Modelling and visualization of surround buckling in electrodynamic audio transducers

The surround (or front-suspension) of electrodynamic transducers typically used in loudspeakers and headphones is a device that provides the axial restoring force for the diaphragm movement and restrains the lateral and tilting movements. A non-linear phenomenon typical of surrounds is pressure-induced buckling, a sudden change in the shape of the surround under load. The question addressed by this paper is how to predict the conditions under which a surround will buckle, and how to measure and visualize it in physical prototypes. The modelling methodology was based on structural finite-element analysis, while the measurement of transducer displacement and video recording with a high-speed camera allowed the experimental verification. This methodology has been applied and tested on semi-circular rubber surrounds. The impact of working temperature and manufacturing tolerances are also discussed. It was found that it's possible to predict the pressure threshold triggering a specific buckling mode within a 10% error. Full 3D modelling is advisable to assess the buckling pressure of non-axisymmetric modes common in real transducers. At the same time, 2D modelling has been proven enough for the evaluation of the worst-case scenario / lowest buckling pressure.