Passive Crossover
I may be able to help. First I need some information from you.
I need a description of your satellite speakers. Tell me as much as you can about the drivers, impedance, sensitivity (SPL) rating, etc. I would recommend a quasi-second order series network. The capacitor value for a Butterworth first order parallel filter is very high.
What you are asking for - a passive multiple turnover frequency crossover - is possible, but not realistic to design. That's why there are active filters in powered subwoofers.
Have you considered this possibility?: Build a bandpass subwoofer that naturally rolls-off on the top-end at about 60 Hz to 100 Hz, depending on the drivers used. If you were to use a dual voice coil woofer, rated at 8 Ohms per coil, you could use these (coils) in parallel with your two satellite speakers, assuming that they are nonimally rated at 8 Ohms, and you'd have a net impedance of about 4 Ohms, which would probably be an acceptable load for your amplifier. The downside: you lose about 4 to 6 dB in SPL with the woofer, but practically speaking, that may not be a problem. You could also build two separate woofers in a bandpass cabinet - two 8's or two 10's, for example, and gain back some of that SPL loss. This gives no filtering to the satellite speakers, however, but it may also help the subs and sats blend.
I can refer you to sources for these designs and you can experiment on your own for very small costs. For example, use a combination of electrolytics, mylars, and a small value poly bypass cap to get the value you need with good sonic results.
Go to
www.partsexpress.com for one of the very best sources of drivers and crossover parts. They even have design software which you can download free of charge. Their Dayton brand of woofers, which run from $16 to $30 apiece, are some of the best values in woofers that can be found. Poly coated paper, rubber surrounds, vented voice coils, etc.
