Step-by-step coupling simulation analysis method for medium-frequency sound field of multiple loudspeakers in closed space

Abstract

The invention discloses a step-by-step coupling simulation analysis method for a frequency band sound field in multiple loudspeakers in a closed space, which comprises the following steps of: firstly, performing multi-physical field coupling simulation on a loudspeaker monomer to obtain a vibration acceleration of a radiation surface of the loudspeaker monomer, and then importing the vibration acceleration of the radiation surface of each loudspeaker into a closed space model to perform simulation calculation; the sound pressure level frequency response curve simulation method comprises the steps of geometric model establishment, simulation analysis model establishment, frequency domain analysis and the like. The method is suitable for research of frequency band sound field information in the closed space, and has application value in frequency band simulation in the sound field in the closed space.

Description

Technical Field

[0001] The invention relates to the technical field of closed space sound field simulation, and in particular to a step-by-step coupling simulation analysis method for mid-frequency sound fields of multiple loudspeakers in a closed space. Background Art

[0002] The in-car audio environment is a key element in the design of a car's intelligent cockpit. In the traditional tuning strategy for the existing in-car audio environment, audio engineers mostly design based on established experience, install multiple speakers at preset locations in the car body, and evaluate key performance parameters such as the sound pressure level and distortion at each fixed point to perform traditional tuning design. However, this traditional tuning strategy is time-consuming and labor-intensive, and frequently involves prototype production and speaker assembly and disassembly.

[0003] The existing numerical simulation method makes up for the shortcomings of the above-mentioned tuning design method, and this method has been applied to the design and development of in-vehicle (enclosed space) sound fields. The existing in-vehicle sound field simulation methods are divided into two types according to the different research frequency bands: 1) a low-frequency simulation method of the in-vehicle sound field based on the finite element method, and 2) a high-frequency simulation method of the in-vehicle sound field based on the ray acoustics method. These two simulation methods are low-frequency simulation methods and high-frequency simulation methods for a single speaker, respectively, but are not suitable for simulation analysis in the mid-frequency band. Because: in the mid-frequency band, if the first traditional finite element analysis method is used, due to the large number of grids, the computer's computing power requirements are high, and the simulation calculation time is long; if the second ray acoustic analysis method is used, the calculation time can be reduced, but the calculation accuracy cannot be guaranteed. Summary of the invention

[0004] The purpose of the present invention is to design a closed space multi-speaker mid-frequency sound field step-by-step coupling simulation analysis method, the method is based on the finite element method to establish a closed space step-by-step coupling model, different from the traditional finite element analysis method, the calculation model is divided into steps.

[0005] The present invention aims to solve the problem that the existing simulation method is used for frequency band simulation in a closed space and cannot take into account both improving the simulation accuracy and reducing the simulation calculation time.

[0006] The present invention provides a step-by-step coupling simulation analysis method for a mid-frequency sound field of multiple loudspeakers in a closed space, comprising at least the following steps: (1) Perform finite element simulation calculations on the loudspeaker unit, including: 1) Simulation calculation of the loudspeaker's magnetic circuit system; Obtain the relevant parameters of the magnetic circuit system, including: the geometric dimensions of the magnet, soft iron and coil, the residual magnetic flux density B0 of the magnet, the number of coil turns N0, and obtain the driving force coefficient BL value and basic impedance Zb of the speaker through simulation calculation: A. Import the 2D geometric model of the loudspeaker magnetic circuit system and surrounding air into the numerical simulation analysis software Comsol; B. Set all geometric model regions to the "Magnetic Field" physical field interface, set the "Constitutive Relationship "BH>Magnetization Model" of the magnetic steel and magnetic soft iron materials to "Residual Magnetic Flux Density" and "BH Curve" respectively, and enter the corresponding material parameters; C. Use the "steady state" study type to simulate and obtain the driving force coefficient BL and basic impedance Zb of the voice coil at different geometric positions in the magnetic gap.

[0007] 2) Simulation calculation of the speaker's vibration system and acoustic field coupling; The geometric dimensions and material parameters of the voice coil, skeleton, centering support, folded ring, elastic wave, dust cover and diaphragm in the vibration system are obtained. The BL value and basic impedance Zb of the speaker in step 1) are used as input parameters, and the vibration acceleration of the radiation surface is obtained by simulating the speaker vibration system.

[0008] A. Import the 3D geometry model of the speaker vibration system and surrounding air into Comsol; B. Set the vibration system to the "Shell" physics interface, set the "Thickness and Offset" of the voice coil, frame, centering support, dust cover, diaphragm, and surround, set the "Fixed Constraint" of the centering support and surround edge, set the "Surface Load" of the voice coil, and enter the corresponding material parameters; C. Use the "frequency domain" study type to simulate the acceleration on the radiation surface of the speaker vibration system and export it as a txt file; (2) Perform finite element simulation calculations on the closed space model, including: 1) Establish a closed space geometry model containing the speaker radiation surface, import the closed space model and speaker unit model into Comsol, and determine the orientation and position of the speaker unit.

[0009] 2) Import the sound absorption coefficient of the boundary material of the closed space and the vibration acceleration of the radiation surface of the loudspeaker unit obtained in step (1) 2); 3) Define the pressure acoustic physical field and set the vibration acceleration and boundary impedance of the speaker radiation surface; 4) Grid division: A. Determine the calculation frequency range to be 500-4000Hz, and select 9 frequency points in one-third octave band, namely 500Hz, 630Hz, 800Hz, 1250Hz, 1600Hz, 2000Hz, 2500Hz, 3150Hz and 4000Hz; B. When calculating each frequency point in step A, the maximum grid size is one sixth of the wavelength corresponding to the calculation frequency.

[0010] 5) Use the "frequency domain" study type to simulate the sound field information in the enclosed space, including the sound pressure level cloud map and the sound pressure level frequency response curve of any point in the enclosed space.

[0011] Preferably, the simulation analysis method is applicable to the mid-frequency band of all closed space sound fields containing loudspeakers.

[0012] Preferably, the frequency band of the frequency response is 500 Hz to 4000 Hz.

[0013] Preferably, the numerical simulation analysis software is not limited to COMSOL Multiphysics or ANSYS, and the geometric drawing software used is not limited to SolidWorks, ProE and CAD. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a 2D axisymmetric CAD drawing of a 6.5-inch car speaker; Figure 2 A flow chart for the implementation method; Figure 3 It is a 2D axisymmetric model of the loudspeaker magnetic circuit system; Figure 4 This is the simulation result of the loudspeaker driving force coefficient; Figure 5 This is a 3D model of one quarter of the speaker (excluding the air domain); Figure 6 Define function interpolation for closed spaces; Figure 7 for the closed space model (three car speakers); Figure 8 Definition of the acceleration type of "x-radiation surface"; Fig. 9 Definition of “z+radiation surface” acceleration type; Fig.10 Definition of the “z-radiation plane” acceleration type; Fig.11 This is the sound pressure level cloud diagram of the enclosed space (2000Hz); Fig.12 Three closed space concerns selected for this method; Fig.13 This is a comparison diagram between this method and the traditional finite element fully coupled method (point 1); Fig.14 This is a comparison diagram between this method and the traditional finite element fully coupled method (point 2); Fig.15 This is a comparison diagram between this method and the traditional finite element fully coupled method (point 3); Fig.16The simulation time comparison between this method and the traditional finite element fully coupled method is shown; Specific implementation methods The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. As shown in the drawings, the present invention is specifically described by taking a 6.5-inch car speaker and a simple car compartment model as examples.

[0015] The speaker is as Figure 1 As shown, the numerical simulation analysis software COMSOL Multiphysics (i.e., numerical simulation analysis software COMSOL) is used to explain the step-by-step coupling simulation method of the car speaker in the frequency band in the closed space using the finite element method. Figure 2 It is a flow chart of the implementation method of the present invention, and the specific steps are as follows: 1. Simulation calculation of loudspeaker magnetic circuit system: (1) Open COMSOL and enter the interface; (2) Establishing finite element model: 1) Determine the spatial dimension. This speaker is axisymmetric, so select "2D axisymmetric"; 2) Add a physical field and select "AC / DC>Electromagnetic field>Magnetic field (mf)"; 3) Select the research mode and choose "steady-state research"; 4) Add a study mode and select "Small Signal Analysis, Frequency Domain".

[0016] (3) Define parameters: 1) Number of coil turns N0: 84; 2) Residual magnetic flux density of magnetic steel B0: 0.375 (T); 3) Coil displacement coilx: 0 (mm).

[0017] (4) Establish a geometric model and import the existing 2D axisymmetric model of the loudspeaker magnetic circuit system, such as Figure 3 As shown; (5) Define the infinite element domain and the average operator; (6) Set up the physical field interface: define the BH constitutive relationship of "magnetic steel" and "soft iron", and the parameters of "coil"; (7) Define material properties: "air", "voice coil", "soft iron", "magnetic steel"; (8) Grid division; (9) Solution calculation: 1) Disable the defined "Coil > Harmonic Perturbation"; 2) Perform a parametric sweep (steady-state study) on the defined parameter coilx to obtain the driving force coefficient BL value of the car speaker, such as Figure 4 As shown, take the value of the driving force coefficient BL at x=0; 3) Enable the defined "Coil > Harmonic Perturbation"; 4) Conduct "frequency domain perturbation study" (steady state) to obtain the basic impedance curve of the car speaker, and derive the real and imaginary parts of the basic impedance curve (txt file).

[0018] 2. Simulation of the vibration acceleration of the loudspeaker unit radiation surface: (1) Open COMSOL and enter the interface; (2) Establishing finite element model: 1) Determine the spatial dimension and select "3D"; 2) Add a physical field and select "Acoustics > Pressure Acoustics > Pressure Acoustics, Frequency Domain (acpr)" and "Structural Mechanics > Shell (shell)"; 3) Select the study mode and select "Frequency Domain Study".

[0019] (3) Define parameters: 1) Input voltage V0: 4 (V); 2) Driving force coefficient BL: 7.516 (Wb / m).

[0020] (4) Setting variables: (5) Create a geometric model and import the existing 3D model of a quarter of a car speaker, such as Figure 5 As shown; (6) Define the infinite element domain and the average operator; (7) Define "Pressure Acoustics, Frequency Domain (acpr)", add "External Field Calculation (pext)" and set the "Symmetry Type" of the quarter 3D model; (8) Define "shell", "linear elastic material > damping", "thickness and offset", "fixed constraints", "symmetry conditions", and "surface loads"; (9) Define “Multiphysics > Acoustic-Structure Boundary”; (10) Grid division: the grid size is one sixth of the wavelength corresponding to the calculation frequency; (11) Solve the calculation and conduct "frequency domain study" with a frequency range of 500~4000 Hz (1 / 3 octave) and a calculation time of 12 min 8 s; (12) Data processing: export the normal acceleration of the speaker radiation surface at each frequency point (txt file).

[0021] 3. Simulation of a closed space containing a loudspeaker radiating surface (1) Open COMSOL and enter the interface; (2) Establishing finite element model: 1) Determine the spatial dimension and select "3D"; 2) Add a physical field and select "Acoustics > Pressure Acoustics > Pressure Acoustics, Frequency Domain (acpr)"; 3) Select the study mode and select "Frequency Domain Study".

[0022] (3) Define the function: Set "Interpolation" and import the normal acceleration of the radiating surface of the speaker at each frequency point obtained in step 2 as interpolation, such as Figure 6 As shown; 1) Create "Interpolation 1" and name it "xrealx", which is the real component of the normal acceleration of the speaker radiation surface in the x direction when the speaker radiation surface faces the x direction; 2) Create "Interpolation 2" and name it "xrealy", which is the real component of the normal acceleration of the speaker radiation surface in the y direction when the speaker radiation surface faces the x direction; 3) Create "Interpolation 3" and name it "xrealz", which is the real component of the normal acceleration of the speaker radiation surface in the z direction when the speaker radiation surface faces the x direction; 4) Create "Interpolation 4" and name it "ximagx", which is the imaginary component of the normal acceleration of the speaker radiation surface in the x direction when the speaker radiation surface faces the x direction; 5) Create "Interpolation 5" and name it "ximagy", which is the imaginary component of the normal acceleration of the speaker radiation surface in the y direction when the speaker radiation surface faces the x direction; 6) Create "Interpolation 6" and name it "ximagz", which is the imaginary component of the normal acceleration of the speaker radiation surface in the z direction when the speaker radiation surface faces the x direction; 7) Create "Interpolation 7", name it "alpha", select "Local Table" as the "Data Source", import the sound absorption coefficient txt file of the boundary material and set the unit.

[0023] (4) Create a geometric model and import the 3D model of the in-car sound field (three car speakers), such as Figure 7 As shown in the figure, six points of interest are set in the model, and the sound pressure level frequency response curve of any point can be derived later; (5) Select the radiation surface: 1) "Define > Select > Explicit", name it "x radiating surface", and select the speaker radiating surface facing the x direction; 2) "Define > Select > Explicit", name it "z+Radiating Surface", and select the speaker radiating surface in the z direction; 3) "Define > Select > Explicit", name it "z-Radiating Surface", and select the speaker radiating surface facing in the opposite z direction; (6) Setting the physical field interface: 1) Define "Pressure Acoustics, Frequency Domain (acpr)", add "Normal Acceleration 1", select "X-Radiation Surface" for "Boundary", and define its acceleration type, such as Figure 8 As shown; 2) Define "Pressure Acoustics, Frequency Domain (acpr)", add "Normal Acceleration 2", select "z+Radiating Surface" for "Boundary", and define its acceleration type, such as Fig. 9 As shown; 3) Define "Pressure Acoustics, Frequency Domain (acpr)", add "Normal Acceleration 3", select "z-Radiating Surface" for "Boundary", and define its acceleration type, such as Fig.10 As shown; 4) Define "Pressure Acoustics, Frequency Domain (acpr)", add "Impedance", select "Absorption Coefficient" for "Impedance Model", and set "Normal Incidence Absorption Coefficient" to "Interpolation 7" > "Alpha".

[0024] (7) Grid division: the grid size is one sixth of the wavelength corresponding to the calculation frequency; (8) Solve the calculation, Fig.11 It is the sound pressure level cloud map of the in-car sound field model, and the sound pressure level frequency response curve of the concerned point can also be obtained; (9) This method is compared with the traditional finite element fully coupled method (calculation time, calculation results). The three car interior sound pressure level concerns are as follows: Fig.12 As shown, the calculation frequency band is 500-4000Hz, and the comparison chart is as follows Fig.13 , 14 , as shown in 15.

[0025] It can be concluded that this method can ensure the calculation accuracy and greatly reduce the calculation time based on the traditional finite element fully coupled simulation method: (1) Calculation accuracy: The average difference between this method and the traditional finite element fully coupled method is about 2 dB; Calculation time: The calculation time of the traditional finite element fully coupled method at 500Hz-4000Hz is about 30min. The calculation time of this method in 500Hz-4000Hz is about 15min. Fig.16 shown.

Claims

1. A step-by-step coupling simulation analysis method for the mid-frequency sound field of multiple loudspeakers in a closed space, characterized in that The method comprises at least the following steps: (1) Perform finite element simulation calculations on the loudspeaker unit, including: Simulation calculation of the loudspeaker's magnetic circuit system; Obtain the relevant parameters of the magnetic circuit system, including: the geometric dimensions of the magnet, soft iron and coil, the residual magnetic flux density B0 of the magnet, the number of coil turns N0, and obtain the driving force coefficient BL value and basic impedance Zb of the speaker through simulation calculation: A. Import the 2D geometric model of the loudspeaker magnetic circuit system and surrounding air into the numerical simulation analysis software Comsol; B. Set all geometric model regions to the "Magnetic Field" physical field interface, set the "Constitutive Relationship" "BH>Magnetization Model" of the magnetic steel and magnetic soft iron materials to "Residual Magnetic Flux Density" and "BH Curve" respectively, and enter the corresponding material parameters; C. Use the "steady state" study type to simulate and obtain the driving force coefficient BL and basic impedance Zb of the voice coil at different geometric positions in the magnetic gap; Simulation calculation of the speaker's vibration system and acoustic field coupling; The geometric dimensions and material parameters of the voice coil, skeleton, centering support, folded ring, elastic wave, dust cover and diaphragm in the vibration system are obtained. The BL value and basic impedance Zb of the speaker in step 1) are used as input parameters, and the vibration acceleration of the radiation surface is obtained by simulating the speaker vibration system. 2.A. Import the 3D geometry model of the speaker vibration system and surrounding air into Comsol; B. Set the vibration system to the "Shell" physics interface, set the "Thickness and Offset" of the voice coil, frame, centering plate, dust cover, diaphragm, and surround, set the "Fixed Constraint" of the centering plate and surround edge, set the "Surface Load" of the voice coil, and enter the corresponding material parameters; C. Use the "frequency domain" study type to simulate the acceleration on the radiation surface of the speaker vibration system and export it as a txt file; (2) Perform finite element simulation calculations on the closed space model, including: Establish a closed space geometry model containing the speaker radiation surface, import the closed space model and speaker unit model into Comsol, and determine the orientation and position of the speaker unit; Import the sound absorption coefficient of the boundary material of the closed space and the vibration acceleration of the radiation surface of the loudspeaker unit obtained in step (1) 2); Define the pressure acoustics physical field, set the vibration acceleration and boundary impedance of the speaker radiation surface; Grid division: A. Determine the calculation frequency range to be 500-4000Hz, and select 9 frequency points in one-third octave band, namely 500Hz, 630Hz, 800Hz, 1250Hz, 1600Hz, 2000Hz, 2500Hz, 3150Hz and 4000Hz; B. When calculating each frequency point in step A, the maximum grid size is one sixth of the wavelength corresponding to the calculation frequency; The "frequency domain" study type is used to simulate the sound field information in the enclosed space, including the sound pressure level cloud map and the sound pressure level frequency response curve of any point in the enclosed space.

3. The method for step-by-step coupling simulation analysis of mid-frequency sound field of multiple loudspeakers in a closed space according to claim 1, characterized in that: This simulation analysis method is applicable to the mid-frequency band of all closed space sound fields containing speakers.

4. The method for step-by-step coupling simulation analysis of mid-frequency sound field of multiple loudspeakers in a closed space according to claim 1, characterized in that: The frequency response has a frequency band of 500 Hz to 4000 Hz.

5. The method for step-by-step coupling simulation analysis of mid-frequency sound field of multiple loudspeakers in a closed space according to claim 1, characterized in that: The numerical simulation analysis software is not limited to COMSOL Multiphysics or ANSYS, and the geometry drawing software used is not limited to SolidWorks, ProE and CAD.

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