Hmm, well I'm not sure I understood exactly what you were saying either.
I'm looking at your sub alignment as I type this, the port looks a tad low for your driver's FS so you're trading moderate extension for SPL, good for you!
I currently run a similar setup, single Adire Tempest 15"(original version) in 10.5 cu ft (297.3L), ported at 16hz and driven somewhere around 240w. This pushes about 112db in room flat to 16hz without audible distortion - no fancy box required but it is huge! This is well below the 'snap' of a bass drum or bass guitar, BUT if it is combined with a smooth high frequency response, it adds perceived 'punch' and more importantly SIZE to the bass line. If you flip off the rest of the speakers, it's very quiet and doesn't seem to be doing much for the transient sounds, but if you do the opposite and disable just the sub, the bass drum and other transients shrink drastically.
I ~think~ you're proposing the type of enclosure one might call a 6th order bandpass, where 2 vented enclosures are joined at the driver and tuned to different frequencies. Bose is using somewhere between 6th and 8th in most of their sub modules (I've used a pro-sound 6th order by them, as well as heard their home stuff..) The 6th order alignment will play 2 notes well, the 2 frequencies where the boxes are tuned to be exact. Below and above this, the roll off is very steep. I tried a 5 string bass through the pro module for fun, knowing it wouldn't work, and just about blew the driver through the side of the box (oops).
Bose is trying to compensate for the laws of physics with a little harmonic distortion, and active electronic equalization to make up for so-so drivers in boxes that are way too small.
I believe that they're actually using a dynamic eq on their volume control to compensate for the Fletcher-Munson ear-response curve. By not adjusting the extreme highs and extreme lows down as far, they give the impression of "better sound" at lower volumes. Also I'm pretty certain they're using the old "add the 5th" trick to their subs to extend perceived response. Play a fundamental note, then add another note a 5th up the scale and a bit softer, and your ear will trick you into thinking that you hear the low octave of the fundamental. This works great until you want to feel that low psuedo octave - you CAN'T because it's not actually there :).
On the top end they might possibly be using an exciter as well, this would make up for the lack of transient response from their sub by over-emphasizing the transients in the high range, thus restoring the perceived response.
Some of this is speculation, and might be over-engineered, they could just be running decent little drivers in little crappy boxes with the engineers working over time trying to eq said crap out of them...
Anywho, if you want to try a 6th+ order box, go ahead and take a whack at it and let us know what you hear, if you like it, life is good.
Freq Freak
PS: if your data is correct, your sub should handle right around 200w and max out at 110db in-room.
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