Where does fatique come from?

I personally feel the worst fatigue comes from a bad mid range followed by a harsh high end. Again I think speakers are the first consideration when trying to battle fatigue. Followed by the source then pre-amp/amp - receiver - int amp. It's actually a combination of all things from your room to power cables and interconnects. So again I think the best place to start battling fatigue is in the speakers. As far as how much - that's what ever you can afford to relieve the fatigue. An example my second set of speakers were the BIC formula 4's {$229 retail)(about 30 years ago). They were extremely bad in the mid's but had what I thought was great bass. Then I got the mission/cyrus 782's ($800 full retail 21 years ago). No they didnt have the bass of the formula 4's but the fatigue was gone. The mids and highs were a world better. Now I have the Dynaudio C1's {$7450 retail}(and demoing the C2's ($13,000 retail) as I type). The Mission/Cyrus never fatigued me so to speak but the Dyn's sound so much better to ME. Some people do not care for the Dyn's. Another example is my son has Klipsch kfl-30's. They have decent bass (although slightly muddy to me) but an IN YOUR FACE mid range which I can't take for much more than an hour. He loves them and I don't. So yes it an individual thing along with the equiptment and what you can afford. In home demo is my highest recommendation for any componets you may be thinking about.

An untreated room (no acoustical panels) can sound fatiguing, especially if your speakers are bright.

My recently treated listening room sounds great now, but before I could only listen at low volume for short periods of time.

Panels (ATS Acoustics, GIK etc) are inexpensive and make a huge difference.

Distortion is very fatiguing.