24db crossover with woofer impedance compensation

[ricesinice]

Hi All,
I want to build a 2 way crossover 24db/oct. with impedance compensation for the woofer. My question is, since the last component going to the woofer is a cap going to ground before the impedance compensating cap and resistor, wouldn't the circuit just see the impedance compensating cap as just another cap in parallel with the last cap in the crossover even if it does have the resistor in series?

[spkrman57]

Re: 24db crossover with woofer impedance compensation

No! You have the combined resistance and capacitive reactance of the zoebel added togethe. They only really help keep the impedance from peaking as much.

Maybe others here can explain it better. There used to be a general rule that the higher the inductance of the woofer, the more necessary the zoebel circuit.

Regards, Ron

[Jeff B.]

Re: 24db crossover with woofer impedance compensation

Hi All,
I want to build a 2 way crossover 24db/oct. with impedance compensation for the woofer. My question is, since the last component going to the woofer is a cap going to ground before the impedance compensating cap and resistor, wouldn't the circuit just see the impedance compensating cap as just another cap in parallel with the last cap in the crossover even if it does have the resistor in series?

If the resistor was not there, then to the circuit it would appear that there was one capacitor with the combined value of these two caps. However, the resistor in series with the cap on the Zobel limits the impedance drop of the cap to that of the resistor. Whereas, the other cap, still drops to zero at high frequencies. That drop in impedance is what causes the presence of this cap to add another 6dB /Oct to the crossover roll-off.

We tend to breakdown crossovers into things like second or third order circuits with Zobels and L-Pads, etc, but in reality they are really just one composite circuit made of all of these components and how they combine together to modify the impedance and the voltage transfer function through the circuit.

Jeff B.

[ricesinice]

Re: 24db crossover with woofer impedance compensation

Thanks guys. It just seemed weird making all of these connections at the same point, coil, cap, woofer, cap for imp. ckt..
I figured the resistor had a lot to do with it.
Thanks again,
Rob

[Chris Roemer]

Re: 24db crossover with woofer impedance compensation

What are you up to? What driver is this? Where's your Fc?

Most 4th order (acoustic) crossovers are NOT 4th order electrical. You've got the woofer's natural rolloff in there (unless it's a full-ranger). Usually, a Zobel gets to be less of an issue as the Fc drops, or as the filter order rises. I'm sure this isn't for a sub, right?