Single driver loudspeakers

Another variation is the "full range" four inch Jordan driver in a transmission line cabinet.  I wanna say Carolina Audio (among others) sells/sold this breed of animal.  I've never heard this type of speaker, but I once worked with a guy who owned a pair swore by it.

Check out Charney Audio, Somerset, NJ.  I own his Concerto horn speaker.  You can see my commentary on his web site.

I recently ran across the Audio Nirvana website. Anyone familiar with these full range drivers or their 300B SET amplifier which is very reasonably priced at $1550?
Thanks for all your informative responses!

I have had some very expensive multi-way speakers and when starting to design my own I saw some single driver speakers, so I bought a pair of 8 inch alnico Audio Nirvana drivers and had a cabinet builder make cabinets using the design shown on the Commonsense Audio website.  The alnico magnet drivers had a much smoother frequency response that that of ferrite and neodynium magnets.  I was completely taken aback with these, especially when mated with my JL Audio subwoofer, which completes what I consider the only real achilles heel of single driver speakers:  bass dynamics.  They can certainly plumb the depths but cannot move air like real woofers and subwoofers. So I then sold these and bought the AN 12 inch drivers and a larger (5.6 liter versus 2.8) cabinets, and they are a significant step up in most parameters.  As far as treble, after hearing these I wonder why anyone makes tweeters, even approaching the sound of the ion tweeters in a pair of Acapellas I once had.  And the midrange is simply unreal, as well as soundstaging and immediacy.  

I unfortunately cannot answer your question about the low-powered tube amps you mentioned as I use as powerful solid-state amp and a tubed preamp and phono stage.  I would think the tube amps to be a good match with the high sensitivity and easy load of the speakers.  Remember, your amp is driving the speaker voice coil directly, and IMO, I can hear what multi-way speakers with crossovers do wrong.

Make sure , on size I had cabinets custom made with 3/4 inch 
Russian birch ply  and AudioNirvanas best 15 inch Alnico driver in 
a 5.6 CF cabinet 44Tall X 18-3/4W X15  D my wife seen that I had to rearrange our little room now I have to sell them to stop the in fighting.  I am in New England .great deal if so one has a SUV .
too bad though ,stay single,