Anechoic chamber automatic measuring device and method

Abstract

The application discloses an automatic measuring device and method for anechoic chamber, which comprises a solid sound source arranged at the center of the ground net of the anechoic chamber, a cable connecting the solid sound source and any vertex angle in the anechoic chamber, a microphone, a motor control system connected with the microphone, a data control analysis module connected with the solid sound source and the motor control system respectively, the data control analysis module is used for sending a control signal to the solid sound source to make the solid sound source sound, the data control analysis module is also used for sending a moving command, the motor control system controls the microphone to move along the starting position of the cable to the end position according to the moving command, the microphone collects sound pressure level signals at each sampling point on the cable and feeds back to the data control analysis module, and the data control analysis module is used for carrying out curve factor analysis and inverse square law processing on the received sound pressure level signals to obtain the free sound field deviation result in the anechoic chamber. The application can eliminate human errors and improve the measuring efficiency.

Description

Technical Field

[0001] This invention relates to the technical field of instrument calibration, and in particular to an automatic measuring device and method for an anechoic chamber. Background Technology

[0002] With the development of science and technology and production, and the corresponding increasingly stringent requirements for noise control (environmental protection), the demand for anechoic chambers has greatly increased. As a fundamental piece of equipment in the field of acoustics, anechoic chambers are commonly used for the use and measurement of various acoustic devices. To ensure the precision and quality of equipment and products, the accuracy of the measured data must be guaranteed. This is especially important in automotive laboratories, where data results can directly affect the accuracy of products and are crucial for vehicle safety. Measurements of noise levels and sound power levels in equipment and industrial products, analysis of the acoustic characteristics of loudspeakers and musical instruments, and research in physiological and psychoacoustics all rely heavily on anechoic chambers. The function of an anechoic chamber is to provide a free sound field free from reflected sound for acoustic testing and experiments. Therefore, its acoustic performance indicators are a major concern for users, directly impacting the results of product testing and evaluation.

[0003] Currently, the metrology (calibration) of anechoic chambers mainly relies on the following standards and specifications: JJF 1147-2006 "Acoustic Characteristics Calibration Specification for Anechoic and Semi-Anechoic Chambers", GB / T 6882-2016 "Acoustic Pressure Method for Determination of Sound Power Levels and Sound Energy Levels of Noise Sources - Precision Methods for Anechoic and Semi-Anechoic Chambers", and ISO 3745:2012 / AMD.1:2017 "Acoustics—Determination of sound power levels and sound energy levels of noise sources using sound pressure—Precision methods for anechoic rooms and hemi-anechoic rooms". These specifications are used to determine the frequency range and spatial range of the free sound field.

[0004] Although the standard specifies in detail the methods for measuring and evaluating the acoustic characteristics of anechoic chambers, relying solely on this standard for measurement and calculation will inevitably lead to errors in the test results. For example, theoretical curves and measured curves often exhibit "far-end alignment." Furthermore, in practical applications, the gravity of devices such as microphones can cause the microphone's transmission path to become curved, no longer the ideal straight line specified in the standard. Therefore, it is impossible to accurately and effectively evaluate the sound field characteristics of anechoic chamber experiments.

[0005] Currently, the metering of anechoic chambers has the following problems:

[0006] Currently, sound pressure levels are measured by manually moving the microphone along each microphone path at 0.1m intervals. This results in time-consuming and cumbersome measurement processes for anechoic chambers, and introduces human error.

[0007] Currently, the microphone path is designed to be a straight line under ideal conditions. However, in practical applications, the weight of the microphone and other equipment causes the straight line (wire) to bend. This means that the actual measurement path is not straight but curved, which leads to additional errors in the calibration (measurement) results of the sound field characteristics of the anechoic chamber. Summary of the Invention

[0008] The purpose of this invention is to provide an automatic measurement device and method for anechoic chambers, which solves the problems of long measurement time, cumbersome measurement, introduction of human error, and additional errors in the calibration (measurement) results of the sound field characteristics of the anechoic chamber.

[0009] To solve the above problems, the present invention is achieved through the following technical solution:

[0010] An automatic measurement device for an anechoic chamber, applied in an anechoic chamber 1, includes: a solid-state sound source 6, disposed at the center of the anechoic chamber's ground grid; a cable 4 serving as a measurement path, with its first end located at the solid-state sound source 6 as the starting position of the measurement path, and its second end located at any apex corner of the anechoic chamber 1 as the ending position of the measurement path; a microphone 3 disposed on the cable 4; a motor control system connected to the microphone 3; and a data control and analysis module disposed outside the anechoic chamber 1 and connected to both the solid-state sound source 6 and the motor control system; the data control and analysis module is used to transmit data to the anechoic chamber. The solid-state sound source 6 sends a control signal to cause it to emit sound; the data control and analysis module is also used to send a movement command to the motor control system, and the motor control system controls the microphone 3 to move along the cable 4 from the starting position to the ending position according to the received movement command; the microphone 3 collects sound pressure level signals at each sampling point on the cable 4 and feeds the sound pressure level signals back to the data control and analysis module, and the data control and analysis module is used to perform curve factor analysis and inverse square law processing on the received sound pressure level signals to obtain the free sound field deviation result in the anechoic chamber.

[0011] Optionally, the motor control system includes: a fixed pulley 2, which is located at any apex of the anechoic chamber 1; a motor drive module 5, which is installed on the ground grid of the anechoic chamber 1; a pulley transmission cable 11, one end of which passes around the fixed pulley 2 and is connected to the microphone 3, and the other end of which is connected to the motor drive module 5; and a motor drive control box 9, which is located outside the anechoic chamber 1 and is connected to the motor drive module 5 and the data control and analysis module, respectively. The data control and analysis module is used to send the movement command to the motor drive module 5 through the motor drive control box 9. The motor drive module 5 retracts the pulley transmission cable 11 according to the received movement command to drive the microphone 3 to move.

[0012] Optionally, the data control and analysis module includes: a computer 8 connected to the motor drive control chassis 9; and a PULSE multi-channel analyzer 7 connected to the computer 8, the microphone 3, and the sound source power amplifier 10, respectively, with the sound source power amplifier 10 connected to the solid-state sound source 6. The PULSE multi-channel analyzer 7 sends an excitation signal to the sound source power amplifier 10, which amplifies the excitation signal and outputs it to the solid-state sound source 6 to control the sound source 6 to emit sound. The PULSE multi-channel analyzer 7 also receives the sound pressure level signal at each sampling point collected by the microphone 3 and transmits it to the computer 8.

[0013] Optionally, the computer 8 is used to perform curve factor analysis on the measurement path to obtain the total deformation of the measurement path; calculate the sound pressure level signal at each sampling point based on the total deformation of the measurement path and in combination with the inverse square law algorithm to obtain the theoretical inverse square law sound pressure level; subtract the sound pressure level signal of the corresponding sampling point from the theoretical inverse square law sound pressure level at each sampling point to obtain the sound pressure level deviation value at each sampling point, and the sound pressure level deviation value at all sampling points is the free sound field deviation result in the anechoic chamber.

[0014] Optionally, the solid sound source 6 is a dodecahedral omnidirectional sound source.

[0015] On the other hand, the present invention also provides a method for automatically measuring an anechoic chamber using the anechoic chamber automatic measuring device described above, comprising: step S1, controlling the solid-state sound source to emit sound; step S2, the microphone moving along a cable from the starting position to the ending position at preset time intervals and step sizes; step S3, acquiring the sound pressure level signal; and step S4, performing curve factor analysis and inverse square law processing on the sound pressure level signal to obtain the free sound field deviation result within the anechoic chamber.

[0016] Optionally, step S3 further includes: Step S3.1, before starting the test, correcting the position of the microphone so that the microphone is located at the starting position. Step S3.2, controlling the microphone to move from the starting position to the ending position. Each movement is called a sampling point, and the microphone collects the sound pressure level signal at this sampling point until the microphone reaches the ending position.

[0017] Optionally, step S4 includes: Step S4.1, performing curve factor analysis on the measurement path to obtain the total deformation of the measurement path. Step S4.2, calculating the sound pressure level signal at each sampling point based on the total deformation of the measurement path and the inverse square law algorithm to obtain the theoretical inverse square law sound pressure level. Subtracting the corresponding sound pressure level signal at each sampling point from the theoretical inverse square law sound pressure level at each sampling point yields the sound pressure level deviation value at each sampling point, and the sound pressure level deviation values ​​at all sampling points are the free sound field deviation results in the anechoic chamber.

[0018] Optionally, step S4.1 includes: selecting two parameters, an arbitrary suspension position p of the microphone and a microphone deflection angle θ, and fitting them respectively to obtain the deformation amount Δd of the measurement path at each sampling point and the relationship curve between the microphone deflection angle θ and the suspension position p.

[0019] Δd=f(p)=A+B1p+B2p 2 +B3p 3 +B4p 4 +B5p 5 +B6p 6 +B7p 7 +B8p 8 +B9p 9

[0020] θ=q(p)=C+D1p+D2p 2 +D3p 3 +D4p 4 +D5p 5 +D6p 6 +D7p 7 +D8p 8 +D9p 9

[0021] Based on geometric relationships, the total deformation ΔD of the measurement path can be obtained as follows:

[0022] ΔD=Δd+acos(θ)=f(p)+acos[q(p)]

[0023] In the formula, a represents the distance between the microphone and the cable, q(p) represents the functional relationship between the microphone deflection angle θ and the microphone suspension position p; where C is the intercept of the functional relationship, and D1 to D9 are the coefficients of the functional relationship; f(p) represents the functional relationship between the suspension position p and the deformation of the wire rope at that point; where A is the intercept of the functional relationship, and B1 to B9 are the coefficients of the functional relationship.

[0024] Optionally, step S4.2 includes: the theoretical inverse square law sound pressure level Lp(r) at the i-th sampling point. i The following formula is used for calculation:

[0025]

[0026] In the formula, r i '=[r i 2 +(ΔD) 2 ] 0.5 , where r i The distance from the assumed sound center of the solid-state sound source to the i-th sampling point is represented by ΔD, where ΔD represents the total deformation of the measurement path; r i 'Represents the corrected distance from the assumed sound center of the solid-state sound source to the i-th sampling point;

[0027] The parameter 'a' is calculated using the following formula:

[0028]

[0029] In the formula, Lp i This represents the sound pressure level signal at the i-th sampling point acquired by the microphone; N represents the total number of sampling points on the measurement path.

[0030] r0 is the compensation for the sound center along the microphone's moving axis, which is the distance between the actual sound center and the assumed sound center of the solid sound source. r0 is calculated using the following formula:

[0031]

[0032] The sound pressure level deviation value ΔLp at the i-th sampling point i The following formula is used for calculation:

[0033] ΔLp i =Lp i -Lp(r i ').

[0034] This invention has at least one of the following advantages:

[0035] The automatic measurement device and method for anechoic chambers provided by this invention can be used to measure the free-field acoustic characteristics of fully automatic and semi-anechoic chambers. Referring to the JJF 1147-2006 Acoustic Characteristic Calibration Standard for Anechoic and Semi-anechoic Chambers, the received sound pressure level signal is processed by the data control and analysis module to obtain the free-field deviation result within the anechoic chamber through curve factor analysis and inverse square law processing. Therefore, by correcting the measurement path and calculating the theoretical inverse square law sound pressure level based on the correction result, and determining the free-field acoustic characteristics within the anechoic chamber based on the difference between the theoretical inverse square law sound pressure level and the actual measured sound pressure level signal, the automatic measurement device for anechoic chambers provided by this invention can correct the deviation between the actual sampling point and the theoretical sampling point, and can improve the phenomenon of excessively good but unreasonable far-end data in procedural data processing. During the testing process, the system can achieve fully automatic measurement, eliminate human error, and improve measurement efficiency. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the main structure of an automatic measuring device for an anechoic chamber according to an embodiment of the present invention;

[0037] Figure 2 This is a flowchart illustrating an automatic measurement method for an anechoic chamber according to an embodiment of the present invention.

[0038] Figure 3 This is a force diagram of a catenary provided in an embodiment of the present invention;

[0039] Figure 4 The curves showing the relationship between the deformation amount Δd and the deflection angle θ and the suspension position p are provided for an embodiment of the present invention. Detailed Implementation

[0040] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the automatic measuring device and method for an anechoic chamber proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0041] like Figure 1 As shown, an automatic measuring device for an anechoic chamber, applied in an anechoic chamber 1, includes: a solid-state sound source 6, which is located at the center of the anechoic chamber's ground grid; a cable 4, with its first end located at the solid-state sound source 6 as the starting position and its second end located at any apex corner of the anechoic chamber 1 as the ending position; a microphone 3, which is mounted on the cable 4; a motor control system connected to the microphone 3; and a data control and analysis module located outside the anechoic chamber 1 and connected to both the solid-state sound source 6 and the motor control system; the data control and analysis module is used to send data to the solid-state sound source 6. The control signal causes the solid-state sound source 6 to emit sound; the data control and analysis module is also used to send a movement command to the motor control system, and the motor control system controls the microphone 3 to move along the cable 4 from the starting position to the ending position according to the received movement command; the microphone 3 collects the sound pressure level signal at each sampling point on the cable 4 and feeds the sound pressure level signal back to the data control and analysis module, and the data control and analysis module is used to perform curve factor analysis and inverse square law processing on the received sound pressure level signal to obtain the free sound field deviation result in the anechoic chamber.

[0042] In this embodiment, since most anechoic chambers measure 1 to 3 paths, and the results of each path can yield the free sound field deviation of the anechoic chamber, it can be understood that in order to achieve a more comprehensive measurement of the sound field inside the anechoic chamber, it is necessary to measure all four paths inside the anechoic chamber. When changing the measurement path, it is only necessary to change the connection position of the second end of cable 4 to the next top corner of the anechoic chamber. Other measurement methods and processes are the same as described above.

[0043] Please continue to refer to this. Figure 1 As shown, the motor control system includes: a fixed pulley 2, which is located at any corner of the anechoic chamber 1; a motor drive module 5, which is installed on the ground grid of the anechoic chamber 1; a pulley transmission cable 11, one end of which passes around the fixed pulley 2 and is connected to the microphone 3, and the other end of which is connected to the motor drive module 5; and a motor drive control box 9, which is located outside the anechoic chamber 1 and is connected to the motor drive module 5 and the data control analysis module, respectively. The data control analysis module is used to send the movement command to the motor drive module 5 through the motor drive control box 9. The motor drive module 5 retracts the pulley transmission cable 11 according to the received movement command to drive the microphone 3 to move.

[0044] Please continue to refer to this. Figure 1As shown, the data control and analysis module includes: a computer 8, which is connected to the motor drive control chassis 9; and a PULSE multi-channel analyzer 7, which is connected to the computer 8, the microphone 3, and the sound source power amplifier 10, respectively. The sound source power amplifier 10 is connected to the solid-state sound source 6. The PULSE multi-channel analyzer 7 is used to send an excitation signal to the sound source power amplifier 10, and the sound source power amplifier 10 is used to amplify the excitation signal and output it to the solid-state sound source 6 to control the solid-state sound source 6 to emit sound. The PULSE multi-channel analyzer 7 is also used to receive the sound pressure level signal at each sampling point collected by the microphone 3 and transmit it to the computer 8.

[0045] In this embodiment, the solid-state sound source 6 is a dodecahedral omnidirectional sound source that can continuously emit pink noise signals.

[0046] Please continue to refer to this. Figure 1 As shown, the computer 8 is used to perform curve factor analysis on the measurement path to obtain the total deformation of the measurement path; based on the total deformation of the measurement path and combined with the inverse square law algorithm, the sound pressure level signal at each sampling point is calculated to obtain the theoretical inverse square law sound pressure level; the theoretical inverse square law sound pressure level at each sampling point is subtracted from the sound pressure level signal at the corresponding sampling point to obtain the sound pressure level deviation value at each sampling point, and the sound pressure level deviation values ​​at all sampling points are the free sound field deviation results in the anechoic chamber. In this embodiment, the motor control system can also be a stepper motor.

[0047] Please continue to refer to this. Figure 1 As shown, this embodiment also includes: a network cable 15 for connecting the computer 8 to the PULSE multichannel analyzer 7; a BNC cable (coaxial cable) 13 for connecting the PULSE multichannel analyzer 7 and the sound source power amplifier 10; an audio cable 14 for connecting the sound source power amplifier 10 and the solid-state sound source 6; a Lemo cable 12 for connecting the PULSE multichannel analyzer 7 and the microphone 3; and a USB cable 16, through which the computer 8 is connected to the motor drive control chassis 9, and the motor drive module 9 is connected to the motor drive module 5.

[0048] On the other hand, such as Figure 2As shown, this embodiment also provides an automatic measurement method for an anechoic chamber using the automatic measurement device for an anechoic chamber as described above, including: Step S1, controlling the solid-state sound source to emit sound; Step S2, the microphone moving along the cable from the starting position to the ending position at preset time intervals and step sizes; Step S3, acquiring the sound pressure level signal; Step S4, performing curve factor analysis and inverse square law processing on the sound pressure level signal to obtain the free sound field deviation result within the anechoic chamber.

[0049] In this embodiment, step S3 further includes: Step S3.1, before starting the test, correcting the position of the microphone so that the microphone is located at the starting position. Step S3.2, controlling the microphone to move from the starting position to the ending position. Each movement is called a sampling point, and the microphone collects the sound pressure level signal at this sampling point until the microphone reaches the ending position.

[0050] To understand the above steps, an example is given below. Using the data control and analysis module or computer 8, the initial theoretical path between the fixed sound source and microphone is set to 50cm. Sound pressure level signal sampling is performed for 30 seconds. After sampling at a fixed point, the path is moved 10cm in a straight line to the next sampling point, continuing until the sampling program stops at the endpoint length set by the program. (For example, if the program sets the path to 3m, then 25 sampling points will be taken along the entire path.) Each time the sound pressure level signal is acquired, the path length needs to be analyzed to determine if the endpoint has been reached. The analyzed path length here is only a preliminary calculation based on the length, width, and height of the anechoic chamber being tested, approximately calculating the path length from the center point to one end, such as 3 meters, 3.5 meters, 4 meters, etc.

[0051] In this embodiment, step S4 includes: Step S4.1, performing curve factor analysis on the measurement path to obtain the total deformation of the measurement path. Step S4.2, calculating the sound pressure level signal at each sampling point based on the total deformation of the measurement path and the inverse square law algorithm to obtain the theoretical inverse square law sound pressure level. Subtracting the sound pressure level signal of the corresponding sampling point from the theoretical inverse square law sound pressure level at each sampling point yields the sound pressure level deviation value at each sampling point. The sound pressure level deviation values ​​at all sampling points are the free sound field deviation results in the anechoic chamber.

[0052] In this embodiment, the microphone can be mounted on a wire rope (cable) via a connector (e.g., a connector consisting of a pulley and a suspension bracket). It is understood that in this embodiment, as long as the microphone can be mounted on the cable, the specific structure of the connector is not limited.

[0053] In actual testing, the high flexibility of the wire rope, along with its own weight and that of the sound transmission device, causes the wire rope, which should be straight, to sag downwards, approximating a catenary. This alters the sound transmission path of the microphone. Existing research indicates that the sag curve of wire rope structures under its own weight is typically approximated using the catenary equation.

[0054] First, establish a coordinate system with the suspended end of the catenary as the origin, as follows: Figure 3 As shown, its left end is subjected to horizontal pretension T0 and hangs down under the action of uniformly distributed gravity. Let its unit weight be λ, the length of the suspension line be L, the tension at the top be T, and the angle with the x-axis be α. According to the mechanical principle, tanα=G / T0.

[0055] Assuming the horizontal tension is constant throughout the catenary, for any segment L of the catenary... x This equilibrium holds true for all cases, tanα=λL x / T0, and tanα=dy / dx, taking the differential of this equation, we have

[0056]

[0057] The differential of the arc length is obtained by separating the variables and integrating equation (1):

[0058]

[0059] Integrating equation (2) yields:

[0060]

[0061]

[0062] Separating the variables and integrating equation (4), we get:

[0063]

[0064] According to the integral formula, we can obtain:

[0065]

[0066] This equation is the general equation for a catenary, and subsequent simulations are based on catenary theory, with this equation serving as the theoretical foundation. In the equation, C1 and C2 represent the integration constants obtained from the above integration. Since this is the general equation (i.e., the general solution) for a catenary, specific values ​​for C1 and C2 do not need to be determined. If C1 and C2 need to be obtained, initial conditions must be set. C1 and C2 will differ under different initial conditions; each set of initial conditions corresponds to a set of values ​​for C1 and C2. Only when a particular solution is required do we need to substitute the initial conditions to find the specific values ​​of C1 and C2.

[0067] In this embodiment, the weight of the wire rope and the microphone causes the wire rope to sag, changing the sound transmission path from a straight line to a sloping curve. This leads to errors in the subsequent sound pressure data measurement. Therefore, it is proposed to use a curve factor to describe and compensate for the error caused by this path change to a certain extent.

[0068] Therefore, in this embodiment, the method of studying the case of the wire rope sags due to the tilt angle of the microphone and the weight of the suspended object (such as the weight of the microphone itself) becomes particularly complicated through theoretical calculation. In order to ensure the accuracy of the results and the simplicity of the calculation, this embodiment can use the finite element simulation method based on the above theory to simulate the situation of the sound transmission device and the weight of the wire rope on the sag of the wire rope, and then obtain its influence on the sound transmission path.

[0069] Based on experimental results, a simulation model was established. To more accurately represent the flexibility of the wire rope, its elastic modulus was set to E = 0.8 × 10⁻⁶. 11 Using the y-direction as the direction of gravity, multiple simulations were conducted with varying suspension positions (parameter p) of the sound transmission device to obtain the coordinates and deformation of each point (sampling point) on the wire rope at different suspension positions p. Since the ratio of the overall model size to the deformation is relatively large, it is difficult to clearly characterize the deformation of the wire rope at different suspension positions. Therefore, a curve showing the relationship between the y-direction deformation Δd and the x-axis can be plotted. When the sound transmission device is suspended near the midpoint of the wire rope, the deformation Δd is larger; as the device moves further away from the midpoint, the deformation Δd gradually decreases.

[0070] To verify the accuracy of the simulation results, this embodiment also compared the simulated paths of the sound transmission device at 1000mm, 2000mm, 3000mm, 4000mm, and 5000mm with experimental values. The comparison of theoretical, simulated, and experimental values ​​demonstrates that the simulation model can accurately describe the actual measurement process, and the simulation results are closer to the experimental values ​​than the theoretical values. As the sound transmission device moves further away from the sound source along the transmission path, the deformation of the steel wire rope exhibits a trend of first increasing and then decreasing. That is, the closer the suspension position of the sound transmission device is to the midpoint of the steel wire rope, the greater the deformation of the entire transmission path. Furthermore, as the sound transmission device moves further away from the midpoint of the steel wire rope, the deformation gradually decreases. This is because the area near the midpoint of the steel wire rope is its center of gravity, so the effect of gravity is most significant, resulting in the largest deformation.

[0071] When the simulation results are closer to the actual values, they can predict the error caused by gravity on the sound transmission path to a certain extent. At the same time, the simulation results at the suspension point of the device are closer to the experimental values.

[0072] Research has found that during sound pressure level testing, the path deformation at the sound transmission device (microphone, or microphone assembly) has a significant impact on the test results. Therefore, we pay more attention to the error of the sound transmission device at the suspension point. Simultaneously, due to the influence of the device's gravity, the microphone's orientation changes at different positions, no longer parallel to the ideal sound transmission path, resulting in a deflection angle.

[0073] like Figure 4 As shown, in order to further understand the influence of the sound transmission device on the sag of the wire rope at different suspension positions, two parameters, different suspension positions p and device deflection angle θ, were selected and fitted to obtain the relationship curves between the deformation Δd and the deflection angle θ and the suspension position p. Based on the curve fitting results, the following functional relationships are obtained, namely, the following formulas (6) and (7).

[0074] In this embodiment, step S4.1 includes: selecting two parameters, an arbitrary suspension position p of the microphone and a microphone deflection angle θ, and fitting them respectively to obtain the deformation amount Δd of the measurement path at each sampling point and the relationship curve between the microphone deflection angle θ and the suspension position p.

[0075] Δd=f(p)=A+B1p+B2p 2 +B3p 3 +B4p 4 +B5p 5 +B6p 6 +B7p 7 +B8p 8 +B9p 9 (7)

[0076] θ=q(p)=C+D1p+D2p 2 +D3p 3 +D4p 4 +D5p 5 +D6p 6 +D7p 7 +D8p 8 +D9p 9 (8)

[0077] Based on geometric relationships, the total deformation ΔD of the measurement path can be obtained as follows:

[0078] ΔD=Δd+acos(θ)=f(p)+acos[q(p)] (9)

[0079] In the formula, a represents the distance between the microphone and the cable, q(p) represents the functional relationship between the microphone deflection angle θ and the microphone suspension position p; where C is the intercept of the functional relationship, and D1 to D9 are the coefficients of the functional relationship; f(p) represents the functional relationship between the suspension position p and the deformation of the wire rope at that point; where A is the intercept of the functional relationship, and B1 to B9 are the coefficients of the functional relationship.

[0080] In this embodiment, the coefficients of equations (7) and (8) are shown in the table below:

[0081] Table 1 Function Coefficients Table

[0082]

[0083]

[0084] After analyzing the curve factors, the algorithm design for the path deviation of the anechoic chamber is carried out. The free field characteristics of the anechoic chamber and the semi-anechoic chamber are measured by continuous measurement using pure tone. The sound pressure level attenuation curves of the sound field on all frequency bands on each selected path are recorded according to the point measurement method. For each measurement frequency of each transmission path.

[0085] Therefore, in this embodiment, step S4.2 includes: the theoretical inverse square law sound pressure level Lp(r) at the i-th sampling point. i The following formula is used for calculation:

[0086]

[0087] In the formula, r i '=[r i 2 +(ΔD) 2 ] 0.5 , where r i The distance from the assumed sound center of the solid-state sound source to the i-th sampling point is represented by ΔD, where ΔD represents the total deformation of the measurement path; r i ' represents the corrected distance from the assumed sound center of the solid sound source to the i-th sampling point.

[0088] The parameter 'a' is calculated using the following formula:

[0089]

[0090] In the formula, Lp i This represents the sound pressure level signal at the i-th sampling point acquired by the microphone; N represents the total number of sampling points on the measurement path.

[0091] r0 is the compensation for the sound center along the microphone's moving axis, which is the distance between the actual sound center and the assumed sound center of the solid sound source. r0 is calculated using the following formula:

[0092]

[0093] The sound pressure level deviation value ΔLp at the i-th sampling point i The following formula is used for calculation:

[0094] ΔLp i =Lp i -Lp(r i ') (13)

[0095] In summary, the existing technical procedures introduce a linear formula for parameter q in the inverse square law calculation of microphone measurement data. This leads to the following problem: the linear formula for parameter q uses linear least squares to calculate the theoretical curves a and r0, but in actual calibration experiments, the change in parameter q becomes irregular with increasing measurement distance, while the change in sound pressure level gradually decreases. The maximum and minimum values ​​of parameter q differ by a factor of 2.5, resulting in the phenomenon that the data is more accurate the further the test distance. The deviation data are shown in Table 2.

[0096]

[0097] This embodiment corrects the distance from the assumed sound center of the solid-state sound source to the i-th sampling point, thereby making the corrected distance infinitely close to the actual measurement path. Based on this corrected distance, the theoretical inverse square law sound pressure level is calculated, thus determining the free-field acoustic characteristics within the anechoic chamber. Therefore, the automatic measurement device for the anechoic chamber provided in this embodiment can correct the deviation between the actual and theoretical sampling points, and improve data processing in the procedure, resulting in more accurate and reasonable deviation results.

[0098] In summary, the automatic measurement device and method for anechoic chambers provided in this embodiment can be used to measure the free-field acoustic characteristics of fully automatic anechoic chambers and semi-anechoic chambers. Referring to the JJF 1147-2006 Acoustic Characteristic Calibration Standard for Anechoic and Semi-anechoic Chambers, the received sound pressure level signal is processed by the data control and analysis module to obtain the free-field deviation result within the anechoic chamber through curve factor analysis and inverse square law processing. Therefore, by correcting the measurement path and calculating the theoretical inverse square law sound pressure level based on the correction result, the difference between the theoretical inverse square law sound pressure level and the actual measured sound pressure level signal is used to determine the free-field acoustic characteristics within the corresponding anechoic chamber. During the detection process, this system can achieve fully automatic measurement, eliminate human error, and improve measurement efficiency.

[0099] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0100] It should be noted that the apparatus and methods disclosed in the embodiments herein can also be implemented in other ways. The apparatus embodiments described above are merely illustrative; for example, the flowcharts and block diagrams in the accompanying drawings show the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments herein. In this regard, each block in a flowchart or block diagram may represent a module, program, or part of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system to perform the specified function or action, or can be implemented using a combination of dedicated hardware and computer instructions.

[0101] In addition, the functional modules in the various embodiments of this article can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0102] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. An automatic measuring device for anechoic chambers, to be applied in an anechoic chamber (1), characterized in that, The application relates to an automatic measuring device for an anechoic chamber. The device comprises: a solid sound source (6) arranged at the center of the ground net of the anechoic chamber; a cable (4) serving as a measuring path, a first end of the cable (4) being arranged at the solid sound source (6) as a starting position of the measuring path, and a second end of the cable (4) being arranged at any one of the corners of the anechoic chamber (1) as an ending position of the measuring path; a microphone (3) arranged on the cable (4); a motor control system connected with the microphone (3); a data control analysis module arranged outside the anechoic chamber (1) and connected with the solid sound source (6) and the motor control system respectively; the data control analysis module is used for sending a control signal to the solid sound source (6) so that the solid sound source (6) generates sound; the data control analysis module is also used for sending a moving command to the motor control system, and the motor control system controls the microphone (3) to move along the cable (4) from the starting position to the ending position according to the received moving command; the microphone (3) collects a sound pressure level signal at each sampling point on the cable (4) and feeds back the sound pressure level signal to the data control analysis module, the data control analysis module comprises a computer (8) used for carrying out curve factor analysis on the measuring path to obtain a total deformation amount of the measuring path; According to the geometric relationship, the total deformation of the measuring path can be obtained is: wherein a represents the distance between the microphone and the cable, represents a function relationship between the microphone deflection angle θ and the microphone suspension position p; wherein C is the intercept of the function relationship, and D1-D9 are the coefficients of each term of the function relationship; represents a function relationship between the suspension position p and the cable deformation amount at the position; wherein A is the intercept of the function relationship, and B1-B9 are the coefficients of each term of the function relationship; two parameters, i.e. any one of the hanging positions p of the microphone and the deflection angle theta of the microphone, are selected to be fitted respectively, and the deformation amount delta d of the measuring path at each sampling point and the relationship curve of the deflection angle theta of the microphone and the hanging position p are obtained; the sound pressure level signal at each sampling point is calculated according to the total deformation amount of the measuring path and in combination with an inverse square law algorithm, and a theoretical inverse square law sound pressure level is obtained; Theoretical inverse square sound pressure level at the i-th sampling point The following formula is used for the calculation: wherein wherein represents the distance of the assumed sound center of the solid sound source to the i-th sampling point, represents the total deformation amount of the measurement path; represents the corrected distance of the assumed sound center of the solid sound source to the i-th sampling point. wherein the parameters The following formula is used for the calculation: In the formula, , Indicates the number of samples collected by the microphone. The sound pressure level signal at each sampling point; This represents the total number of sampling points along the measurement path; for compensation of the sound center along the microphone movement axis, i.e. the distance between the actual sound center of the solid sound source and the assumed sound center, The following formula is used for the calculation: sound pressure level deviation value at the i-th sampling point is calculated using the following equation: 。 2. The anechoic chamber automatic measuring device according to claim 1, characterized in that, the theoretical inverse square law sound pressure level at each sampling point is subtracted from the sound pressure level signal at the corresponding sampling point to obtain a sound pressure level deviation value at each sampling point, and the sound pressure level deviation values at all the sampling points are free sound field deviation results in the anechoic chamber; the motor control system comprises: a fixed pulley (2) arranged at any one of the corners of the anechoic chamber (1); a motor driving module (5) arranged on the ground net of the anechoic chamber (1); a pulley transmission cable (11) having one end connected with the microphone (3) by passing through the fixed pulley (2) and the other end connected with the motor driving module (5); a motor transmission control cabinet (9) arranged outside the anechoic chamber (1) and connected with the motor driving module (5) and the data control analysis module respectively, the data control analysis module is used for sending the moving command to the motor driving module (5) through the motor transmission control cabinet (9), and the motor driving module (5) contracts the pulley transmission cable (11) to drive the microphone (3) to move according to the received moving command.

3. The automatic measuring device for the anechoic chamber according to claim 2, wherein the data control analysis module comprises: a computer (8) connected with the motor transmission control cabinet (9). A PULSE multi-channel analyzer (7) is connected with the computer (8), the microphone (3) and a sound source power amplifier (10) respectively, and the sound source power amplifier (10) is connected with the solid sound source (6); The PULSE multi-channel analyzer (7) is used to send an excitation signal to the sound source power amplifier (10), and the sound source power amplifier (10) is used to amplify and output the excitation signal to the solid sound source (6) to control the solid sound source (6) to sound. The PULSE multi-channel analyzer (7) is also used to receive the sound pressure level signal collected by the microphone (3) at each sampling point and transmit to the computer (8).

4. The anechoic chamber automatic measuring device according to claim 1, characterized in that, The solid sound source (6) is a dodecahedron non-directional sound source.

5. A method for automatically measuring an anechoic chamber by using the automatic measuring apparatus for an anechoic chamber according to any one of claims 1 to 4, characterized by, Comprising: Step S1, controlling the solid sound source to sound, Step S2, the microphone moves from the starting position to the end position along the cable at a preset time interval and step length; Step S3, obtaining the sound pressure level signal, Step S4, performing curve factor analysis and inverse square law processing on the sound pressure level signal to obtain the free sound field deviation result in the anechoic chamber.

6. The anechoic chamber automatic measurement method according to claim 5, characterized in that, The step S3 further comprises: Step S3.1, before starting the test, correcting the position of the microphone so that the microphone is located at the starting position; Step S3.2, controlling the microphone to move from the starting position to the end position, and each time the microphone moves, the position is called a sampling point, and the microphone collects the sound pressure level signal at the sampling point until the microphone reaches the end position.

7. The anechoic chamber automatic measurement method according to claim 6, characterized in that, The step S4 comprises: Step S4.1, performing curve factor analysis on the measurement path to obtain the total deformation of the measurement path; Step S4.2, calculating the sound pressure level at each sampling point according to the total deformation of the measurement path and combining the inverse square law algorithm to obtain the theoretical inverse square law sound pressure level; Subtracting the sound pressure level signal of each sampling point from the theoretical inverse square law sound pressure level of each sampling point to obtain the sound pressure level deviation value of each sampling point, and the sound pressure level deviation values of all the sampling points are the free sound field deviation results in the anechoic chamber.

8. The anechoic chamber automatic measurement method according to claim 7, characterized in that, The step S4.1 comprises: selecting any one of the two parameters of the hanging position p of the microphone and the deflection angle θ of the microphone, fitting respectively, to obtain the deformation ∆d of the measurement path at each sampling point and the relationship curve of the deflection angle θ of the microphone and the hanging position p. According to the geometric relationship, the total deformation of the measuring path can be obtained is: wherein a represents the distance between the microphone and the cable, represents the function relationship between the microphone deflection angle θ and the microphone suspension position p; wherein C is the intercept of the function relationship, and D1-D9 are the coefficients of each term of the function relationship; represents the function relationship between the suspension position p and the cable deformation amount at the position; wherein A is the intercept of the function relationship, and B1-B9 are the coefficients of each term of the function relationship.

9. The anechoic chamber automatic measurement method according to claim 8, characterized in that, The step S4.2 comprises: a theoretical inverse square law sound pressure level of the i-th sampling point The calculation is performed using the following formula: wherein wherein represents the distance of the assumed sound center of the solid sound source to the i-th sampling point, represents the total deformation amount of the measurement path; represents the corrected distance of the assumed sound center of the solid sound source to the i-th sampling point. wherein the parameters The following formula is used for the calculation: In the formula, , Indicates the number of samples collected by the microphone. The sound pressure level signal at each sampling point; This represents the total number of sampling points along the measurement path; for compensation of the sound center along the microphone movement axis, i.e. the distance between the actual sound center of the solid sound source and the assumed sound center, The calculation is performed using the following formula: a sound pressure level deviation value at the i-th sampling point is calculated using the following equation: 。

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