JPH03222508A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To drive a speaker linearly regardless of impedance fluctuation by providing an output voltage control means varying an output voltage to the speaker corresponding to an impedance change due to generation of heat at the voice coil of the speaker. CONSTITUTION:A control information signal Ec outputted from an impedance detection means 1 detecting the impedance of a voice coil of a speaker 6 in real time during the operation of a speaker is inputted to an output voltage control means 2. The output voltage control means 2 varies an input voltage Ei of the reproduction system to obtain the input voltage Eo of an amplifier 5 and corrects the fluctuation of input power to the speaker 6 by controlling the input voltage to the amplifier 5 for driving the speaker 6. Thus, even when the voice coil temperature rises during the speaker operation and the impedance changes, the speaker is driven linearly regardless of the impedance fluctuation.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention provides a method for generating heat in the voice coil due to the power applied to the speaker, and even if the impedance changes, the actual power input to the speaker will fluctuate. Concerning an amplifier circuit without.

[Prior Art] Conventionally, an amplifier for driving a speaker in an audio device or the like is usually called a constant voltage amplifier, and an amplifier is used in which the music signal output voltage remains constant even if the load fluctuates.

[Problems to be Solved] Normally, the voice coil of a speaker generates heat in proportion to the applied power, and as the temperature rises, the impedance fluctuates. In a reproduction system using a conventional amplifier with the above-mentioned characteristics as such a load, the actual power flowing into the speaker also varies as the impedance of the voice coil varies. In other words, depending on the state of the music signal, the input power may differ even though the signal is the same, and linear reproduction is not performed, which is a problem to be solved.

Therefore, the present invention provides an amplifier circuit with an output voltage change function that follows impedance fluctuations caused by temperature changes, and has a configuration in which the speaker input power is always the same when amplifying music signals with the same signal voltage level. By doing so, the present invention aims to solve the problems of the above-mentioned conventional example.

[Means for Solving the Problems] A first embodiment of the amplifier circuit according to the present invention for achieving the above object will be described with reference to FIGS. 1 to 3. an output having a function of receiving a control information signal outputted from the impedance detecting means 1 and changing an output voltage to the speaker in response to a change in impedance due to voice coil heat generation of the speaker 6; The amplifier circuit is characterized in that it has a voltage control means 2, and as a second embodiment shown in FIGS. means 3, and an output voltage control means 4 having a function of receiving a control information signal from the control information generating means 3 and changing the output voltage applied to the speaker, The present invention is characterized in that by inputting information corresponding to the variation response characteristic of the applied load force versus the voice coil heat/impedance of the speaker 6, the speaker input power is maintained at a set level in response to impedance changes due to voice coil heat generation of the speaker. It is an amplifier circuit.

[Function] In an amplifier circuit configured like this, for example, when the speaker input level becomes high, the voice coil temperature rises,
When the impedance becomes high, in the case of a conventional amplifier, the set voltage level is constant, so the input power level substantially decreases and the output sound pressure level from the speaker is not reproduced linearly, but in the embodiment of the present invention Then, the impedance detection means 1 searches the speaker impedance and outputs an information signal regarding voice coil impedance fluctuation, and the information signal controls the output voltage control means 2 included in the amplifier circuit for driving the speaker to set the voltage level to the speaker. Since the output voltage of the amplifier is increased to apply a predetermined input power level to the speaker, the speaker will be driven linearly regardless of impedance variations.

The first embodiment has a configuration in which the output voltage control means 2 is controlled by searching for impedance fluctuations in real time,
The present invention is characterized in that it can be immediately applied to speakers with any thermal time constant or heat dissipation characteristics.

In the second embodiment, the speaker's overall heat and
The impedance fluctuation characteristics are measured in advance, and the control information generating means 3 generates information corresponding to the overall heat/impedance fluctuation characteristics of the speaker with respect to the input power obtained by the measurement.
Alternatively, the output voltage control means 4 is inputted to the output voltage control means 4, and the output voltage control means 4 is operated based on the obtained control information and the set voltage level to increase the output voltage of the amplifier so that a predetermined input power level is applied to the speaker. be.

In this second embodiment, it is necessary to measure the thermal characteristics of the connected speakers when used, but if the connected speakers are determined, impedance detection means is not required, so the configuration of the device can be made inexpensive. This configuration is suitable for, for example, a speaker device incorporating an amplifier.

[Embodiment] FIG. 1 shows the basic configuration of the first embodiment of the present invention, which includes an amplifier 5,
A reproduction system including a speaker 6 is shown, and 1 is an impedance detection means for detecting the voice coil impedance of the speaker 6 in real time while the speaker is operating. To explain the specific configuration and functions with reference to FIG. 2, the DC power supply 1a
A minute DC current is passed through the voice coil of the speaker, and only the DC voltage across the voice coil is detected by the low-pass filter 1b, which is converted into a voltage by the arithmetic circuit IC and outputted as a control information signal Ec. The low-pass filter 1b of this embodiment has a cutoff frequency il! ! , attenuation +8DB1
0c1, a filter with Butterworth characteristics is used. In addition, the minute DC current for detection and the audio signal current for driving the speaker are connected to the choke coil 1d and capacitor 1e.
and the low-pass filter 1b.

The control information signal Ec (voltage) output from the impedance detection means 1 is input to the output voltage control means 2, which changes the input voltage Ei of the reproduction system to adjust the input voltage E of the amplifier 5.
0, and the input voltage of the amplifier 5 for driving the speaker 6 is controlled to correct fluctuations in the input power of the speaker 6. An example of the configuration of the output voltage control means 2 is shown in FIG. 2a and 2b are logarithm units, the input signal Ei is input to the logarithm unit 2a, the control information signal Ec is input to the logarithm unit 2b, and the outputs of each logarithm unit are added by an adder 2c, and further, an anti-logarithm unit 2d is input. By Eo
=Ei·Ec, and as a result, the gain is changed by the control information signal Ec.

In addition, as the impedance detection means, any means other than the above structure may be adopted as long as it has an equivalent function, and as the output voltage control means, the voltage amplification circuit of the amplifier 5 may be used as a Vollag Con1+old Amptier.
A method may also be used in which the total gain of the amplifier 5 is changed isometrically as follows.

FIG. 4 shows the basic configuration of a second embodiment of the present invention, which also shows a reproduction system including an amplifier 5 and a speaker 6, and 3 is a control information generating means, which is known in advance by actual measurement. Information Es corresponding to the variation response characteristic of the applied power to the voice coil versus the thermal self-impedance of the speaker is inputted from the input terminal 3a, and information E of the input power to the speaker is inputted, and a control information signal Ec is outputted. Further, depending on the case, the information Ex corresponding to the fluctuation response characteristic is inputted from the input terminal 4a to the output signal control means 4 and becomes the input signal Eo of the amplifier 5, so that even if the voice coil impedance fluctuates, the speaker Hold input power at a constant level.

Further, depending on the circuit configuration such as a modified example, the reproduction system input signal E1 may be used as is instead of the input power information E to the speaker.

In FIG. 5, assuming that the temperature change with respect to the applied voltage E (solid line) of the speaker can be approximated by a logarithmic function (rise) or an exponential function (fall) that has a time constant specific to the speaker, The change in voice coil impedance Z with respect to time t is set as Z=ZC-1(El) (dotted line), and the input voltage E is set by activating the output voltage control means 4 so that E=e
-LF[te..., the speaker power W can be kept constant as W=E2/z=e2/Zc.

Here, 2c can be considered to be the saturation value of the voice coil impedance when the time t has passed sufficiently long with respect to the voltage E and the amount of heat generation and the amount of heat radiation are balanced.

The time constant of the above temperature characteristic is based on the voice coil specifications of the speaker,
A value specific to the speaker determined by the structural dimensions of components near the voice coil such as a magnetic circuit is measured in advance for each speaker, and is input to the control information generation means 3 or the output signal control means 4, and is input to the simulation circuit of the same means. Set.

FIG. 6 shows the output signal control means 2 in a modification of the first embodiment, which is a system in which digital signal processing is performed at the stage of the input signal E1 of the reproduction system. The main part is the reference voltage E from the control information signal equivalent to the nominal impedance R of the speaker and the actual impedance Z obtained by the impedance detection means 1.
A computing unit 2j that obtains d, an FIR filter 21, and the F
Adaptive control unit 2g that changes the coefficients of the IR filter 2f
The input signal Ei is digitized by the /D converter 2h and divided into two parts, one of which is input to the arithmetic unit 2j and becomes the reference voltage Ed, and the other is input to the FIR filter 21.

The reference voltage Ed and the output of the FIR filter 21 are compared, and error information ε between the image information is input to the adaptive control unit 2g.
FIR filter 2] is adaptively changed. The output of the FIR filter subjected to the adaptive change is converted into an analog signal by a D/^ converter 2j, and becomes an input signal EO of the amplifier 5.

FIG. 7 shows the control information generation means 3 and the output signal control means 4 in a modification of the second embodiment, and shows the stage of the input signal E of the reproduction system as in the modification of the first embodiment. This is a method of digital signal processing.

The input signal Ei is digitized by the A/D converter 3h, and
One of the divided signals is inputted to the signal average value calculating section 3c as input signal information, the average level is calculated, and the control information signal E is obtained.
c and is applied to the output signal control means 4. The other side receives a delay corresponding to the above average level calculation time by the signal delay memory 3b, and then outputs the input signal equivalent information Ei' again.
and is applied to the output signal control means 4.

The main body of the output signal control means 4 is an arithmetic processing unit 4a, and the fluctuation response characteristic equivalent information Es inputted from the input terminal
The input signal equivalent information Ei is based on the control information signal Ec and the control information signal Ec.
' is changed and converted into an analog signal by the D/^ converter 4b, and becomes the input signal Eel of the amplifier 5.

Above, the amplifier circuit according to the present invention has been described in detail based on the embodiments that are considered to be representative, but the circuit configuration according to the present invention is not limited to the structure of the above embodiments, and the constituent elements described in the claims described above are As long as it has the following features, exhibits the functions of the present invention, and has the effects described below, it may be implemented with appropriate modifications.

[effect] The amplifier circuit according to the present invention has the following effects.

In other words, even if the voice coil temperature rises and the impedance changes during speaker operation, the impedance fluctuation information increases the output voltage of the amplifier so as to apply a predetermined input power level to the speaker for the set voltage level, so the impedance of the speaker changes. It will be driven linearly regardless of fluctuations.

Furthermore, since the above-mentioned impedance fluctuations are searched in real time, it is possible to immediately respond to any speaker with any thermal time constant or heat dissipation characteristics, and no matter how long the operating time is. In a case where the level constantly fluctuates, the input power is corrected to follow the fluctuations in the average level, which has the effect of faithfully reproducing the dynamic range.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a first embodiment of the present invention, Fig. 2 is a block diagram of an example of impedance detection means, Fig. 3 is a block diagram of an example of output voltage control means, and Fig. 4 is a block diagram of an example of the output voltage control means. Configuration diagram,
FIG. 5 is a functional explanatory diagram of the output voltage control means of the second embodiment;
FIG. 6 is a configuration diagram of an example of an output voltage control means of a modification of the first embodiment, and FIG. 7 is a configuration diagram of an example of control information generation means and output voltage control means of a modification of the second embodiment. . 1 is an impedance detection means, 2 is an output voltage control means,
3 is a control information generating means, 4 is an output voltage control means, 5 is an amplifier, and 6 is a speaker.

Claims (1)

[Claims] 1. An impedance detection means (1) for detecting the impedance of a speaker in operation, and an impedance detection means (1) that detects the impedance due to voice coil heat generation of the speaker in response to a control information signal output from the impedance detection means (1). 1. An amplifier circuit comprising: output voltage control means (2) having a function of changing the output voltage applied to a speaker in response to changes. 2. A control information generating means (3) for outputting a control information signal based on information corresponding to the connected speaker input power level, and an output voltage to be applied to the speaker upon receiving the control information signal from the control information generating means (3). The output voltage control means (4) is equipped with an output voltage control means (4) having a function of changing the output voltage, and by inputting information corresponding to the previously known variation response characteristics of the applied power to the voice coil heat/impedance of the connected speaker. An amplifier circuit characterized by maintaining speaker input power at a set level in response to impedance changes due to heat generation in the speaker's voice coil. 3. The amplifier circuit according to claim 1, wherein the output voltage control means (2) is a digital circuit comprising an FIR filter and an adaptive control section for changing coefficients of the FIR filter. 4. A claim characterized in that the control information generating means (3) is a digital circuit comprising a signal delay memory and a signal average value calculating section, and the output voltage controlling means (4) is a digital signal processing device. Term 2 amplifier circuit.