Summary of the invention
The objective of the invention is to design the method for numerical simulation of a kind of loudspeaker vibration and acoustic characteristic.
The present invention will solve is the design later stage of must waiting until that empirical method exists could find loudspeaker problem and the construction cycle is long, cost the is high problem and the problem that when frequency is higher, can't analyze loudspeaker performance with equivalent electrical circuit of equivalent circuit method existence.
The vibration of a kind of loudspeaker of the present invention and the method for numerical simulation of acoustic characteristic, concrete steps are:
(1) use three-dimensional drawing software to draw three-dimensional (3D) the geometric model figure of loudspeaker.
(2) set up the loudspeaker finite element model.Concrete steps are following:
A, loudspeaker 3D geometric model figure is imported grid dividing software, it is carried out grid dividing, obtain the used body unit of finite element analysis.If need to consider the influence of air, also in model, add air and be body unit its grid dividing to loudspeaker vibration.
B, definition unit type.Define the cell type that is complementary for each several part unit in the A step.
C, definition material parameter.The material parameter of each parts of definition model comprises Young modulus, Poisson ratio, density and material damping.If comprise air in the model, also need define the material parameter of air, comprise the velocity of sound, density and acoustical absorption coefficient.
D, definition boundary condition.The boundary condition of loudspeaker finite element model is following: 1) fixed boundary condition.Because diaphragm of loudspeaker edge is fixed on the basin frame, need at its edge definition fixed boundary condition, if loudspeaker also includes locating branch slice, the edge that it and basin bridge joint touch also should define fixed boundary condition; 2) the solid coupled boundary condition of stream.If consider air influence when analyzing the vibration characteristics of loudspeaker, coupling can take place at the surface of contact of loudspeaker and air, need to flow coupled boundary condition admittedly in the interphase definition of loudspeaker and air.
E, give the finite element model imposed load, apply driving force at the voice coil loudspeaker voice coil position of model.
F, above-mentioned model is saved as the finite element model file.
(3) set up the loudspeaker boundary element model.The surface of extraction loudspeaker finite element model obtains the veil lattice with finite element model body unit coupling; Because baffle has very big influence to the acoustic characteristic of loudspeaker; Also to set up the veil lattice of baffle, define the cell type of above-mentioned veil lattice, above-mentioned model is saved as the boundary element model file.
(4) with the finite element solving device finite element model file is found the solution.The finite element model file is imported the finite element solving device and carries out model analysis, can obtain the natural frequency and the mode of oscillation (vibration shape) of loudspeaker, carry out frequency analysis again, can obtain displacement response, strain-responsive and the stress response of loudspeaker.
A, finite element model is carried out model analysis
The fundamental equation of dynamic analysis is following:
In the following formula; [M] is the mass of system matrix; [C] is the system damping matrix; [K] is the system stiffness matrix;
is the node vector acceleration,
be the node speed vector, { u} is the nodal displacement vector; { F} is the load vector that applies, with time correlation.
Suppose that loudspeaker does undamped-free vibration, equation is:
For linear system, suppose that system does simple harmonic motion
{u}={u}
i?cosω
it
The above-mentioned equation of motion becomes
([K]-ω
i 2[M]){u}
i={0}
Find the solution above-mentioned equation and can obtain ω
i{ u}
i, ω
iBe the intrinsic circular frequency in i rank, { u}
iBe proper vector, i.e. the corresponding mode of oscillation (vibration shape) of the intrinsic circular frequency in i rank.
is i rank natural frequency.
B, finite element model is carried out frequency analysis
In frequency analysis, { F}, { u} is a simple harmonic quantity.Have:
{F}=({F
1}+i{F
2})e
iΩt
{u}=({u
1}+i{u
2})e
iΩt
([K]-Ω
2[M]+iΩ[C])({u
1}+i{u
2})={F
1}+i{F
2}
In the following formula, { u
1, { u
2Be respectively the real part and the imaginary part of displacement, { F
1, { F
2Being respectively the real part and the imaginary part of loading force, Ω is the angular frequency of loading force.
Find the solution above-mentioned equation and can obtain the real part { u of displacement
1And imaginary part { u
2, further can derive strain and stress by displacement.
(5) the finite element solving device is found the solution the displacement and the boundary element model file that obtain and be submitted to the boundary element solver, can find the solution the frequency response curve and the directive property curve that obtain loudspeaker.
In isotropic ideal fluid medium, for the sound wave that simple harmonic quantity changes, acoustic pressure satisfies Helmholtz equation:
▽
2p(r)+k
2p(r)=0
According to divergence theorem, can above-mentioned equation be become borderline integral equation:
In the formula, k is the wave number of sound wave, and p (r) is the acoustic pressure of any arbitrarily in the outer sound field of loudspeaker, r
qFor on the border a bit, G (r, r
q) be Green function, n
qUnit normal vector for the border.
In the formula, p
0=2 * 10
-5Pa is a reference acoustic pressure.
Solve the sound pressure level of loudspeaker under ad-hoc location (referring generally to the position along acoustic axis line direction apart from loudspeaker acoustic centre of source 1m) different frequency and can obtain frequency response curve, the sound pressure level that solves loudspeaker space diverse location under a certain CF can obtain the directive property curve.
Used loudspeaker comprises various dynamic loudspeakers.
Described through finding the solution the undamped-free vibration secular equation analysis of loudspeaker finite element model, the multiple mode of oscillation of analysis loudspeaker comprises plug vibration, rocking vibration, flexural vibrations, twisting vibration and compound vibration thereof.
Described three-dimensional drawing software is Pro/E, draws the 3-D geometric model figure of loudspeaker with its, and Pro/E is the incorporate three-dimensional software of a CAD/CAM/CAE, and function comprises that Element Design, mould design, sheet metal component design, virtual assembling and engineering publish picture.
Described grid dividing software is HyperMesh, can divide grid to loudspeaker 3D geometric model with it.
Described finite element solving device is finite element software ANSYS, is used for finding the solution structure, fluid, heat, electromagnetic problem.The boundary element solver is LMS Virtual.Lab, sunykatuib analysis vibration noise characteristic.
Advantage of the present invention is: the present invention designs finite element method and Application of Boundary Element Methods in the loudspeaker analysis; Overcome the shortcoming that equivalent circuit method is confined to low frequency effectively; And can have a fling at the performance of estimating loudspeaker early stage at sample, thus accelerate the loudspeaker design progress, reduce cost of development.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is further described.
The present invention is an example with 6.5 inches auto loud hailers, its vibration of sunykatuib analysis and acoustic characteristic.As shown in Figure 1, step of the present invention is following:
Step 1: use three-dimensional drawing software Pro/E to create loudspeaker 3D geometric model figure.
Fig. 2 is the 3D geometric model figure of this loudspeaker 1, and Fig. 3 is the diagrammatic cross-section of this loudspeaker 1, can be known by figure; This loudspeaker 1 is made up of three parts: (1) magnetic circuit system; Comprise T iron 11, magnet steel 10 and train wheel bridge 9, mainly produce magnetic field, can produce driving force energized coils; (2) vibrational system comprises paper awl 6, dust cap 2, ring 3, locating branch slice (bullet ripple) 7, skeleton 8 and voice coil loudspeaker voice coil 8-1, vibration and radiate sound under driving force; (3) backup system comprises basin frame 5 and flanging 4, supports to reach fixedly vibrational system.
Step 2: set up loudspeaker finite element model (see figure 4).Concrete steps are following:
1) the loudspeaker three-dimensional model is imported in the HyperMesh software,, driving force is provided, in the numerical simulation process, be equivalent to the effect of load to speaker vibration system because the magnetic circuit of loudspeaker mainly produces uniform magnetic field.Loudspeaker backup system significant feature is fixing vibrational system, in the numerical simulation process, may instead be fixed boundary condition.Like this, only need in HyperMesh, paper awl 6, ring 3, dust cap 2, voice coil loudspeaker voice coil 8-1 and skeleton 8 to be carried out the body unit that grid dividing obtains each several part.
2) definition unit type.Cell type is selected the Solid45 unit for use.
3) definition material parameter.For this routine loudspeaker 1; It is polypropylene (pp) that 2 of vibrating diaphragm and dust caps are selected material for use, and ring 3 materials are rubber, and locating branch slice (bullet ripple) 7 materials are cotton; Skeleton 8 materials are polyimide (kapton); Voice coil loudspeaker voice coil 8-1 material is a copper, and the material properties of definition above-mentioned material comprises Young modulus, Poisson ratio, density and material damping.
4) definition boundary condition.Because loudspeaker ring 3 is fixed on the basin frame 5 with locating branch slice 7 edges, at the edge of loudspeaker ring 3 and locating branch slice 7 definition fixed boundary condition (along coordinate system x, y, the translation of z axle and rotation displacement are 0).
5) imposed load.On voice coil loudspeaker voice coil 8-1, apply size and be the power of Bil, direction is parallel to voice coil loudspeaker voice coil 8-1 direction of motion, and wherein B is a magnetic density, and i is the electric current of flowing through voice coil 8-1, and l is the length of voice coil loudspeaker voice coil 8-1 lead.
6) preserve the finite element model file.
Step 3: set up the boundary element model (see figure 5).From paper awl 6, ring 3, the body unit surface extraction of dust cap 2 and the veil lattice that body unit is complementary, set up baffle veil lattice again.The veil lattice are selected the shell63 unit for use, preserve the boundary element model file.
Step 4: the finite element model file is imported ANSYS, carry out model analysis, obtain the natural frequency and the mode of oscillation of loudspeaker, several kinds of typical mode of oscillations are seen Fig. 6 A~Fig. 6 C; Carry out humorous response analysis, calculate loudspeaker under a series of frequencies response and obtain displacement, stress, strain curve with change of frequency.Fig. 7 is the displacement curve of analog computation.
Step 5: the displacement result of boundary element model file and step 4 is imported LMS Virtual.Lab, find the solution the frequency response curve and the directive property curve that obtain loudspeaker.Fig. 8 is the frequency response curve of analog computation.Fig. 9 is the directive property utmost point figure of the 1kHz of analog computation.
Above embodiment only in order to the explanation the present invention and and unrestricted technical scheme described in the invention.Therefore, although this instructions has carried out detailed explanation to the present invention with reference to each above-mentioned enforcement,, those of ordinary skill in the art should be appreciated that still and can make amendment or be equal to replacement the present invention; And all do not break away from the technical scheme and the improvement thereof of the spirit and scope of the present invention, and it all should be encompassed in the claim scope of the present invention.