CN117202072A - Device and method for measuring impedance characteristics of loudspeaker - Google Patents
Device and method for measuring impedance characteristics of loudspeaker Download PDFInfo
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- CN117202072A CN117202072A CN202311236941.0A CN202311236941A CN117202072A CN 117202072 A CN117202072 A CN 117202072A CN 202311236941 A CN202311236941 A CN 202311236941A CN 117202072 A CN117202072 A CN 117202072A
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Abstract
The invention discloses a measuring device and a measuring method for the impedance characteristic of a loudspeaker, wherein the measuring device specifically adopts a microcontroller to output a programmable clock signal to be connected to an impedance converter, the impedance converter outputs a frequency-adjustable amplitude-modulated voltage signal to be connected to a driving gain circuit, the driving gain circuit outputs a driving signal to be connected to an amplifier, a measured loudspeaker is connected in series in a feedback loop of the amplifier, the amplifier outputs a voltage measuring signal to be connected to a measuring input end of the impedance converter, and the voltage measuring signal is converted into impedance information through the impedance converter. The measuring device can measure the impedance characteristic of the loudspeaker and integrate the circuit into an audio signal chain, and can measure the impedance characteristic of the loudspeaker when the system is powered on, so that the impedance characteristic can be directly compared with the factory calibration characteristic, and once the characteristic is changed, the impedance characteristic can be timely detected and further diagnosis can be carried out, thereby avoiding permanent damage.
Description
Technical Field
The invention belongs to the technical field of speaker fault diagnosis, and particularly relates to a speaker impedance characteristic measurement device and a measurement method.
Background
As the application range of the speaker is wider and wider, the quality requirement on the speaker is higher and higher, so that it is particularly important to accurately measure the impedance characteristic of the speaker.
The existing loudspeaker impedance measuring method mainly relies on a special loudspeaker impedance tester for measurement, but is quite expensive and inconvenient for system integration, and is independent of an audio system for driving a loudspeaker.
Disclosure of Invention
The invention aims to provide a device and a method for measuring the impedance characteristics of a loudspeaker, wherein a tested loudspeaker is connected in series in a feedback loop of an amplifier, the amplifier outputs a voltage measurement signal, and the voltage measurement signal is converted into impedance information through an impedance converter, so that the test cost is reduced.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a loudspeaker impedance characteristic measuring device, comprising: the device comprises a microcontroller, an impedance converter, a driving gain circuit and an amplifier;
the microcontroller is connected with the impedance converter; the microcontroller is used for outputting a pulse width modulation signal as a clock signal of the impedance converter;
the impedance converter is used for converting the received clock signal into a driving voltage signal; the impedance converter is connected to the drive gain circuit;
the driving gain circuit is used for amplifying the driving voltage signal and is used as the input of the amplifier;
the tested loudspeaker is connected in series in a feedback loop of the amplifier, the output end of the amplifier is connected to the measurement input end of the impedance converter, and the impedance converter is used for converting an output voltage measurement signal of the amplifier into impedance information;
the microcontroller is connected with the impedance converter through a serial bus and is used for reading impedance information of the tested loudspeaker through the serial bus.
Further, the impedance converter adopts an AD5933 impedance converter.
Further, the microcontroller is particularly adapted to,
changing the frequency of the output pulse width modulation signal, thereby changing the frequency of the driving voltage signal output by the impedance converter;
the method comprises the steps of,
and setting related parameters of the impedance converter, and controlling the amplitude of the driving voltage signal output by the impedance converter.
Further, the driving gain circuit comprises an operational amplifier U3A and an operational amplifier U4;
the resistor R4 and the resistor R11 are connected in series and divided and then connected to the non-inverting input end of the operational amplifier U4; the inverting input end of the operational amplifier U4 is connected to the output end of the operational amplifier U4; the other end of the resistor R4 is connected with a power supply VCC, and the other end of the resistor R11 is grounded;
the output end of the operational amplifier U4 is connected to the inverting input end of the operational amplifier U3A through a resistor R5;
the VOUT pin of the impedance converter is connected to the non-inverting input end of the operational amplifier U3A through a resistor R2; a feedback resistor R1 is arranged between the non-inverting input end and the output end of the operational amplifier U3A;
a feedback resistor R6 and a sampling resistor R3 are arranged between the inverting input end and the output end of the operational amplifier U3A; one end of the feedback resistor R6 is connected with the inverting input end of the operational amplifier U3A, the other end of the feedback resistor R6 is connected with the non-inverting input end of the amplifier U3B, one end of the sampling resistor R3 is connected with the output end of the operational amplifier U3A, and the other end of the sampling resistor R3 is connected with the non-inverting input end of the amplifier U3B; the amplifier U3B is an amplifier where the tested loudspeakers are connected in series.
Further, the feedback resistor R1 is connected in parallel with the capacitor C2.
Further, the operational amplifier U3A adopts an LMV321; the operational amplifier U4 adopts AD8532; the amplifier U3B employs AD8532.
Further, the tested loudspeaker is connected in series on the feedback loop of the amplifier U3B, and the resistors R12 and R13 are connected in series and divided and then connected to the inverting input end of the amplifier U3B; the output end of the amplifier U3B is connected to the analog-to-digital converter of the impedance converter through a resistor R7 and a resistor R8;
the analog-to-digital converter of the impedance converter is used for performing digital processing on the voltage signal output by the amplifier U3B and performing single-point discrete time Fourier transform based on frequency to obtain a real part and an imaginary part of the impedance of the tested loudspeaker.
The speaker impedance characteristic measuring method based on the speaker impedance characteristic measuring apparatus includes:
the high-precision resistor is connected in series with the feedback loop of the amplifier U3B instead of the impedance of the tested loudspeaker;
outputting a pulse width modulation signal through a microcontroller, acquiring measurement results of the real part and the imaginary part of the high-precision resistance impedance, and calculating a gain coefficient and a calibration phase;
taking down the high-precision resistor and connecting the impedance of the tested loudspeaker in series to the feedback loop of the amplifier U3B;
the frequency of the output pulse width modulation signal is controlled by the microcontroller to change, and at each frequency, the frequency is processed in the following way to obtain a measured loudspeaker impedance characteristic change curve within a set frequency range:
the microcontroller outputs a pulse width modulation signal with a certain frequency, and outputs a driving voltage signal under the frequency through the impedance converter;
real and imaginary data of the impedance of the measured speaker at the frequency are acquired by the microcontroller and the measured speaker impedance and phase are calculated.
Further, the gain factor and calibration phase are calculated as follows:
wherein Gain represents Gain factor, G R REAL and IMAG each represent high-precision electricityReal and imaginary parts of impedance, θ CAL Representing the calibration phase.
Further, the measured speaker impedance and phase are calculated as follows:
wherein REAL x And IMAG x Representing the real and imaginary parts of the measured speaker impedance.
The beneficial effects of the invention are as follows:
the invention provides a highly accurate low cost speaker impedance measurement solution that can integrate this simple test circuit with the audio chain with very little circuit board space taken up, except for AD5933, which requires only a few external components.
The measuring device can measure the impedance characteristic of the loudspeaker and integrate the circuit into an audio signal chain, and can measure the impedance characteristic of the loudspeaker when the system is powered on, so that the impedance characteristic can be directly compared with factory calibration characteristics stored in a memory, and once the characteristics change, the impedance characteristic can be timely detected and further diagnosis can be carried out, thereby avoiding permanent damage.
Drawings
FIG. 1 is a diagram of a speaker impedance characteristic measuring apparatus according to the present invention;
fig. 2 is a circuit diagram of a speaker impedance characteristic measuring apparatus according to the present invention.
Detailed Description
The invention is further described below. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
The present invention provides a speaker impedance characteristic measuring apparatus, referring to fig. 1, comprising: the device comprises a microcontroller, an impedance converter, a driving gain circuit and an amplifier;
the microcontroller is used for outputting a pulse width modulation signal as a programmable clock signal of the impedance converter, and is connected to the impedance converter;
the impedance converter is used for converting the programmable clock signal into a driving voltage signal and is connected to the driving gain circuit;
the driving gain circuit is used for amplifying the driving voltage signal and is used as an input of the amplifier; the driving gain circuit is connected to the input end of the amplifier;
the measured loudspeaker is connected in series in the feedback loop of the amplifier, the output voltage measurement signal of the amplifier is connected to the measurement input end of the impedance converter, and the impedance converter is used for converting the voltage measurement signal of the amplifier into impedance information.
The microcontroller is connected with the impedance converter through a serial bus, and reads impedance information through the serial bus.
It should be noted that, in the present invention, the impedance converter is an AD5933 impedance converter.
It should be noted that, initially, the impedance converter performs a corresponding initializing operation.
It should be noted that the microcontroller may also be used for,
the frequency of the driving voltage signal output by the impedance converter is further changed by changing the frequency of the programmable clock signal, so that frequency modulation is realized;
the method comprises the steps of,
by setting the relevant parameters of the impedance converter, the amplitude of the driving voltage signal output by the impedance converter is changed, namely, amplitude modulation is realized.
Referring to fig. 2, a microcontroller pin PWM is connected with a pin MCLK of the AD5933 impedance converter, a microcontroller pin SCL is connected with a pin SCL of the AD5933 impedance converter, a microcontroller pin SDA is connected with a pin SDA of the AD5933 impedance converter, and the microcontroller pin PWM outputs a pulse width modulation signal as a clock signal of the AD5933 impedance converter, and the frequency of the pulse width modulation signal is adjustable to meet measurement requirements of different bandwidth ranges.
The microcontroller and the AD5933 impedance converter are communicated through a serial bus formed by SCL and SDA, the working frequency, the working amplitude and the like of the AD5933 impedance converter can be set, and the impedance conversion result is obtained.
The pin VOUT of the AD5933 impedance converter outputs an adjustable frequency amplitude modulation voltage signal VOUT, and the adjustable frequency amplitude modulation voltage signal VOUT is connected with the driving gain circuit and used as an input signal of the driving gain circuit.
The driving gain circuit is used for amplifying the voltage signal VOUT and improving driving capability. The driving gain circuit is composed of two operational amplifiers U3A and U4, resistors R4 and R11 are connected in series and divided and then connected to the non-inverting input end of the operational amplifier U4, the other end of the R4 is connected with a power supply VCC, the other end of the R11 is grounded, the inverting input end of the operational amplifier U4 is connected to the output of the operational amplifier U4, and the output voltage of the operational amplifier U4 is an adjustable reference voltage Vc.
The pin VOUT of the AD5933 impedance converter is connected to the non-inverting input end of the operational amplifier U3A through a resistor R2, a feedback resistor R1 is arranged between the non-inverting input end and the output end of the operational amplifier U3A, and a capacitor C2 is connected with the resistor R1 in parallel to prevent oscillation. The output of the operational amplifier U4 is connected to the inverting input of the operational amplifier U3A through a resistor R5. One end of the feedback resistor R6 is connected with the inverting input end of the operational amplifier U3A, the other end of the feedback resistor R6 is connected to the Vb point, one end of the sampling resistor R3 is connected with two ends of the output end of the operational amplifier U3A, and the other end of the sampling resistor R3 is connected to the Vb point. The point Vb is the non-inverting input terminal of the amplifier U3B.
In the present invention, the operational amplifier U3A employs the LMV321. The operational amplifier U4 employs AD8532.
The driving gain circuit works as follows:
under the simultaneous action of positive and negative feedback, the current IOUT flowing through the sampling resistor R3 is calculated as follows:
where Va is the output voltage of the operational amplifier U3A, vb is the voltage at the other end of the sampling resistor R3, vc is the output voltage of the operational amplifier U4, and VOUT is the adjustable amplitude modulation voltage output by the impedance converter.
Since the adjustable reference voltage Vc and the resistors R3, R5, R6 are known, the current IOUT is independent of the impedance of the load and is only related to the adjustable amplitude modulated voltage signal VOUT. In addition, it is necessary to ensure that R6> R3 allows the current flowing through the resistor R3 to flow uniformly to the load.
The tested loudspeaker is connected in series on the feedback loop of the operational amplifier U3B, and the resistors R12 and R13 are connected in series for voltage division and then connected to the inverting input end of the operational amplifier U3B, so that the system obtains the optimal dynamic range. The voltage signal is digitized, single-point discrete time Fourier transform (DFT) is performed based on the scanned frequency, so that the REAL part REAL and the imaginary part IMAG of impedance information of the tested loudspeaker at each frequency are obtained, and then a variation curve of impedance characteristics of the tested loudspeaker in a certain frequency range can be obtained. The frequency here refers to the frequency of the driving voltage signal output from the impedance converter, and is controlled by the microcontroller.
In the present invention, the amplifier U3B employs AD8532.
Based on the measuring device, the invention provides a measuring method for the impedance characteristics of a loudspeaker, which comprises the following steps:
the system is calibrated before effective impedance measurements can be made. The calibration method is to use a high-precision resistor Calibration Resistor to replace the impedance of a loudspeaker to be measured, measure in the system, read out the REAL part REAL and the imaginary part IMAG of the measurement result of the system, and calculate the Gain coefficient Gain in the following manner:
wherein G is R Representing the resistance of the high-precision resistor Calibration Resistor, REAL and IMAG representing the REAL and imaginary parts of the Calibration Resistor impedance, respectively;
calibration phase θ of the system CAL The calculation method is as follows:
after calibration is completed, speaker impedance measurements may be made, as follows:
the microcontroller outputs a programmable clock signal with a certain frequency, and outputs a driving voltage signal under the frequency through the impedance converter;
measuring real and imaginary data of the impedance of the speaker at the frequency and calculating the speaker impedance and phase;
the frequency of the programmable clock signal is changed by the microcontroller, so that the frequency of the driving voltage signal output by the impedance converter is changed;
measuring real and imaginary parts of impedance of the loudspeaker at different frequencies, and calculating impedance and phase of the loudspeaker;
repeating the operation to obtain the impedance characteristic change curve of the tested loudspeaker in a certain frequency range.
In the invention, the impedance Z of the loudspeaker SPEAKER And phase theta SPEAKER The calculation method is as follows:
wherein REAL x And IMAG x Is the real and imaginary parts of the measured speaker impedance.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (10)
1. A speaker impedance characteristic measuring apparatus, comprising: the device comprises a microcontroller, an impedance converter, a driving gain circuit and an amplifier;
the microcontroller is connected with the impedance converter; the microcontroller is used for outputting a pulse width modulation signal as a clock signal of the impedance converter;
the impedance converter is used for converting the received clock signal into a driving voltage signal; the impedance converter is connected to the drive gain circuit;
the driving gain circuit is used for amplifying the driving voltage signal and is used as the input of the amplifier;
the tested loudspeaker is connected in series in a feedback loop of the amplifier, the output end of the amplifier is connected to the measurement input end of the impedance converter, and the impedance converter is used for converting an output voltage measurement signal of the amplifier into impedance information;
the microcontroller is connected with the impedance converter through a serial bus and is used for reading impedance information of the tested loudspeaker through the serial bus.
2. A speaker impedance characteristics measuring apparatus according to claim 1, wherein the impedance converter is an AD5933 impedance converter.
3. A loudspeaker impedance characteristic measuring apparatus according to claim 1, wherein the microcontroller is specifically adapted to,
changing the frequency of the output pulse width modulation signal, thereby changing the frequency of the driving voltage signal output by the impedance converter;
the method comprises the steps of,
and setting related parameters of the impedance converter, and controlling the amplitude of the driving voltage signal output by the impedance converter.
4. A speaker impedance characteristic measuring apparatus according to claim 1, wherein the drive gain circuit includes an operational amplifier U3A and an operational amplifier U4;
the resistor R4 and the resistor R11 are connected in series and divided and then connected to the non-inverting input end of the operational amplifier U4; the inverting input end of the operational amplifier U4 is connected to the output end of the operational amplifier U4; the other end of the resistor R4 is connected with a power supply VCC, and the other end of the resistor R11 is grounded;
the output end of the operational amplifier U4 is connected to the inverting input end of the operational amplifier U3A through a resistor R5;
the VOUT pin of the impedance converter is connected to the non-inverting input end of the operational amplifier U3A through a resistor R2; a feedback resistor R1 is arranged between the non-inverting input end and the output end of the operational amplifier U3A;
a feedback resistor R6 and a sampling resistor R3 are arranged between the inverting input end and the output end of the operational amplifier U3A; one end of the feedback resistor R6 is connected with the inverting input end of the operational amplifier U3A, the other end of the feedback resistor R6 is connected with the non-inverting input end of the amplifier U3B, one end of the sampling resistor R3 is connected with the output end of the operational amplifier U3A, and the other end of the sampling resistor R3 is connected with the non-inverting input end of the amplifier U3B; the amplifier U3B is an amplifier where the tested loudspeakers are connected in series.
5. The apparatus according to claim 4, wherein the feedback resistor R1 is connected in parallel with the capacitor C2.
6. The apparatus according to claim 4, wherein the operational amplifier U3A adopts an LMV321; the operational amplifier U4 adopts AD8532; the amplifier U3B employs AD8532.
7. The device for measuring impedance characteristics of loudspeaker according to claim 4, wherein the measured loudspeaker is connected in series with the feedback loop of the amplifier U3B, and the resistors R12 and R13 are connected in series and divided and then connected to the inverting input terminal of the amplifier U3B; the output end of the amplifier U3B is connected to the analog-to-digital converter of the impedance converter through a resistor R7 and a resistor R8;
the analog-to-digital converter of the impedance converter is used for performing digital processing on the voltage signal output by the amplifier U3B and performing single-point discrete time Fourier transform based on frequency to obtain a real part and an imaginary part of the impedance of the tested loudspeaker.
8. The speaker impedance characteristic measurement method based on the speaker impedance characteristic measurement apparatus according to any one of claims 1 to 7, characterized by comprising:
the high-precision resistor is connected in series with the feedback loop of the amplifier U3B instead of the impedance of the tested loudspeaker;
outputting a pulse width modulation signal through a microcontroller, acquiring measurement results of the real part and the imaginary part of the high-precision resistance impedance, and calculating a gain coefficient and a calibration phase;
taking down the high-precision resistor and connecting the impedance of the tested loudspeaker in series to the feedback loop of the amplifier U3B;
the frequency of the output pulse width modulation signal is controlled by the microcontroller to change, and at each frequency, the frequency is processed in the following way to obtain a measured loudspeaker impedance characteristic change curve within a set frequency range:
the microcontroller outputs a pulse width modulation signal with a certain frequency, and outputs a driving voltage signal under the frequency through the impedance converter;
real and imaginary data of the impedance of the measured speaker at the frequency are acquired by the microcontroller and the measured speaker impedance and phase are calculated.
9. The method of claim 8, wherein the gain factor and calibration phase are calculated as follows:
wherein Gain represents Gain factor, G R REAL and IMAG represent the REAL and imaginary parts of the high-precision resistance, respectively, θ CAL Representing the calibration phase.
10. The method of claim 9, wherein the measured speaker impedance and phase are calculated as follows:
wherein REAL x And IMAG x Representing the real and imaginary parts of the measured speaker impedance.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311236941.0A CN117202072A (en) | 2023-09-25 | 2023-09-25 | Device and method for measuring impedance characteristics of loudspeaker |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311236941.0A CN117202072A (en) | 2023-09-25 | 2023-09-25 | Device and method for measuring impedance characteristics of loudspeaker |
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| CN117202072A true CN117202072A (en) | 2023-12-08 |
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| CN202311236941.0A Pending CN117202072A (en) | 2023-09-25 | 2023-09-25 | Device and method for measuring impedance characteristics of loudspeaker |
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- 2023-09-25 CN CN202311236941.0A patent/CN117202072A/en active Pending
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