Simulation in COMSOL Multiphysics
Simulating mechanical, electrical and acoustical properties
Losses in iron
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COMSOL Multiphysics enables Ole Wolff to make confident decisions based on simulation results and optimize parts of acoustic products for best price/performance ratio.
Agreement between CAD drawing and physical samples is key to obtain correct simulation results.
Magnetic analysis
Simulating the motor
2D Axisymmetric simulation includes
Plots gives insight about
Mesh used in the axisymmetric magnetic simulation.
Plot of flux density in the magnet system.
Coil resistance and reactance as function of frequency is derived. These analysis results are later used as lumped parameters in the acoustic analysis.
The BL(x) plot is very close to the measured Klippel response and reveals that the voice coil is slightly off-center. Ole Wolff have both Comsol for simulation and Klippel for verification, which is a very powerful combination.
Mechanical analysis
Simulating the diaphragm.
The diaphragm is analyzed using a combination of Solid Mechanics for the voice coil and Shell physics using geometric nonlinearities for the diaphragm.
In the static study, diaphragm deformations and stresses can be displayed.
Displacement and breakups at selected frequencies.
The cms analysis has pretty good agreement with the Klippel data. Correlation between simulation and test data will always depend on the initial accuracy of the CAD file and production tolerances of the tested unit.
Acoustic analysis
Combining physics to simulate the resulting acoustic output.
The acoustic analysis is performed using the following physics:
- Solid and Shell mechanics (for the diaphragm and voice coil)
- Electrical Circuit (for lumped parameters)
- Solid-Shell connection (for the diaphragm and voice coil)
- Acoustic-Structure boundary x2 (couples the diaphragm and voice coil to the air)
The lumped motor of the speaker couples the voice coil impedance as well as the (static) BL value found in the magnetic study to the force on the voice coil in the mechanical study using the relation
Force = BL*i
Feedback to the motor is ensured via the voltage source with the voltage defined as BL*v0, with v0 being the voice coil velocity.
Example of tuning the acoustics of an earphone by blocking leakage holes and reducing front volume using sticky tack.
Simulated impedance curve shows very good agreement with test results. The rear hole resonance is visible at around 7.7 kHz due to the feedback to the lumped motor.
The sensitivity plot also shows very good agreement with the measurement. There are some losses in the rear holes (resonance around. 7.7kHz) that are not included in the basic Pressure acoustic analysis. To simulate theses losses, a Thermoviscous Acoustics study could be used for high precision. Alternatively a simpler “resistive” impedance could be applied to the rear holes.
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