What creates the effortlessness in sound reproduction?

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. 

This is all about distortion.

If higher ordered harmonics not part of the music are present, the ear will sense them as brightness and harshness.


If there are room reflections that are occurring at less than about 10mS or so, the ear will sense them as brightness and harshness.

So the amplifier plays a role- as does the rest of the system! The rule of thumb I use is the system doesn't ever sound loud, even when at 100dB. So I do everything I can to prevent the system making higher ordered harmonic distortion, preventing vibration from affecting the components and insuring that the speakers are properly set up in the room. If all this is done correctly, you will find that many speakers can be quite effortless. I find it easier with higher efficiency speakers as they tend to have less thermal compression. ESLs can work nicely too, since they have no thermal compression at all.