High-Efficiency Single Driver Speaker System

Seikosa---thanks for your thorough insight and for listing the shortcomings of a Single Driver system as well as the advantages. Taking the plunge is tempting, but not without trepidation considering I've yet to hear this type of system with my own ears---only read reviews and feedback from other audiophiles like yourself and Germanboxers. My musical taste are very similar, but I occasionally like to turn it up and hear deep, distinct notes on both upright bass and bass guitar. Thank you both and I'll keep you posted.

My 4" Merrill drivers really roll off in the lows. However, you wouldn't guess it while listening. The bass you can get out of a quarter wave design is astounding! Every person that has ever heard them goes looking for the subwoofer. The highs literally "float" up to about 15khz. The sound is so fluid and seamless. Since this is my office system, I can listen 30-40 hours a week. I never tire/fatigue from the sound.
This is all driven by a 12 watt vintage Masterwork receiver.

Are single drivers the end-all? Probably not. I've got a fairly robust theater at home running 2000 watts to shake the house. It's fun and can be overwhelming. Great for SACD's too. However, my Sota table mates better with the work system.

If you made me choose-I would have a really hard time deciding between a Coincident 5 channel system and my Merrill Zigmahornets...try it for yourself.

I listen to jazz, classical & rock and while I'm not very good at describing sound like those posts before mine, I just know it when its right. Having said that, I owned a very rare pair of wide baffle Omega Grande 8's several years ago, had them for a couple of years and then sold them. In the interim I had a couple pair of nice 2 way British monitor speakers (Celestion 100s & Linn Helix LS150s) and now I've recently re-purchased my old Omegas.

Also, several years back I had the opportunity to hear a bunch of different systems at The Vacuum Tube Valley show in Central NJ. I heard PP & SET systems that used KT88's, EL34s, 6L6s, EL84s, 6BG4s, 300Bs, 2A3's, 45s, 50s, 10s as well as Class D amps w/tube preamps. My overall favorite was the one with the lowest power, an SET amp, played on a single driver pair of Beauhorns. Next, I liked the digital amp/tube preamp with a pair of single driver Omegas and next were the Omegas being played on an EL84 Dyna mark II remake. I don't know how to describe it, much more immediacy and it just sounded right. Single driver speakers and Single ended tube amps (hence my a'gon name) just sounds the best to me. Horn speakers on SE amps also sound great as well.

Don't know if i fit your description fully, but I have done a road trip down the lane of low efficiency speaker systems (probably not any of them known to anyone outside Scandinavia), through commercial hi efficiency horns from Avantgarde (Uno, Duo and Duo Omegas). I went all in and sold my Duo Omegas and went for an all out single driver design, barely known to anyone outside Japan. As Fostex made a new limited edition (500 pcs)fullrange driver, the Fe 203 En-S, there was finally an available suitable driver for the Nagaoka 3m long backloaded horn enclosure. This BLH construction provides an acoustic output down to 40Hz. After trying the driver in the Fostex recommended BLH enclosures i decided to go all in on a speaker system based on this driver in the legendary and "mythical" beerguts enclosure. The fullrange driver in the Nagaoka BLH is a fullworthy speaker in itself, but can be utterly be refined by adding help in both frequency flanks. See my system for reference. My point of all this is; To build my speaker system around this exeptional Nagaoka/Fostex fullrange BLH gave me a great possibility to build a system optimized for my personal preference with the freedom of choosing xover points more freely and keeping them in optimal range for the high/low drivers have given me the opportunity to keep the basic qualities the fullragne hieff BLH Nagaoka construction gave.

So to the first question: I listen to: prog-rock, fusion, prog-metal, metal, jazz. I like to see myself as a musical lover, loving music more than genres. So if it is good it works for me :)

Second question; A lot of good points have already been pointed out in this thread. I recognice most of the pros and cons mentioned.

I played for many months on the "bare" fullrange driver and loved the lack of overlapping problems i have heard on so many multiple driver speakers. To hear female vocals on a fullrange driver is a joyful and quite educating experience imo. The fullrange driver is good, but not state of the art in frequency extremes. As i had ambitions with my speaker system and had a lot of skilled people backing my project i decided to go all out with a system based on the best skills of the Fostex fullrange drivers. I am very happy with the result. It suits my preferences, my room and did not cost me more than the Avantgarde Duo Omegas in the end. I was very happy with my Duo Omega's and still regard them as very attractive speakerss:), but the BeerGuts reference system plays in another league imo.

Germanboxers nails it. Just add to that music list some indie rock and folk and anything with intricate, complicated, overlapping percussion and / or melody to a one note solo.
To my ear you just don't seem to notice a little lack of coherency in most well designed speakers but with the Rethm Saadhanas I drive with a Shindo 20w push pull tube amp and I can imagine some other crossoverless speakers, you do notice the very coherent sound in a speaker of this type.