Ok, here goes your home work assignment. Do this in a room with a really nice carpet.
Find a nice piece of plexiglass or piece of glass like what you'd use on the bottom of an aquarium. (The rest of you can see where this is going.)
Get a paper bag ... get two (room within a room and all that). Put one bag inside the other and place that assembly over the glass/plastic plate.
Get some Rit dye ... I suggest purple ... and mix it in a gallon of water.
Pour the gallon of water into the paper bags.
What leaks on to your very nice carpet resembles the amount of sound that will flank out of your room if you do not sound isolate the walls.
If you're married, I suggest you take a long walk.
Here's an article on that ... http://www.soundproofingcompany.com/soundproofing-articles/flanking/
Granted you're on a budget, money is tight, etc. Understand, just doing the ceiling is a waste of money. So if you cannot do the walls, use that money somewhere else.
If you do the walls properly, that may hit your budget more than you'd want. On the other hand, you can get a better projector later, better speakers later; but, you cannot fix the walls later.