[plymjack]

Originally Posted by kmarei

I have a strong feeling people who say they noticed the sound got enter after their speakers broke in, are just getting used to the sound
Listen to any sound system for a few days and your ears start to get used to it
What was shrill initially, sounds "normal" now

High end audio speakers are often soak tested for 48 hours - I visited such a factory doing this when I used to sell such gear. Speakers especially do settle down after being powered up for an initial period. Ears do get used to shrill sound and will accept it, but the brain does not "remember" such experience and so each time you get in the car you will have to get used to it again if it is shrill (and yes the time period will reduce over time but it will still sound shrill if it is...)!

However it does improve over time as posters are here are repeatedly trying to explain.