Spare 2ch amp for a diy sub?

[MarkR]

I am keen to build my own subwoofer and have a spare 100w
2ch amp. Can this be used to run a bipolar subwoofer and are there
any kits or plans out there for such a beast?

[JonMarsh]

By bipolar subwoofer, I'm guessing you mean a cabinet with two drivers, arranged on opposite walls for force cancellation.

In principle, this is possible to do with reasonable results with a 100W per chanel amplifier, IF certain criteria are followed. First, you'll have to pick moderately sensitive medium throw drivers which are available to you in New Zealand. Over here, good candidates would be the Ascendent Audio Atlas 12, the Peerles XLS 12 (less Xmax, but not a problem with 100W), and the TC Sounds/OAudio TC2+. Then, you'd have to use them in a fairly large box, because you don't have the power available to use an equalizer and overcome the bottome end roll off. I'd shoot for an alignment using Unibox for a Q of 0.566 to 0.6. If building a box isn't your thing, then a sonotube sub might be the say to go- those are the cardboard formers used for making concrete tubes. With a really large box, you might even consider an EBS alignment ported, instead of sealed (see the thread on this board about Atlas 12 in ported alignment), but it might be more practical to build into two boxes.

What you have to give up if you want deep bass with not much power is the small enclosure- physics dictate you'll have to have a large enclosure, or go IB (infinite baffle) if you have the room to build it in to your home, with the rear wave venting into a basement or attic.