That’s a slightly nuanced issue, they don’t need to be loud but they sound very clean at elevated volumes which is not really a criticism.Perhaps more useful input from me to the OP…
I love what ATCs can do. I’ve had active 50s.
My only criticism is that IMO they need to be played quite loud to come alive. By no means awful at lower volumes, but the temptation was always there to crank them up a smidge (or more than a smidge!), which is not always ideal.
Perhaps in a bigger room that’s less of an issue.
So, audition at home, and try to audition at varying levels, not just “audition loud”!
Hope that helps.
I do find myself cranking them up a bit subconsciously so a decibel app on the phone can be useful. They don’t sound loud when they are loud if that makes sense? Lack of usual distortion.
I suppose it’s a bit like driving a very fast car.