Obviously when you put a 10" woofer into a 30-liter enclosure and have over 1100-grams of moving mass you’ll need to make sure it is properly constructed. Thick box walls and bracing are the only means we have to counter unwanted resonances or box panels adding to the reproduction of the loudspeaker. With most loudspeakers 10 to 35% of the sound generated doesn’t originate from the loudspeaker cones, but from the box panels themselves. This makes sense as most panels have a far greater surface area than the effective cone area, hence even the smallest movement, primarily caused by the woofer and midrange in the box, will add to the sound generated. This naturally is unwanted as it adds coloration to the sound reproduction that wasn’t in the original recording.
In our design the box didn’t only have to accommodate the woofer and the passive radiator, we’re also going to have to make room for the subwoofer amplifier. This amplifier has a minimum rated output of 120-watts at 8-ohm, as per the requirements set forth in the previous pages. There are several amplifiers that fit the bill, our recommendation is one of the following; the Thommessen SW2.5, Hypex's excellent DS4.0, Detonation DT300, or for the real conaisseurs, the Thommessen SW6.0. Either one of these should have ample room to breathe in its own enclosure, which is sealed off from the rest of the box.
Our enclosure design is a result of testing different enclosure designs, with different panel thickness and with varying amounts of inner bracing. As a result we’ve applied a bit of common sense and structural engineering expertise to break up each panel into multiple smaller panels by using bracing. All box panels are now supported at more than 4 sides, which adds to the overal structural integrity of the enclosure. The enclosure is built from 22mm MDF, medium density fibre board, panels and uses 45-degree cuts on the outer panels to make for a perfect finish. We’ve omitted damping, as no damping material offers any damping at the frequency range the subwoofer is to be used at.
- 4 x side panel, 350 x 600-mm, all sides cut at a 45-degree angle
- 2 x top and bottom panel, 350 x 350-mm, all sides cut at a 45-degree angle
- 1 x inside panel, 306 x 556-mm
- 1 x inside panel, 194 x 306-mm, with two Ø 100-mm holes
- 1 x inside panel, 90 x 306-mm, with one Ø 20-mm hole
- 2 x vertical brace, 75 x 267-mm
- 4 x horizontal brace, 75 x 142-mm
As you can see from the drawing, of which the larger version can be found here
, we used bracing throughout the design and created a separate enclosure for the amplifier. The cut-out dimensions given for this enclosure are for the Thommessen SW6.0 amplifier, so if you use one of the other amplifiers we’ve listed you’ll need to change that accordingly. Also note that the upper right part of the enclosure has another enclosure, this needs to be filled with fine dry sand or lead pellets through the 20-mm hole, which needs to be plugged afterwards, you’ll need about 7-kg of sand to fill it. The woofer and passive radiator are acoustically coupled by two Ø 100-mm holes in the center bracing panel.