inna wrote: "Bass gives a foundation. This is a very big disadvantage of high efficiency design. "
I respectfully beg to differ. My fully horn loaded DIY speakers have a measured output at 25 Hz that is identical to the 1kHz reference. There is an 18sdB/octave roll off below 25 Hz. This is accomplished with Bill Fitzmaurice designed HT Tuba folded corner horns which have a sensitivity of about 103 or 104 dB/2.83v/meter.