CN110022522B - System and method for measuring resonant frequency of loudspeaker vibrating component excited by vibration exciter - Google Patents
System and method for measuring resonant frequency of loudspeaker vibrating component excited by vibration exciter Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R29/00—Monitoring arrangements; Testing arrangements
- H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
Abstract
The invention provides a system and a method for measuring the resonance frequency of a loudspeaker vibrating component excited by a vibration exciter. The measuring system provided by the invention comprises a signal acquisition and processing system, a power amplifier, a measuring bracket, a vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor. The invention is used for measuring the resonant frequency f of a loudspeaker vibrating component 0 . The tested loudspeaker vibrating part is clamped by a clamp, the clamp is fixed on the vibration exciter, and the acceleration sensor is arranged on the clamp; the laser displacement sensor is fixed on the measuring bracket. The signal acquisition processing system generates a voltage signal to drive the vibration exciter, and acquires, analyzes, processes, stores and displays output signals of the laser displacement sensor and the acceleration sensor. The invention can accurately measure the acceleration of the actual vibration of the outer ring fixed part of the vibration part to be measured, and can ensure that the vibration part to be measured clamped by the clamp vibrates stably up and down in the measuring frequency range, thereby accurately measuring the frequency response curve of the vibration displacement of the vibration part to be measured; and then the resonant frequency of the measured vibration component is calculated through the measured frequency response curve of the measured vibration component.
Description
Technical Field
The invention belongs to the field of electroacoustic technology application, and relates to a system and a method for measuring the resonant frequency of a loudspeaker vibrating component excited by a vibration exciter. The invention can measure the resonance frequency of the loudspeaker vibrating component (including cone, vibrating diaphragm, centering support piece, etc.), and can be widely applied to the quality inspection (control), the design and research of the loudspeaker vibrating component.
Background
Brief introduction of the vibrating parts of the speaker:
the loudspeaker is an electric-force-acoustic coupling system and mainly comprises a magnetic circuit system, a vibration system and a support auxiliary system.
The speaker vibration part mainly includes: cone, centring disk and diaphragm (shown in figures 19, 20, 21 respectively). These three types of vibrating components generally include three parts: 1. an outer ring fixing portion (111) for being adhered to the tub frame at the time of installation; 2. an elastically deformable portion (112) that can be elastically deformed relatively linearly with a large amplitude; 3. the central rigid portion (113) is the main acoustic radiation area (the centring disk itself has no central portion, and is typically held centrally by a rigid clamp during measurement, with the clamp being the central portion). If the points of the central rigid portion are approximately considered to be moving synchronously, the loudspeaker vibrating element can be regarded as a spring vibrator system of a single spring (elastically deformable portion) single vibrator (mainly the central rigid portion). The first order resonance frequency of this spring vibrator system is referred to as the resonance frequency of the loudspeaker vibrating member.
The vibration part of the loudspeaker is used as the main part of sound production of the loudspeaker, and the resonance frequency of the vibration part is one of important technical indexes of the vibration part, and the indexes play a critical role in the overall performance of the loudspeaker.
Existing techniques and methods:
earlier methods of measuring the resonant frequency of a loudspeaker vibrating member were mainly indirect measurements. Chinese patent application publication 200710125713.0 discloses a method for obtaining the resonant frequency of a diaphragm (cone) by testing the electrical impedance curve of an excited loudspeaker. The method is characterized in that a measured diaphragm (cone) is fixed right above an excitation loudspeaker, the excitation loudspeaker is driven by a sine sweep frequency signal, the cone of the excitation loudspeaker vibrates and radiates sound waves outwards to enable the measured diaphragm (cone) to vibrate along with the excitation loudspeaker, an air cavity between the measured diaphragm (cone) and the excitation loudspeaker reacts on the excitation loudspeaker, current flowing through the excitation loudspeaker changes, an electrical impedance curve of the excitation loudspeaker is measured, and frequency corresponding to a peak value of the curve is the resonant frequency of the measured diaphragm (cone). However, this method has a limitation that it is suitable for measuring a diaphragm (cone) having a large resonance Q value, a large size, and a moderate mass, and requires that the resonance frequency of the excitation speaker is far smaller than that of the measured diaphragm (cone). Therefore, the versatility and accuracy of this method have a problem.
A relatively widely used method for measuring the resonant frequency of a loudspeaker vibrating member is the direct measurement method using indirect excitation. The method still adopts indirect excitation (the loudspeaker is used for emitting sound, and the vibration of the vibration part to be measured is indirectly excited through sound field transmission), and meanwhile, the vibration condition of the vibration part to be measured is directly measured through technical means such as a laser displacement sensor. Chinese patent application publication CN201310157000.8 discloses a method for directly reading displacement signals of a loudspeaker diaphragm (cone) by a laser displacement sensor and determining the resonant frequency of the measured diaphragm (cone) according to a vibration displacement graph of the loudspeaker diaphragm (cone) when vibrating at different frequencies. The method implies the premise that exciting forces received by the central part of the vibration part at each frequency point are the same, but the actual stress situation of the central part of the measured part cannot be accurately measured when indirect excitation is adopted, and the stress situation is influenced by a plurality of factors such as the shape of the measured vibration part, the shape of a clamp, the performance of a loudspeaker, the environment of a sound field and the like, and is difficult to control. The instability of the excitation force is reflected in the vibration displacement curve, causing fluctuation of the curve, thereby affecting the accuracy of the resonance frequency measurement result.
In order to solve the problems of the measuring method, the invention provides a system and a method for measuring the resonance frequency of a vibrating component (comprising a cone, a vibrating diaphragm, a centering support sheet and the like) of a loudspeaker, wherein a vibration exciter is adopted to directly excite the outer ring fixed part of the vibrating component to vibrate, an acceleration sensor is used for measuring the vibration acceleration (comprising amplitude and phase) of the outer ring fixed part of the vibrating component to be measured, and a laser displacement sensor is used for measuring the vibration displacement of the central rigid part of the vibrating component to be measured, so that the frequency response curve of the vibration displacement of the vibrating component to be measured can be accurately obtained; and then the resonant frequency of the measured vibration component is calculated through the measured frequency response curve of the measured vibration component.
Disclosure of Invention
The invention provides a system and a method for measuring the resonant frequency of a loudspeaker vibrating component excited by a vibration exciter, which can accurately measure the resonant frequency of the loudspeaker vibrating component (comprising a cone, a vibrating diaphragm, a centering support sheet and the like).
The technical scheme adopted for solving the technical problems is as follows:
the invention provides a loudspeaker vibrating component resonance frequency measurement system excited by a vibration exciter, which comprises a signal acquisition and processing system, a power amplifier, a measurement bracket, a vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein a measured loudspeaker vibrating component is clamped by the clamp, the clamp is arranged on the vibration exciter, the vibration exciter is arranged on the measurement bracket, and the acceleration sensor is arranged on the clamp; the laser displacement sensor is arranged on the measuring bracket, the signal acquisition and processing system is connected with the acceleration sensor and the laser displacement sensor, the signal acquisition and processing system is connected with the vibration exciter through the power amplifier, the signal acquisition and processing system generates a voltage signal with a specified frequency, the vibration exciter is driven after the voltage signal is amplified by the power amplifier, and the vibration exciter drives the measured vibration component clamped by the clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the measured vibration component through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the measured vibration component through the acceleration sensor; the signal acquisition processing system processes and analyzes the signals to obtain the resonant frequency of the vibration component of the tested loudspeaker.
The measuring bracket is a cube frame, the laser displacement sensor is fixed on the upper part of the measuring bracket, and the measuring laser beam emitted by the laser displacement sensor points to a certain fixed point of the vibrating component of the measured loudspeaker. The clamp consists of a pair of upper and lower clamping plates, and the upper and lower clamping plates tightly clamp the outer edge of the vibration part to be tested together; the clamp is fixed on the vibration exciter; the vibration exciter is arranged at the lower part of the measuring bracket, at least three acceleration sensors are arranged near the contact position of the clamp and the measured vibration part, and all the acceleration sensors are not positioned on the same straight line. The acceleration sensors are distributed in a triangular mode on the outer edge of the clamp and are respectively and firmly connected with the three vibration exciters, the three vibration exciters are horizontally arranged on the horizontal plane in the vibration exciter frame, and the vibration exciting direction of each vibration exciter is vertically upward. The vibration part to be measured comprises a loudspeaker cone, a vibrating diaphragm and a centering support piece.
The method for measuring the resonant frequency of the loudspeaker vibrating component excited by the vibration exciter comprises the following steps: mounting the tested loudspeaker vibrating component on a fixture; the signal acquisition and processing system generates a voltage signal with a designated frequency, and excites a vibration exciter to work after the voltage signal is amplified by a power amplifier, and the vibration exciter drives a tested vibration part clamped by a clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the vibration part to be measured through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the vibration part to be measured through an acceleration sensor; the voltage signals of all frequencies in the appointed frequency range are used for carrying out the measurement and calculating to obtain the frequency response curve of the vibration part to be measured; and calculating the resonant frequency according to the frequency response curve.
The frequency response curve of the vibration of the measured vibration part is a frequency response curve which takes the vibration signal of the outer ring fixed part of the measured vibration part as input and the vibration signal of the central rigid part of the measured vibration part as output, and the vibration signal is an acceleration signal, a speed signal or a displacement signal.
The method for obtaining the resonance frequency according to the frequency response curve comprises two steps: according to the measured frequency response curve of the vibration of the measured vibration component, calculating to obtain the frequency corresponding to the curve peak value, wherein the frequency is approximately regarded as the resonance frequency of the measured vibration component; the other method is to fit the natural angular frequency and attenuation factor of the vibration part to be measured according to the frequency response curve, and calculate the resonant frequency according to the formula.
The method for measuring the frequency response curve of the vibration of the measured vibration component comprises the following steps:
firstly, setting a measured frequency range and a frequency interval, then measuring the ratio of a vibration signal (output) of a central rigid part of a measured vibration part corresponding to each frequency point to a vibration signal (input) of an outer ring fixed part of the measured vibration part from low frequency to high frequency, namely forming a frequency response curve of vibration of the measured vibration part, and before measuring the vibration signal of each frequency point, self-adaptively adjusting respective input voltages of three vibration exciters to enable the measured vibration part clamped by a clamp to vibrate stably.
The parameter setting method for enabling the measured vibration component clamped by the clamp to vibrate stably comprises the following steps: 1. outputting a mathematical relation between the vibration acceleration vector and the input voltage vector and solving a linear equation corresponding to the mathematical relation; 2. the input voltage is adaptively adjusted. The specific description is as follows:
1. mathematical relationship of output vibration acceleration vector and input voltage vector and solving linear equation corresponding to mathematical relationship
Three vibration exciters are respectively marked as e, f and g, and three acceleration sensors are respectively marked as h, i and j. Setting input voltage for three vibration exciters, wherein the three vibration exciters drive a tested vibration part clamped by a clamp to vibrate up and down; three acceleration sensors fixed on the clamp respectively measure vibration acceleration signals at 3 positions of the outer ring fixed part of the vibration component to be measured. When the three vibration exciters perform the nth vibration, the input voltages of the three vibration exciters are respectively recorded asAnd->The vibration acceleration of the outer ring fixed part of the measured vibration part acquired by the three acceleration sensors is respectively recorded as +.>And->Input voltage vectors of three vibration exciters>Expressed as:
and vibration acceleration vectors output by three acceleration sensorsCan be expressed as:
can be regarded as an output vectorAnd input vector +.>The following linear relation is provided:
in the above, M n As a coefficient matrix, it can be expressed as:
wherein,(p=e, f, g, q=h, i, j) represents the coefficient component of the exciter p at the position of the acceleration sensor q at the nth vibration.
Because of coefficient matrix M n The number of unknowns is 9, so that the coefficient matrix M can be obtained by solving the input and output data obtained by continuously vibrating the front surfaces of three vibration exciters for 3 times n 。
From the inputs and outputs at the n-2 th, n-1 th and n-th times of these 3 rd vibrations, the following linear equations can be listed:
the above equation can also be written as U n M n ＝A n Wherein U is n And A n The input matrix and the output matrix of the linear equation are respectively obtained by solving the linear equation:
M n ＝U n -1 ·A n
where n > =3.
2. Adaptively adjusting input voltage
Initial input voltage vectors of the first 3 times of vibration of the three vibration exciters are respectively set asAnd->And setting the vibration acceleration expected value of the outer ring fixed part of the vibration part to be measured after the 3 rd vibration +.>The allowable acceleration error value is e 0 . The specific steps for adaptively adjusting the input voltage are as follows:
1) According to preset initial input voltage vectors of three vibration excitersAnd->Exciting the vibration exciter to work, wherein the 1st vibration acceleration vector, the 2 nd vibration acceleration vector and the 3 rd vibration acceleration vector of the outer ring fixed part of the measured vibration part acquired by the three acceleration sensors are respectively +.>And->
2) After the nth (n > =3) vibration is performed by the three exciters, their input voltage vectors at the next (i.e., n+1th) vibration can be calculated according to the following formula:
wherein the coefficient matrix M n It is needed to obtain the output-input linear equation by solving the last 3 times of vibration, namely M n ＝U n -1 ·A n 。
3) Will beIn the vibration sensor, three vibration exciters are excited to work by the input voltage signals, and vibration acceleration vectors actually output by the three acceleration sensors are +.>Then->And the desired value->The difference e between them is:
if the difference is smaller than the preset acceleration error value e 0 (including amplitude and phase), the adjustment ends; otherwise, go to step 2), continue the next adjustment.
The method for specifically measuring the frequency response curve of the vibration part to be measured comprises the following steps:
firstly, setting amplitude, phase, frequency range and frequency interval of input voltage, and setting expected value of vibration acceleration of outer ring fixed part of tested vibration component and error value of allowable acceleration; then, from low frequency to high frequency, the ratio of the vibration signal of the central rigid part of the measured vibration part corresponding to each frequency point to the vibration signal of the outer ring fixed part of the measured vibration part is measured, and a frequency response curve of the vibration of the measured vibration part is formed. The flow chart of the method is shown in fig. 11.
The measurement process of the single frequency point is as follows: assuming that the frequency of the input voltage signal is f, the measuring process of the output-input ratio of the frequency point is as follows: firstly, adaptively adjusting the input voltage of a vibration exciter to enable a tested vibration part clamped by a clamp to vibrate stably; the vibration acceleration of the outer ring fixed part of the measured vibration part acquired by the acceleration sensor is recorded as a 1 The vibration displacement of the central rigid part of the measured vibration component acquired by the laser displacement sensor is recorded as x; relation a= - (2 pi f) using acceleration and displacement 2 X or the relation between velocity and displacement v=j2pi f.x, the signal acquisition and processing system can convert the vibration displacement x into the acceleration a or velocity v, and can also convert the vibration acceleration a 1 Conversion to speed v 1 Or displacement x 1 Thus, when a voltage signal with frequency f is input, the vibration to be measuredThe calculation formula of the ratio h (f) of the vibration signal (output) of the part center rigid part to the vibration signal (input) of the outer ring fixed part of the tested vibration part is as follows:
the values of the displacement, the velocity and the acceleration are all complex.
The method for calculating the resonant frequency according to the frequency response curve comprises the following steps:
the method for calculating the resonant frequency of the measured vibration component comprises two methods: according to the measured frequency response curve of the vibration of the measured vibration component, calculating to obtain the frequency corresponding to the curve peak value, wherein the frequency can be approximately regarded as the resonance frequency of the measured vibration component; the other method is to fit the natural angular frequency and attenuation factor of the vibration part to be measured according to the frequency response curve, and calculate the resonant frequency according to the formula.
The method 2 is relatively complex, and is specifically described in terms of theoretical formula derivation, fitting process and calculation.
1. Theoretical formula derivation
The invention provides a system for measuring the resonance frequency of a loudspeaker vibrating component excited by a vibration exciter, which is characterized in that the vibration exciter excites a measured vibrating component clamped by a clamp to vibrate. The mass of the vibration part to be measured is m, and the natural angular frequency is omega 0 The damping factor is gamma, and the vibration displacement of the central rigid part of the vibration part to be measured is x=Xe jωt Wherein X is amplitude, omega is angular frequency, and the vibration acceleration of the central rigid part of the vibration part to be measured is known to beSpeed is +.>The same can be provided with the outer ring fixing part of the vibration part to be measuredVibration displacement of x 1 ＝X 1 e jωt Vibration acceleration of->Speed is +.>The theoretical calculation formula of the frequency response of the vibration component to be measured can be expressed as
2. Fitting procedure
Inputting the output/input ratio data H (f) of all frequency points in the set measurement frequency range obtained by actual measurement, converting the corresponding relation between the ratio H and the frequency f into the corresponding relation between the ratio H and the angular frequency omega according to the formula omega=2pi f, selecting a nonlinear parameter fitting method, fitting with the curve of the theoretical formula H (omega) according to the curve of the frequency response H (omega) obtained by actual measurement, and obtaining the natural angular frequency omega of the measured vibration part 0 And an attenuation factor gamma.
3. Calculation of
The natural angular frequency omega obtained by fitting 0 And the value of the attenuation factor gamma is substituted into the expression of the resonance frequencyThe resonant frequency of the vibration component to be measured can be calculated.
Drawings
FIG. 1 is a block schematic diagram of a measurement system.
Fig. 2 is a schematic front view of the measuring device.
Fig. 3 is a schematic left-hand view of the measuring device.
Fig. 4 is a schematic right-hand view of the measuring device.
Fig. 5 is a schematic rear view of the measuring device.
Fig. 6 is a schematic top view of the measuring device.
Fig. 7 is a schematic diagram of a main body of the measuring apparatus.
FIG. 8 is a schematic view of the vibration exciter in a fixed position.
FIG. 9 is a schematic cross-sectional view of a vibration member and a jig to be measured.
Fig. 10 is a schematic diagram showing the structure of the vibration member to be measured and the jig detached.
FIG. 11 is a flow chart of a method of measuring vibration acceleration of a vibration component under test and a clamp vibration acceleration frequency response curve.
Fig. 12 is a graph of the frequency response of the measured vibration acceleration of the vibration member and the vibration acceleration of the jig.
FIG. 13 is a schematic diagram of a curve fitting tool interface.
FIG. 14 is a schematic diagram of a curve fitting tool fitting mode selection.
FIG. 15 is a schematic diagram of a curve fitting tool fitting parameter selection.
FIG. 16 is a graphical representation of the results of curve fitting tool parameter fitting.
FIG. 17 is a graph showing a comparison of a fitted curve and an actual measured curve of the curve fitting tool.
Fig. 18 is a schematic diagram of the results of parameter fitting and resonance frequency calculation.
Fig. 19 is a schematic view of the cone structure.
Fig. 20 is a schematic structural view of the centering support.
FIG. 21 is a schematic diagram of a diaphragm structure.
Detailed Description
The invention will be further described with reference to the drawings and the specific examples.
As shown in the figure, the system for measuring the resonance frequency of the loudspeaker vibrating component excited by the vibration exciter comprises a signal acquisition and processing system, a power amplifier, a measuring bracket, a vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein the measured loudspeaker vibrating component is clamped by the clamp, the clamp is arranged on the vibration exciter, the vibration exciter is arranged on the measuring bracket, and the acceleration sensor is arranged on the clamp; the laser displacement sensor is arranged on the measuring bracket, the signal acquisition and processing system is connected with the acceleration sensor and the laser displacement sensor, the signal acquisition and processing system is connected with the vibration exciter through the power amplifier, the signal acquisition and processing system generates a voltage signal with a specified frequency, the vibration exciter is driven after the voltage signal is amplified by the power amplifier, and the vibration exciter drives the measured vibration component clamped by the clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the measured vibration component through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the measured vibration component through the acceleration sensor; the signal acquisition processing system processes and analyzes the signals to obtain the resonant frequency of the vibration component of the tested loudspeaker.
The measuring bracket is a cube frame, the laser displacement sensor is fixed on the upper part of the measuring bracket, and the measuring laser beam emitted by the laser displacement sensor points to a certain fixed point of the vibrating component of the measured loudspeaker. The clamp consists of a pair of upper and lower clamping plates, and the upper and lower clamping plates tightly clamp the outer edge of the vibration part to be tested together; the clamp is fixed on the vibration exciter; the vibration exciter is arranged at the lower part of the measuring bracket, at least three acceleration sensors are arranged near the contact position of the clamp and the measured vibration part, and all the acceleration sensors are not positioned on the same straight line. The acceleration sensors are distributed in a triangular mode on the outer edge of the clamp and are respectively and firmly connected with the three vibration exciters, the three vibration exciters are horizontally arranged on the horizontal plane in the vibration exciter frame, and the vibration exciting direction of each vibration exciter is vertically upward. The vibration part to be measured comprises a loudspeaker cone, a vibrating diaphragm and a centering support piece.
The method for measuring the resonant frequency of the loudspeaker vibrating component excited by the vibration exciter comprises the following steps: mounting the tested loudspeaker vibrating component on a fixture; the signal acquisition and processing system generates a voltage signal with a designated frequency, and excites a vibration exciter to work after the voltage signal is amplified by a power amplifier, and the vibration exciter drives a tested vibration part clamped by a clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the vibration part to be measured through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the vibration part to be measured through an acceleration sensor; the voltage signals of all frequencies in the appointed frequency range are used for carrying out the measurement and calculating to obtain the frequency response curve of the vibration part to be measured; and calculating the resonant frequency according to the frequency response curve.
The frequency response curve of the vibration of the measured vibration part is a frequency response curve which takes the vibration signal of the outer ring fixed part of the measured vibration part as input and the vibration signal of the central rigid part of the measured vibration part as output, and the vibration signal is an acceleration signal, a speed signal or a displacement signal.
The method for obtaining the resonance frequency according to the frequency response curve comprises two steps: according to the measured frequency response curve of the vibration of the measured vibration component, calculating to obtain the frequency corresponding to the curve peak value, wherein the frequency is approximately regarded as the resonance frequency of the measured vibration component; the other method is to fit the natural angular frequency and attenuation factor of the vibration part to be measured according to the frequency response curve, and calculate the resonant frequency according to the formula.
The following detailed description will now follow in accordance with the accompanying drawings: as shown in fig. 1 to 8, the system for measuring the resonance frequency of the loudspeaker vibrating component of the invention comprises a signal acquisition and processing system (1), a power amplifier (2), a measuring bracket (3), a vibration exciter (4), a clamp (5), an acceleration sensor (6) and a laser displacement sensor (7). The vibration exciter (4) is fixed at the bottom end of the measuring bracket (3), and the laser displacement sensor (7) is fixed at the top end of the measuring bracket (3); the tested loudspeaker vibrating component (8) is clamped by a clamp (5), the clamp (5) is arranged above the vibration exciter (4), and an acceleration sensor (6) is also arranged above the clamp (5).
The measuring bracket (3) is a cubic frame, the bottom end of the measuring bracket is provided with a group of cross beams (9) for placing and fixing the vibration exciter (4), the top end of the measuring bracket is provided with a cross beam (11) for installing a linear guide rail (10), and the linear guide rail (10) is used for fixing the laser displacement sensor (7); damping blocks (12) are respectively arranged between the square framework at the bottom end and the four vertical beams. The three vibration exciters (4) are horizontally arranged and fixed on the cross beam (9) at the bottom end, the horizontal position of the cross beam (9) can be adjusted back and forth, and the horizontal position of the three vibration exciters (4) can be adjusted left and right, so that the vibration exciters can move back and forth and left and right to fix clamps with different sizes. The linear guide rail (10) is arranged on the cross beam (11) at the top end, and the laser displacement sensor (7) is fixed on the linear guide rail (10); the horizontal position of the cross beam (11) at the top end can be adjusted left and right, the horizontal position of the linear guide rail (10) can be adjusted back and forth, and the laser displacement sensor (7) can move up and down through the linear guide rail (10), so that the laser displacement sensor (7) fixed on the linear guide rail (10) can move up and down, back and forth and left and right, and the focusing requirements of different distances and different positions are met. The focusing point of the laser should be adjusted to the position where the measured vibration part is gentle as much as possible.
As shown in fig. 9 and 10, the clamp (5) of the present invention is composed of a pair of upper and lower clamping plates, the upper clamping plate (13) and the lower clamping plate (14) together tightly clamp the outer edge of the vibration member (9) to be measured; the three equal division points of the clamp (5) are respectively provided with a through hole, three set screws respectively penetrate through the three through holes of the clamp (5) from top to bottom and are fixed on the axes of the three vibration exciters (4), and three acceleration sensors (6) are respectively arranged at the tops of the three set screws.
The signal acquisition and processing system (1) outputs a voltage signal, the voltage signal is amplified by the power amplifier (2) and then drives the vibration exciter (4), and the vibration exciter (4) drives the tested vibration component (8) clamped by the clamp (5) to vibrate; the signal acquisition processing system (1) acquires vibration displacement signals of the tested vibration component (8) through the laser displacement sensor (7), and acquires vibration acceleration signals of the clamp (5) through the acceleration sensor (6); the signal acquisition processing system (1) processes, analyzes and stores the signals and displays the processing results.
Based on the system for measuring the resonance frequency of the loudspeaker vibrating component, the method for measuring the resonance frequency of the loudspeaker vibrating component is divided into two 2 steps: step one: measuring to obtain a frequency response curve of the vibration part to be measured; step two: and calculating the resonant frequency according to the frequency response curve. These two steps will be specifically described next.
Step one: measuring frequency response curve of vibration component to be measured
Firstly, setting a measured frequency range and a frequency interval, and then measuring the ratio of a vibration signal (output) of a central rigid part of the measured vibration component corresponding to each frequency point to a vibration signal (input) of an outer ring fixed part of the measured vibration component from low frequency to high frequency to form a frequency response curve of the vibration of the measured vibration component. Before measuring the vibration signal of each frequency point, the input voltage of each of the three vibration exciters needs to be adaptively adjusted, so that the tested vibration component clamped by the clamp can vibrate stably.
The vibration signal can be an acceleration signal, or a speed signal or a displacement signal. In this embodiment, the method for measuring the resonant frequency of the vibration component of the speaker according to the present invention is specifically described by taking the acceleration signal as an example.
The method for enabling the tested vibration component clamped by the clamp to vibrate stably is characterized in that 1, the mathematical relation between the output vibration acceleration vector and the input voltage vector and the corresponding linear equation are solved; 2. the two aspects of adaptively adjusting the input voltage are described in detail.
1. Mathematical relationship of output vibration acceleration vector and input voltage vector and solving linear equation corresponding to mathematical relationship
Three vibration exciters are respectively marked as e, f and g, and three acceleration sensors are respectively marked as h, i and j. Setting input voltage for three vibration exciters, wherein the three vibration exciters drive a tested vibration part clamped by a clamp to vibrate up and down; three acceleration sensors fixed on the clamp respectively measure vibration acceleration signals at 3 positions of the outer ring fixed part of the vibration component to be measured. When the three vibration exciters perform the nth vibration, the input voltages of the three vibration exciters are respectively recorded asAnd->The vibration acceleration of the outer ring fixed part of the measured vibration part acquired by the three acceleration sensors is respectively recorded as +.>And->Input voltage vectors of three vibration exciters>Expressed as:
and vibration acceleration vectors output by three acceleration sensorsExpressed as:
can be regarded as an output vectorAnd input vector +.>The following linear relation is provided:
in the above, M n As a coefficient matrix, it can be expressed as:
wherein,(p=e, f, g, q=h, i, j) represents the coefficient component of the exciter p at the position of the acceleration sensor q at the nth vibration.
Because of coefficient matrix M n The number of unknowns is 9, so that the coefficient matrix M can be obtained by solving the input and output data obtained by continuously vibrating the front surfaces of three vibration exciters for 3 times n 。
From the inputs and outputs at the n-2 th, n-1 th and n-th times of these 3 rd vibrations, the following linear equations can be listed:
the above equation can also be written as U n M n ＝A n Wherein U is n And A n The input matrix and the output matrix of the linear equation are respectively obtained by solving the linear equation:
M n ＝U n -1 ·A n
where n > =3.
2. Adaptively adjusting input voltage
Initial input voltage vectors of the first 3 times of vibration of the three vibration exciters are respectively set asAnd->And setting the vibration acceleration expected value of the clamp after the 3 rd vibration +.>The allowable acceleration error value is e 0 . The specific steps for adaptively adjusting the input voltage are as follows:
1) According to preset initial input voltage vectors of three vibration excitersAnd->Exciting the vibration exciter to work, wherein the 1st vibration acceleration vector, the 2 nd vibration acceleration vector and the 3 rd vibration acceleration vector of the clamp acquired by the three acceleration sensors are respectively +.>And->
2) After the nth (n > =3) vibration is performed by the three exciters, their input voltage vectors at the next (i.e., n+1th) vibration can be calculated according to the following formula:
wherein the coefficient matrix M n It is needed to obtain the output-input linear equation by solving the last 3 times of vibration, namely M n ＝U n -1 ·A n 。
3) Will beIn the vibration sensor, three vibration exciters are excited to work by the input voltage signals, and vibration acceleration vectors actually output by the three acceleration sensors are +.>Then->And the desired value->The difference e between them is:
if the difference is smaller than the preset acceleration error value e 0 (including amplitude and phase), the adjustment ends; otherwise, go to step 2), continue the next adjustment.
The specific method for measuring the frequency response curve of the vibration component to be measured comprises the following steps:
firstly, setting amplitude, phase, frequency range and frequency interval of input voltage, and setting expected value of vibration acceleration of outer ring fixed part of tested vibration component and error value of allowable acceleration; then, from low frequency to high frequency, the ratio of the vibration acceleration signal of the central rigid part of the measured vibration part corresponding to each frequency point to the vibration acceleration signal of the outer ring fixed part of the measured vibration part is measured, and a frequency response curve of the vibration of the measured vibration part is formed. The flow chart of the method is shown in fig. 11.
The measurement process of the single frequency point is as follows: assuming that the frequency of the input voltage signal is f, the measuring process of the output-input ratio of the frequency point is as follows: firstly, adaptively adjusting the input voltage of a vibration exciter to enable a tested vibration part clamped by a clamp to vibrate stably; the vibration acceleration of the outer ring fixed part of the measured vibration part acquired by the acceleration sensor is recorded as a 1 The vibration displacement of the central rigid part of the measured vibration component acquired by the laser displacement sensor is recorded as x; relation a= - (2 pi f) using acceleration and displacement 2 X, the signal acquisition and processing system can convert the vibration displacement x into the acceleration a, so that when the voltage signal with the frequency f is input, the calculation formula of the ratio h (f) of the vibration acceleration signal (output) of the vibration part to the vibration acceleration signal (input) of the clamp is as follows:
the values of the displacement and the acceleration are complex.
A method of measuring a frequency response curve of vibration of a vibration member of a speaker will now be specifically described by taking a 6.5-inch speaker cone as an example.
Setting the frequency range of input voltage signals of three vibration exciters to 40-100 Hz, the frequency interval to 1Hz, and setting the acceleration expected value to 5e i0 m/s 2 Acceleration error value of 0.05e i1 m/s 2 The method comprises the steps of carrying out a first treatment on the surface of the And after the measured vibration component clamped by the clamp stably vibrates from low frequency to high frequency, measuring the ratio of the vibration acceleration signal (output) of the central rigid part of the measured vibration component to the vibration acceleration signal (input) of the outer ring fixed part of the measured vibration component corresponding to each frequency point, namely a frequency response curve of the vibration of the measured vibration component, as shown in fig. 12.
Step 2: calculating the resonant frequency according to the frequency response curve
The method for calculating the resonant frequency of the measured vibration component comprises two methods: according to the measured frequency response curve of the vibration of the measured vibration component, calculating to obtain the frequency corresponding to the curve peak value, wherein the frequency can be approximately regarded as the resonance frequency of the measured vibration component; the other method is to fit the natural angular frequency and attenuation factor of the vibration part to be measured according to the frequency response curve, and calculate the resonant frequency according to the formula.
The first method will now be described using a 6.5 inch speaker cone as an example.
From the frequency response curve of the vibration of the measured vibration member actually measured shown in fig. 12, it can be calculated that the curve has a maximum value at a frequency of 56Hz, that is, the resonance frequency of the measured vibration member is approximately 56Hz.
The second method 2 is relatively complex, and the method will be specifically described in terms of three aspects, namely, theoretical formula derivation, fitting process and calculation.
1. Theoretical formula derivation
The invention provides a system for measuring the resonance frequency of a loudspeaker vibrating component excited by a vibration exciter, which is characterized in that the vibration exciter excites a measured vibrating component clamped by a clamp to vibrate. The mass of the vibration part to be measured is m, and the natural angular frequency is omega 0 The damping factor is gamma, and the vibration displacement of the central rigid part of the vibration part to be measured is x=Xe jωt Wherein X is amplitude, omega is angular frequency, and the vibration acceleration of the central rigid part of the vibration part to be measured is known to beThe vibration displacement of the outer ring fixing part of the vibration part to be measured can be set as x in the same way 1 ＝X 1 e jωt Vibration acceleration of->The theoretical calculation formula of the frequency response of the vibration component to be measured can be expressed as
2. Fitting procedure
Inputting the output/input ratio data H (f) of all frequency points in the set measurement frequency range obtained by actual measurement, converting the corresponding relation between the ratio H and the frequency f into the corresponding relation between the ratio H and the angular frequency omega according to the formula omega=2pi f, selecting a nonlinear parameter fitting method, fitting with the curve of the theoretical formula H (omega) according to the curve of the frequency response H (omega) obtained by actual measurement, and obtaining the natural angular frequency omega of the measured vibration part 0 And an attenuation factor gamma.
3. Calculation of
The natural angular frequency omega obtained by the fitting is obtained 0 And attenuation factor gamma substituted into the expression of resonance frequencyThe resonant frequency of the vibration component to be measured can be calculated.
A second method will now be described using a 6.5 inch speaker cone as an example.
The data analysis processing software used in the fitting process comprises all commercial software which can perform curve fitting, including Matlab, origin, 1st opt and the like. The Matlab software will now be described in detail. In the actual fitting process, the fitting is performed according to the square of the amplitude of the frequency response.
The square of the frequency response amplitude value obtained by actual measurement is marked as H2 (f), the square of the frequency response theoretical value is marked as H2 (omega), and the calculation formula of the square H2 (f) of the frequency response amplitude value obtained by actual measurement is as follows according to the deduction process in the step two
h2(f)＝h(f) 2
And the square H2 (omega) of the theoretical value of the frequency response is calculated as
Let a=ω 0 2 ，B＝4γ 2 The above can be simplified into
The specific fitting process is as follows: opening Matlab software, importing a frequency response h (f) of a ratio of a vibration acceleration signal of a measured vibration component and a vibration acceleration signal of a clamp, converting a corresponding relation of the ratio h and the frequency f into a corresponding relation of the ratio h and an angular frequency omega according to a formula omega=2pi f, drawing a curve of the frequency response h (omega) obtained by actual measurement, and calculating a square value h2 (omega) of the frequency response; inputting cftool and returning in a software command window, displaying a fitting interface (shown in fig. 13), selecting a Custom Equation in a right fitting mode and inputting a theoretical formula of square H2 (omega) of a theoretical value of frequency response (shown in fig. 14), filling in a name H2 of a fitting curve in a parameter column Fit name on the left, sequentially selecting values of X data, ydata and weights as w, H2 and H2 (shown in fig. 15), wherein the left side below the interface is a fitting result (shown in fig. 16), and the right side is a comparison graph of an actual measurement curve and a fitting curve (shown in fig. 17).
Calculating the natural angular frequency omega according to the values of B and a obtained by fitting 0 And an attenuation factor gamma, the calculation formula is as follows:
the natural angular frequency omega obtained by the fitting is obtained 0 And attenuation factor gamma substituted into the expression of resonance frequencyThe resonant frequency of the vibration component to be measured can be calculated.
The results of the parameter fitting and the resonance frequency calculations for the 6.5 inch cone are shown in fig. 18.
Finally, it should be noted that: the above embodiments are only for illustrating the present invention and not for limiting the technical solutions described by the present invention; thus, although the present invention has been described in detail with reference to the above embodiments, it will be understood by those skilled in the art that the present invention may be modified or equivalent; all technical solutions and modifications thereof that do not depart from the spirit and scope of the invention are intended to be covered by the scope of the appended claims.
Claims (8)
1. The system is characterized by comprising a signal acquisition and processing system, a power amplifier, a measuring bracket, a vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein the measured loudspeaker vibrating part is clamped by the clamp, the clamp is arranged on the vibration exciter, the vibration exciter is arranged on the measuring bracket, and the acceleration sensor is arranged on the clamp; the laser displacement sensor is arranged on the measuring bracket, the signal acquisition and processing system is connected with the acceleration sensor and the laser displacement sensor, the signal acquisition and processing system is connected with the vibration exciter through the power amplifier, the signal acquisition and processing system generates a voltage signal with a specified frequency, the vibration exciter is driven after the voltage signal is amplified by the power amplifier, and the vibration exciter drives the measured vibration component clamped by the clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the measured vibration component through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the measured vibration component through the acceleration sensor; the signal acquisition processing system processes and analyzes the signals to obtain the resonant frequency of the vibration component of the tested loudspeaker.
2. The system for measuring the resonant frequency of a vibrating member for a loudspeaker according to claim 1, wherein the measuring bracket is a cubic frame, the laser displacement sensor is fixed to the upper portion of the measuring bracket, and the measuring laser beam emitted from the laser displacement sensor is directed to a fixed point of the vibrating member for a loudspeaker to be measured.
3. The system for measuring the resonant frequency of a vibrating member for a speaker according to claim 1, wherein the jig is composed of a pair of upper and lower clamping plates which clamp the outer edge of the vibrating member to be measured together; the clamp is fixed on the vibration exciter; the vibration exciter is arranged at the lower part of the measuring bracket, at least three acceleration sensors are arranged near the contact position of the clamp and the measured vibration part, and all the acceleration sensors are not positioned on the same straight line.
4. The loudspeaker vibrating member resonant frequency measurement system of claim 1, wherein the measured vibrating member comprises a loudspeaker cone, a diaphragm, and a centering support.
5. A method for measuring the resonance frequency of a loudspeaker vibrating component excited by a vibration exciter is characterized by comprising the following steps: mounting the tested loudspeaker vibrating component on a fixture; the signal acquisition and processing system generates a voltage signal with a designated frequency, and excites a vibration exciter to work after the voltage signal is amplified by a power amplifier, and the vibration exciter drives a tested vibration part clamped by a clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the vibration part to be measured through a laser displacement sensor, and acquires a vibration acceleration signal of an outer ring fixed part of the vibration part to be measured through an acceleration sensor; the voltage signals of all frequencies in the appointed frequency range are used for carrying out the measurement and calculating to obtain the frequency response curve of the vibration part to be measured; and calculating the resonant frequency according to the frequency response curve.
6. The method for measuring the resonance frequency of the vibration component of the loudspeaker excited by the vibration exciter according to claim 5, wherein the method for measuring the frequency response curve of the vibration component to be measured is as follows: firstly, setting a measured frequency range and a frequency interval, then measuring the ratio of a vibration signal of a central rigid part of a measured vibration component to a vibration signal of an outer ring fixed part of the measured vibration component corresponding to each frequency point from low frequency to high frequency, namely forming a frequency response curve of vibration of the measured vibration component, and before measuring the vibration signal of each frequency point, adaptively adjusting respective input voltages of three vibration exciters to enable the measured vibration component clamped by a clamp to vibrate stably.
7. The method for measuring the resonant frequency of a vibrating member for a speaker excited by a vibration exciter according to claim 5, wherein the frequency response curve of the vibration of the vibrating member to be measured is a frequency response curve in which a vibration signal of a fixed portion of an outer ring of the vibrating member to be measured is input and a vibration signal of a rigid portion of a center of the vibrating member to be measured is output, and the vibration signal is an acceleration signal, a velocity signal or a displacement signal.
8. The method for measuring the resonant frequency of a vibrating member of a speaker excited by a vibration exciter according to claim 5, wherein the method for obtaining the resonant frequency from the frequency response curve comprises two steps: according to the measured frequency response curve of the vibration of the measured vibration component, calculating to obtain the frequency corresponding to the curve peak value, wherein the frequency is approximately regarded as the resonance frequency of the measured vibration component; the other method is to fit the natural angular frequency and attenuation factor of the vibration part to be measured according to the frequency response curve, and calculate the resonant frequency according to the formula.
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