Low-frequency calibration device and method for normal vector microphone of laser piston sounder

Abstract

The invention discloses a laser piston sounder normal vector microphone low-frequency calibration device and method, and solves the technical problems that the calibration frequency range is limited, the model dependence is strong and the environmental noise interference is obvious in a low-frequency band in the existing vector microphone calibration method. The device comprises a piston sounder, a laser interferometer, a vector microphone and a data acquisition system, the piston sounder comprises a piston, an excitation source and a piston cavity, an end cover of the piston cavity is provided with an optical window, and the laser interferometer measures the movement speed and displacement of the piston through the optical window; the vector microphone is hermetically coupled to the piston sounder from the side wall of the piston cavity through the adapter; and electric signal outputs of the laser interferometer and the vector microphone are connected to an input channel of the data acquisition system. The calculation model of the sound pressure and the particle vibration velocity in the piston sounder is clear, does not depend on the type of a piston excitation source, and is high in universality.

Description

Technical Field

[0001] The present invention relates to the technical field of microphone calibration, and in particular to a low-frequency calibration device and method for a normal vector microphone of a laser piston generator. Background Art

[0002] A vector microphone integrates a sound pressure sensor (microphone) and a particle velocity sensor. It can simultaneously measure scalar sound pressure and vector particle velocity, and comprehensively describe the characteristics of the sound field by calculating parameters such as sound intensity and sound power. It is also called a PU probe, air sound vector sensor, etc. Vector microphones have the characteristics of small size and easy integration. The particle velocity sensor has an "8"-shaped directivity that is basically independent of frequency. It can effectively suppress environmental background noise during the measurement process. Compared with traditional scalar field measurements, it has obvious principle advantages in noise source location and identification applications, breaking through the minimum array aperture limit of traditional sound detection systems. The operating frequency range of a vector microphone is generally 100Hz to 10kHz. In applications such as multi-target sound detection, the operating frequency range can be as low as 10Hz or lower.

[0003] Based on the actual needs of acoustic measurement, vector microphones are commonly found in one-dimensional and three-dimensional forms. A one-dimensional vector microphone includes a particle velocity measurement channel and a sound pressure measurement channel, and is primarily used in applications such as directional voice pickup, acoustic impedance and sound absorption measurements, automotive NVH measurements, and condition monitoring and fault diagnosis for industrial equipment. A three-dimensional vector microphone includes three mutually orthogonal particle velocity measurement channels and a sound pressure measurement channel, enabling complete three-dimensional sound field measurement, sound field visualization, and noise source location and identification.

[0004] The metrological parameters that characterize vector microphone performance include sound pressure and particle velocity sensitivity and their frequency response, amplitude consistency, phase consistency, spatial directivity, and background noise. The sound pressure and particle velocity sensitivity and their frequency response are fundamental. In 2006, Finn Jacobsen and Virginie Jaud of the Technical University of Denmark (DTU) proposed several possible vector microphone calibration methods, including the far-field comparison method using a spherical sound source, the near-field comparison method using a monopole source with an opening in a rigid plane or spherical baffle, and the standing wave tube comparison method. The calibration principles of each method are essentially the same: in a sound field where the theoretical relationship between sound pressure and particle velocity is well defined, the sound pressure measurement results of a calibrated microphone are used as a reference. Based on the theoretical model of acoustic impedance, a reference value for the sound particle velocity is calculated to calibrate the sensor's particle velocity sensitivity.

[0005] The calibration frequency range of the far / near-field comparison method for a spherical sound source covers 10 Hz to 10 kHz. However, the calibration accuracy of the particle velocity sensitivity depends on the theoretical relationship between the sound pressure radiated by the sound source and the particle velocity, that is, the accuracy of the modeling of the acoustic impedance. This acoustic impedance model is highly dependent on the characteristic parameters of the specific sound source and is not universally applicable. In standing wave tubes and free-field devices, there is a clear theoretical relationship between sound pressure and particle velocity. The calculation model of acoustic impedance is independent of the sound source and is only related to parameters such as the density and sound velocity of the transmission medium. The calculation model of acoustic impedance in standing wave tubes is also related to the wave number and the distance between the calibration position and the end of the tube, making it universal. However, the applicable calibration frequency range of standing wave tubes is related to their structural parameters and is generally 250 Hz to 4 kHz. The applicable calibration frequency range of free-field devices is related to their low-frequency cutoff frequency and the operating frequency range of the test sound source and is generally 100 Hz to 20 kHz. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-frequency calibration device and method for a laser piston generator normal vector microphone, so as to solve the technical problems of the existing vector microphone calibration method in the low frequency band, such as limited calibration frequency range, strong model dependence, and significant environmental noise interference.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] In the first aspect, the present invention provides a low-frequency calibration device for a normal vector microphone of a laser piston generator, comprising: a piston generator, a laser interferometer, a vector microphone and a data acquisition system, wherein the piston generator comprises a piston and an excitation source, and a piston cavity, and an optical window is provided on the end cover of the piston cavity, and the laser interferometer measures the piston movement speed and displacement through the optical window; the end cover or side wall of the piston cavity is also provided with a pressure sensor and a temperature sensor; the vector microphone is sealed and coupled to the piston generator from the side wall of the piston cavity through an adapter, and the adapter has a rotation adjustment function, which adjusts the speed sensitive direction of the sound particle velocity sensor to be consistent with the piston movement direction when calibrating the particle velocity sensitivity of the vector microphone; the electrical signal output of the laser interferometer is connected to the input channel of the data acquisition system, and the electrical signal outputs of the sound pressure channel and the particle velocity channel of the vector microphone are respectively connected to the data acquisition system.

[0009] Furthermore, the excitation source is one of an electromagnetic vibration table, a linear motor, and a dynamic loudspeaker.

[0010] In a second aspect, the present invention provides a method for low-frequency calibration of a normal vector microphone of a laser pistonphone, comprising the following steps:

[0011] Step 1: Seal the vector microphone to the piston generator through the adapter on the side wall of the piston cavity. Connect the sound pressure channel and particle velocity channel of the vector microphone to the input channels of the data acquisition system respectively.

[0012] Step 2: Start the pistonphone and set its operating frequency and drive voltage. The laser interferometer measures the piston's velocity and displacement through the optical window on the piston chamber end cap. The laser interferometer's electrical signal output is connected to the input channel of the data acquisition system.

[0013] Step 3: Based on the lumped parameter model of the radiated sound pressure in the piston generator, combined with the piston displacement measured by a laser interferometer and the static pressure and temperature measured by a pressure sensor and a temperature sensor, the sound pressure in the piston cavity is calculated. The sensitivity of the sound pressure channel is calibrated based on the response voltage of the vector microphone sound pressure channel.

[0014] Step 4: Adjust the rotary adapter that couples the vector microphone to the piston cavity. Simultaneously, observe the response voltage of the vector microphone's particle velocity channel through the data acquisition system. Lock the rotary adapter when the response voltage reaches its maximum value. At this point, the velocity-sensitive direction of the vector microphone's particle velocity sensor is consistent with the direction of the particle vibration velocity in the piston cavity.

[0015] Step 5: Based on the axial distribution model of the particle vibration velocity in the piston generator, combined with the piston movement velocity measured by the laser interferometer, and the response voltage of the particle vibration velocity channel of the vector microphone, the particle vibration velocity channel sensitivity is calibrated;

[0016] Step 6: Change the operating frequency of the pistonphone and repeat the above steps to calibrate the sound pressure, particle velocity sensitivity and frequency response of the vector microphone.

[0017] Furthermore, the lumped parameter model of the radiated sound pressure in the piston generator is:

[0018]

[0019] Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, R1 is the piston radius, x is the piston displacement, V0 is the volume of the closed cavity when the piston is in equilibrium, and Δp(H,L,W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuations.

[0020] Furthermore, the sensitivity of the sound pressure channel is calibrated according to the response voltage of the sound pressure channel of the vector microphone, and the calculation formula is as follows:

[0021]

[0022] Where V pis the response voltage of the sound pressure channel of the vector microphone, l p is the sensitivity of the sound pressure channel of the vector microphone.

[0023] Furthermore, the axial distribution model of the particle vibration velocity in the piston sounder is:

[0024]

[0025] Where Δp(H,L) is the coupling correction coefficient of heat conduction and cavity leakage, υ0 is the piston speed, R1 is the piston radius, a is the piston cavity radius, k is the wave number, z is the axial coordinate position with the piston center as the origin, and υ z is the vibration velocity of the particle at position z in the piston cavity, and L is the length of the piston cavity.

[0026] Furthermore, the sensitivity of the particle velocity channel is calibrated according to the response voltage of the particle velocity channel of the vector microphone, and the calculation formula is as follows:

[0027]

[0028] Where V υ is the response voltage of the vector microphone particle velocity channel, l υ is the sensitivity of the particle velocity channel of the vector microphone.

[0029] Based on the above technical solution, the embodiments of the present invention can produce at least the following technical effects:

[0030] (1) The present invention provides a low-frequency calibration device for a laser pistonphone normal microphone. The lower limit of the frequency range of the pistonphone normal microphone calibration depends on the low-frequency pistonphone technology. The calibration frequency can cover at least 10Hz to 100Hz. The pistonphone is integrated into this device as a standard equipment module, and the lower limit of the calibration frequency can reach 0.01Hz or even lower.

[0031] (2) The low-frequency calibration method of the normal vector microphone of the laser piston sounder provided by the present invention clarifies the acoustic coupling mode between the vector microphone and the piston cavity, and provides a calculation model for the sound pressure and axial particle vibration velocity distribution in the piston cavity. The piston movement displacement and speed are measured by a laser interferometer, and the sound pressure and particle vibration velocity at the calibration position are calculated to achieve absolute calibration of the sound pressure and particle vibration velocity sensitivity of the vector microphone. The calculation model of the sound pressure and particle vibration velocity in the piston sounder is clear, does not depend on the type of piston excitation source, and has strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0033] Figure 1 It is a structural diagram of an embodiment of the present invention;

[0034] In the figure: 1. Piston generator; 11. Piston and excitation source; 12. Piston cavity; 2. Laser interferometer; 3. Vector microphone; 31. Sound pressure channel; 32. Particle velocity channel; 4. Data acquisition system; 5. Pressure sensor; 6. Temperature sensor. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] Example 1

[0037] like Figure 1 As shown, the present invention provides a low-frequency calibration device for a normal vector microphone of a laser piston sounder, comprising a piston sounder 1, a laser interferometer 2, a vector microphone 3 and a data acquisition system 4, with a specific configuration as follows: the piston sounder 1 is composed of a piston and an excitation source 11, and a piston cavity 12. An optical window is provided on the end cover of the piston cavity 12, and the laser interferometer 2 measures the movement speed and displacement of the piston through the optical window. In addition, a pressure sensor 5 and a temperature sensor 6 are provided on the end cover or the side wall of the piston cavity 12; the vector microphone 3 is hermetically coupled to the piston sounder from the side wall of the piston cavity 12 through an adapter, and the adapter has a rotation adjustment function, which adjusts the speed sensitive direction of the sound particle velocity sensor to be consistent with the piston movement direction when calibrating the particle velocity sensitivity of the vector microphone 3; the electrical signal output of the laser interferometer 2 is connected to the input channel of the data acquisition system 4, and the electrical signal outputs of the sound pressure channel 31 and the particle velocity channel 32 of the vector microphone 3 are respectively connected to the data acquisition system 4.

[0038] In this embodiment, the piston excitation source may be an electromagnetic vibration table, a linear motor, a dynamic speaker, etc. The arrangement of the optical measurement window and the laser interferometer on the piston cavity is related to the piston excitation source, and any measurement method and layout that can achieve piston motion displacement and speed measurement can be used as a substitute.

[0039] Example 2

[0040] The present invention provides a low-frequency calibration method for a normal vector microphone of a laser pistonphone, comprising the following steps:

[0041] Step 1: The vector microphone is sealed and coupled to the piston generator through an adapter on the side wall of the piston cavity. The sound pressure channel and particle velocity channel of the vector microphone are connected to the input channels of the data acquisition system respectively.

[0042] Step 2: Start the pistonphone and set its operating frequency and drive voltage. The laser interferometer measures the piston's velocity and displacement through the optical window on the piston chamber end cap. The laser interferometer's electrical signal output is connected to the input channel of the data acquisition system.

[0043] Step 3: Based on the lumped parameter model of the radiated sound pressure in the piston sounder, as shown in Equation (1), combined with the piston motion displacement measured by the laser interferometer, and the static pressure and temperature measured by the pressure sensor and temperature sensor, the sound pressure in the piston cavity is calculated. Based on the response voltage of the sound pressure channel of the vector microphone, the sensitivity of the sound pressure channel can be calibrated, as shown in Equation (2).

[0044]

[0045] Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, R1 is the piston radius, x is the piston displacement, V0 is the volume of the closed cavity when the piston is in equilibrium, and Δp(H,L,W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuations.

[0046]

[0047] Where V p is the response voltage of the sound pressure channel of the vector microphone, l p is the sensitivity of the sound pressure channel of the vector microphone.

[0048] Step 4: Adjust the rotating adapter that couples the vector microphone to the piston cavity. At the same time, observe the response voltage of the vector microphone's particle velocity channel through the data acquisition system. Lock the rotating adapter when the response voltage reaches its maximum value. At this time, the velocity-sensitive direction of the vector microphone's particle velocity sensor is consistent with the direction of the particle vibration velocity in the piston cavity.

[0049] Step 5: Based on the axial distribution model of the particle vibration velocity in the piston generator, as shown in Equation (3), combined with the piston motion velocity measured by the laser interferometer, the sensitivity of the particle vibration velocity channel can be calibrated based on the response voltage of the vector microphone particle vibration velocity channel, as shown in Equation (4). The sound pressure error correction involved in Equation (3) consists of sound pressure fluctuation correction and heat conduction and cavity leakage coupling correction. The influence of the sound pressure fluctuation effect can be ignored by optimizing the piston cavity structural parameters. Here, only the coupling correction Δp(H,L) of heat conduction and cavity leakage is considered.

[0050]

[0051] Where Δp(H,L) is the coupling correction coefficient of heat conduction and cavity leakage, υ0 is the piston speed, R1 is the piston radius, a is the piston cavity radius, k is the wave number, z is the axial coordinate position with the piston center as the origin, and υ z is the vibration velocity of the particle at position z in the piston cavity, and L is the length of the piston cavity.

[0052]

[0053] Where V υ is the response voltage of the vector microphone particle velocity channel, l υ is the sensitivity of the particle velocity channel of the vector microphone.

[0054] Step 6: Change the operating frequency of the pistonphone and repeat the above steps to calibrate the sound pressure, particle velocity sensitivity and frequency response of the vector microphone.

[0055] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-frequency calibration device for a laser pistonphone normal vector microphone, characterized in that: include: A piston sounder, a laser interferometer, a vector microphone and a data acquisition system, wherein the piston sounder includes a piston, an excitation source and a piston cavity, and an optical window is provided on the end cover of the piston cavity, and the laser interferometer measures the piston movement speed and displacement through the optical window; the piston cavity end cover or side wall is also provided with a pressure sensor and a temperature sensor; the vector microphone is hermetically coupled to the piston sounder from the side wall of the piston cavity through an adapter, and the adapter has a rotation adjustment function, which adjusts the speed sensitive direction of the sound particle velocity sensor to be consistent with the piston movement direction when calibrating the particle velocity sensitivity of the vector microphone; the electrical signal output of the laser interferometer is connected to the input channel of the data acquisition system, and the electrical signal outputs of the sound pressure channel and the particle velocity channel of the vector microphone are respectively connected to the data acquisition system.

2. The laser pistonphone normal vector microphone low-frequency calibration device according to claim 1, characterized in that: The excitation source is one of an electromagnetic vibration table, a linear motor, and a dynamic loudspeaker.

3. A method for low-frequency calibration of a normal vector microphone for a laser pistonphone, using the low-frequency calibration device for a normal vector microphone for a laser pistonphone according to claim 1 or 2, characterized in that: The following steps are involved: Step 1: Seal the vector microphone to the piston generator through the adapter on the side wall of the piston cavity. Connect the sound pressure channel and particle velocity channel of the vector microphone to the input channels of the data acquisition system respectively. Step 2: Start the pistonphone and set its operating frequency and drive voltage. The laser interferometer measures the piston's velocity and displacement through the optical window on the piston chamber end cap. The laser interferometer's electrical signal output is connected to the input channel of the data acquisition system. Step 3: Based on the lumped parameter model of the radiated sound pressure in the piston generator, combined with the piston displacement measured by a laser interferometer and the static pressure and temperature measured by a pressure sensor and a temperature sensor, the sound pressure in the piston cavity is calculated. The sensitivity of the sound pressure channel is calibrated based on the response voltage of the vector microphone sound pressure channel. Step 4: Adjust the rotary adapter that couples the vector microphone to the piston cavity. Simultaneously, observe the response voltage of the vector microphone's particle velocity channel through the data acquisition system. Lock the rotary adapter when the response voltage reaches its maximum value. At this point, the velocity-sensitive direction of the vector microphone's particle velocity sensor is consistent with the direction of the particle vibration velocity in the piston cavity. Step 5: Based on the axial distribution model of the particle vibration velocity in the piston generator, combined with the piston movement velocity measured by the laser interferometer, and the response voltage of the particle vibration velocity channel of the vector microphone, the particle vibration velocity channel sensitivity is calibrated; Step 6: Change the operating frequency of the pistonphone and repeat the above steps to calibrate the sound pressure, particle velocity sensitivity and frequency response of the vector microphone.

4. The laser pistonphone normal microphone low-frequency calibration method according to claim 3, characterized in that: The lumped parameter model of the radiated sound pressure in the pistonphone is: Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, R1 is the piston radius, x is the piston displacement, V0 is the volume of the closed cavity when the piston is in equilibrium, and Δp(H,L,W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuations.

5. The laser pistonphone normal microphone low-frequency calibration method according to claim 4, characterized in that: The sensitivity of the sound pressure channel is calibrated according to the response voltage of the sound pressure channel of the vector microphone, and the calculation formula is as follows: Where V p is the response voltage of the sound pressure channel of the vector microphone, l p is the sensitivity of the sound pressure channel of the vector microphone.

6. The laser pistonphone normal microphone low-frequency calibration method according to claim 3, characterized in that: The axial distribution model of the particle vibration velocity in the piston sounder is: Where Δp(H,L) is the coupling correction coefficient of heat conduction and cavity leakage, υ0 is the piston speed, R1 is the piston radius, a is the piston cavity radius, k is the wave number, z is the axial coordinate position with the piston center as the origin, and υ z is the vibration velocity of the particle at position z in the piston cavity, and L is the length of the piston cavity.

7. The laser pistonphone normal microphone low-frequency calibration method according to claim 6, characterized in that: The sensitivity calibration of the particle velocity channel is achieved based on the response voltage of the vector microphone particle velocity channel, and the calculation formula is as follows: Where V υ is the response voltage of the vector microphone particle velocity channel, l υ is the sensitivity of the particle velocity channel of the vector microphone.

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