FEM Simulation in Loudspeakers Design: Focus on Mechanical and Acoustic-Structural Analysis
Finite Element simulations are becoming an increasingly powerful tool in the transducer design process. The development of user-friendly software and predefined interfaces able to provide physics setup to predict the loudspeaker complex behavior helps designers in the product development and/or improvement.
During the development, designers may be focused on several aspects at the same time, such as the kind of electro-acoustic device (i.e. cone loudspeakers, compression driver, etc.), the frequency useful range and the industrial application/area of applicability.
In this work, we will focus on the mechanical analysis of both non-moving and moving parts and the acoustic-solid interaction problem. Other types of simulation (i.e. magnetic circuit analysis [1], thermal analysis [2] or non-linear acoustic models) are usually performed, but we will not face this topic in the current study.
Non-moving parts
Both in the automotive and professional audio industry, loudspeakers need to be developed according to the technical specifications related to the application and typical usage. Eigenfrequency and quasi-static analysis, resistance to vibration and shock, fatigue and PSD analysis are usually required.
If needed, non-linear effects in material behaviour or pre-stress conditions, due to the counterpart mounting configurations, may be considered. These tests are usually developed together with a parametric geometrical model to highlight geometry influence on the mechanical response.
Moving parts
Analyzers are mainly focused on the definition of the geometry of dust cup-membrane-spider (cone loudspeakers) or dome/annular diaphragm (high frequency driver) to answer technical specifications. Performed analysis are eigenfrequency studies and vibration response. Variables of interest are eigenfrequencies, stress distribution and the approximate evaluation of sound pressure level. Variables are monitored as functions of material and geometrical parameters.
Acoustic Solid Interaction problem
Acoustic-structure interaction models are developed to evaluate virtual prototypes and to compare with experimental data. COMSOL Multiphysics® provides the Acoustic-Solid Interaction interface to reproduce the reciprocal influence between the movement of the diaphragm and the acoustic pressure of the air surrounding the speaker. Thermal and Viscous losses may be taken into account, adding the proper physics node.
Coupled models are developed both for woofer and high frequency driver. Nevertheless, the compression driver design process is also characterized by the development of phase plugs [3] [4]. Phase plug development is usually performed thanks to the development of optimization strategies [5].
Simulation analysis allow to decrease the number of physical prototypes, and the accuracy prototypes performance improvement Vs expectation helps the time-to-market reduction.
[1] S.G.T.R. Baratelli, "A finite element approach to predicting the effect of the demodulation ring in a loudspeaker," in CAE Conference, 2017.
[2] S.G.C.E.T.R. Baratelli, "FEM Thermal Model of a Compression Driver: Comparison with Experimental Results," in AES, 2018.
[3] O.-B.J., Wideband Compression Driver Design Part 1: a theoretical Approach to design Compression Driver with non -rigid Diaphrams, in 139th AES, New York, 2015.
[4] D.M., "Wideband Compression Driver Design. Part 2: application to a high power compression driver with a novel Diaphram geometry," in 139th AES, New York, 2015.
[5] B.A., "Numerical Optimization Strategies for Acoustic Elements in Loudspeakers Design," in 145th AES, 2018.
