CN110022522A - The loudspeaker vibration component resonant frequency measuring system and measurement method motivated using vibration excitor - Google Patents
The loudspeaker vibration component resonant frequency measuring system and measurement method motivated using vibration excitor 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
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- H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
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Abstract
The invention patent proposes a kind of loudspeaker vibration component resonant frequency measuring system and measurement method motivated using vibration excitor.Measuring system proposed by the invention includes signal acquiring processing system, power amplifier, measurement bracket, vibration excitor, fixture, acceleration transducer and laser displacement sensor.The present invention is used to measure the resonant frequency f of loudspeaker vibration component0.Tested loudspeaker vibration component is clamped by fixture, which is fixed on vibration excitor, and acceleration transducer is mounted on fixture；Laser displacement sensor is fixed on measurement bracket.Signal acquiring processing system generates voltage signal driving vibration excitor, is acquired to the output signal of laser displacement sensor and acceleration transducer, analysis processing, saves and show.The present invention can accurately measure the acceleration of tested vibration component outer ring fixed part actual vibration, it can ensure that the tested vibration component clamped by fixture stationary vibration up and down within the scope of measurement frequency, to accurately measure to obtain the frequency response curve of tested vibration component vibration displacement；Again by the measured frequency response curve for obtaining tested vibration component vibration, the resonant frequency of tested vibration component is calculated.
Description
Technical Field
The invention belongs to the field of electroacoustic technology application, and relates to a system and a method for measuring resonance frequency of a loudspeaker vibration component excited by a vibration exciter. The invention can be used for measuring the resonance frequency of the loudspeaker vibration component (including a cone, a vibrating diaphragm, a centering support plate and the like), and can be widely applied to the quality inspection (control) of the loudspeaker vibration component and the design and research and development of the loudspeaker.
Background
Introduction of loudspeaker vibration component:
the loudspeaker is an electro-force-sound coupling system and mainly comprises a magnetic circuit system, a vibration system and a supporting auxiliary system.
The speaker vibration part mainly includes: cone, spider and diaphragm (shown in figures 19, 20 and 21, respectively). These three types of vibration parts generally comprise three parts: 1. an outer ring fixing part (111) for being bonded to the tub frame when mounted; 2. an elastically deformable portion (112) which is relatively linearly elastically deformable with a large amplitude; 3. the central rigid portion (113) is the main acoustic radiation area (the centering disk itself has no central portion, and is generally held centrally by a rigid holder with the holder as the central portion during measurement). If the points of the central rigid portion are approximately considered to move synchronously, the speaker vibrating member 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 vibrating part of the loudspeaker.
The vibration component of the loudspeaker is used as the main component for the sound production of the loudspeaker, and the resonance frequency of the loudspeaker is one of important technical indexes of the loudspeaker, and the indexes play a crucial role in the overall performance of the loudspeaker.
The prior art and methods:
earlier methods of measuring the resonant frequency of a vibrating component of a loudspeaker have been 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 comprises the steps of fixing a tested vibrating diaphragm (cone) right above an exciting loudspeaker, driving the exciting loudspeaker by a sine frequency sweeping signal, exciting the cone of the exciting loudspeaker to vibrate, radiating sound waves outwards to enable the tested vibrating diaphragm (cone) to vibrate, enabling an air cavity between the tested vibrating diaphragm (cone) and the exciting loudspeaker to generate a reaction on the exciting loudspeaker, enabling current flowing through the exciting loudspeaker to change, measuring an electrical impedance curve of the exciting loudspeaker, and determining the frequency corresponding to the peak value of the curve as the resonance frequency of the tested vibrating diaphragm (cone). However, this method has certain limitations, and is suitable for measuring a diaphragm (cone) with a large resonance Q value, a large size, and a moderate mass, and requires that the resonance frequency of the excitation speaker is much smaller than the resonance frequency of the diaphragm (cone) to be measured. Therefore, there is a problem in the versatility and accuracy of the method.
The method for measuring the resonant frequency of the vibration component of the loudspeaker which is widely applied at present adopts a direct measurement method of indirect excitation. The method still adopts indirect excitation (sound is emitted by a loudspeaker, and the vibration of the vibration component to be measured is indirectly excited through sound field transmission), and simultaneously the vibration condition of the vibration component to be measured is directly measured through technical means such as a laser displacement sensor and the like. Chinese patent application publication CN201310157000.8 discloses a method for directly reading the displacement signal of a loudspeaker diaphragm (cone) by a laser displacement sensor, and calculating the resonant frequency of the measured diaphragm (cone) according to the vibration displacement curve chart of the loudspeaker diaphragm (cone) when vibrating at different frequencies. The method has the premise that the excitation force applied to the central part of the vibration component at each frequency point is the same, but the actual stress condition of the central part of the tested piece cannot be accurately measured when indirect excitation is adopted, and the stress condition is influenced by various factors such as the shape of the tested vibration component, the shape of a clamp, the performance of a loudspeaker, the sound field environment and the like and is difficult to control. The instability of the exciting force can be reflected in the vibration displacement curve, so that the fluctuation of the curve is caused, and the accuracy of the measurement result of the resonance frequency is influenced.
In order to solve the problems existing in the measuring method, the invention provides a system and a method for measuring the resonance frequency of a loudspeaker vibration component (comprising a cone, a vibrating diaphragm, a centering support plate and the like). the system and the method adopt a vibration exciter to directly excite the outer ring fixed part of the tested vibration component to vibrate, utilize an acceleration sensor to measure the vibration acceleration (including amplitude and phase) of the outer ring fixed part of the tested vibration component, and utilize a laser displacement sensor to measure the vibration displacement of the central rigid part of the tested vibration component, thereby accurately obtaining the frequency response curve of the vibration displacement of the tested vibration component; and calculating the resonance frequency of the vibration component to be measured according to the measured frequency response curve of the vibration component to be measured.
Disclosure of Invention
The invention provides a system and a method for measuring the resonance frequency of a loudspeaker vibration component excited by a vibration exciter, which can accurately measure the resonance frequency of the loudspeaker vibration component (comprising a cone, a vibrating diaphragm, a centering support plate and the like).
The technical scheme adopted by the invention for solving the technical problem is as follows:
the invention provides a system for measuring the resonant frequency of a loudspeaker vibration part excited by a vibration exciter, which comprises a signal acquisition and processing system, a power amplifier, a measuring bracket, the vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein the loudspeaker vibration part to be measured is clamped by the clamp; the laser displacement sensor is arranged on the measuring support, 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 specified frequency, the voltage signal is amplified through the power amplifier and then drives the vibration exciter, and the vibration exciter drives the tested 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 vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; the signal acquisition and processing system processes and analyzes the signals to obtain the resonance frequency of the vibration component of the tested loudspeaker.
The measuring support is a cubic frame, the laser displacement sensor is fixed on the upper part of the measuring support, and a measuring laser beam emitted by the laser displacement sensor points to a certain fixed point of the vibrating component of the loudspeaker to be measured. The clamp consists of a pair of upper and lower clamping plates which tightly clamp the outer edge of the vibration component to be measured; the clamp is fixed on the vibration exciter; the vibration exciters are 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 component, and the acceleration sensors are not positioned on the same straight line. The three vibration exciters are horizontally arranged on a horizontal plane in the vibration exciter frame, and the vibration exciting directions of the vibration exciters are vertical and upward. The vibration component to be measured comprises a loudspeaker cone, a vibrating diaphragm and a centering support sheet.
The invention relates to a method for measuring the resonance frequency of a loudspeaker vibration component excited by a vibration exciter, which comprises the following steps: mounting a vibration component of the loudspeaker to be tested on a clamp; the signal acquisition and processing system generates a voltage signal with specified frequency, the voltage signal is amplified by the power amplifier and then excites the vibration exciter to work, and the vibration exciter drives the tested vibration part clamped by the clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; performing the measurement by using the voltage signals of all frequencies in the specified frequency range and calculating to obtain a frequency response curve of the vibration component to be measured; and calculating the resonant frequency according to the frequency response curve.
The frequency response curve of the vibration component to be measured is a frequency response curve which takes a vibration signal of an outer ring fixed part of the vibration component to be measured as input and takes a vibration signal of a central rigid part of the vibration component to be measured 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 methods: one method is that according to the measured frequency response curve of the vibration of the tested vibration component, the frequency corresponding to the peak value of the curve is calculated, and the frequency is approximately regarded as the resonance frequency of the tested vibration component; the other method is to obtain the natural angular frequency and the attenuation factor of the tested vibration component by fitting according to a frequency response curve and calculate the resonance frequency according to a formula.
The method for obtaining the frequency response curve of the vibration of the tested vibration component by measurement comprises the following steps:
firstly setting a measured frequency range and a measured frequency interval, 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, and before measuring the vibration signal of each frequency point, adaptively adjusting the respective input voltage of three vibration exciters to enable the measured vibration component clamped by a clamp to stably vibrate.
The parameter setting method for enabling the tested vibration component clamped by the clamp to stably vibrate comprises the following steps: 1. outputting a mathematical relation expression of the vibration acceleration vector and the input voltage vector and solving a linear equation corresponding to the mathematical relation expression; 2. and adaptively adjusting the input voltage. Now, the following is described in detail:
1. mathematical relation formula of output vibration acceleration vector and input voltage vector and linear equation corresponding to the mathematical relation formula
The three exciters are respectively marked as e, f and g, and the three acceleration sensors are respectively marked as h, i and j. Setting input voltage for three vibration exciters, and driving a tested vibration part clamped by the clamp to vibrate up and down by the three vibration exciters; three acceleration sensors fixed on the fixture 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 vibrate for the nth time, the input voltages of the three vibration exciters are recorded asAndand the vibration acceleration of the outer ring fixed part of the vibration component to be measured acquired by the three acceleration sensors is respectively recorded asAndinput voltage vector of three vibration excitersExpressed as:
and the vibration acceleration vectors output by the three acceleration sensorsCan be expressed as:
can be thought of as an output vectorAnd an input vectorThere is a linear relation between:
in the above formula, MnIs a coefficient matrix, which can be expressed as:
wherein,and represents the coefficient component of the vibration exciter p at the position of the acceleration sensor q at the time of the nth vibration.
Because of the coefficient matrix MnThere are 9 unknowns, so that the coefficient matrix M can be obtained by solving according to the input and output data obtained by continuously vibrating for 3 times in front of three vibration excitersn。
From the inputs and outputs at the times of the (n-2) th, (n-1) th and (n-3) th vibrations, the following linear equations can be listed:
the above equation can also be expressed as UnMn＝AnWherein, UnAnd AnSolving the linear equation to obtain an input matrix and an output matrix of the linear equation respectively:
Mn＝Un -1·An
wherein n > is 3.
2. Adaptive adjustment of input voltage
Setting initial input voltage vectors of the first 3 times of vibration of the three vibration exciters to be respectivelyAndand setting the expected value of the vibration acceleration of the fixed part of the outer ring of the vibration component to be measured after the 3 rd vibrationAllowable acceleration error value is e0. The specific steps of adaptively adjusting the input voltage are as follows:
1) according to the preset initial input voltage vector of three vibration excitersAndexciting vibration exciter to work, and the 1st, 2 nd and 3 rd vibration acceleration vectors of the outer ring fixed part of the tested vibration component collected by three acceleration sensors are respectivelyAnd
2) after the three exciters perform the nth (n > -3) vibration, their input voltage vectors at the next (i.e. n + 1) vibration can be calculated according to the following formula:
wherein, the coefficient matrix MnIt needs to be obtained by solving the output-input linear equation of the last 3 vibration, namely Mn＝Un -1·An。
3) Will be provided withThe three vibration exciters work as input voltage signals, and the vibration acceleration vector actually output by the three acceleration sensors isThenAnd expected valueThe difference e between is:
if the difference is smaller than the preset acceleration error e0(including amplitude and phase), the adjustment is over; otherwise, go to step 2) and continue the next adjustment.
The method for measuring the frequency response curve of the vibration of the tested vibration component comprises the following steps:
firstly, setting the amplitude, phase, frequency range and frequency interval of input voltage, and setting the expected value of vibration acceleration and the error value of allowable acceleration of the fixed part of the outer ring of the tested vibration component; then, from low frequency to high frequency, measuring the ratio of the vibration signal of the central rigid part of the vibration component to be measured corresponding to each frequency point to the vibration signal of the fixed part of the outer ring of the vibration component to be measured, namely forming the frequency response curve of the vibration component to be measured. A method flowchart is shown in fig. 11.
The measurement process of a single frequency point is as follows: assuming that the frequency of the input voltage signal is f, the measurement process of the output-input ratio at the frequency point is as follows: firstly, adaptively adjusting the input voltage of a vibration exciter to ensure that a tested vibration part clamped by a clamp performs stable vibration; recording the vibration acceleration of the fixed part of the outer ring of the vibration component to be measured acquired by the acceleration sensor as a1The vibration displacement of the central rigid part of the vibration component to be measured, which is acquired by the laser displacement sensor, is recorded as x; using the relation of acceleration and displacement, a ═ - (2 pi f)2X or the relation v between speed and displacement is j2 pi f x, the signal acquisition and processing system can convert the vibration displacement x into acceleration a or speed v, and can also convert the vibration acceleration a into acceleration a1Conversion to velocity v1Or a displacement x1Thus, when a voltage signal with the frequency f is input, the calculation formula of the ratio h (f) of the vibration signal (output) of the central rigid part of the tested vibration component to the vibration signal (input) of the fixed part of the outer ring of the tested vibration component is as follows:
the values of displacement, velocity and acceleration are 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: one method is that according to the measured frequency response curve of the vibration of the tested vibration component, the frequency corresponding to the peak value of the curve is calculated, and the frequency can be approximately regarded as the resonance frequency of the tested vibration component; the other method is to fit the natural angular frequency and the attenuation factor of the measured vibration component according to the frequency response curve, and calculate the resonance frequency according to a formula.
The method 2 is relatively complex, and the method is specifically introduced from three aspects of theoretical formula derivation, fitting process and calculation.
1. Theoretical formula derivation
The invention provides a system for measuring the resonant frequency of a vibrating component of a loudspeaker excited by a vibration exciter, which is characterized in that the core of the system is a vibrating system for exciting a tested vibrating component clamped by a clamp by the vibration exciter to vibrate. Let the mass of the vibration component to be measured be m and the natural angular frequency be omega0The damping factor is gamma, and the vibration displacement of the central rigid part of the vibration component to be measured is x-XejωtWherein X is amplitude and omega is angular frequency, the vibration acceleration of the central rigid part of the vibration component to be measured is easy to knowAt a speed ofIn the same way, the vibration displacement of the fixed part of the outer ring of the vibration component to be measured can be set as x1＝X1ejωtAcceleration of vibration ofAt a speed ofThe theoretical calculation formula of the frequency response of the vibration of the measured vibration component can be expressed as
2. Fitting procedure
Inputting output and input ratio data H (f) of all frequency points in a set measuring frequency range obtained by actual measurement, converting the corresponding relation of the ratio H and the frequency f into the corresponding relation of the ratio H and the angular frequency omega according to a formula omega of 2 pi f, selecting a nonlinear parameter fitting method, fitting a curve of frequency response H (omega) obtained by actual measurement with a curve of a theoretical formula H (omega), and obtaining the inherent angular frequency omega (omega) of the vibration component to be measured0And an attenuation factor gamma.
3. Computing
The natural angular frequency omega obtained by fitting0Expression of substituting value of attenuation factor gamma into resonance frequencyThe resonance 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 a measuring device.
Fig. 3 is a schematic left view of the measuring device.
Fig. 4 is a schematic right view of the measuring device.
FIG. 5 is a schematic rear view of the measuring apparatus.
FIG. 6 is a schematic top view of a measuring device.
FIG. 7 is a schematic view of the main body of the measuring apparatus.
Fig. 8 is a schematic view of the exciter mounting position.
FIG. 9 is a schematic cross-sectional view of the vibration member and the jig.
FIG. 10 is a schematic view showing a disassembled structure of the vibration part and the clamp.
FIG. 11 is a flow chart of a method for measuring the vibration acceleration frequency response curves of a tested vibration component and a clamp.
FIG. 12 is a graph of frequency response of measured vibration acceleration of the vibrating member and vibration acceleration of the clamp.
FIG. 13 is a schematic view of a curve fitting tool interface.
FIG. 14 is a schematic diagram of the fitting choice of the curve fitting tool.
FIG. 15 is a schematic diagram of curve fitting tool fitting parameter selection.
FIG. 16 is a graph showing the results of a curve fitting tool parameter fit.
FIG. 17 is a schematic diagram comparing a fitted curve of a curve fitting tool and a measured curve.
FIG. 18 is a diagram showing the results of parameter fitting and the results of resonance frequency calculation.
Fig. 19 is a schematic view of the structure of the cone.
FIG. 20 is a schematic view of a centering disk.
Fig. 21 is a schematic view of the diaphragm structure.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
As shown in the figure, the system for measuring the resonant frequency of the vibrating part of the loudspeaker excited by the vibration exciter comprises a signal acquisition and processing system, a power amplifier, a measuring bracket, the vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein the vibrating part of the loudspeaker to be measured 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 support, 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 specified frequency, the voltage signal is amplified through the power amplifier and then drives the vibration exciter, and the vibration exciter drives the tested 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 vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; and the signal acquisition and processing system processes and analyzes the signals to obtain the resonance frequency of the vibration component of the tested loudspeaker.
The measuring support is a cubic frame, the laser displacement sensor is fixed on the upper part of the measuring support, and a measuring laser beam emitted by the laser displacement sensor points to a certain fixed point of the vibrating component of the loudspeaker to be measured. The clamp consists of a pair of upper and lower clamping plates which tightly clamp the outer edge of the vibration component to be measured; the clamp is fixed on the vibration exciter; the vibration exciters are 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 component, and the acceleration sensors are not positioned on the same straight line. The three vibration exciters are horizontally arranged on a horizontal plane in the vibration exciter frame, and the vibration exciting directions of the vibration exciters are vertical and upward. The vibration component to be measured comprises a loudspeaker cone, a vibrating diaphragm and a centering support sheet.
The invention relates to a method for measuring the resonance frequency of a loudspeaker vibration component excited by a vibration exciter, which comprises the following steps: mounting a vibration component of the loudspeaker to be tested on a clamp; the signal acquisition and processing system generates a voltage signal with specified frequency, the voltage signal is amplified by the power amplifier and then excites the vibration exciter to work, and the vibration exciter drives the tested vibration part clamped by the clamp to vibrate; the signal acquisition and processing system acquires a vibration displacement signal of a central rigid part of the vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; performing the measurement by using the voltage signals of all frequencies in the specified frequency range and calculating to obtain a frequency response curve of the vibration component to be measured; and calculating the resonant frequency according to the frequency response curve.
The frequency response curve of the vibration component to be measured is a frequency response curve which takes a vibration signal of an outer ring fixed part of the vibration component to be measured as input and takes a vibration signal of a central rigid part of the vibration component to be measured 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 methods: one method is that according to the measured frequency response curve of the vibration of the tested vibration component, the frequency corresponding to the peak value of the curve is calculated, and the frequency is approximately regarded as the resonance frequency of the tested vibration component; the other method is to obtain the natural angular frequency and the attenuation factor of the tested vibration component by fitting according to a frequency response curve and calculate the resonance frequency according to a formula.
Referring now to the drawings, in which: as shown in fig. 1 to 8, the system for measuring the resonant frequency of the vibrating component of the loudspeaker 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 loudspeaker vibration component (8) to be measured is clamped by a clamp (5), the clamp (5) is installed above the vibration exciter (4), and an acceleration sensor (6) is also installed above the clamp (5).
The measuring support (3) is a cubic frame, a group of cross beams (9) used for placing and fixing the vibration exciter (4) are arranged at the bottom end of the measuring support, a cross beam (11) used for installing a linear guide rail (10) is arranged at the top end of the measuring support, and the linear guide rail (10) is used for fixing the laser displacement sensor (7); and damping blocks (12) are respectively arranged between the square frame 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 cross beam (9) can be adjusted in the front-back direction to achieve the horizontal position, the three vibration exciters (4) can be adjusted in the left-right direction to achieve the horizontal position, and therefore the vibration exciters can be moved in the front-back direction and the left-right direction to fix clamps of different sizes. The linear guide rail (10) is arranged on a 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 beam (11) at the top end can be adjusted left and right, the horizontal position of the linear guide rail (10) can be adjusted front and back, 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 gentle position of the vibration part to be measured 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) tightly clamp the outer edge of the vibration component (9) to be measured; three through holes are respectively arranged at trisection points of the clamp (5), three fastening 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 fastening 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 part (8) clamped by the clamp (5) to vibrate; the signal acquisition and processing system (1) acquires vibration displacement signals of the vibration component (8) to be measured through the laser displacement sensor (7), and acquires vibration acceleration signals of the clamp (5) through the acceleration sensor (6); the signal acquisition and processing system (1) processes, analyzes and stores the signals and displays the processing result.
Based on the system for measuring the resonance frequency of the loudspeaker vibration component, the method for measuring the resonance frequency of the loudspeaker vibration component comprises two 2 steps: the method comprises the following steps: measuring to obtain a frequency response curve of the vibration of the tested vibration component; step two: and calculating the resonant frequency according to the frequency response curve. These two steps will be specifically described next.
The method comprises the following steps: measuring to obtain the frequency response curve of the vibration component to be measured
Firstly setting a measured frequency range and a measured 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 adjusted in a self-adaptive manner, so that the vibration part to be measured 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 vibrating component of the speaker according to the present invention is specifically described by taking an acceleration signal as an example.
The method for enabling the tested vibration component clamped by the clamp to stably vibrate is characterized in that a linear equation corresponding to the mathematical relational expression of the output vibration acceleration vector and the input voltage vector is solved from 1; 2. both aspects of adaptive adjustment of the input voltage are detailed.
1. Mathematical relation formula of output vibration acceleration vector and input voltage vector and linear equation corresponding to the mathematical relation formula
The three exciters are respectively marked as e, f and g, and the three acceleration sensors are respectively marked as h, i and j. Setting input voltage for three vibration exciters, and driving a tested vibration part clamped by the clamp to vibrate up and down by the three vibration exciters; three acceleration sensors fixed on the fixture 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 vibrate for the nth time, the input voltages of the three vibration exciters are recorded asAndand the vibration acceleration of the outer ring fixed part of the vibration component to be measured acquired by the three acceleration sensors is respectively recorded asAndinput voltage vector of three vibration excitersExpressed as:
and the vibration acceleration vectors output by the three acceleration sensorsExpressed as:
can be thought of as an output vectorAnd an input vectorThere is a linear relation between:
in the above formula, MnIs a coefficient matrix, which can be expressed as:
wherein,and represents the coefficient component of the vibration exciter p at the position of the acceleration sensor q at the time of the nth vibration.
Because of the coefficient matrix MnThere are 9 unknowns, so that the coefficient matrix M can be obtained by solving according to the input and output data obtained by continuously vibrating for 3 times in front of three vibration excitersn。
From the inputs and outputs at the times of the (n-2) th, (n-1) th and (n-3) th vibrations, the following linear equations can be listed:
the above equation can also be expressed as UnMn＝AnWherein, UnAnd AnSolving the linear equation to obtain an input matrix and an output matrix of the linear equation respectively:
Mn＝Un -1·An
wherein n > is 3.
2. Adaptive adjustment of input voltage
Setting initial input voltage vectors of the first 3 times of vibration of the three vibration exciters to be respectivelyAndand setting expected value of vibration acceleration of the jig after the 3 rd vibrationAllowable acceleration error value is e0. The specific steps of adaptively adjusting the input voltage are as follows:
1) according to the preset initial input voltage vector of three vibration excitersAndexciting the vibration exciter to work, wherein the 1st, 2 nd and 3 rd vibration acceleration vectors of the clamp collected by the three acceleration sensors are respectivelyAnd
2) after the three exciters perform the nth (n > -3) vibration, their input voltage vectors at the next (i.e. n + 1) vibration can be calculated according to the following formula:
wherein, the coefficient matrix MnIt needs to be obtained by solving the output-input linear equation of the last 3 vibration, namely Mn＝Un -1·An。
3) Will be provided withThe three vibration exciters work as input voltage signals, and the vibration acceleration vector actually output by the three acceleration sensors isThenAnd expected valueThe difference e between is:
if the difference is less than the preset acceleration error e0(including amplitude and phase), the adjustment is over; otherwise, turning to the step 2) and continuing the next adjustment.
The specific method for measuring the frequency response curve of the vibration of the tested vibration component comprises the following steps:
firstly, setting the amplitude, phase, frequency range and frequency interval of input voltage, and setting the expected value of vibration acceleration and the error value of allowable acceleration of the fixed part of the outer ring of the tested vibration component; then, from low frequency to high frequency, measuring the ratio of the vibration acceleration signal of the central rigid part of the vibration component to be measured corresponding to each frequency point to the vibration acceleration signal of the fixed part of the outer ring of the vibration component to be measured, namely forming the vibration frequency response curve of the vibration component to be measured. A method flowchart is shown in fig. 11.
The measurement process of a single frequency point is as follows: assuming that the frequency of the input voltage signal is f, the measurement process of the output-input ratio at the frequency point is as follows: firstly, adaptively adjusting the input voltage of a vibration exciter to ensure that a tested vibration part clamped by a clamp performs stable vibration; recording the vibration acceleration of the fixed part of the outer ring of the vibration component to be measured acquired by the acceleration sensor as a1The vibration displacement of the central rigid part of the vibration component to be measured, which is acquired by the laser displacement sensor, is recorded as x; using the relation of acceleration and displacement, a ═ - (2 pi f)2X, the signal acquisition and processing system can convert the vibration displacement x into an acceleration a, so that when a voltage signal with the frequency f is input, the calculation formula of the ratio h (f) of the vibration acceleration signal (output) of the tested vibration part to the vibration acceleration signal (input) of the clamp is as follows:
the values of the displacement and acceleration are complex.
The method for measuring the frequency response curve of the vibration of the vibrating component of the loudspeaker is specifically described by taking a 6.5-inch loudspeaker cone as an example.
Setting the frequency range of input voltage signals of three vibration exciters to be 40-100 Hz, setting the frequency interval to be 1Hz, and setting the expected acceleration value to be 5ei0m/s2Acceleration error value of 0.05ei1m/s2(ii) a After the measured vibration component to be clamped by the clamp is subjected to stable vibration from low frequency to high frequency, the ratio of the vibration acceleration signal (output) of the central rigid part of the measured vibration component corresponding to each frequency point to the vibration acceleration signal (input) of the fixed part of the outer ring of the measured vibration component is measured, that is, the frequency response curve of the vibration of the measured vibration component is obtained, 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: one method is that according to the measured frequency response curve of the vibration of the tested vibration component, the frequency corresponding to the peak value of the curve is calculated, and the frequency can be approximately regarded as the resonance frequency of the tested vibration component; the other method is to fit the natural angular frequency and the attenuation factor of the measured vibration component according to the frequency response curve, and calculate the resonance frequency according to a formula.
The first method will now be described using a 6.5 inch speaker cone as an example.
From the actually measured frequency response curve of the vibration member to be 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 vibration member to be measured is approximately 56 Hz.
The second equation 2 is relatively complex, and the method will be specifically described in the following starting from three aspects of theoretical formula derivation, fitting process and calculation.
1. Theoretical formula derivation
The invention provides a system for measuring the resonant frequency of a vibrating component of a loudspeaker excited by a vibration exciter, which is characterized in that the core of the system is a vibrating system for exciting a tested vibrating component clamped by a clamp by the vibration exciter to vibrate. Let the mass of the vibration component to be measured be m and the natural angular frequency be omega0The damping factor is gamma, and the vibration displacement of the central rigid part of the vibration component to be measured is x-XejωtWherein X is amplitude and omega is angular frequency, the vibration acceleration of the central rigid part of the vibration component to be measured is easy to knowIn the same way, the vibration displacement of the fixed part of the outer ring of the vibration component to be measured can be set as x1＝ X1ejωtAcceleration of vibration ofThe theoretical calculation formula of the frequency response of the vibration of the measured vibration component can be expressed as
2. Fitting procedure
Inputting output and input ratio data H (f) of all frequency points in a set measuring frequency range obtained by actual measurement, converting the corresponding relation of the ratio H and the frequency f into the corresponding relation of the ratio H and the angular frequency omega according to a formula omega of 2 pi f, selecting a nonlinear parameter fitting method, fitting a curve of frequency response H (omega) obtained by actual measurement with a curve of a theoretical formula H (omega), and obtaining the inherent angular frequency omega (omega) of the vibration component to be measured0And an attenuation factor gamma.
3. Computing
The natural angular frequency omega obtained by the fitting0Expression of substituting attenuation factor gamma into resonance frequencyThe resonance frequency of the vibration component to be measured can be calculated.
The 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 includes all commercial software capable of curve fitting, including Matlab, Origin, and 1st opt, etc. Now, Matlab software will be specifically described as an example. In the actual fitting process, the fitting is performed according to the square of the magnitude of the frequency response.
And (3) recording the square of the actually measured frequency response amplitude value as H2(f), recording the square of the frequency response theoretical value as H2 (omega), and according to the derivation process in the step two, calculating the square of the actually measured frequency response amplitude value H2(f) by the formula of
h2(f)＝h(f)2
And the square H2 (omega) of the theoretical value of the frequency response is calculated as
Let a be ω0 2，B＝4γ2The above formula can be simplified into
The specific fitting process is as follows: opening Matlab software, introducing 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 obtained through actual measurement, converting a corresponding relation of the ratio h and the frequency f into a corresponding relation of the ratio h and angular frequency omega according to a formula omega of 2 pi f, drawing a curve of the frequency response h (omega) obtained through actual measurement, and calculating a square value h2 (omega) of the frequency response; inputting cftool in a software command window and returning, displaying a fitting interface (as shown in fig. 13), selecting Custom Equation and inputting a theoretical formula of the square H2 (omega) of a frequency response theoretical value in a fitting mode on the right side (as shown in fig. 14), filling the name H2 of a fitting curve in a parameter column Fit name on the left side, sequentially selecting the values of X data, Ydata and weight as w, H2 and H2 (as shown in fig. 15), setting the result obtained by fitting on the left side below the interface (as shown in fig. 16), and setting the comparison graph of the measured curve and the fitting curve on the right side (as shown in fig. 17).
Calculating the natural angular frequency omega according to the values of B and a obtained by fitting0And an attenuation factor γ, the calculation formula is as follows:
the natural angular frequency omega obtained by the fitting0Expression of substituting attenuation factor gamma into resonance frequencyThe resonance frequency of the vibration component to be measured can be calculated.
The results of the parameter fitting and the calculation of the resonance frequency of the 6.5-inch cone are shown in fig. 18.
Finally, it should be noted that: the above embodiments are only used to illustrate the present invention and not to limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the appended claims.
Claims (8)
1. A system for measuring the resonant frequency of a loudspeaker vibration component excited by a vibration exciter is characterized by comprising a signal acquisition and processing system, a power amplifier, a measuring support, the vibration exciter, a clamp, an acceleration sensor and a laser displacement sensor, wherein the loudspeaker vibration component to be measured is clamped by the clamp, the clamp is arranged on the vibration exciter, the vibration exciter is arranged on the measuring support, and the acceleration sensor is arranged on the clamp; the laser displacement sensor is arranged on the measuring support, 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 specified frequency, the voltage signal is amplified through the power amplifier and then drives the vibration exciter, and the vibration exciter drives the tested 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 vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; the signal acquisition and processing system processes and analyzes the signals to obtain the resonance frequency of the vibration component of the tested loudspeaker.
2. The system of claim 1, wherein the measuring frame is a cubic frame, the laser displacement sensor is fixed on the upper portion of the measuring frame, and the measuring laser beam emitted from the laser displacement sensor is directed to a fixed point of the loudspeaker vibrating component to be measured.
3. The system of claim 1, wherein the fixture comprises a pair of upper and lower clamping plates, the upper and lower clamping plates together tightly clamping the outer edge of the vibrating member to be measured; the clamp is fixed on the vibration exciter; the vibration exciters are 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 the acceleration sensors are not positioned on the same straight line.
4. The system of claim 1, wherein the vibration member to be measured comprises a speaker cone, a diaphragm, and a centering pad.
5. A method for measuring the resonant frequency of a loudspeaker vibration component excited by a vibration exciter is characterized by comprising the following steps: mounting a vibration component of the loudspeaker to be tested on a clamp; the signal acquisition and processing system generates a voltage signal with a specified frequency, the voltage signal is amplified by the power amplifier and then excites the vibration exciter to work, and the vibration exciter drives the tested 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 vibration component to be measured through the laser displacement sensor and acquires a vibration acceleration signal of an outer ring fixed part of the vibration component to be measured through the acceleration sensor; performing the measurement by using the voltage signals of all frequencies in the specified frequency range and calculating to obtain a frequency response curve of the vibration component to be measured; and calculating to obtain the resonant frequency according to the frequency response curve.
6. The method for measuring the resonant frequency of a vibrating member of a loudspeaker excited by an exciter according to claim 5, wherein the method for measuring the frequency response curve of the vibration of the vibrating member to be measured comprises the following steps: firstly setting a measured frequency range and a measured frequency interval, then measuring the ratio of a vibration signal of a central rigid part of the measured vibration component corresponding to each frequency point to a vibration signal 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, and before measuring the vibration signal of each frequency point, adaptively adjusting the respective input voltage of three vibration exciters to enable the measured vibration component clamped by a clamp to stably vibrate.
7. The method according to claim 5, wherein the frequency response curve of the vibration member is a frequency response curve obtained by inputting a vibration signal from a fixed portion of an outer ring of the vibration member and outputting a vibration signal from a rigid portion of a center of the vibration member, and the vibration signal is an acceleration signal, a velocity signal or a displacement signal.
8. A method according to claim 5, wherein said method of obtaining a resonant frequency from a frequency response curve comprises two of: one method is that according to the measured frequency response curve of the vibration of the tested vibration component, the frequency corresponding to the peak value of the curve is calculated, and the frequency is approximately regarded as the resonance frequency of the tested vibration component; the other method is to obtain the natural angular frequency and the attenuation factor of the tested vibration component by fitting according to a frequency response curve and calculate the resonance frequency according to a formula.
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