Opera house electronic libretto systems have begun to be used in some opera houses, including New York's Metropolitan Opera, Milan's La Scala, and the Crosby Theatre of The Santa Fe Opera, which provide two lines of text on individual screens attached to the backs of the seats so as to not interfere with the visual aspects of the performance. A subtle type of sound reinforcement called acoustic enhancement is used in some opera houses. Acoustic enhancement systems help give a more even sound in the hall and prevent "dead spots" in the audience seating area by "...augment[ing] a hall's intrinsic acoustic characteristics."
Opera house (with 2,200), the Royal Opera House in London (with 2,268) and the Vienna State Opera (the new auditorium with 2,280). Modern opera houses of the 20th century such as New York's Metropolitan Opera House (with 3,800) and the War Memorial Opera House in San Francisco (with 3,146) are larger. Many operas are better suited to being presented in smaller theaters, such as Venice's La Fenice with about 1,000 seats. In a traditional opera house, the auditorium is U-shaped, with the length of the sides determining the audience capacity. Around this are tiers of balconies, and often, nearer to the stage,