6.5 vs 8 vs 10 woofer

Okay here’s may take, don’t be mean. I agree that an 8” driver is just about ideal for most music, vocals and instruments. But you do need a couple subwoofers to fill out the bottom end. I have found single full range coaxial drivers sound best to me. Multiple drivers tend to fracture the sound and you lose clarity of vocals and instruments if they are not aligned vertically AND horizontally . This is true if you are NOT trying to achieve concert volume levels! I have yet to hear a multiple driver system that does not have aligned point source drivers, match the clarity in the critical listening frequency range of say 70 Hz. to 5 kHz. I personally like Altec 601’s for the clarity and efficiency, they are what I want to afford. That being said, I would love to hear some Voxativ. You ABSOLUTELY need analog electronic crossovers and multiple amplifiers because passive crossovers I've heard sound bad. Started making my own electronic crossovers 45 years ago. So, Altec 601’s for the critical range, subwoofers below 45 Hz. and JBL 2405’s without the horns pointing straight up for highs above 8 kHz. with ANALOG ELECTRONIC crossovers and 3 stereo amplifiers. My ears have told me over the years that more is not better, just louder.

I am listening to right now, a 15 that is 95db sensitivity, but only goes down to 38hz

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I would have figured a 15 goes BELOW 20hz.. Ok so the inner core also makes a huge dif on how low a 8 inch will go.

Yeah, because 95db is an extremely high efficiency 15" woofer and the problem here is that high efficiency woofers have to be engineered different and they do not have a "free air resonance" frequency low enough to do bass down at the 20hz point.  The woofers that do have a low enough resonance will need to be heavier in weight with a stiffer spider and therefore will not have as high of efficiency.  It's all a design compromise and we are dealing with physics here (no speaker manufacturer can give you everything on a silver platter with just one driver).  $$$ doesn't necessarily mean "best" or "better".

You can't expect all woofers to be your perfect dream.  Everything is a compromise. 

I've had discussions with mozatfan in the past where I suggested Markaudio drivers (he was on a full range driver kick), but he apparently poo-poo'd these drivers because they were British and he thinks British speakers suck.  At that point, I lost interest in discussion with him.

Full range drivers are always a complete compromise anyways where you sacrifice some aspect of the sound/characteristics to get what you want.  It is actually incredibly difficult to engineer and manufacture a full range driver that really works well throughout the entire frequency range.

He also seems to try to do "best speaker" arguments by selecting drivers he thinks will prove his point.  I do agree with others here, I think we have another Kenjit.

6.5 vs 8 vs 10 woofer ?
. . . uh, mine aren't round.

I've got 4 pairs of full range speakers with dual 7"s, 10", 12" and 15" woofers.  Of these, the 15" Tannoys have the LEAST amount of bass. The ported 12's go the lowest, but the 10's are in a sealed cab, so they roll off more gently.  The dual 7's are lightning quick, but don't have the 'gravitas' and punch of the larger woofers.  BUT, since the OP has declared that 8" is the ideal size, I guess I will just dump all these great speakers and find some with 8-inchers.   

@douglas_schroeder --

My favorites? None, if not set up well. Several, if set up well.
Over the years I am moving away from standard dynamic speaker towers. I am moving increasingly toward Open Baffle and Dipole (with or without subs). I can hardly stand the sound of a bass driver 8" or under; too earnest, too much popping of the driver when pushed. They just can’t handle LF and higher levels (Zero interest in arguing with people about this).

If you have poor amplification, you suck the life/quality out of the bass. If you have poorer cables, ditto. It’s a spectrum of performance, but also a spectrum of genres of bass technology - none of them definitively the best. YMMV

To me passive cross-overs, by and large, have a thickening and dulling effect on the bass (and the remainder of the spectrum), so active configuration is one step towards better performance here.

Going on from here I have no qualms stating that high efficiency 15" drivers are the best compromise up through the lower midrange, not least relieved of low bass reproduction when high-passed actively. Arguably the very best scenario in the power region - again, to my mind - is loading a proper 15" HE driver in a simple-fold horn (i.e.: not all too many folds), actively; this way the bass to lower mids will have an effortless "twang," smoothness, texture and dynamics that's simply unparalleled by any other bass principle that I know of. A "proper" 15" HE driver for this type of horn loading is rare though these days, if they're made at all other than by boutique, small scale manufacturers. Horn loading this way lends you ~105dB sensitivity, so the (15") bass driver cone will barely move at all, even at very high SPL's - not least when high-passed down low - and that's exactly what you want to achieve: less cone movement with high efficiency and lots of displacement area, not to mention via good air coupling. The only midrange/HF solution that can match such a bass horn is another, preferably large horn and compression driver combo, so there you have it; that's my preference, though it's not to say I can't enjoy a range of other well set up speaker principles.

However, it still goes to show that the typical love for smaller diameter, lower efficiency and direct radiating drivers comes down to convenience and what's most widely available; not a true choice per se. Who have heard a big, folded bass horn loaded with a 15" HE driver in their home - not to mention even bigger horn subs? Close to none, and so the predominant bias away from this segment of speakers is founded in conjecture or that it simply doesn't exist, and not actual experience. Added of course to the mere thought of having such behemoths placed in a home environment, that will no doubt scare most away. That, at least, I'm sympathetic to, though the lack of all-out and to hell with practicalities and WAF is still to be lamented.