Loudspeaker and Crossover Simulation with Qucs

In the Acoustics 2 course we had a practical part where we determined the Thiele-Small parameters of loudspeaker chassis and with there help designed the loudspeaker cabinet volume and the crossover network.

To get more insight into the Thiele-Small parameters and the design of crossover networks for loudspeakers I used Qucs to do some simulations.

The project contains five independent simulations:

  • Thiele-Small-Messung, a simple calculations sheet, processing the measured data
  • Thiele-Small-simulation, simulation of the classical Thiele-Small equivalent circuit for a loudspeaker chassis. Displays impedance, sound power and sound particle flux.
  • woofer, extension to the Thiele-Small-simulation, includes a impedance resonance compensation network
  • crossover, calculates the 2-way crossover network component values based on separation frequency and woofer/tweeter impedance. Simulates the resulting crossover network.
  • crossover_real, simulation of a simple 2-way crossover network. Used to verify the frequency response when using real component values instead of the calculated ones.

Example

This is the schematic for a classical Thiele-Small simulation. Note that all simulation parameters, constants, user changeable variables etc. are visible in the schematic and therefor automatically included in the documentation. It is possible to define more than one simulation per schematic.

The simulation results show the expected impedance curve with its dominant parallel resonance and its rise with higher frequencies due to the coil impedance.

The blue sound particle flux curve is equivalent to the frequency response of the chassis. This curve is only a first approximation as there are more effects which are not included in the Thiele-Small model.

I would like to thank Jürgen Micka for publishing his works on loudspeaker simulation and his introduction into Thiele-Small simulations with LTspice. This was very helpful and gave me a reference to compare my results with.

Discussion

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