I think listening fatigue arises from some kind of aberration in the reproduction of sound by the speakers. An unnaturalness of the sound frequencies, or something like that. Can physically make your ears hurt. Happened to me when I had some Klipsch speakers. Although I did like the speakers I couldn't listen to them for more than an hour or so. Movies made me cringe during the loud bits.

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose