Convert a passive (non-powered) subwoofer to powered subwoofer

Picture of Convert a passive (non-powered) subwoofer to powered subwoofer
The issue...I had a 5.1 Home Theatre in a Box speaker set that was of good quality (made by a company that specializes in speakers) that had a built in receiver/amplifier.  This system worked fine for several years until I got a new 7.1 receiver.  All of the other speakers from the system hooked up as you would expect to the new receiver, except for the subwoofer.  Seems that today's surround receivers require a powered subwoofer as part of the system.  The subwoofer from the HTIB was in perfect condition and sounds fine as is, so the solution became to add a separate amplifier to drive it.

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Step 1: Remove back of subwoofer

Picture of Remove back of subwoofer
sub back.jpg
My sub had the receiver/amp built in to the back of it.  I removed these parts since they weren't being used and found the two (+ and -) wires to the speaker.

Step 2: Buy a subwoofer plate amplifier

Picture of Buy a subwoofer plate amplifier
I found a 25 watt subwoofer plate amplifier that was in the $50 range and had positive reviews.  You can get much more powerful ones but the price goes up accordingly.  That said 25 watts seems to be more than enough for my purposes and for this sub.  It is audible from outside of the house when cranked and can go far louder than is comfortable to actually listen to.

Source (US):  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-782

Source (Canada):  http://www.solen.ca/pub/cms_nf_catalogue_fiche.php?id=2366&recherche=&numRows=&manufacturiers=&niveau1=1&niveau2=2&niveau3=41

Step 3: Build a box for the plate amplifier

Picture of Build a box for the plate amplifier
The plate amplifier I purchased was the exact width of the case for my subwoofer, but the cavity was not quite deep enough so I built a little box for the back to add more space.  I pre-drilled some holes for the screws and slapped some old black paint onto it.  I used some leftover MDF that was the right width.  I didn't take to much time with this as the subwoofer is sitting inside a component niche in my living room and can't really be seen.

Step 4: Add some cushioning material to the box

Picture of Add some cushioning material to the box
Even though the box is being screwed on tightly I added a bit of double sided foam tape to the back edge of the box just to be sure that there would be no rattles down the road.

Just use this amp http://www.amazon.com/gp/product/B0049P6OTI/ref=oh_details_o00_s00_i01?ie=UTF8&psc=1 its awesome I have one hooked up to a 5.1 receiver. took the sub out from the receiver to the left input channel of the amp and wired up the left out from the amp to the left input of the sub and boom your done. lil amp packs a punch

mgrunwel2 years ago
Awesome, I'll be doing this to my old Radioshack passive woofer when I move my home theater into the basement. Since the under floor there is concrete I am thinking there won't be as much vibration felt through the floor like it currently is. I figure a pair of powered woofers (one came with the current steroe) should transfer a lot of rumble into the furniture to compensate.
amcayanan3 years ago
Thanks for sharing, this is what I was looking for.
captain_dl4 years ago
Thanks for this. I have upgraded my surround receiver to get more HDMI inputs and found my older passive sub would not work either. I will be ordering the plate amp and doing this too.
DIY Dave5 years ago
 I think I'll do this with an old subwoofer I have