Suggestions for high efficiency speakers?

@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. 

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

@phusis 

I’m not sure even though we’ve used them at shows quite a bit. You might inquire with John at CAL.

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.

It sounds to me as if you are not familiar with the Swarm sub made by Audiokinesis. Its 1 foot square and 2 feet tall. Its also meant to be placed as close to the wall as possible because its designed to take advantage of the room boundary effect (+3db/octave going down from 100Hz). This allows it to be small and easily placed. In my installation I have the drivers facing the wall rather than the room, to insure the output really is within the room boundary. They work quite well- I use a pair in tandem with my CAL T-3s, which by themselves are flat to 20Hz (and are 97.5dB). Because there is a standing wave in my room, there’s no bass at the listening chair despite the speakers’ capabilities.

Swarm subwoofers

So I use the Swarm subs to break up the standing wave, and now the bass is good anywhere in the room. FWIW, IIRC the Swarms are about 3500/set (don’t quote me on that) so are very reasonably priced and give you excellent bass.

You've been given a ton of good recommendations and you're not in a hurry which is great. Since you can get down to this area I would suggest stopping by Deja Vu Audio in VA, they are the AN dealer running the room at CAF. In addition to AN speakers they also build their own hornspeakers so a good chance to compare and contrast.

@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.

As Larryi suggests, there are so many great candidates. I haven't had chance to hear many, although I was invited to hear the Musical Affair Grand Crescendo with PHY driver. I could live with them, as I do like single driver design philosophy. Larryi say's to  listen to as many as you can. Yes!!