Notch filter design calculator – for speakers
using Re, Qes, Qms and fs

The function of the series notch filter is to dampen the effects the driver resonance has on filter networks. Most drivers has a large impedance peak at it's resonance.
For crossovers to works as expected, it's important to have a nearly resistive impedance, at least in the crossover frequency region. Most drivers benefits from using notch filters, specially tweeters and midranges where the component values can be kept small. Using this filter on bass drivers calls for very large (and expensive) components.
Many modern tweeters are using magnetic oil (Ferrofluid) in the voice coil gap to mechanically damp the resonance. These tweeters will probably not need such a curcuit, or does not depend so much on it.

  • Re: The DC resistance. Not to be confused with the impedance of the driver. The driver impedance depends on frequency anyway. DC resistance is like taking the voice coil of the speaker and pretend it’s a resistor.
  • Qes: Also called electrical Q – The damping made by the coil – magnet assembly. When the coil moves through the magnetic field, it generates a current which opposes this motion (hence the electrical damping). Another factor which contributes to the electrical damping is the amplifier. This depends on your particular amplifier. The Qes provided by the speaker manufacturer does not include amplifier damping, for he does not know which amplifier you are going to use.
  • Qms: Also called mechanical Q – The damping made by the suspension of the driver : the surround and the spider of the speaker.
  • fs: resonant frequency of speaker

  • The absorption circuit can also be placed in front of the complete crossover to smooth impedance peaks for e.g. tube amplifiers.


Re – DC resistance Ohm
Qes – Electrical Q factor
Qms – Mechanical Q factor
fs – resonant frequency Hz


R = Ohm
L = mH
C = uF
Start Frequency: 10 Hz
Stop Frequency: 25000 Hz

Notch filter design calculator – for speakers using the Inpedance Curve

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