Electrical Model for Vented Enclosure



Calculate Res - Lces - Cmes - Rep - Reb - Lceb - Cmep
for the vented 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 measured in millihenries (mH) (measured at 1 kHz).
  • fs = is the free-air resonant frequency of a speaker
  • Bl = The product of magnet field strength in the voice coil gap and the length of wire in the magnetic field, in tesla-metres (T·m).
  • Mms = Mass of the diaphragm/coil, including acoustic load, in kilograms. Mass of the diaphragm/coil alone is known as Mmd
  • Cms = Compliance of the driver's suspension, in metres per newton (the reciprocal of its 'stiffness').
  • Rms = The mechanical resistance of a driver's suspension (i.e., 'lossiness') in N·s/m
  • Vas = The Thiele-Small parameter that measures the overall compliance of a loudspeaker transducer. The Vas is defined as the volume of air that has the same compliance as the driver.
  • Qms =The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a driver at Fs, considering only its mechanical (non-electrical) resistances.
  • Qes = The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a driver at Fs, considering only its electrical (non-mechanical) resistances.
  • Qts = The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a driver, considering both mechanical and electrical resistances.
  • Sd = Projected area of the driver diaphragm, in square metres.


  • Res = Mechanical Damping Speaker
  • Lces = Compliance Speaker
  • Cmes = Moving Mass Speaker

  • Reb = Enclosure Losses
  • Lceb = Compliance Enclosure
  • Cmep = Compliance Port
  • Rep = Port Losses


Parameter Input


Voice Coil DC Resistance, Re [Ω] = Equivalent Stiffness Air Volume, Vas [L] =
Voice Coil Inductance, Le [mH] = Mechanical Quality Factor, Qms =
Resonance Frequency, Fs [Hz] = Electrical Quality Factor, Qes =
Motor Force Factor, Bl [Tm] = Total Quality Factor, Qts =
Moving Mass, Mms [g] = Piston Surface, SD [m^2] =
Compliance, Cms [mm/N] =
Mechanical Resistance, Rms [kg/s] =
Enclosure Volume, Vb [L] =
Vent Length, Lvent [mm] =
Vent Diameter, Dvent [mm] =




Calculations:




Plot Impedance Curve




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