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.