How loud is too loud


Hi. Im new to the world of audiophile and am hoping someone can help with a problem only nine months in to spending £3000  on my set up. I've got an audiolab 8200p power amp, audiolab 8300cd and monitor audio silver 8 speakers. After playing some fairly heavy house music at -10db I noticed a distinct lack in sound quality when I played music at a lower volume and now it sounds as if I've lost a whole frequency level. There is not distortion as such, it's just that music sounds quieter and less definition in the top end. I always run my system in before turning up the volume and never push it too hard for too long. Normal listening level is around -30db.
Any suggestions greatly appreciated.
tcapone
In my experience, if/when the sound quality appears deteriorated after playing the music real real loud, either the tweeters or the listener’s ears, or both are damaged.
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Just a little addendum to roberjerman's explanation. "Loudness" switch was pretty much ubiquitous on 1970s-1980s amplifiers/receivers. However, these days Luxman and Accuphase still include "Loudness" on, at least, their integrated amplifiers. It works.
Here's a calibrated microphone. You need to grab the calibration file online and move it to your phone, and not every app will use it. Audio Tools does.

https://amzn.to/2JutQI5

Best,

E