
PAFEC VibroAcoustics  Large displacement analysis of a spider 

The spider (suspension / outer centering device (OCD)) is excited
via the former.
At low frequencies the former tends to vibrate with relatively large
amplitude. It is important to avoid distortion of the spider due to nonlinearity
within the normal operating range, but beneficial if the stiffness
increases for larger extensions, to prevent "jump out" from the gap.
With the corrugated design, small axial movement is opposed by the
bending stiffness. Near maximum displacement as the corrugations begin to
flatten out, membrane stiffness (material) properties predominate.
Finite element analysis can be used to compute the load/displacement curve.


270^{o} cutaway of spider


Finite element model of a loudspeaker spider 
Maximum positive deformation

Maximum negative deformation

At small displacements the strains and rotations are assumed to be infinitesimal and the load displacement response is linear; as can be seen by the central linear section of the large displacement graph (blue line). When the deformation includes large rotations, the assumptions of linear theory are no longer appropriate, and it becomes necessary to choose a more accurate strain measures (objective). The large displacement solution shown opposite is based on a total Lagrangian formulation using the logarithmic strain. 
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