Need some help with 3-way crossover network...

[Wigwam Jones]

The tweeter crossover is a variant of a 12dB/oct. highpass... that extra cap and resistor acts as sort of a level control, but instead of just increasing the level as you turn it up, it actually reduces the crossover frequency as well. I wonder how well THAT works, in practice? It may well work, with the shallow slope (only 6dB/oct) of the midrange... it may function to create a "shelving function (where the tweeter is "shelved down" in level- i.e, there's a "step" in the response between the mid and tweeter- both are flat, but at different levels) to allow the tweeter response to be turned up and down, wholesale, in relation to the mid, without resulting in as much of a "discontinuity" in the response at high levels...

Regards,
Gordon.

Thanks, Gordon! That tweeter crossover sounds pretty weird. I hope it works out OK when I recap it. Still, I guess they designed it that way for a reason, eh?

 

[elnaldo]

If I understand this correctly, signals of a higher frequency than the 50 Ohm capacitor represents are going to return to common. Those signals of a lower frequency than the 50 Ohm capacitor represents are going to go to the woofer and be converted into sound energy.

I am still not sure what the function of the inductor is in this circuit, though. All signals have to pass through it, right? What signals would not?

Regarding your questions, imagine an inductor as a resistor that offers more resistance when the frequency increases. So, the higher the frequency, more resistance the inductor offers to the signal. In this way, low freq can pass through the inductor, and hi-freq can't. So, the filter for the woofer is that inductor you see there. The simplest low pass filter is just an inductor in series with the woofer. The capacitor in parallel with the woofer offers an easier path to some frequencies, that instead to go to the woofer, return through the capacitor.

A capacitor, would be a resistance that offers more resistance when the frequency decreases. In this way, only hi-frequencies can pass through it. So in a tweeter a capacitor allows only hi freq to pass.

In your midrange, the inductor blocks some hi-freq, and the capacitor block some low-freq, so only midrange frequencies can pass.

In your tweeter, you have 2 caps in parallel. Two 1uf caps in parallel, make 2uF. So in your drawing, with that variable resistor, you can add capacitance, adding the 2nd cap to the first one.
The inductor in parallel with the tweeter offers an easier path to some signals (low freq) that already passes trough the capacitor and return through the inductor instead to go to the tweeter.

Take a look at this site (no affiliation)
http://www.bcae1.com/passxovr.htm
http://www.bcae1.com/xoorder.htm

Regarding your idea of buying a pre-made 3 ways crossover.. It's not a good idea. There are very low chances that it will work as expected with your drivers... Trust the engineers that made your xover (you can try to tweak it later, if you are not satisfied with the sound anyway...)

 

[elnaldo]

Just a question to those more experienced.....

Doesn't some driver need to be OUT of phase (positive wire to NEGATIVE terminal) with this kind of crossover?

 

[Wigwam Jones]

Regarding your idea of buying a pre-made 3 ways crossover.. It's not a good idea. There are very low chances that it will work as expected with your drivers... Trust the engineers that made your xover (you can try to tweak it later, if you are not satisfied with the sound anyway...)

Thank you for the information! I am learning as I go, and yes, now I see why a pre-made crossover is generally a bad idea. Fascinating stuff!