What is your take on high efficient speakers vs. low efficient speakers?

It’s about the implementation and physics. Sure you can have, say, 97dB sensitivity and honest 20-25Hz extension - that’s from a tapped horn at 20cf. volume with a high-ish fs (35Hz) pro 15," proper motor strength, not too low mms (i.e.: +150 grams) and overall complementary parameters for its specific use. The horn does the heavy lifting and fills out the extension and amplitude gap the driver normally couldn’t handle. Way smart.

I would be cautious pairing high eff. main speakers with low eff. subs - it doesn’t really gel. You want high eff. and extension to boot you go the distance with size to follow and high eff. all the way; it pays off sonically and certainly is realistic - where there is a will to let size (and the required design) have it’s say.

Run it all actively with high-passed mains and treat it as one speaker system pr. channel incl. subs with carefully implemented delay settings and overall filter parameters via a capable DSP - not just with the latter patched on where the (passively configured) mains roll off naturally. Just my $0.02..

After reading (and re-reading) all of "bache" posts, I think I understand what he's saying-   "High sensitivity loudspeakers roll off rather high in the bass department".

Forgive me but Isn't this captain obvious? Are there many folks that listen to high sensitivity speakers without a sub or two?

My mains (104db) start to drop like a stone at around 80Hz. 

Sure theres still some output at 40Hz. but its very light in the a#$. I use dual subs to fill in those bottom two octaves.It also helps smooth room modes..

So after going through the trouble to blend them into the system, I would never go back to 

@johnnycamp5   100% , just want to figure out , how  you know( My mains (104db) start to drop like a stone at around 80Hz. )

Because the speaker manufacturer displays frequency response graphs for each loudspeaker they sell.

i’ve also run sweeps myself, seeing the same response.

My experience this is not a particularly unique frequency response using high sensitivity loudspeakers. More common than not.

My friend is a DIY speakers builder. He also fixes drivers.

He had and measured dozens different 15' driver JBL, Tannoy, Altec,... He says the maximal sensitivity of 15' driver in vented box (of any size) at 100Hz is 94-95dB. Some 15' drivers like Altec have higher sensitivity around 200-300Hz but it drops to 95dB at 100Hz. 10'-12' have even smaller sensitivity at 100Hz.