JP6862825B2 - Drive device - Google Patents

Description

The present invention relates to a drive device for driving a speaker.

As a conventional drive device for driving a speaker, a detection resistor is connected in series to the voice coil of the speaker, and the voltage of the detection resistor is measured to detect the current flowing through the speaker and a signal corresponding to the magnitude of the current. There is known a technique of positive feedback to an input (see Patent Document 1). According to this drive device, it is possible to efficiently emit low-pitched sound from the speaker.

JP-A-2015-204600

By the way, the resistance value of the voice coil may be smaller than the standard due to the manufacturing variation of the speaker. Further, when a current flows through the detection resistor, the detection resistor may self-heat and its resistance value may increase.
Considering the variation in the resistance value of the voice coil and the temperature characteristics of the detection resistor, the gain of the positive feedback system from the detection of the voltage of the detection resistor to the output of the feedback signal is expected to allow a margin so that the drive unit does not oscillate. I had to set it. Therefore, there is a problem that the bass cannot be sufficiently enhanced.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to emit a sound with enhanced bass from a speaker while operating the drive device in a stable manner.

In order to solve the above-mentioned problems, the drive device according to the present invention includes an adder that adds an input signal and a feedback signal, an amplification unit that amplifies the output signal of the adder and drives the speaker, and the speaker. A current detection unit that outputs a detection signal according to the flowing current, a bandpass filter to which the detection signal is input, and a feedback signal generation unit that generates the feedback signal by multiplying the output signal of the bandpass filter by a coefficient. And a control unit that executes a reduction process that reduces the coefficient when the gain of the output signal of the addition unit with respect to the input signal exceeds the reference value.

It is a block diagram which shows the drive device of the speaker which concerns on embodiment of this invention. It is explanatory drawing for demonstrating operation of this apparatus.

<Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of the drive device 100 that drives the speaker 12 according to the embodiment. The drive device 100 includes a processor P such as a DSP (Digital Signal Processor) or a CPU (Central Processing Unit), a memory M, an amplification unit 11 that supplies a drive signal Vout to the speaker 12, and a drive that flows through the voice coil of the speaker 12. It includes a current detection unit 13 that detects the current I and outputs a detection signal 13a.

The processor P functions as an addition unit 10, a bandpass filter (hereinafter referred to as BPF) 14, a feedback signal generation unit 15, and a control unit 16 by executing a program stored in the memory M. The memory M is, for example, a recording medium of any known type such as a semiconductor recording medium, a magnetic recording medium, or an optical recording medium, or a recording medium in which these recording media are combined. In the present specification, the “non-transient” recording medium is readable by all computers except a recording medium such as a transmission line that temporarily stores a transient propagation signal (transitory, propagating signal). It does not exclude volatile recording media, including various recording media.

The addition unit 10 adds the input signal V1 and the feedback signal V2 and outputs the addition signal V3. The input signal V1 in this example is a digital signal. The amplification unit 11 includes a DA converter (hereinafter referred to as DAC) 111 that converts an addition signal V3 from a digital signal to an analog signal, and a power amplifier 112 that amplifies the output signal of the DAC 111 and outputs a drive signal Vout.
The current detection unit 13 includes a detection resistor 131 through which a drive current I flows, a preamplifier 132 that amplifies and outputs the voltage across the detection resistor 131, and an AD converter that converts the output signal of the preamplifier 132 from an analog signal to a digital signal (hereinafter referred to as an AD converter). , ADC) and 133.

The BPF 14 outputs the output signal 14a by passing the frequency component of the predetermined frequency band among the frequency components of the detection signal 13a. The pass band of the BPF 14 becomes a sound band in which the pass band is enhanced. When enhancing the bass, the pass band of the BPF 14 may be set to, for example, 50 Hz or more and 200 Hz or less.

The feedback signal generation unit 15 multiplies the output signal 14a of the BPF 14 by a coefficient K, and the feedback signal V2
To generate. The feedback signal generation unit 15 includes an attenuator 151 and a multiplier 152. The attenuator 151 multiplies the output signal 14a by the coefficient K1 and outputs the signal. Further, the multiplier 152 multiplies the output signal of the attenuator 151 by the coefficient K2 and outputs the signal. The coefficient K1 is variable, while the coefficient K2 is fixed. The coefficient K is given by the product of the coefficient K1 and the coefficient K2.

The resistance value of the speaker 12 (the resistance value of the voice coil) is RL, the resistance value of the detection resistance 131 is RS, the gain of the amplification unit 11 is A, and the gain from the current detection unit 13 to the feedback signal generation unit 15 is β. Assuming that the gain G is V3 / V1, the total gain G is given by the following equation 1.
G = V3 / V1 = (RL + RS) / {RL + RS (1-Aβ)} ... Equation 1
As is clear from Equation 1, in order for the drive device 100 not to oscillate, it is necessary to satisfy (RL + RS) / RS> Aβ. In the present embodiment, the total gain G is monitored based on the input signal V1 and the feedback signal V2, and when the total gain G exceeds the reference value Gmax, β is controlled to be lowered.

The control unit 16 has a feedback level detection unit 161 that detects the level of the feedback signal V2, an input level detection unit 162 that detects the level of the input signal V1, and a predetermined cycle of whether or not the total gain G exceeds the reference value Gmax. A determination unit 163 that repeatedly determines the coefficient K1 and a coefficient control unit 164 that controls the coefficient K1 based on the determination result of the determination unit 163 are provided.

The determination unit 163 calculates the total gain G by calculating (V1 + V2) / V1. The reference value Gmax is the maximum value of the total gain G that is allowed. The reference value Gmax is set not only to prevent oscillation but also to prevent the gain in the low frequency range from becoming excessive. When the normal total gain G is set to "4", the reference value Gmax is set to be, for example, in the range of "6" or more and "8" or less. The reference value Gmax is stored in the memory M in advance, and the determination unit 163 reads the reference value Gmax from the memory M and uses it for the determination.

Next, the coefficient control unit 164 performs a reduction process for reducing the coefficient K1 or a release process for increasing the coefficient K1 reduced from the initial value kini toward the initial value kini according to the determination result of the determination unit 163. Execute. The coefficient control unit 164 reduces the coefficient K1 with a predetermined slope (−X) in the reduction process. On the other hand, the coefficient control unit 164 controls the coefficient K1 to return to the initial value kini with a predetermined slope (Y) in the release process. The coefficient K1 is used in the attenuator 151. Therefore, the initial value kini is "1". In the release process, when the coefficient K1 returns to the initial value kini, the coefficient K1 maintains the initial value kini even if the subsequent determination result is negative.

Further, the absolute value (X) of the slope (change amount of the coefficient K1 per unit time) in the reduction process is larger than the absolute value (Y) of the slope in the release process. This is because when the total gain G exceeds the reference value Gmax, it is necessary to improve the responsiveness from the viewpoint of suppressing oscillation, while the release process only requires a gentle response.

The determination unit 163 executes the determination at a predetermined cycle. The slope of the coefficient K1 in the reduction process may be realized, for example, by reducing the current coefficient K1 by a predetermined value Z1 when the affirmative determination result is continuous Q (Q is an arbitrary natural number). When the predetermined period is Tx, the predetermined slope “−X” is −Z1 / (Q * Tx). On the other hand, the slope of the coefficient K1 in the release process may be realized by increasing the current coefficient K1 by a predetermined value Z2, for example, when the negative determination result is J (J is an arbitrary natural number) consecutive times. .. The predetermined slope "Y" is Z2 / (J * Tx).

FIG. 2 shows an example of the relationship between the determination result and the coefficient K1. In this example, the determination result of the determination unit 163 is negative in the period T1, the period T3, and the period T4, and the determination result of the determination unit 163 is affirmative in the period T2. Then, at the start of the period T1, the coefficient K1 has an initial value of kini. Therefore, in the period T1, the coefficient K1 maintains the initial value kini. Next, in the period T2, the determination result of the determination unit 163 becomes affirmative, and the coefficient K1 decreases with the slope −X. Then, in the period T3, the determination result of the determination unit 163 is negative, and the coefficient K1 increases with the slope Y. When the coefficient K1 recovers to the initial value kini, the initial value kini is maintained in the period T4.

As described above, in the present embodiment, since the total gain G is monitored and the magnitude of the feedback signal V2 that positively returns is controlled, the resistance value RS of the detection resistor 131 and the resistance value RL of the speaker 12 may vary or fluctuate. The total gain G can be set to a desired value without being restricted.
Further, even if the specifications of the speaker 12 are changed and the resistance value RL is significantly changed, or even if a component having an unexpected constant is attached to the detection resistance 131, it is possible to prevent the total gain G from becoming infinite.

<Modification example>
The present invention is not limited to the above-described embodiment, and various modifications described below are possible. Moreover, the embodiment and various modifications can be combined as appropriate.
(1) In the above-described embodiment, the release process has been described as increasing the coefficient K1 reduced from the initial value kini by the decrease process toward the initial value kini, but the present invention is not limited to this. The release process may include a process of stopping the decrease of the coefficient K1 and maintaining the coefficient K1.
For example, when the power is turned on, the coefficient K1 becomes the initial value kini. Then, when the total gain G exceeds the reference value Gmax, the reduction process is executed. As a result, when the total gain G becomes equal to or less than the reference value Gmax, the cancellation process for stopping the reduction of the coefficient K1 and maintaining the coefficient K1 is executed. After that, when the power is turned off, the drive device 100 stops operating. Then, when the power is turned on again, the coefficient K1 is reset to the initial value kini.
By the way, the reduction process was necessary for stable operation by suppressing oscillation. The cause of the unstable operation is the variation in the resistance value of the voice coil and the temperature characteristics of the detection resistance. Of these, the variation in the resistance value of the voice coil is fixed rather than dynamically changing. As described above, since the release process stops reducing the coefficient K1 and maintains the coefficient K1, the variation in the resistance value of the voice coil can be fixedly removed.

(2) In the above-described embodiment, the input level detection unit 162 detects the level of the input signal V1, but the total gain G is calculated by (V1 + V2) / V1. In this case, when the input signal V1 approaches zero cross, the calculation accuracy decreases. As a result, the input signal V1 becomes smaller than the true value, and the total gain G may be larger than the true value and may be erroneously detected. Therefore, the input level detection unit 162 may output the value obtained by peak-holding the input signal V1 as the level of the input signal V1. In this case, the feedback level detection unit 161 preferably outputs the instantaneous value of the feedback signal V2 as the level of the feedback signal V2.

(3) In the above-described embodiment, the control unit 16 calculates the total gain G (= (V1 + V2) / V1) based on the input signal V1 and the feedback signal V2, but the present invention is limited to this. The total gain G (= V3 / V1) may be calculated based on the input signal V1 and the addition signal V3. In this case, the level of the addition signal V3 may be supplied to the determination unit 163 by using the addition level detection unit that detects the level of the addition signal V3 instead of the feedback level detection unit 161.

The following inventions can be grasped from the above-described embodiments and modifications.
One aspect of the drive device according to the present invention corresponds to an adder that adds an input signal and a feedback signal, an amplifier that amplifies the output signal of the adder and drives the speaker, and a current flowing through the speaker. A current detection unit that outputs a detection signal, a bandpass filter to which the detection signal is input, a feedback signal generation unit that generates the feedback signal by multiplying the output signal of the bandpass filter by a coefficient, and the input signal. When the gain of the output signal of the addition unit exceeds the reference value, a control unit that executes a reduction process for reducing the coefficient is provided.
According to this aspect, since the reduction process is executed when the gain exceeds the reference value, the gain of the positive feedback path including the current detection unit, the bandpass filter, and the feedback signal generation unit can be reduced. As a result, it is possible to stabilize the operation of the drive device while preventing oscillation, and to emit a sound with enhanced bass from the speaker.

In one aspect of the drive device described above, when the gain is equal to or less than the reference value, the control unit increases the coefficient reduced from the initial value by the reduction process toward the initial value or decreases the coefficient. It is preferable to stop the operation and execute the release process for maintaining the coefficient.
According to this aspect, when the gain becomes equal to or less than the reference value, the coefficient is increased toward the initial value or the decrease of the coefficient is stopped and maintained, so that the bass is produced in a state where the drive device operates stably. It will be possible to reinforce it again.

In one aspect of the drive device described above, the control unit calculates the gain based on the input signal and the feedback signal, and determines whether or not the gain exceeds the reference value, and the determination unit. It is preferable to include a coefficient control unit that executes the reduction process when the determination result of the determination unit is affirmative and executes the release process when the determination result of the determination unit is negative. According to this aspect, the gain can be calculated based on the input signal and the feedback signal.

In one aspect of the drive device described above, when the release process increases the coefficient reduced from the initial value by the decrease process toward the initial value, the coefficient control unit reduces the coefficient in the decrease process. It is preferable to control the amount of change per unit time to be caused to exceed the amount of change per unit time for increasing the coefficient in the release process. According to this aspect, the reduction process can improve the responsiveness as compared with the release process from the viewpoint of prioritizing the stability of the operation, while the release process responds slowly, so that the sound changes suddenly. Can be suppressed.

10 ... Addition unit, 11 ... Attenuator, 12 ... Speaker, 13 ... Current detection unit, 14 ... BPF, 15 ... Feedback signal generation unit, 16 ... Control unit, 161 ... Feedback level detection unit, 162 ... Input level detection unit, 163 ... Judgment unit, 164 ... Coefficient control unit, 151 ... Attenuator, 100 ... Drive device.

Claims (2)

An adder that adds the input signal and the feedback signal,
An amplification unit that amplifies the output signal of the addition unit and drives the speaker,
A current detection unit that outputs a detection signal according to the current flowing through the speaker, and
A bandpass filter to which the detection signal is input and
A feedback signal generator that generates the feedback signal by multiplying the output signal of the bandpass filter by a coefficient.
When the gain of the output signal of the addition unit with respect to the input signal exceeds the reference value, the coefficient is reduced, and when the gain is equal to or less than the reference value, the coefficient is reduced from the initial value by the reduction process. A control unit that executes a release process of increasing the value toward the initial value or stopping the decrease of the coefficient and maintaining the coefficient.
With
When the release process increases the coefficient reduced from the initial value by the decrease process toward the initial value, the control unit may use the control unit.
The amount of change per unit time that increases the coefficient does not exceed the amount of change per unit time that decreases the coefficient in the reduction process.
A drive device characterized by being controlled.
The control unit
A determination unit that calculates the gain based on the input signal and the feedback signal and determines whether or not the gain exceeds the reference value.
A coefficient control unit that executes the reduction process when the determination result of the determination unit is affirmative and executes the release process when the determination result of the determination unit is negative.
The drive device according to claim 1 , wherein the drive device comprises.

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