Speaker equivalent circuit / electrical model
for free air



Calculate Res - Lces - Cmes for the electrical speaker model


The speaker equivalent circuit is the actual core of the theories crafted by Thiele and Small.
Every component of a speaker can be “transformed” into an electrical component, to form a circuit that acts exactly the same as the speaker (electrically).

Now imagine that you get different resistors, inductors and capacitors, and arrange them in such a way, that when you measure the impedance of this newly formed circuit, it’s exactly the same as the impedance of the speaker. A similar thing happens when you place the speaker in a box. Additional components are added to the circuit. That is how Thiele and Small manage to predict the behavior of enclosures.

  • Re = DC resistance of a loudspeaker transducer, measured in ohms.
  • Le = Voice coil inductance in mH
  • fs = is the free-air resonant frequency of a speaker
  • Re = Voice Coil DC Resistance, Re [Ω]
  • Bl = Motor Force Factor, Bl [Tm]
  • Cms = Compliance, Cms [mm/N]
  • Mms = Moving Mass, Mms [g]

  • Lces = Cone mass
  • Res = Cone Losses
  • Cmes = Cone Suspension



Voice Coil DC Resistance, Re [Ω] =
Voice Coil Inductance, Le [mH] =
Resonance Frequency, Fs [Hz] =
Motor Force Factor, Bl [Tm] =
Moving Mass, Mms [g] =
Compliance, Cms [mm/N] =
Mechanical Resistance, Rms [kg/s] =


You will need the following tools:

LTSPICE: http://www.linear.com/designtools/software/
Speaker datasheet or own measurements


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