Eh hem!...Subwoofers... What do ya know?

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That’s why this is such an uphill battle. As if the physics, psycho-acoustics, mono, and "integrating" aren’t hard enough, you got to try and convince people the concept is so powerful it overrides the need for great big expensive drivers. Oh, and lamp cord will do just fine. Its just too much to swallow. Even though its all true.

@millercarbon --

Something to consider: if the 10" Morel units of yours are anything to go by two "big expensive drivers" from the pro sector, like 21" B&C’s, in a given enclosure design (like the "Skram") would be no more expensive or probably even cheaper than four Morel’s. Add in the need for two extra amp channels for the quad-approach while factoring in that a pair of 21" drivers are ~10dB’s more sensitive and sports more than twice the radiation area. "Overriding the need" as you point out in this context dismisses the importance of headroom, although to some a quad array of 10" subs would seem more than enough (and it well may be in a specific context). And yet, a dual 21" set-up like the one suggested would excite more air (even with less cone movement) and have lower distortion at a given SPL, all of which translates into an even more relaxed and effortless presentation of the lower octaves. You’d miss out on the advantage of going quads in regards to response smoothness sans digital correction, but a great result is still attainable via duals without excessive use of DSP and maintaining a fairly even coverage for more than one listener.

You could even go with smaller and (all things being equal) cheaper drivers, like a 15" driver in a horn variant and end up with a bigger effective air radiation area, force multiplied by the horn, than a 21" direct radiating driver (the 21" in the "Skram" isn’t DR, I might add, but rather hidden inside the cab and loaded on both sides of the cone), in providing a better coupling of the cone to the air and a different (to my ears ’better’) bass presentation (my preferred choice of dual-sub approach, actually). The downside: a need for a bigger cab and thereby wood.

A 4-sub approach with, say, 10" drivers like you propose in all likelihood will find more wide-spread use in hifi-systems than what I’m advocating, and they would have excellent augmentation in the bottom octaves. That being said and to reiterate: there are other excellent sub-solutions, and adhering to physics I’d say my dual-sub propositions will fit the bill quite nicely as something that can’t be overridden as an essential in bass augmentation, but that are nonetheless typically overlooked.

@luisma31 --

apologies in advance as you were addressing someone else, I understand the bass augmentation can be achieved easily with the distributed array, there is such a thing as too much bass, in my array (4x10 inches not morels) I have to tune down the amps to 50 percent and sometimes plug one or two ports, I also understand that if you add more 5 6 even 8 small enclosures which are easy to hide the effect increases even more. I had 2 powered subs with dual 18 inch drivers before and it didn’t sound natural (to me), also from the amps you can change phase for two subs etc. which blends the bass even more.
I’m not trying to be argumentative with you but I respectfully differ from your opinion
Luis

No apologies needed, and I like a difference of opinion - oftentimes it makes a conversation more interesting. To "diagnose" a difference of opinion though and where it really rests some effort must be made as to the context and more precise nature of each of our viewpoints; sometimes what we initially deem ’different opinions’ is muddled by factors like lack of context and insufficient information rather than actually being in disagreement on a subject - were we to have a more "level ground" of understanding (which, for obvious reasons, we usually don’t have from the get-go). That being said there certainly are preferences, and I find them inspiring as it can lead myself to change or modify a direction, or simply appreciate and ponder other choices (just as well as it can reassure my own direction).

"Too much bass" as you write to me is simply about level adjustment rather than the capacity at hand. Practically I don’t find one can have an over-abundancy of bass capacity (as is similarly the case with dynamics), for as they say: headroom is your friend, so embrace all there is and even wish for more (to a certain point at least, but usually more than many would deem necessary). So long the enclosures themselves do not obstruct the acoustics too severely I’d have no problem adding their size or numbers as space and/or spouse permits.

Let me be clear that I only have few reservations with the multiple sub approach, the only real one being the potential lack of symmetrical placement of the subs in relation to the mains. This is controversial, it seems - i.e. mono vs. stereo bass and the supposed lack of directionality in the lower frequencies. To my sensory abilities spatiality in particular is aided more effectively via symmetrically placed subs (usually a pair, coupled in stereo) relative to and in close conjunction to the mains, and while we may not be able to distinctly assess, via our ears, where bass is coming from (depending on the chosen lower cut-off), I’d wager we can feel it via our bodies. On whether actual stereo information is available in the source material (digital), also a controversial matter, it is hardly debunked from testing a few hundred titles (a very obvious case of the problem of induction - if one were to side with named, limited testing).

On your less than favorable experience with the twin dual 18" subs, I find it hard to comment other than asking for more specifics (context) and what in particular you found less satisfying about their sound. A friend of mine is using a pair of cinema subs fitted with twin 18" drivers as well to augment his mains, and while I find they’re very capable, tuneful and rather successfully integrated, I’ve never warmed to them fully. My main gripe mainly has to do with some acoustic challenges here (generated by the floor), but also the fact that they’re direct radiators. I favor bass cabs with hidden drivers, preferably loaded via horns, but that’s another subject entirely.

Implementation is paramount. I’m using a Xilica digital cross-over that provides ample adjustment possibilities, while tentatively using DRC Designer for digital correction in both amplitude and time domain from the outset of a measured performance, choosing a target curve, specific filter types used, etc.