A full range speaker?

Millercarbon has it right - the low extension depends more on your room than you would think.I do not see yet the question answered though: can a single driver speaker reproduce an orchestra?Yes it can. Fostex FE204 Voigt pipes I built can. It has particularly truthful piano reproduction, the best approaching a real piano I heard so far from speakers.
How can it be?The brain makes sense of the fundamentals ONLY when the upper harmonic spectrum is correct. With single driver speakers there is a flawless continuity with the upper harmonics, so even though the 26Hz fundamental is already quite rolled off, but you have the 52Hz & up harmonics PERFECTLY lined up, so your brain will reconstruct the 26hz fundamental that's not physically audible, and the lowest note will be there in absolute harmonic richess, although lighter in weight (versus the heavy handed, but dried up 26Hz that you get from a powered sub or additional base driver that has different resonant characteristics than the upper drivers, hence the tonal spectrum goes south.)
Audio technology is not perfect, each solution has advantages and disadvantages. People assume that adding more drivers is a perfect solution, however, it has its own compromises.
Also, I'd like to add that I have not heard any commercial full ranger that comes anywhere to a full range experience, although I have not heard any properly set up. (With FR speakers proper speaker placement & amp matching is beyond vital.) Improper FR speaker set up: shrill and annoying sound. Proper set up: listened to Beethoven IX on them right after listening to Bethoven IX with live orchestra, and the FR gave a better experience than the live one. Just a thought... FR can sound great.  Also, I heard the best timpani on these FRs. ;). They are not brutes, don;t expect titanic crashing the iceberg and peeling your plaster to strike massive egos. Think base that has 3D definition, kettle drum that you literally can see in your room, with the skin vibrating and the waves washing over you and stopping your heart for a second - not from brute speed, not the sound-trying-to-rape-your-room, but the intense speed that defies what we expect from recorded sound. FR drivers can do more in the base department, because the ultra high sensitivity gives them the dynamic / speed edge.   (Need I add: 95dB and higher sensitivity FR...)
Bruce Edgar had a FR speaker made with Lowther 6PMA, maybe you can find one around... (he made very few though.) That's an outstanding FR!!!! Practically no Lowther shout, yet all of the Lowther speed and best low extension of any FR I heard.

I like feeling my music, and my system is used for home theater as well, so a solid 25hz satisfies me. But my pair of KEF R 400 b's only go comfortably to 28, so for now that’s it. 
Oddly enough, using some furniture, not to my wife’s liking, to fashion a horn, really increases the volume and decreases the distortion.

My newly acquired PBN Montana XPS speakers have an in room rating of 25 hz to 22 khz, pretty full range to me. However I do back them up with dual Rythmick F12 subs. Never enough bass!

@realworldaudio


Yes, if you go back to the beginning horns were necessary to reproduce bass because the amps only had so much power, so a good full range can get you most of the way there with a folded horn box, or a BAB. 

I currently have 3 sets of Fostex laying around waiting for cabinets, 4, 6, and 8 inches, two Sigma and a pair of Fostex FE206NV 8"ers.

Agree with @douglas_schroeder  that listening to a system with strong output down through 15 Hz is a completely different listening animal than most people would suppose. Whoever said that there's just not that much musical info below 40 Hz was absolutely wack. 

Also recall that "20 Hz" does Not represent the "lowest sound we can hear"...it simply is the lowest sound we can hear that most people can Identify as a **musical pitch** or **tone**. But, there is all kinds of musical information - having to do with tone,  dynamics And spatial relationships - that can easily be felt as well as heard. Not to mention the idea of properly pressurizing a room of a given volume vs amp power vs typical listening levels.

But I certainly agree with others that, more than anything else, it really doesn't just take a custom system (which indeed it does) but it takes a truly custom room. A nice, reasonable, typically good set of dimensions might be on the order of 25 or 30 ft long, by say 20 ft wide and at least 14 or 15 ft tall(!) And kiss goodbye any thoughts of 2x4 construction - you'll need more like 2x12's, instead - floor, walls and ceiling alike. And you will still need room treatments, maybe not as much as in a 'bad' room, but you'll still need them...and EQ.

People do engage in these sorts of projects from time to time, but all that is a major barrier that most people aren't quite willing to try to scale for obvious reasons. The rewards are there, particularly if you're looking to build your next home, or modify you're existing house (if you've accumulated home equity over the years, that can come in handy). True, full-range sound can be had, but, done right, it will come as a nasty sticker shock. But impractical problems sometimes require just plain impractical solutions.