What creates the effortlessness in sound reproduction?


Hello, 
I have a chance to listen some speakers in the last 10 years. I notice that there are 2 speakers which produced sound 'effortlessly', even at low or high volume levels (I never tried max levels on them since they are not mine). With this effortlessness, listening to music is very relaxing. 

I wonder what makes the effortlessness in these speakers? 

Please shed some light on this. 

Thank you. 
Huy
Ag insider logo xs@2xquanghuy147
As geoffkait indicated, but, in two words, dynamic range. Every listener, should have some experience, to listen to live, unamplified music, to get an understanding of what dynamic range, really is. ( real musicians, in a real space ). I am speaking of music and sound, as dynamic range is also associated with  vision ( photography.and video ).
I'm sorry for my ignorance but I am not sure I understand this correctly. Do you mean that in an experiment of several systems which are playing at 100dB, some system will be louder than the rest?
@quanghuy147  No. Some systems will **sound** louder. This is because higher ordered harmonics are used by the ear to sense sound pressure. If a system is making more of them than a 2nd system, that 1st system will sound louder even though it isn't. In fact this is so profound that the 1st system could be a good 15dB quieter and still sound louder.

Eliminating intermodulations and higher ordered harmonic distortion is the key. 
Larger drivers being slower is a misnomer. Often smallish drivers are wrongly claimed to image better, sound quicker, etc. It's mostly attempted justification for a lesser rig. Listen sometime to how much distortion a 6.5" woofer puts out in comparison to 15". I prefer not to introduce that level of distortion into low end performance. :)
As usual, YMMV
+1 to Doug

I find 18 inch Scaena subwoofer to be fast enough to match Lansche 4.1.

The most effortless speaker that I had heard is vintage Western big horn with  field coil magnet.

Because of high efficiency you need less than 20 watts of power to fill the big room.
The biggest problem though I believe is the lack of good recordings. Let me mention one that holds for any sound level - Cream reunion live at the Albert Hall. Bluray.