 Since the 2010s, one of the increasing sources of competition for movie theaters is the increasing ownership by people of home theater systems which can display high-resolution Blu-ray disks of movies on large, widescreen flat-screen TVs, with 5.1 surround sound and a powerful subwoofer for low-pitched sounds.The relatively strong uniformity of movie ticket prices, particularly in the U.S., is a common economics puzzle, because conventional supply and demand theory would suggest higher prices for more popular and more expensive movies, and lower prices for an unpopular "bomb" or for a documentary with less audience appeal.Unlike seemingly similar forms of entertainment such as rock concerts, in which a popular performer's tickets cost much more than an unpopular performer's tickets, the demand for movies is very difficult to predict ahead of time.