Where to cross? If we double cross so filter both sub/s and mains, we're flexible where to do it as long as we remain above the speaker's native reach so we don't create a hole. When I started my double-crossing adventures, I instinctively assumed that lower would be better. Looking at my inventory of speakers, 40Hz seemed most reasonable. That's the fixed frequency I thus ordered for my autoformer preamp. It also seemed intuitive that with just one subwoofer, not crossing too high would be advantageous. With now two, those concerns were gone. So I tried the below setup anywhere between 40Hz and 120Hz. John's choice of 2nd-order Butterworth vs. my usual 4th-order Linkwitz-Riley filter meant broader overlap so expectation predicted that lower would again be better since it'd still take the sub up higher with the shallower slope. The Grimms were ultra clean, tight and fast to not protest playing high. Exploring my handover options, I eventually settled again on 40Hz as my preferred transition. Why?

Without playing bass EQ or subwoofer gain tricks, I felt that crossing higher still made the sound a bit darker and heavier. It also bolted on more dynamics. That telegraphed as just a bit different than what followed above. Have you heard AMT-tweeter'd speakers whose top end felt bright not in frequency response but dynamic range? The highs were dynamically more exuberant than what the cone mid/woofer managed so felt forward and imbalanced to a degree. After all, playing more dynamic means getting temporarily louder. That 'leading with the AMT' was a similar effect to my higher filter experiments just at the opposite end.

The quickest airiest most lucid sound really came from crossing at 40Hz even with two subs on hand. My original instinct when I first ordered my icOn 4Pro SE had been right after all. At least that was so for the bigger downstairs speakers. How about upstairs? First I had to combat a noisy ground loop. That thankfully vanished with the first attempt, a cheater plug on the sub. Some ground loops can prove devilishly evasive. This one happened to be the cooperative sort. Time to work the eX1's menu and re-evaluate the crossover choices. By now the Grimms were packed up for their return trip and I was down to our usual 2 x 9.5" balanced-force affair.

With a mono sub, a 120Hz crossing on a shallow slope told directional porkies so went too high. As I had downstairs, I still heard the same small fattening effect at 80Hz. Working my way down in 10Hz steps, I landed on 50Hz as my eventual favorite. My thing really was crossing low. Now I knew for sure.

That's academic of course. It varies from room to room, owner to owner. The real takeaway is the ease and repeatability whereby an e1X user makes this decision without extra chassis, power cords or shelves. If I owned this Bel Canto, I'd gain one free rack space.

But our black's arts don't end there. All audiophiles worth a grey hair have played tonal-balance roulette with cables, footers and sundry tweaks. Their goal was to land in the subjective middle, their personal bull's eye. The road to it is rarely straight, short or sweet.

"The Lord giveth with one hand then taketh away with the other. Mysterious are His ways." [From the Wailings of Harry, 3rd lament, 2nd verse.]

It's decisively easier and far more surgical to exploit John Stronczer's tilt control. Don't fancy the result? Defeat it in the menu without hitting up online classifieds to sell off suddenly useless tweaks. Overshot a bit? Dial it back. Want just a bit of bass boost without a parallel mid/treble reduction? Engage the bass shelving instead.

The most effective such ministrations step very lightly like the proverbial pinch o' salt. Gifted with these precision tools, audiophile pilgrims can chart their lone path up Mt. Less Compromise without risk of failure or specialized kit.

Puritans will predictably scoff whilst failing to see that in their ways, they do exactly the same: nip 'n' tuck their sound until they're happy. But if this really is the 21st century, why not embrace better tools? From caveman to rocket man really is on the menu – this one.

If there's a PC in our sound den, various plug-ins can accomplish the same. If not—perhaps we're pure vinylists or Mr. Simpleton SD card like yours truly—having such core functionality embedded in a phono-ready DAC is quite the saving grace.

It's an effective educational tool, too. It can help us learn more about how we hear, what we like/dislike whilst observing the tango of cause and effect. Swap cables. We might dig the result without any clear insight into what made it so. With the e1X we know values and freqs. We can play around then safely return to bypass. It's uncomplicated but can advance our sound. Since I wasn't 100% there yet with our new ground-floor soundroom, I'd play the tilting/shelving games next. Nothing ventured, nothing learnt. With the Grimm subs sayonara, the extra tonal heft of the clock-slaved Gaia/Terminator Plus combo worked in its favor versus the e1X run straight-lined.  Would coming off the straight 'n' arrow turn tables? I was already suspicious that the final piece of my downstairs puzzle really would be the sound|kaos RiPol sub. For me, a distinctive sense of persuasiveness comes from often nearly subliminal infrasonics where active subwoofers have technical advantages. Until the arrival of the 2×15" beast, could I mock up some anticipated effect with John Stronczer's tilt control and/or bass shelving? The former hinges on 775Hz and mirror-images up to 3dB of boost/cut at the outer extremes. The latter begins to ramp up at 300Hz and hits its full boost/cut value at 100Hz. Here too the max deviation from neutral is ±3dB.