Televisions reach up to 15 tiles away. So when trying to lure in some zombies to a house, you'll only attract the ones within 15 tiles. However, when it comes to your character getting passive XP gains, they must be in the same room as the TV. You don't have to be facing the TV; you can sew the holes in your pants while you listen, but as long as you're in the same room as the TV, you'll get passive XP.