Everybody"s input has been very helpful to me. To get an additional viewpoint, my long-awaited (not really a "long" wait) visit to Stereo Integrity happened last week. Nick met me in the parking lot & called me over to the back of his Jetta. He lifted up the hatch & showed me his new 15" SQL-15 he had mounted into a remarkably small box he bought for $20 for on Amazon. He had a 1000w amp driving the sub. He also had one of his mid-range woofers & tweeters on each door (he's now discontinued those speakers). He cranked up the volume & actually played some pipe organ music for me first.
It was impressive. The vibrations from the extremely deep bass hit me hard in the chest (& everywhere else). Nick said one note was 16Hz. I believed him. It was very deep & loud. My poor wife was in the back seat & during the demo she told me her hair was blowing from the air being moved by the sub. It's not a big surprise. The Xmax on this driver is 28.4mm. That's not 38mm Xmax like his HST-15 mkII, but it's pretty damn good. Air was being moved - a lot of air.
Anyway... after a long & enjoyable demo ( including every type of music) & me quizzing Nick about every bass topic I could think of, we began to say "Good-bye" - but even that took a few minutes. He's just a really nice guy. In addition, he was incredibly patient & knowledgable. Of course, I left knowing I would buy one of those babies. They won't be ready to ship until late December, but I'm in no hurry.
Now I need more specific advice. I've decided to build a ported sub with ST's 15" SQL-15 driver. Nick recommended 1000w for the amplifier & I'm considering a Crown XLS 1002 with 1100w @ 4 ohms bridged. From SI's website: Ported = 3.75 ft^3 tuned to 29 Hz.
I have a Mac & no easy access to a PC, so my access to speaker design software is limited. I found a limited web-based subwoofer design program, but I'd appreciate any feedback on the sketch I'm u ploading. I like the idea of a "pipe" port, but I have an open mind. How many braces should I add inside? All suggestions are welcome.