Ole Wolff Elektronik A/S, Roedengvej 14, 4180 Soroe
sales@owolff.com, T: +45 5783 3830
21-09-2021

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Simulation in COMSOL Multiphysics

Simulating mechanical, electrical and acoustical properties

Simulating both mechanical, electrical and acoustic parameters


Ole Wolff have been using COMSOL Multiphysics® 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.

Magnetic analysis

Simulating the motor

Streg

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



Comsol axisymmetric magnetic simulation


Mesh used in the axisymmetric magnetic simulation
flux density in the magnet system a


Plot of flux density in the magnet system
the acoustic analysis._1a


Coil resistance and reactance as function of frequency is derived. These analysis results are later used as lumped parameters in the acoustic analysis.
the acoustic analysis a


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.

Streg

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 .


Comsol analysis mechanical_1a

Displacement and breakups at selected frequencies.


Comsol analysis mechanical_1


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.


Read more about diaphragm design



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.


Comsol_acoustic analysis a

Example of tuning the acoustics of an earphone by blocking leakage holes and reducing front volume using sticky tack.


Comsol_impedance a


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 a


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.
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.


Streg

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