According to some website I found, 30dB is a pretty quiet room and a rock concert is around 120+dB so you’d need -90dB to hear quiet at a rock concert. However even if you completely blocked all sound through the ear canal you’d probably get sound going through your skull so there’s just a limit to what’s going to really work.

There's no such thing as complete quietness for a human to experience. Not getting external signals brain immediately, and unavoidably starts to hallucinate noise