I could use someone's input on soundproofing my apartment. I've attached a picture. Those are mirrors on the wall, just so you don't get confused as to what's going on. The wall you see separates the bedroom from the livingroom. Said wall does not go all the way to the ceiling, nor is there a door. Is there a way I can cover up that top space and create a makeshift door?

Some more background info: I'm renting, so I would like to keep the price as low as possible. Since I don't plan on making any permanent structural changes, hopefully the cost won't be too bad. The entire apartment is about 700 sq ft.

Thanks to anyone who can help!