Best Efficient versatile Speaker reaching 30Hz?

Klipsch K-horn is quite possibly the loudest speaker on earth

I do like the K-horns when paired off with the right amp, and at 104db they are mighty efficient. They will not, however reach down much below 30hz in my experience. Tight bass is not their forte, though of the range of the older Klipsch Heritage line they do Bass the best of the bunch given the corners they were designed to be positioned in. Their specs indicate 33hz at the bottom. Fast dynamic midrange, crystaline clear, and yes, loud as you can take if that's your poison. If you are hooked on sub-30hz bass you will need a sub with K-horns (or any of the Klipsch Heritage line for that matter).

Marco

I also believe that speaker efficiency is very important. While I have also heard many non efficient speakers that also sounded great they don't IMO have the same type of life like dynamics that you get from good quality highly efficient speakers unless they are driven with huge power amps. Josep you didn't mention what your budget was as this might greatly narrow the playing field. If money were no object the choice would be easy, Wilson Alexandria. I am partial to JM Lab speakers as most models are quite efficient. I have a pair of JM Lab 946 Electra's which will dip below 30Hz. They are rated 32Hz-32KHz and -6db at 27Hz at 93 db efficiency, nominal impedance 8 ohms and minimal impedance 3.2 ohms. These speakers really rock! With the dual 10 inch woofers they deliver clean, powerful, tight, accurate bass that can really fill a room without sounding boomy or boxy. What I do like about them is that they really do play all types of music very well, including rock and you do NOT need a 500 watt amp to drive them and they also sound great at low volume. I previously had a set of Infinity's with 87 db efficiency that I drove with a 150 watt amp and what a difference the JM Labs made in dynamics and bass energy. There are many good speakers out there but most of them IMO sound quite lean on the bottom end even though they may be rated down to 30 Hz or so. There are very few if any that I have heard that better the bass performance of the 946 Electra's without sounding boomy or costing a LOT more money.

I have the Zu Druid Mk4 (although they were originally the Rune model that I had upgraded). Efficiency is 101dB, frequency response 35Hz to 20kHz, 12 Ohm nominal impedance (8 minimum) , 10" proprietary woofer, augmented by a proprietary 1" supertweeter with a split shelf high-pass filter network at 12kHz (as close to no crossover as none at all). Although not quite as low as what you're after, at the price ($2,800) they are a stupendous value. Add a decent subwoofer if you need more low end grunt and you'll be laughing.

I am driving the Druids with 2Wpc of tube power, which replaced 125Wpc of ss (which was also very good), and couldn't be happier. Still require some break-in on the upgraded drivers, but the music is already sweet and satisfying. Very even across the frequencies, mid-range is excellent. Bass is accurate and clean, although not the deepest. A decent sub will fill in the lowest notes if desired.