Didn't know what to call this title, anyway I was wondering why the sub seems louder in another room?

We have the radio running all the time when not watching TV. In the lounge where the receiver is, the volume is quite low as is the sound from the sub.

But when we go to bedroom which is located across a small hallway approx 30 feet from the sub with the door closed (or open) the sub is quite a bit louder and boomy.