Ole Wolff Elektronik A/S, Roedengvej 14, 4180 Soroe
sales@owolff.com, T: +45 5783 3830
12-08-2020

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Simulation in COMSOL Multiphysics®

Simulating mechanical, electrical and acoustical properties.

Ole Wolff have been using COMSOL since 2016 and are now using it to simulate both mechanical, electrical and acoustical parameters of loudspeakers and enclosures.


This page gives a quick overview of some of these simulations using the (now discontinued) 19mm speaker OWS-1943T-8CP as an example.


This particular Ole Wolff speaker has been modeled in close cooperation with COMSOL and is now featured as a model in the COMSOL Multiphysics® software.

OW_comsol

Magnetic analysis

Simulating the motor

2D Axisymmetric simulation includes:

  • Losses in iron
  • Thin low permeability gaps between iron and magnets due to glue.

Plots gives insight about

  • Static flux density
  • Induced current density at various frequencies
  • Saturation of iron

Also very useful for optimizing magnet and iron for performance and cost.


Comsol_motor
Mesh used in the axisymmetric magnetic simulation
Comsol_motor2
Plot of flux density in the magnet system.
Comsol_coil1
Coil resistance and reactance as function of frequency is derived. These analysis results are later used as lumped parameters in the acoustic analysis.
Comsol_BL

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 .


OW_comsol_ows-1943_dp_analysis
Displacement and breakups at selected frequencies.
Comsol_cms

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)
  • Pressure acoustics
  • 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.


Comsol_acoustic1
In the pressure acoustics study, the front grill, rear holes and casing is set up as sound hard boundaries, to take internal resonances into account.
Comsol_acoustic2
Using the Acoustic-structure physics, diaphragm breakups and rocking modes are included in the acoustic analysis.
Comsol_impedance
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.
Comsol_SPL
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.

Conclusion

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.



Acoustics_designed_and_engineered_in_Denmark_LOWRES