A microphone sensitivity testing and adjusting device and method

Abstract

The present invention discloses a microphone sensitivity testing and adjusting device and method, including the following steps: S01. Place a reference microphone on the device, and use a signal generator to output a sine signal A with a fixed frequency and amplitude to the metal diaphragm and the rear electrode plate to cause the metal diaphragm to vibrate; S02. Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S01 and record it as X; S03. Remove the reference microphone and replace it with the microphone to be adjusted; S04. Use a signal generator to output a sine signal A with a fixed frequency and amplitude to the microphone to be adjusted to cause the metal diaphragm to vibrate; S05. Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S04 and record it as Y; S06. Compare the difference between X and Y, and adjust the tension of the metal diaphragm of the microphone to be adjusted; S07. Repeat S05 - S06 until the sensitivities of the adjusted microphone and the reference microphone are consistent. The present invention can solve the technical problem that there are large errors in the test results of the existing microphone sensitivity testing and adjusting methods.

Description

Technical Field

[0001] The present invention relates to the technical field of microphones, and particularly to a microphone sensitivity test and adjustment device and method. Background Art

[0002] A condenser microphone consists of a rear plate and a stretched metal diaphragm that are parallel to each other. The rear plate and the diaphragm are electrically insulated from each other and form two electrodes of a capacitor with air as the dielectric. Then, by applying a polarization voltage between the two electrodes or coating a layer of electret material on the rear plate and polarizing it, the capacitor is given a certain charge. Therefore, for a microphone in production, when the distance, area, charge amount, and structure between the two electrodes are determined, the sensitivity is mainly adjusted by changing the tension of the metal diaphragm.

[0003] As Figure 1 shown, in the existing production process, the sensitivity adjustment of a microphone is usually achieved by applying a varying electric field force to the metal diaphragm of the microphone through an electrostatic actuator, causing the diaphragm to vibrate at a certain frequency and amplitude. The amplitude of the microphone vibration is equivalent to the amplitude generated by a certain sound pressure. At this time, the value obtained by dividing the output voltage amplitude of the microphone by the equivalent sound pressure is the sensitivity of the microphone. According to the difference between the sensitivity obtained from this detection and the reference sensitivity of the microphone, the tension of the metal diaphragm on the condenser microphone is adjusted, and the sensitivity detection is repeated again. This process of adjusting the tension of the metal diaphragm is repeated until the measured sensitivity of the microphone in production is basically the same as the reference sensitivity of the microphone, and then the adjustment work is completed.

[0004] Although this method can relatively quickly test the sensitivity of a condenser microphone, the structure of the electrostatic actuator is to fix a circular metal plate with holes on an insulating ring structure, and then determine a certain distance parallel and spaced from the clamping ring that fixes the metal diaphragm on the microphone through this ring structure. Such a structure has high requirements for parallelism and distance. Otherwise, under the same excitation voltage, there will be a large error in the amplitude of the metal diaphragm of the microphone, and the accuracy of sensitivity detection cannot be guaranteed. Summary of the Invention

[0005] 1. Technical Problems to be Solved by the Invention

[0006] The present invention provides a microphone sensitivity test and adjustment device and method, which can solve the technical problem that there are large errors in the test results of the existing microphone sensitivity test and adjustment methods.

[0007] 2. Technical Solutions

[0008] To solve the above problems, the technical solutions provided by the present invention are as follows:

[0009] A microphone sensitivity testing and adjusting device and method, including the following steps: S01. Place a reference microphone on the device, and use a signal generator to output a sine signal A with a fixed frequency and amplitude to the metal diaphragm and the back plate to cause the metal diaphragm to vibrate; S02. Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S01 and record it as X; S03. Remove the reference microphone and replace it with the microphone to be adjusted; S04. Use a signal generator to output a sine signal A with a fixed frequency and amplitude to the microphone to be adjusted to cause the metal diaphragm to vibrate; S05. Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S04 and record it as Y; S06. Compare the difference between X and Y, and adjust the tension of the metal diaphragm of the microphone to be adjusted; S07. Repeat S05 - S06 until the sensitivities of the adjusted microphone and the reference microphone are the same.

[0010] Optionally, at least the calculation method of the displacement amplitude Y is as follows: Select a period T of the diaphragm vibration caused by a non - sine signal A in the workshop with regularity, and divide a period of time with relatively gentle vibration displacement deviation of the metal diaphragm into two segments. In one time segment, the sine signal A is not sent, and the vibration displacement of the metal diaphragm at this time is recorded as Y1; in the other time segment, the sine signal A is sent, and the vibration displacement of the metal diaphragm at this time is recorded as Y2. Comparing the difference between Y1 and Y2 can obtain the displacement amplitude Y.

[0011] Optionally, the Doppler vibrometer detects the vibration amplitude of the central area of the metal diaphragm.

[0012] A microphone sensitivity testing and adjusting device, including a microphone base, a microphone, a Doppler vibrometer and a signal generator. The microphone base is arranged at the bottom of the microphone. The signal generator is electrically connected to the metal diaphragm and the back plate of the microphone through the microphone base. The Doppler vibrometer is placed directly above the microphone to detect the displacement amplitude of the metal diaphragm.

[0013] Optionally, the metal diaphragm is connected to the microphone through a diaphragm ring.

[0014] Optionally, the Doppler vibrometer is placed directly above the microphone to detect the displacement amplitude of the central area of the metal diaphragm.

[0015] 3. Beneficial effects

[0016] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0017] 1. It can solve the problem that the detection sensitivity of the electrostatic actuator is affected by the inability to ensure the parallelism between the metal diaphragm and the circular metal plate of the electrostatic actuator, thus affecting the detection accuracy.

[0018] 2. It can solve the problem that the distance between the metal diaphragm and the circular metal plate of the electrostatic actuator changes during the tension adjustment of the metal diaphragm, which affects the detection accuracy.

[0019] 3. It can eliminate the noise generated by the vibration of the metal diaphragm caused by the vibration of the work station, and the detection result is more accurate. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of an existing microphone sensitivity test and adjustment device;

[0021] Figure 2 It is a schematic structural diagram of a microphone sensitivity test and adjustment device proposed in an embodiment of the present invention;

[0022] Figure 3 It is a schematic diagram of the vibration curve of the metal diaphragm caused by external interference;

[0023] Figure 4 It is a schematic diagram of the period T in the schematic diagram of the vibration curve;

[0024] 1. Microphone base; 2. Microphone; 3. Doppler vibrometer; 4. Signal generator; 5. Metal diaphragm; 6. Rear plate; 7. Diaphragm ring. Detailed Embodiments

[0025] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0026] It should be noted that when an element is referred to as being "fixed to", "disposed on", "fixedly provided on" or "mounted on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. Further, when an element is considered to be "fixedly connected" to another element, the two can be fixed in a detachable connection manner or in a non-detachable connection manner, such as socket connection, snap connection, integrally formed fixation, welding, etc., which can be realized in the prior art and will not be elaborated herein. When an element is perpendicular or approximately perpendicular to another element, it means that the ideal state of the two is perpendicular, but due to manufacturing and assembly effects, there may be a certain vertical error. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only embodiment.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0028] In the present invention, "first" and "second" involved do not represent specific quantities and orders, but are only used for name distinction.

[0029] Combined with the attached Figures 2 - 4 For a method for testing and adjusting the sensitivity of a microphone according to this embodiment, it includes the following steps. S01: Place a reference microphone on the device, and use a signal generator to output a sine signal A with a fixed frequency and amplitude to the metal diaphragm and the back plate to cause the metal diaphragm to vibrate. S02: Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S01 and record it as X. S03: Remove the reference microphone and replace it with the microphone to be adjusted. S04: Use a signal generator to output a sine signal A with a fixed frequency and amplitude to the microphone to be adjusted to cause the metal diaphragm to vibrate. S05: Use a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S04 and record it as Y. S06: Compare the difference between X and Y, and adjust the tension of the metal diaphragm of the microphone to be adjusted. S07: Repeat S05 - S06 until the difference between X - Y approaches 0, that is, the adjustment is completed. At this time, the sensitivity of the microphone to be adjusted is the same as that of the reference microphone.

[0030] This method for testing and adjusting the sensitivity of a microphone changes the traditional detection method of detecting the sensitivity of a condenser microphone by using a standard sound source or an electrostatic exciter to vibrate the metal diaphragm of the condenser microphone and then detecting the electrical signal output by the microphone. Instead, a sine wave signal with a fixed frequency and amplitude is output by a signal generator to the metal diaphragm and the back plate of the microphone. Since the microphone is a charged capacitor during operation, when a sine wave signal with a fixed frequency and amplitude is input to the metal diaphragm and the back plate, the metal diaphragm will generate vibrations with corresponding frequencies and amplitudes. At this time, a Doppler vibrometer fixed directly above the metal diaphragm is used to detect the displacement signal of the metal diaphragm vibration in real time, and this signal presents a sine wave curve on the time axis. For the same type of microphone, with the same structure, the same mass of the metal diaphragm, and the same charge amount, when the tension of the metal diaphragm is the same, under the same sine wave signal given by the signal generator, the vibration displacement generated by the metal diaphragm is also the same. Based on this principle, under the input of the same sine wave signal, the vibration amplitude of the central area of the metal diaphragm of the microphone to be adjusted is measured and output by the Doppler vibrometer, and compared with the vibration amplitude of the central area of the metal diaphragm of the adjusted reference microphone. When the difference between the two is too large, the tension of the metal diaphragm of the microphone to be adjusted is adjusted to be the same as the vibration amplitude of the reference microphone, and the sensitivity adjustment of the microphone to be adjusted is completed.

[0031] In the original electrostatic exciter scheme, when the electrostatic excitation plate is assembled with the insulating ring structure, non-parallel errors will occur. At the same time, non-parallel errors will also occur in the fixation of the diaphragm and the diaphragm ring on the microphone. These errors will accumulate to form relatively large errors, making it difficult to ensure the sensitivity accuracy of the produced microphones and resulting in poor consistency.

[0032] This method for testing and adjusting the sensitivity of a microphone solves the problem in the original electrostatic exciter scheme that because the metal diaphragm is fixed on the diaphragm ring, and then the diaphragm ring is threadedly or press-fitted onto the microphone housing with interference. During this process, the metal diaphragm will be blocked by the annular edge on the microphone housing. As the diaphragm ring moves downward continuously, the metal diaphragm is continuously tightened and the tension increases. During this process, the distance between the electrostatic excitation plate and the upper edge of the diaphragm ring remains unchanged, but the distance between the electrostatic excitation plate and the metal diaphragm changes, resulting in a second variable in addition to the tension of the metal diaphragm during this process, and the detection result is inaccurate. This method for testing and adjusting the sensitivity of a microphone uses the method of directly measuring the vibration amplitude of the metal diaphragm of the microphone under a specific electrical signal, with accurate results and good adjustment consistency.

[0033] However, in the workshop production, it is not only the input sine signal A that can cause the vibration of the metal diaphragm. There are also influencing factors such as the noise in the workshop and the vibration of the machine. Therefore, in order to ensure the accuracy, it is necessary to find a way to eliminate the vibration of the metal diaphragm caused by non-sine signal A as much as possible. Fortunately, the microphone production workshop is mostly automated production, and its process is repetitive. Therefore, the generated noise and vibration are also periodic. The law of the vibration displacement of the metal diaphragm caused by these factors over time is as Figure 3 shown. Therefore, a period T of the metal diaphragm vibration displacement deviation that is relatively gentle can be selected and divided into two segments: t1 - t2, t2 - t3. No sine signal A is sent in the time period t1 - t2. At this time, the vibration displacement Y1 of the metal diaphragm is the vibration of the metal diaphragm caused by non-sine signal A. Sine signal A is sent in the time period t2 - t3. At this time, the metal diaphragm vibrates under the combined action of this signal and influencing factors such as the noise in the workshop and the vibration of the machine. At this time, the vibration displacement of the metal diaphragm is Y2. Y2 - Y1 is the true displacement vibration Y of the metal diaphragm caused by sine signal A. In this way, the noise is eliminated. Figure 4 The dashed box shows the metal diaphragm displacement curve and the noise elimination curve intercepted for one period T.

[0034] It should be noted that the reference microphone in S01 can be measured in an environment without external interference. At this time, X is the vibration amplitude of the metal diaphragm of the reference microphone. If the reference microphone is measured in an environment with external interference, the above method should also be used for measurement to eliminate the noise.

[0035] As a preferred embodiment of the present invention, a device for implementing the above-mentioned microphone sensitivity test and adjustment method includes a microphone base 1, a microphone 2, a Doppler vibrometer 3, and a signal generator 4. The microphone base 1 is provided at the bottom of the microphone 2. The signal generator 4 is electrically connected to the metal diaphragm 5 and the rear electrode plate 6 of the microphone 2 through the microphone base 1. The Doppler vibrometer 3 is placed directly above the microphone 2 to detect the displacement amplitude of the central area of the metal diaphragm 5. The Doppler vibrometer 3 is mainly used to detect the displacement amplitude of the center of the metal diaphragm 5 because the displacement amplitude of the center of the metal diaphragm 5 is the largest and the detection result is more accurate.

[0036] As a preferred embodiment of the present invention, the metal diaphragm 5 is connected to the microphone 2 through a diaphragm ring 7. The diaphragm ring 7 is threadedly sleeved on the upper end of the microphone 2.

[0037] The specific embodiments are as follows:

[0038] When a DC polarization voltage U0 (generally 800V) is superimposed on an AC signal u (about 30V - 50V) and applied to the electrode plate of the electrostatic actuator, due to the action of the Coulomb force, the instantaneous electrostatic pressure p(t) generated on the diaphragm is calculated by the following formula:

[0039]

[0040] In the formula:

[0041] p(t) is the equivalent instantaneous sound pressure, with the unit of Pa (Pascal);

[0042] ε gas is the dielectric constant of the gas between the electrostatic actuator and the diaphragm, with the unit of F / m (Farad per meter). (In air, ε gas = 8.85 * 10 -12 F / m);

[0043] d is the effective distance between the electrostatic actuator and the diaphragm, with the unit of m (meter);

[0044] a is the ratio of the effective area of the electrostatic actuator to the effective area of the diaphragm;

[0045] p is the root mean square value of the fundamental frequency sound pressure, with the unit of Pa (Pascal);

[0046] t is the time, with the unit of s (second);

[0047] U0 is the DC voltage applied between the electrostatic actuator and the microphone diaphragm, with the unit of V (volt);

[0048] u is the root mean square value of the AC voltage applied between the electrostatic actuator and the microphone diaphragm, with the unit of V (volt);

[0049] ω is the angular frequency, with the unit of rad / s (radian per second).

[0050] In the existing production process, the sensitivity adjustment of a microphone is usually achieved by applying an AC signal of around 500 Hz and 30 V (the amplitude is related to the distance between the electrostatic actuator and the metal diaphragm and the sound pressure level to be generated. The farther the distance or the greater the sound pressure level to be generated, the higher the required voltage) to the metal diaphragm on the microphone through an electrostatic actuator. At this time, the diaphragm will vibrate up and down at a frequency of 1000 Hz. In the embodiment, the designed sensitivity of the microphone used is 27 mV / Pa. At this time, the output sound pressure level of this microphone should be 85 dB. If the actually measured sound pressure level is not equal to 85 dB, then the tension of the metal diaphragm needs to be adjusted. From the above formula, it can be seen that in this scheme, there are two main factors affecting the accuracy of the d value. One is that the parallelism between the metal diaphragm 5 and the upper plane of the diaphragm ring 7 cannot be guaranteed, resulting in non-parallelism between the metal diaphragm and the electrostatic actuator plate, causing errors. The other is that to tighten the tension of the metal diaphragm 5, the diaphragm ring 7 needs to move downward. At this time, the metal diaphragm 5 is blocked by the annular edge on the microphone housing and will not move downward. However, the electrostatic actuator is connected to the upper plane of the diaphragm ring 7. At this time, the distance between the metal diaphragm 5 and the excitation plate of the electrostatic actuator becomes closer, and the resulting electrostatic force becomes larger, so that the measured value is no longer only generated by adjusting the metal diaphragm.

[0051] To solve these two problems, in this embodiment, a microphone with a sensitivity of 27 mV / Pa is taken as an example. An AC sine signal A with an amplitude of 27 mV and a frequency of 1000 Hz is input from both ends of the metal diaphragm 5 and the rear plate 6 of the microphone. Under the action of the original charge amount, the metal diaphragm 5 will generate a corresponding vibration displacement Y, and the frequency is also 1000 Hz. This Y can be measured by a Doppler vibrometer 3. At the same time, for the same type of microphone, this vibration displacement Y corresponds one-to-one with the sensitivity. Assuming that the vibration displacement of the metal diaphragm after inputting the AC sine signal A with a frequency of 1000 Hz for a microphone with a sensitivity of 27 mV / Pa is X, then as long as the tension of the metal diaphragm is adjusted to make the vibration displacement Y consistent with X, the adjustment is completed. During this process, the position of the diaphragm within the area of the annular edge inside the microphone housing will always remain unchanged, and the Doppler vibrometer 3 measures the displacement data of the diaphragm (the accuracy can reach 0.1 nm), so the data accuracy is improved a lot.

[0052] The above schematically describes the present invention and its embodiments. This description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and design similar structural forms and embodiments to this technical solution without creative work without departing from the purpose of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A microphone sensitivity test and adjustment method, characterized in that: The following steps are included: S01, placing a reference microphone on the device, using a signal generator to output a sinusoidal signal A with a fixed frequency and amplitude to the metal diaphragm and the rear plate to cause the metal diaphragm to vibrate; S02, using a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S01 and record it as X; S03, remove the reference microphone and replace it with the microphone to be adjusted; S04, using a signal generator to output a sinusoidal signal A with a fixed frequency and amplitude to the microphone to be adjusted so that its metal diaphragm vibrates; S05, using a Doppler vibrometer to measure the displacement amplitude of the metal diaphragm in S04 and record it as Y; S06, comparing the difference between X and Y, and adjusting the tension of the metal diaphragm of the microphone to be adjusted; S07. Repeat S05-S06 until the sensitivity of the adjustment microphone is consistent with that of the reference microphone.

2. A microphone sensitivity test and adjustment method according to claim 1, characterized in that: At least the calculation method of the displacement amplitude Y is to select a period T of the diaphragm vibration caused by the regular workshop non-sinusoidal signal A, and divide it into two sections when the metal diaphragm vibration displacement deviation is relatively gentle. In one period of time, no sinusoidal signal A is emitted, and the metal diaphragm vibration displacement at this time is recorded as Y1; in another period of time, a sinusoidal signal A is emitted, and the metal diaphragm vibration displacement at this time is recorded as Y2. The displacement amplitude Y can be obtained by comparing the difference between Y1 and Y2.

3. A microphone sensitivity test and adjustment method according to claim 1 or 2, characterized in that: The Doppler vibrometer detects the vibration amplitude of the central area of ​​the metal diaphragm.

4. A microphone sensitivity test and adjustment device, characterized in that: The invention comprises a microphone base, a microphone, a Doppler vibrometer and a signal generator. The microphone base is arranged at the bottom of the microphone. The signal generator is electrically connected to the metal diaphragm and the rear plate of the microphone through the microphone base. The Doppler vibrometer is placed directly above the microphone to detect the displacement amplitude of the metal diaphragm.

5. A microphone sensitivity test and adjustment device according to claim 4, characterized in that: The metal diaphragm is connected to the microphone through a diaphragm ring.

6. A microphone sensitivity test and adjustment device according to claim 4 or 5, characterized in that: The Doppler vibrometer is placed just above the microphone to detect the displacement amplitude of the central area of ​​the metal diaphragm.

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