Well I am new to this site but am a serious HT enthusiast that dosnt have a lot of money. Well all in all my dad used to own a Professional Audio Company doing concert sound. We had all Crown MA3600 amplifiers in out mains totaling over 100,000 watts of power. Well all of the equipment had to be sold off. He still had 16 Custom Built single 18" Subwoofers and just traded 8 of them for 4 JBL 4688 Dual 18" Triple Chamber Bandpass Subwoofers. All I can say is that with an F3 of 23 HZ they put out some incredible bass that fills up our 3000 SQFT garage. Ill have to take some pictures of these things so that you can really get an I dea of what they are like. But the sound is tight, detailed, and huge. The box is gigantic and with all 4 of them hooked up it takes your breath away. My dad tried to paint 2 of them to match the interior of the house and put or wall unit ontop of the two side by side and my Mother just about had a heart attack! But check out the website that I put on here to see the spec's of this sub. I am able reproduce this sub with my dad for anyone who wants to get a hold of one of these enclosure.
They are also passive enclosures. I am currently powering them with a Crown 1400CL.