Best Efficient versatile Speaker reaching 30Hz?

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.