On Background Sounds

I've discovered something about reading while having music playing in the background. 

In order for the music to not distract you from whatever you are reading the music has to be at a very low volume so that your mind doesn't pay attention to it, it doesn't even try. When you are reading you hear the words in your mind and, if you can hear them, then they must have volume. So the sounds have to be quieter than your mind's internal soundscape. 

In the case of music that is loud it won't disturb your reading because the mind simply ignores that loud sound deeming it to be irrelevant. It sounds counterintuitive but that's what happens and I have a hypothesis as to why. If we are able to ignore very quiet and loud ones, what can't we ignore or tune out? Well we can't, or don't, ignore sounds that are within the range of human speech and sound organised enough to be a language. So if the music has lyrics then it becomes almost impossible to ignore unless it doesn't get hooked by your attention. Maybe it's a leftover of something that was once a positive survival trait. I can't prove that so it's only a hypothesis at this point. I can say that in my personal experience it seems to ring true. Interesting to contemplate.

P.S.  This hypothesis might go some way to explain how I am able to go to sleep with headphones on listening to Motörhead. Perhaps it's because we do not pay attention to sleeping, so what is there to interrupt?