People are not machines and react differently to their senses over time. Could just be you which is normal.
Sound variation from good to incredible?
I notice that although my system always sounds good sometimes it sounds incredible. When all is right with ac and other factors I find I get a good 3D holographic type imaging with sound from everywhere but the speakers but other times the sound will still be good but less magical. Could this be ac issues and would a Keces IQRP 3600 conditioner help?