Subwoofer crossover design

[Einric]

Hello,

I have a dual 4 ohm subwoofer that I'd like to use for home.
I have an 8 ohm pair of speakers I'd like to use with it.

The tricky part is designing a passive crossover that will accept the two voice-coils in series to present an 8 ohm load to the amp.

I need two inputs and two outputs.
I could get two massive 4 ohm non-ind resistors to series with each voice-coil but I would like to avoid that.

I'm looking for a subwoofer crossover at 80hz.

Thanks

[Moondog55]

I have replied to a couple of these questions. To clarify; you want a single sub 80Hz signal to go to each voice coil?

Cheapest easiest and often the best is to use each VC as a first order XO and use the speakers as a 2.5//3.5 system.
Use the inductor with the lowest DCR you can find and if the big drivers have bad break-up it may be beneficial to add a Zobel type network before the break-up.
So really all you need are 2 very large coils and cored is fine and I would go a little bigger than simple calculations suggest, 8mH -> 10mH.
Most amps will handle the load reasonably well, then experiment with the cable, you may need to reverse the connection to the speakers.

[Einric]

So, you suggest that I put large coils on each VC and the amplifier would see them as a 4ohm load but since they don't cover much of the audio spectrum my amp won't be bothered much?

[Moondog55]

The load would probably be lower than 4R but a good amp should have little problem in driving a low impedance.
This is the easiest implementation if you do not want to Bi-Amp ( Personally I prefer Bi-Amping for subs but the point 5 is easy and cheap ) The only problem I have is when I crank the volume up; if you want it louder than half your amps output the load may be too much. Can your amp deliver full output into a 4R load?

[Einric]

I have a Panasonic SA-HE2000 in Low Impedance mode for the extra current to the main channels. I have driven 4 ohm loads before so I'm not too concerned.