Building a Subwoofer

Where to start? There's two parts to this project. Amplifier and the Box.

Subwoofer Amplifier
In Auckland you can go to either Jaycar Electronics or Dick Smith Electronics and find some bits and pieces to put together. The prices stated below are subject to change.

K5403 Subwoofer filter $35.20 (actually, just a couple of tuned coils would work)
An alternative to the above is the K5404 a full active cross-over network $48.20
K3442 The 100W into 4ohm amp, yeeehaaa $59.40
K3438 Power supply (some darn biggun caps and dethump relay) $42
M0144 Big Transformer $59.95
H2812 305x90x200mm case (which is probably too small) $36.80
An alternative to the above is the H2481 rack case $88
Frankly, those boxes are quite expensive. Maybe Jaycar has some better alternatives or you could make your own. Metal is better. It ignites less often than wood.

That's about $233. Maybe about $250 after you get the extra things:

A mains plug (tap-on plugs are the best), a fuse holder, some cool flashy lights and switches :) and some power cable (3 metres is probably about right) and some heavy MDF for the box. Jaycar has some very impressive speaker grills.

You need to have as much technical information about your subwoofer speaker as possible because there is a bunch of physics calculations needed to get the box right.

Subwoofer Box and Speaker