Gluttony lives. "Very good question… and it's already built into your crossover board as a shelving low-pass circuit, just not for the sub part but as an option for the HP section which in your SE is currently empty. It's a correction for the mid-bass region mainly for my own future use with the KEF LS50, Quad ESL and my DIY open-baffle bass enhancer. I won't call it sub since it's built into an Ikea box, has a cheap 15" Eminence Alpha 15A [below right] and unfortunately hasn't seen use in the last two years. My Linkwitz LX521 crossover too has some shelving filters.
"So it's absolutely doable to add an LF boost which is limited to say four different characteristics plus bypass. If I change a component value too much, a filter parameter will change with it but we can easily find four different pleasant boost characteristics. For the low pass, variable gain with a good stereo pot will be important too. To find the required characteristics, the easiest way is to use a miniDSP box with on-the-fly changeable filters." With four options, I suggested +3dB and +6dB boost at 20Hz starting its lift at 80Hz across two octaves; and at 160Hz for a gentler longer lift to include the upper bass. This would be gentle enough to create a linear mildly rising response. Bypass defeats it. To mock up my proposed curves, Pál asked for useful test tracks. I Dropbox'd him "Gold Dust Bacchanalia" from Mychael Danna's soundtrack to the Mira Nair movie Kamasutra for its powerful infrasonics; and "Oriental Bass" from Patrick Chartol's Istanbul for its meandering powerful electric bass. He'd work them over with my curves then return the files so I could play them back and confirm the EQ choices. That he really enjoyed the music as well was an extra bonus.
On December 21st, Pál checked back with "interesting coincidence". Three embedded links pointed at a review of the Wilson crossover, a PDF of its owner's manual, then a Sound & Vision tutorial on perfect subwoofer phase. This he followed with a question. "Perhaps I should add the phase adjustment to the sub channel? Remote adjustment is a must to find proper settings. Adding phase could be useful." I agreed if he could do it. "After more research and tinkering, it may not be worth to add that variable all-pass section. For the hundreds of different subs, other factors can be much more important than an all-pass can address to perhaps do more harm than good. The variable LP, HP and shelving EQ seem the better choice."
If we could observe the paths of R&D, more often than not they must look like meandering rivers, not straight canals. I've always wondered. How do manufacturers calculate lengthy R&D time and prototypes—both equate money—back into a sell price? Nobody should work for free. Nobody knows upfront how much of anything they'll sell. Then how to amortize all expenses prior to actual manufacture in a manner fair to consumer and maker? Being bad at math, I'm glad that onus isn't on me. At this juncture, a Geoffrey Heinzel email hit: "Infrasonic bass isn't audible but an essential part of any high-performance theater. It pressurizes the room and evokes the physical response intended by more movie soundtracks than you might think. True infrasonic subs are extremely hard to engineer, not inexpensive and must work in tandem with other subs to do their part of extending bass into the single Hz digits. This isn't about boom, bloated bass nor marketing claims by me-too big cone alternatives. The demands of these frequencies and durations in some soundtracks quickly separate Ascendo from those masquerading as me-too. When calibrated correctly on time, phase and level with the rest of the theater channels, the result of including Ascendo infrasonic bass is an engaging and completely immersive experience one doesn't forget. These frequencies are often used in quiet passages that can at first be very subtle to cause the body to react with a "what was that?" followed by dynamic contrast and system headroom requirements that separate really good home theaters from exceptional private cinemas.
"Ascendo's smallest infrasonic sub [above] has a 62cm/24" super woofer with an incredible 9cm of linear stroke. That moves a gigantic 10-liter volume of air per stroke to pressurize the room. Due to its ultra-low resonant frequency and sealed enclosure, group delay is several times faster than that of smaller 18", 15" or 12" subwoofers at the same frequency. Its acoustic power output per cubic inch is by far in favor of this unique design over stacked multiple smaller subwoofers. This Ascendo-developed super woofer is powered by one of the best high-current amplifiers delivering 6'000 watts of power for multiple seconds. Its state-of-the-art DSP allows perfect alignment of the SMSG24 to any existing setup by adjusting crossover, phase and amplitude."
