6.5 vs 8 vs 10 woofer

I was able to get the7” scan speak revelator that Fritz uses in the Carreras to play -3db at 24hz and 0db from 28 hz to 120hz in a 12x14 room.  
I used Sonarworks reference 4 and the supplied calibrated mic to get those measurements.

I’m guessing though that I’ve gotten Rels to play down to 20Hz, possibly lower, at 0db.  I’ve felt Rel play lower than I can hear

Mercy Doug.. I just read your post... Not like the calm collected fellow you normally are.. OP ticked you off a bit did he?

Deep breaths... LOL

Regards

Four 8" woofers of good quality will always outperform a single 15" in terms of speed and resolution while providing about 15% more cone radiating area to move air.

This is a general statement, not withstanding the quality/performance of each driver.

Four 8" woofers of good quality will always outperform a single 15" in terms of speed and resolution while providing about 15% more cone radiating area to move air.

This is a general statement, not withstanding the quality/performance of each driver.

~~~~~~~~~~~~
Well yes dual 6.5's do havea  certain ~~Punch~~ in the bass whicha  single 8 evena  10 might not mtach.

had the Thors been , if we can fantise a  bit, over 91db sens,  they would have made my perfect ideal speaker, But 87db, is ridiculously UN-sensitive.
So I have to give up deal 6.5's with Neodymium magnets. 
A single 8 might be a bit limp in the bass vs dual 6.5's. 
Perhaps not, if we throw in 95 db sensitivity on the single 8, might easily match dual 6.5's 87db.
10 inch with high sensitivity will bring my system all the bass i've been missing all these decades. 
I'm expecting good things from the 10 in my full ~~cellos, double bass, timpini ~percussion~~orchestral  recordings. 
Building the cabinet now, for the 10, but will  use the 8 til i order the 10. 
Just going to stuff a  bunch of fill in bottom section for the 8's parimeters.

double 6" or 7", per side.

Fast, clean. mates up better with a tweeter.

MTM arrangement (midbass-tweeter-midbass)
with the right crossover, pointed straight out, you at the tip of the triangle between them. if done right, the levels will be fine. Then a window of toe in is available, of maybe 15 degrees. quasi 18 on the tweeter, quasi 12 on the woofers.

Tweeter must be a monster. King of the hill in bottom range, power handling, and efficiency. The Holy Trifecta of Tweeters. MDT33 or the ET338, is a good choice. Crossover in the 2.2k range. Some ribbons might work. Probably don't have the efficiency, though. You generally want a good 91db for one watt on the tweeter, preferably 92-93db efficiency. You'll be doing phase and crossover tuning and that will eat efficiency up, so you need to start with overhead.

be at least 9 feet away, for the pair of woofers to integrate better, and be more like a point source, than a line source.

But then again, anything can be tweaked.