Design

During the preliminary design stages, I considered sand filled walls, and using 2 passives. In the end and with after a lot of modelling time in Unibox I settled for a single passive and a smaller enclosure.

I like the modeled response of between 25 and 30 litres internal volume. A 320mm cubed enclosure (internal) would result in 32.8 litres and after negating the volume from the driver, passive, amp and bracing, the net volume should be around my target.

I looked for the best price-per-watt plate amp I could find and modeled the enclosure using its dimensions.

250W Active Subwoofer Module (from CPC)
"An active speaker module for high power home cinema subwoofer speakers. The amplifier module consists of a pre-amplifier, power amplifer and mains power supply and the unit will accept many kinds of low level input connections."

The conceptual design employs a simple shelf bracing scheme with the main driver pointing outward and the passive firing downward.

Another view of the enclosure design.

Addendum

I get lots of emails requesting the final design (as shown on the next page) dimensions (although I've already mentioned that it's simply a 320mm cube - grrrr ;) ). The missing side wall is 356 x 356 x 18mm, and both braces are 320 x 320 x 18mm. If you build it as shown and fix the sides on you will get an internal cube of 320 x 320 x 320 which equates to 32.8 litres. After negating the brace, drivers and amp volume displacement the net volume sits nicely within the target range.