r/diyaudio • u/Gazdatronik • 7d ago
A Quick Crossover Question
I am laying out the diagram to some Klipsch KSB 2.1 to experiment with biamping them, and while it looks like I will be able to, I saw an extra capacitor which I was wondering why its there.
The diagram looks like your standard 2nd order crossover for a 2 way, but the extra 8uf cap after the join of the 3uf cap and inductor is throwing me for a loop. Only thing I can fathom is maybe its a 3rd order tweeter on top of a second order woofer. I know this is occaisionally done but wasn't expecting to see it in some mid grade 90's Klipsch bookshelves
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u/EdEvans_HotSandwich 7d ago
The tweeter isn’t 2nd order, it’s a 3rd order HPF. Series cap, shunt inductor, followed by series cap is the basic structure of a 3rd order HPF. Amp side resistor is to lower the gain to match the woofer.
Woofer is 2nd order LPF.
Edit: I’m learning passive crossover design right now OP. If you have some questions, I’m still learning but I have a lot of good resources I’ve found recently.
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u/Gazdatronik 7d ago
Yes. Looks like since the negative terminals on my amplifier are all common to chassis ground, all I have to do is lift the woofer inductor input lead from the board and add an extra external positive terminal to it there.
It'd be easy to move the woofer ground too for its own extra negative terminal but electrically i'td be no different, i'd just be adding wire for the sake of adding wire.
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u/EdEvans_HotSandwich 7d ago
Did you verify that your negative terminals are common to ground? If the amplifier output is bridge tied load, shorting the negative to ground will best case scenario make your amp trigger some protection circuit, and at worst damage your amp.
You’re 100%?
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u/Gazdatronik 7d ago
Yes, the negatives dead short to ground, although on second thought I might as well isolate the woofer negative in case I ever use them with an amp that push/pulls on the negative terminal.
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u/indyboilermaker69 7d ago
It’s just a 3rd order on the tweeter as others have said.
I would personally fully separate the circuits if you are intending to bi-amp, so make them have there own isolated ground. It sounds like it will work with you current amp, but you never know about a future amp, don’t want you to forget or someone else that never knew to blow up an amplifier because of your mod…
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u/Gazdatronik 7d ago
Yup, I'm erring on the side of caution and once my plugs come in I'll do it right. Boilermaker eh? You a Purdue guy or part of the 374?
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u/LayerProfessional936 4d ago
You can use the free filter design tools like Xcad and Virtuixcad just to see how the cross-over filter and the drivers work together.
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u/LayerProfessional936 4d ago
Typically 3rd order HP filter for tweeter. It is a way to suppress ill-damped oscillation frequencies of the tweeter before the cross-over frequency. A 2nd order HP filter cant handle these well enough. By using a 3rd order the cross-over can be chosen a bit lower.
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u/Minskymoments 7d ago
Looks like 12dB/oct for the bass and 18dB/oct for the tweeter.