I found this crossover circuit in a construction set and it puzzled me a while. I have absolutely no idea, why I should combine a 2nd order low pass with half a band stop. The low pass alone has a corner frequency of roughly 155Hz. A full scale notch filter would have a center frequency of roughly 73Hz (impedance as shown).


simulate this circuit – Schematic created using CircuitLab

Finally the sub woofer sits in a very small enclosure (<10L) and is itself quite small. The vented cabinet seems to be tuned as expected (Hoge). I'm a bit uncertain about that since the parameters (volume, opening's surface and high channel length) don't differ that much in comparison to tunings over-emphasizing at the lower end (B4).

So I assume this is an additional filter trick to make the small thing sound better at lower frequencies. There is a peak at 34Hz before the band stop takes over, a drop around the mid frequency and the expected cut off now at roughly 210Hz.

Is this correct or did I miss something? There is no additional filter stage for satellite speakers. And my goal is to replace the passive filter network with an active one (before the amplifier).

  • \$\begingroup\$ It's possible that it's meant to compensate for the speaker's resonance, but if so, it's a poor way to do it. I don't know what "correct" can mean, everyone seems to have their own ideas, but you can try to see the response with and without the notch. It could be that the speaker's resonance is unusually high? \$\endgroup\$ – a concerned citizen Nov 29 '20 at 9:12
  • \$\begingroup\$ If you would have posted this as answer I'd have accepted it. I came to no other conlusion. And yes, the rather small speaker in that small cabinet has a rather high resonance frequency then. I also examined similar designs of the same manufacturer, some of them do the same. Brilliant way to sell expensive sets of crossovers. \$\endgroup\$ – motzmann Dec 3 '20 at 13:11
  • \$\begingroup\$ It would hardly make an answer for an uncertainty. Assuming the amp output resistance is 0.1 and some series resistances for inductors, a comparison between a bare resistor and a rather bogus speaker shows minimal differences. Then again, the box is not included, which would imply even more assumptions. Best leave it to your conclusion: they "sound" different. It may even be an answer. \$\endgroup\$ – a concerned citizen Dec 3 '20 at 14:13
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    \$\begingroup\$ I know experts that hear the difference of oxygen saturation in cables. Nevertheless: thanks. I'm going to check the electronic version with and without a notch filter. \$\endgroup\$ – motzmann Dec 3 '20 at 16:56

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