Suggestions for high efficiency speakers?

@atmasphere --

It sounds to me as if you are not familiar with the Swarm sub made by Audiokinesis. ...

Oh, I am, I simply made an attempt into outlining the possibilities of the horn sub route, and that it needn’t break the bank.

A DBA setup can be a great subs approach, no doubt. Different ways to skin your cat, as they say, and you could go all-out and make a horn sub DBA. I’ve heard a few of those.

Personally I favor a pair of symmetrically placed horn subs or other large high order bandpass variant. I’ve been given numerous long speeches on the supposed prowess of DBA - and it has its merits, for sure - but the proof is in the eating of the pudding, as they say. Not to imply all should feel the same way about that I do - on the contrary, actually - but simply that all mayn’t cry ’halleluja’ over the sonic outcome of the DBA approach, even after being preconditioned by theory.

@atmasphere --

The Classic Audio Loudspeakers Hartsfield is a speaker that has the efficiency to work with SET power since its about 105dB/1 watt.

That would be a great option indeed. What's the price of these?

But you might consider an alternative- first, high efficiency speakers often trade off bass extension for efficiency and otherwise might be enormous. So what I would do (even if not using high efficiency and also since getting that bottom octave is really expensive with high efficiency speakers) ...

It's not the price, really, but size. That is: few pre-assembled high efficiency subwoofer options are available, and the ones that are from the hifi-oriented segment would likely cost a small fortune the likes of Cessaro, Living Voice (not least) and a small handfull of others. 

The only viable way, practically, is going for pro alternatives from, as an example, Danley Sound Labs and their TH50, DTS10, DTS20 or TH118XL. They're all tapped horn subs, are rather efficient (way more than typical hifi subs) and sound great. Or, you can go DIY and make it even cheaper. If one is not comfortable building them yourself, have a cabinet maker do it for you. 

To reiterate: the one true obstacle for most people is size and preconceptions/prejudice, not price. ~20Hz extension from a 1/4 wave horn sub of some variation equates into roughly 20 cf. volume, and if you really wanted to a pair of such behemoths could be made for less, amp and DSP included, than single options from REL, JL Audio or other. It's just the ability to see the importance, give a sh*t about the norm and the will to do it. That's it. No need to go bonkers craze price-wise to realize one's goals here. 

@atmasphere --

"You can look at this as theory or fact; works the same regardless ..."

That's dangerously arrogant. You're not acknowledging the alternative, which is conspicuous in itself, and I doubt you've had a pair of symmetrically-to-the-mains placed horn subs or other efficient, large 6th order bandpass ditto (from a point of other design criteria) in your home setup augmenting your CAL's to counter your rigid claim. That is: fact, apart from the scientific approach (and business venture) you're readily advocating, is actually hearing the stuff up close to challenge your theory. Smoothness in bass response is an important boon, but it's not all their is to excellent bass reproduction and overall integration. I work from an (active) outset where high-passing the mains, preferably no lower than ~80Hz, is an important trait in securing the best integration with the subs while adding headroom and cleanliness in reproduction from the mains. It's also why symmetry of placement as outlined is important.

Again, different ways to skin you cat. 

@atmasphere --

"Its just physics, physiology and its not my theory- its that of Dr. Earl Geddes IIRC."

I'm aware of that. By "your theory" I simply implied that you presented it.

"I'm not certain of what you are trying to say in parenthesis."

That was a bit elusive, yes. I tried to touch upon that using a sub setup the way I outlined as being my preference is a matter of having a different "design" goal - i.e.: high-passing the mains fairly high to a pair of subs, (the need for) symmetrical subs placement, high sensitivity, pro drivers, very large overall size and usually not direct radiation - all in the service of loads of headroom in the lower frequencies (that translates into easy of reproduction and very low distortion) and optimum integration. 

"If you are careful with placement, you can get good bass at the listening position with only two subs."

Indeed. 

"In my case, having done many installations at shows and the like over the last three decades, I've found the DBA to be a nice solution for a vexing problem of getting the bass to play properly where the listeners will be sitting."

Makes sense, and not least over a wider listening area for more people to enjoy a fairly smooth sounding presentation in the lower octaves. 

"I recommend the Swarm becuase its designed to be as innocuous as possible. Its also reasonably priced. I've no financial association."

The Swarm a la Duke is no doubt a capable solution, but for high efficiency main speaker designs there are compelling reasons to go high eff. with the subs as well, and that requires very big size - plain and simply. It's not a requirement that sells well in audiophilia in general, but sonically I'd say it's a necessity in this particular context. DBA with high eff. subs is an option as well and just a scaled up Swarm, if you would. Maintaining symmetry of placement, be that with pairs or DBA, is paramount to my ears. 

"Having recorded a number of LPs, some of which I mastered myself, its nice to be able to compare to my own expericence of having been there when the recording was made. If you can better that reproduction as you seem to be claiming, I'd love to hear it."

I don't know if that's my claim other than recommending another viable subs option, but what I'm advocating would certainly be benefitial into vital aspects of live acoustic music reproduction as well as other genres - again, not least in the context of coupling to high eff. main speakers.  

@atmasphere --

"If you're crossing higher than about 80-100 Hz, won't you have to place the subs very near the rest of the speaker system?"

Yes indeed, no way around that. You can see it in my system's picture where the two tapped horns are flanking more or less the mains being positioned just behind them in their respective corner. Corner loading, as I'm sure you know, is a double edged sword; there's boundary gain but also a typical addition of peaks and nulls in the frequency respons. In my case it's a fairly decent outcome with limited absorbtion implemented, the biggest audible issue being a slight suck-out in the midbass region and a (more manageable) peak just below around 30Hz. All in all it makes for a smooth integration with the mains, and I've never seen the 15" B&C drivers in the TH subs move (or rather vibrate) more than a single mm or two at most - even at volumes where the air shakes violently for a very visceral and immersive experience. 

"I get the desire for a high efficiency sub- that prevents thermal compression from being as profound. FWIW I only have 2 of Duke's Swarm subs, as my CAL T-3s take care of everything down to 20Hz in the front of the room. Even at very high volumes, I'v found that the Swarm's drivers aren't moving much. I imagine that could be very different in a bigger room. They are really only there to break up the standing wave though, and apparently don't have to move as much as the front woofers (dual 15" in each cabinet) to do so. So I'm not concerned about thermal compression in this case."

It's a smart way to make a DBA, using the mains full-range and thus adding two bass sources in addition to the subs. Where are two Swarm subs positioned in relation to the CAL T-3's? It would seem the T-3's 15" woofers are carrying the heavy load, and they've got displacement to do it rather effortlessly. 

I've tried a near similiar, quasi-DBA in my own setup running the EV mains close to full-range (high-passed at 40Hz) and moving the right channel TH sub to the right corner behind me for a total of 3 bass sources, but even after a lengthy fiddling with delay/polarity, gain, and cross-overs I never came to a satisfying result. My efforts weren't exhausutive, but it became apparent that what was missing was a unified wavefront and the positive effect of high-passing the mains somewhat higher. If I were to try out a DBA again it would be maintaining my TH subs where they are currently positioned and low-passed, and then adding two smaller TH subs (10"-loaded version tuned similarly) placed behind me, symmetrically. Right now though I'm looking into a different sub design, but still a high eff. high-order bandpass, loaded with a 21" neodymium pro woofer.