First of all, I would like to say that I was really impressed with the composure and description that you used in explaining your quest for an SQ sub. You seem educated overall, yet undereducated in car audio. But no matter, I have been on this forum for like 6 months, have upgraded my system 1 time since joining here, and I find that my friends know nothing compared to the experiance I have gotten here/ installing things I learned here.
Anyway, I found myself asking very similar type questions not so long ago. I find that the basis for subwoofer design is the balance between SQ and SPL. I think it is pretty easy to design a SPL subwoofer, granted a few hundred watts, a very large cone and a huge magnet; Rockford Fosate, Audiobahn ect. But in my opinion, they sound very bad, maybe throwing a large magnet or a huge cone (anything larger than 12) it becomes alot harder to control that kind of stucture. Those 50oz magnets might be able to shake your back end, but the bass does not cut off after the note is played (it continues to rumble) and it may have a hard time with really fast hits of bass.
Then you have Infinity (pretty much the opposite woofer than anything Rockford), I felt that their woofers were crystal clear, with the only downside being it wasnt that load. Again, maybe that is because they use a small magnet that is easier to control, but it can't produce the same sound levels as an SPL sub. Other companies that do this are Focal, MB Quart, Boston, and maybe Crystal something, but those are premium SQ brands.
And then you have something that strives to be both. Some call it SQL subs, a combination of SQ and SPL. Perfect example is the W7, because it can get hella loud as well as remaining incredibly tight. Others that do this well are Eclipse Titanium, RE XXX, Adire Brahama (so I hear) and most ED subs. Most of these strive for a combination of SQ and SPL, they are all different, like the W7 is like 50/50 and the XXX is like 60/40 in favor of SPL. I found that on my Eclipse Titanium, the whole structure was huge, the magnet was very large (almost as big as the cone) - giving it some very good loudness, but I suspect the reason it can still maintain SQ is that there is a massive amount of structure other than just the cone and the magnet (I think the rule of thumb is .07 cu ft of deplacement on an ordinary 12, and mine was like .19cuft!!!) the coils on this thing are massive, also the surrounds on the sub are very large, probabbly making it easier to control.
But all these things are relative, mostly in $$$ and watts. I spent 110$ on an Infinity Kappa woofer that was probabbly 80/20: SQ/SPL, I probabbly could have gotten the Rockford HE2 for the same price for a 20/80 SQ/SPL mix. And then send them both 300w. But for my upgrade, I purchased an Eclipse Titanium for a $$$ figure at least 3x those other subs, but this thing has probabbly a 45/55 SQ/SPL mix and now I have to send this thing upwords of 700w. I think some people send W7's like 1000w to get that incredible mix of SPL and SQ.
I am sure there are things I am forgeting, like how different enclosures can change a systems direction (ie Sealed-SQ, ported-SPL) ect. But anyway, that is my long explanation that I started 6 months ago after originally searching for a pure SQ sub.
Anyway, I found myself asking very similar type questions not so long ago. I find that the basis for subwoofer design is the balance between SQ and SPL. I think it is pretty easy to design a SPL subwoofer, granted a few hundred watts, a very large cone and a huge magnet; Rockford Fosate, Audiobahn ect. But in my opinion, they sound very bad, maybe throwing a large magnet or a huge cone (anything larger than 12) it becomes alot harder to control that kind of stucture. Those 50oz magnets might be able to shake your back end, but the bass does not cut off after the note is played (it continues to rumble) and it may have a hard time with really fast hits of bass.
Then you have Infinity (pretty much the opposite woofer than anything Rockford), I felt that their woofers were crystal clear, with the only downside being it wasnt that load. Again, maybe that is because they use a small magnet that is easier to control, but it can't produce the same sound levels as an SPL sub. Other companies that do this are Focal, MB Quart, Boston, and maybe Crystal something, but those are premium SQ brands.
And then you have something that strives to be both. Some call it SQL subs, a combination of SQ and SPL. Perfect example is the W7, because it can get hella loud as well as remaining incredibly tight. Others that do this well are Eclipse Titanium, RE XXX, Adire Brahama (so I hear) and most ED subs. Most of these strive for a combination of SQ and SPL, they are all different, like the W7 is like 50/50 and the XXX is like 60/40 in favor of SPL. I found that on my Eclipse Titanium, the whole structure was huge, the magnet was very large (almost as big as the cone) - giving it some very good loudness, but I suspect the reason it can still maintain SQ is that there is a massive amount of structure other than just the cone and the magnet (I think the rule of thumb is .07 cu ft of deplacement on an ordinary 12, and mine was like .19cuft!!!) the coils on this thing are massive, also the surrounds on the sub are very large, probabbly making it easier to control.
But all these things are relative, mostly in $$$ and watts. I spent 110$ on an Infinity Kappa woofer that was probabbly 80/20: SQ/SPL, I probabbly could have gotten the Rockford HE2 for the same price for a 20/80 SQ/SPL mix. And then send them both 300w. But for my upgrade, I purchased an Eclipse Titanium for a $$$ figure at least 3x those other subs, but this thing has probabbly a 45/55 SQ/SPL mix and now I have to send this thing upwords of 700w. I think some people send W7's like 1000w to get that incredible mix of SPL and SQ.
I am sure there are things I am forgeting, like how different enclosures can change a systems direction (ie Sealed-SQ, ported-SPL) ect. But anyway, that is my long explanation that I started 6 months ago after originally searching for a pure SQ sub.
