 22.

The secondary coil 2 is arranged in the space 23. In this example, the secondary coil 2 is a pipe or a cylindrical body made of a non-magnetic conductive material, for example, aluminum, and is a one-turn coil.

Further, the inner peripheral portion of the cone 32, the dust-proof cap 33, and the inner peripheral portion of the damper 34 are attached to the secondary coil 2, and the speaker frame 35 is attached to the plate 22. An edge 31 is attached to an outer peripheral portion of the cone 32, and the edge 31 and a gasket 36 are attached to a speaker frame 35, and an outer peripheral portion of the damper 34 is attached to the speaker frame 35.

If the input digital audio signal SD has a quantization bit number of 16 bits and is a natural binary code, the above-described primary coil 1 corresponds to the digital audio signal SD. , 16 coils 1A ~
1P, and the number of turns of the coils 1A to 1P is a value corresponding to the weight of each bit of the digital audio signal SD. That is, for example, the coils 1A to 1P
Corresponds to the LSB to MSB of the digital audio signal SD, the number of turns of the coil 1A is two,
B has four turns, coil 1C has eight turns,..., And so on.
The number of turns of the coil corresponding to the next lower bit is twice as large.

Therefore, the ratio of the number of turns of the coils 1A to 1P is 2 ** 0 to 2 ** 15 in a geometric series of a term ratio of 2 (x ** y indicates x to the yth power). And so on).

FIG. 3 shows an example of a signal system of a digitally driven speaker device. That is, the digital audio signal SD is supplied from the input terminal 221 to the serial / parallel conversion circuit 222, and is converted into parallel data by one sample. Then, the LS of the converted parallel data
B to MSB are supplied as control signals to the switch circuits 41A to 41P, and the switch circuits 41A to 41P are turned off when the corresponding bit is "0" and turned on when the corresponding bit is "1".

Further, impedance circuits 42A-42
P is provided, and primary coils 1A to 1P, switch circuits 41A to 41P, and impedance circuits 42A to 42P are connected in series between the DC power supply 43 and the ground. In this case, the impedance circuits 42A to 42A
The 2P impedances ZA to ZP are the primary coils 1A to 1
Among P, the values are such that the sum with the impedance of the corresponding primary coil becomes equal to each other.

Therefore, the switch circuits 41A to 41P
Are on, the currents IA to IP flow through the primary coils 1A to 1P, respectively, but the impedance circuits 41A to 41P
Of the impedances ZA to ZP and the impedances of the primary coils 1A to 1P are equal to each other, so that the currents IA to IP have the same value I.

When a certain bit of the digital audio signal SD becomes "1", the switch circuits 41A-41
Among the primary coils 1A to 1P, the current I (= IA) is applied to the primary coil corresponding to the turned on switch circuit among the primary coils 1A to 1P. ~ IP) flows.

Here, in general, the driving force F of the vibration system of the electromagnetic coupling type speaker is determined by 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 magnetic circuit. Product F = BLi with the length L of the secondary coil in the air gap
Is represented by In this case, 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 is proportional to the product of the magnitude of the signal current flowing through the primary coil and the resistance of the primary coil.

In the above-described speaker unit 10, since the number of turns of the coils 1A to 1P, which are the primary coils 1, is set in proportion to the weight of each bit of the digital audio signal SD. When the current I flows as a signal current in the secondary coil, the secondary coil 2
A secondary current having a magnitude proportional to the weight of the bit corresponding to the primary coil is induced.

Therefore, the cone 32 provided with the secondary coil 2 is displaced by a magnitude proportional to the weight of each bit of the digital audio signal SD, and the digital audio signal SD is transmitted from the speaker unit 10.
Will be output.

In this case, the digital audio signal SD is generally digitized at a sampling frequency outside the audible band, for example, at a sampling frequency of 44.1 kHz or 48 kHz, and the primary coils 1A to 1P Since the analog audio signal is driven by the SD, the low-frequency component of the analog audio signal before being digitized also has a signal current flowing through each coil 1A to 1P of the primary coil 1 as 20
The frequency becomes higher than kHz. Therefore, reproduction up to a low frequency can be performed by the speaker unit 10.

Further, like a general loudspeaker, the vibration system of the loudspeaker unit 10 is hardly responsive to high frequencies.
High frequency components exceeding kHz are hardly reproduced. Therefore, even if the primary coils 1A to 1P are driven by a digital signal having a sampling frequency of 44.1 kHz or 48 kHz, the components of the sampling frequency are hardly reproduced. Even if the sound is reproduced with a very small sound pressure, a sound exceeding 20 kHz can hardly be heard by a human ear, so that no trouble occurs.

Thus, according to this speaker device, a digital audio signal can be converted into a reproduced sound without D / A conversion.

However, in the case of only the above configuration, the following problem actually occurs. That is, the relationship between the LSB-MSB bit clock CK output from the serial-parallel conversion circuit 222 and the LSB-MSB is
For example, as shown in FIGS. 4A and 4B. Note that the period τ is LSBＢ output from the serial / parallel conversion circuit 222.
This is the bit period of the MSB, which is equal to the sampling period of the digital audio signal SD supplied to the input terminal 221.

Then, as shown in FIG.
A certain bit of the MSB may be continuously “0” or “1” for two or more bit periods (sampling periods) τ.

If an arbitrary bit has a period of 2τ or more,
Even if it continuously becomes "0", the switch circuits 41A to 41A
There is no problem since only the corresponding switch circuit of P is continuously turned off. However, when a certain bit continuously becomes “1” for a period of 2τ or more, the corresponding one of the switch circuits 41A to 41P is continuously turned on. , The current I continuously flows through the corresponding primary coil.

However, as described above, the period of 2
The fact that the current I continuously flows over τ or more is equivalent to an increase in the apparent bit period during that period, that is, a decrease in the apparent sampling frequency. For this reason, the electromagnetic coupling force of the speaker unit 10 becomes small, and optimal driving cannot be performed.

For example, even if the original sampling frequency is 44.1 kHz, the period in which the bit is "1" is
For example, when continuous over 3τ, the apparent sampling frequency at that time is 44.1 kHz / 3, that is, 14.7 k
Hz, so this sounds audible.

Therefore, in the speaker device shown in FIG. 3, the power supply circuit 43 is constituted by a switching power supply, and no smoothing circuit for smoothing the output voltage V43 is provided. Further, a clock CK is extracted from the conversion circuit 222, and the clock CK is supplied to the switching power supply circuit 43 as a switching clock.

Therefore, the output voltage V43 of the power supply circuit 43
Becomes a pulsed DC voltage synchronized with the clock CK, and becomes 0 (or a value close to 0) at the cycle τ of the clock CK.

As a result, as shown in FIG. 4B, for example, even if the LSB to MSB from the series / parallel circuit 222 are "1" for a period of 2τ or more, the primary coils 1A to 1P
As shown in FIG. 4C, the currents IA to IP flowing through the primary coil 1 become 0 at the cycle of the clock CK, and the primary coils 1A to 1P are driven by the currents IA to IP having the cycle τ. Therefore, the electromagnetic coupling force of the speaker unit 10 does not decrease, and the apparent sampling frequency does not fall in the audible frequency band.

Further, by synchronizing the switching of the power supply circuit 43 with the clock CK, the period in which the currents IA to IP become 0 coincides with the period in which the DC voltage V43 becomes 0. That is, when the DC voltage V43 is 0, Current I
Since A to IP are not set to 0, there is no decrease in power supply efficiency.

[0030]

As a method for adjusting the volume of the reproduced sound output from the speaker unit 10, the peak value of the DC voltage V43 is controlled to control the current I.
A method of controlling the peak values of A to IP and a method of multiplying the digital audio signal SD supplied to the terminal 221 by a coefficient of a value corresponding to the volume can be considered.

However, in general, the switching power supply circuit obtains a desired output voltage by thinning out the input voltage temporally and stabilizes the output voltage. Therefore, the peak value of the DC voltage V43 is controlled as in the former method. And the current IA ~
It is difficult to control the peak value of IP. Also, in the case of the latter method, when the volume is reduced, the LSB side bits of the digital audio signal SD are ignored, resulting in deterioration of sound quality.

The present invention is intended to solve the above-described problems and realize volume adjustment.

[0033]

According to the present invention, a speaker unit, a plurality of n impedance circuits,
The speaker unit includes n switch circuits and a switching power supply circuit that outputs a DC voltage in a pulsed form. The speaker unit includes a magnetic circuit having a gap formed therein, and n primary coils disposed near the gap. Is fixed to the cone, a secondary coil is disposed in the gap, and the n 1
A current is induced in the secondary coil by a current flowing through the secondary coil, and the cone is vibrated to form an electromagnetic coupling type speaker. The n impedance circuits and the n 1
The next coil and the n switch circuits are connected in series to the power supply circuit, one set at a time. The switching power supply circuit supplies, as a switching clock, an integer multiple of the sampling frequency of the digital audio signal. Is supplied, and the n switch circuits are
On / off control is performed by each bit of the digital audio signal.
A speaker device in which the number or width of pulses of the pulse-like DC voltage supplied to the series connection in a sample period is changed by data indicating a sound volume.

Therefore, according to the volume data, 1
The current flowing through the next coil is controlled, and the volume of the reproduced sound is controlled.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a case where an input digital audio signal SD is a natural binary code with one sample being a 16-bit serial signal.

In FIG. 1, the speaker unit 10 is of electromagnetic coupling type as described with reference to FIG. 2, and its primary coil 1 has 16 primary coils 1 corresponding to the number of bits of the digital audio signal SD. Primary coil 1
A to 1P. In this case, the coils 1A to 1P
As described above, the ratio of the number of turns is 2 ** 0 to 2 ** 15 in a geometric series with a term ratio of 2.

The digital audio signal SD is supplied to the serial / parallel conversion circuit 220 through the input terminal 221, and the signal SD is converted from serial / parallel by one sample to parallel data. Then, the LSB to MSB of the converted parallel data are supplied to the switch circuits 41A to 41P as control signals thereof, and the switch circuits 41A to 41P
P is turned off when the corresponding bit is “0”,
It is turned on when it is "1".

Further, a switching power supply circuit 51 is provided as a power supply circuit for outputting a DC voltage. in this case,
The switching power supply circuit 51 is not provided with a smoothing circuit for smoothing the output voltage. Further, the clock CK from the conversion circuit 222 is supplied to the multiplying circuit 53 and multiplied to a pulse P53 having a frequency of Q times (Q is an integer, for example, Q = 1000). It is supplied as a switching clock.

Thus, the power supply circuit 51 outputs the pulse P
The pulsed DC voltage V51 which is synchronized with 53 and is not smoothed
And the pulse voltage V51 is supplied to a control circuit 52 described later.

The pulse P53 is supplied to the down counter 54 as its count input. Further, digital data DVOL indicating the volume is supplied to a counter 5 through a terminal 55.
4 as its load input, and the clock CK is supplied to the counter 54 as a load control signal.

Therefore, the counter 54 has a clock
For example, each time CK rises, the volume data DVOL is loaded, and then the loaded value is counted down for each pulse P53. Thus, the counter 54
5, the signal D54 which becomes "1" during the period from the value indicated by the volume data DVOL to "0" every period τ, that is, the volume data A signal D54 that has been PWM-modulated by DVOL is extracted.

The signal D54 is supplied to the control circuit 52, and the control circuit 52 outputs a pulse voltage V51 in the period of D54 = "1" among the pulse voltages V51 from the power supply circuit 51 every period τ. Taken out. In this case, as described above, the pulse width of the signal D54 is
Therefore, the number of pulses of the pulse voltage V51 extracted from the control circuit 52 for each period τ is:
It changes in accordance with the value indicated by the volume data DVOL, which means that PNM modulation is performed by the volume data DVOL.

The primary coils 1A to 1P and the switch circuit 4 are connected between the output terminal of the control circuit 52 and the ground.
1A to 41P and impedance circuits 42A to 42P are connected in series one by one. In this case, the impedances ZA to ZP of the impedance circuits 42A to 42P are
Among the primary coils 1A to 1P, the values are set so that the sum with the impedance of the corresponding primary coil becomes equal to each other.

According to such a configuration, the switching circuit 4
When 1A to 41P are on, currents IA to IP flow through the primary coils 1A to 1P, respectively.
Since the sum of the impedances ZA to ZP of 1A to 41P and the impedances of the primary coils 1A to 1P are equal to each other, the currents IA to IP have the same value I.

Then, L of the digital audio signal SD
When a certain bit of SB to MSB is "1", a corresponding one of the switch circuits 41A to 41P is turned on, and the corresponding one of the primary coils 1A to 1P is turned on. Current I to the primary coil
(= IA to IP) flows. At this time, the number of turns of the primary coils 1A to 1P is equal to the digital audio signal SD.
Are assigned weights corresponding to the respective bits.

Therefore, the cone 32 of the speaker unit 10 is displaced by an amount corresponding to the weight of each bit for each sample of the digital audio signal SD, and the speaker unit 10 outputs the digital audio signal SD. A playback sound is output.

In this case, the volume of the reproduced sound changes in accordance with the number of pulses of the pulse voltage V51 in the period τ, and the number of pulses changes in accordance with the volume data DVOL. Therefore, since the volume of the reproduced sound from the speaker unit 10 changes in accordance with the volume data DVOL, the volume of the reproduced sound can be adjusted according to the volume data DVOL.

Thus, according to the above-described speaker device,
The digital audio signal SD can be converted into a reproduced sound without D / A conversion, and the volume can be adjusted.

In this case, in particular, according to the above-described speaker device, it is not necessary to control the peak value of the voltage V51 output from the switching power supply circuit 51. Terminal 2
Since it is not necessary to multiply the digital audio signal SD supplied to 21 by a coefficient indicating the volume, the reproduced sound does not deteriorate.

Further, even in two or more continuous periods τ, the currents IA to IP flowing through the primary coils 1A to 1P are pulse currents synchronized with the clock CK, so that the electromagnetic coupling force of the speaker unit 10 is reduced. Optimum driving can be performed without any problem. Also, since the apparent sampling frequency does not fall into the audible frequency band, the frequency component is not heard as a reproduced sound.

In the above description, the primary coils 1A to 1A
The ratio of the number of turns of 1P is L of the digital audio signal SD.
Although it is assumed that 2 ** 0 to 2 ** 15 corresponding to SB to MSB, the number of turns of the primary coils 1A to 1P is all equal, and the ratio of the magnitudes of the currents IA to IP is expressed as a term ratio. A geometric series of 2 may be 2 ** 0 to 2 ** 15.

Alternatively, both can be combined, that is, the ratio of the product of the square of the magnitude of the currents IA to IP and the number of turns of the primary coils 1A to 1P is determined by the LSB to MSB of the digital audio signal SD. It is only necessary to correspond to the weight of.

Further, a part of the primary coil 1 (1A to 1P) may be attached to the inner peripheral surface of the plate 22 facing the coil 1. Alternatively, all of the primary coils 1 can be attached to the inner peripheral surface of the plate 22. Further, when the digital audio signal SD is not a natural binary code, it may be converted or decoded into a natural binary code.

In the above description, the primary coils 1A to 1A
Although the pulse voltage V51 supplied to the series circuit of 1P, the switch circuits 41A to 41P, and the impedance circuits 42A to 42P is PNM-modulated by the volume data DVOL, it may be PWM-modulated.

[0055]

According to the present invention, when an electromagnetically coupled speaker unit is driven by a digital audio signal with a current, the volume of the reproduced sound can be adjusted, and the deterioration of sound quality due to the volume adjustment can be avoided. be able to.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating one embodiment of the present invention.

FIG. 2 is a cross-sectional view for explaining the present invention.

FIG. 3 is a connection diagram for explaining the present invention.

FIG. 4 is a waveform chart for explaining the present invention.

FIG. 5 is a waveform chart for explaining the present invention.

[Explanation of symbols]

1, 1A-1P ... primary coil, 2 ... secondary coil, 10 ...
Speaker unit, 11: pole piece, 12: center pole, 18: terminal, 20: magnetic circuit, 21: permanent magnet, 22: plate, 23: void, 31: edge, 3
2 ... cone, 33 ... dustproof cap, 34 ... damper, 3
5 speaker frame, 41A to 41P switch circuit, 42A to 42P impedance circuit, 51 switching power supply circuit, 52 control circuit, 53 multiplier circuit,
54 counter, 222 serial-parallel conversion circuit, SD digital audio signal

Claims (5)

[Claims] A speaker unit, a plurality of n impedance circuits, an n number of switch circuits, and a switching power supply circuit for outputting a DC voltage in a pulsed form, wherein the speaker unit has a gap in a magnetic circuit. While being formed, n primary coils are fixed in the vicinity of the gap, a secondary coil is fixed in the cone, and the secondary coil is arranged in the gap. An electromagnetic coupling type speaker in which a current is induced in the secondary coil and the cone vibrates is provided. The n impedance circuits, the n primary coils, and the n switch circuits are each composed of the switching power supply. The digital audio signal is sampled as a switching clock in the switching power supply circuit by a set connected in series to the circuit. A clock having an integer multiple of the switching frequency is supplied, and the n switch circuits are turned on / off by the respective bits of the digital audio signal, and supplied to the serial connection during one sample period of the digital audio signal. The number or width of the pulses of the pulsed DC voltage is changed by data indicating the volume. 2. The speaker device according to claim 1, wherein the switching power supply circuit outputs a pulse voltage of an integral multiple of the sampling frequency as the pulsed DC voltage. A speaker device configured to supply a number of pulse voltages corresponding to the data indicating the volume to the serial connection every one sample period. 3. The speaker device according to claim 2, wherein the n primary coils have a number of turns corresponding to the bit weight of the digital audio signal, and the impedance of the n primary coils is A speaker device wherein the impedances of the n impedance circuits are set such that the sum of the impedances of the n impedance circuits is equal to each other. 4. The speaker device according to claim 2, wherein the n primary coils have the same number of turns as each other, and a current flowing through the n primary coils is a bit weight of the digital audio signal. A speaker device in which the impedance of the impedance circuit is set so as to have a size corresponding to the following. 5. The speaker device according to claim 2, wherein the magnitude of a current flowing through the n primary coils and the n
A speaker device wherein the product of the number of turns of the primary coils is a size corresponding to the bit weight of the digital audio signal.