Why can I hear bass if I have Low Frequency Deafness?

All my family have it and there has been official diagnosis and yet I can hear Bass, I never thought of this until a friend pointed it out.
But if there is bass around I can't hear anything else, If I'm at a gig and people are talking, I can hear that they're talking but can't distiguish thier words because I can't hear in loud music, at all, you have to shout directly in my ear.
or if I'm on a bus and someone with a deep voice starts talking to me, I can't hear a word they're saying. it's so bad that while I was working at the same place as my sister we met this guy that without any background noise at all, we couldn't hear a word he was saying, I just couldn't make him out? my sister was really polite, but in the end I had to tell him, I just couldn't hear anything he was saying his voice was just in the wrong range for me to hear!
And doing research on this I find there isn't much info out there on Low Frequency Deafness, only High Frequency?
Does someone have any answers?

I do not know the medical or scientific reason but I have the same trouble, my cure is to avoid loud noise situtations. In normal sound levels everything is fine.