Passive Subwoofer with Small Rear Speakers

Feb 3, 2019
First time here. I've been swinging between hi-fi and lo-fi for many years. Still swinging.

Setting up my first surround system, on the cheap, with 2 sets of legacy speakers and the rest used purchases. I just need an active subwoofer to complete. Along the way, I picked up an incidental subwoofer, my first. It's a passive one, by Mission (it matches a third pair of speakers that I currently use). I like it, it has a subtlety. I had an idea, I could use it with the Small Rear Speakers in my surround system.

My (bargain) AV Receiver has 100 watts per channel, into 8 ohms (the warning on the back says 8-16 ohms). The Small Rear Speakers are 40 watts each at 4 ohms. I'm not too concerned with the differences in power and resistance, I would be careful not to overburden either the amplification or the speakers.

The Passive Subwoofer has just the basic high input and output connections between the receiver and the speakers. I'm quite sure it has it's own crossover filter built in. And it's rated for 15-100 watts at 8 ohms.

I thought it might work well with the Small Rear Speakers, maybe share the power, and take the low end pressure from the smaller cones.

One concern is that the Subwoofer and Small Rear Speakers won't share the power well.

My main concern is that the combined impedances are damaging. For all the searching I've done, I can't quite figure if the impedances are added, or halved? That's my question.

Thanks everyone. Wish me luck
Feb 3, 2019

Thanks jsmithepa. Yes, I found that information very simple. Which leads me to the more specific question: Which circuit is it, precisely?

I'm assuming it's parallel, and it's designed to operate that way. I don't think it would be so bad in my application.
If the sub has speaker level inputs and outputs then it's simple.
Connect the receiver surround speaker out to the sub speaker input. Connect the sats to the sub speaker output.
Set the rear speakers to large in the receiver speaker set up menu.
Most subs don't have a high pass crossover built in so the sats will play as full range and the connection would be the same as parallel. If yours does then there isn't a simple way to calculate the impedance to the receiver since the crossover will affect that but should maintain a safe impedance.
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