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shmb 11th February 2013 02:01 AM

Passive xover for a sub. How to?
Quick question. Hopefully this is posted in the correct place.

Is it safe for the stereo amplifier, to run an 'off the shelf' type pair of 80-100Hz passive crossovers, run the HPF outputs to the L &R speakers and then sum (join) the 80-100Hz LPF outputs to a single passive subwoofer?

Was thinking of doing this for a cheap garden system setup, just for background low listening levels.

Is it safe? Good/Bad practice?


Andrew Eckhardt 11th February 2013 02:18 AM

You can't do it and expect the power amplifiers to survive. Only under special design conditions of the amplifiers, or large coupling cap isolation, can you even do it after guaranteeing that the channel to channel bass signal and amplifier gain is identical. DC coupling of the usual consumer electronics stereo amplifiers together even with no signal can drive large currents between them and destroy the output stage. You may possibly get away with the general idea by using a dual coil woofer.

Moondog55 11th February 2013 05:32 AM

Much better to make stereo subs for this type of application * 8R dual VC subs are rare lately
Dual subs are cheaper than replacing an amplifier BTDT

shmb 11th February 2013 08:28 AM

Ok, fair enough, I won't be trying it then. :o

Thanks for the replies.

Drew Eckhardt 11th February 2013 07:31 PM


Originally Posted by shmb (
Ok, fair enough, I won't be trying it then. :o

Thanks for the replies.

You can use stereo speaker level low-pass filters each feeding one of the voice coils on a dual voice coil sub-woofer.

tvrgeek 11th February 2013 07:39 PM

Even for low levels, passive is not the way to go. For one thing, when you price the copper for the coils it will take your breath away. You would do far better with an inexpensive plate amp.

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