From the New Yorker:
The modern classical-music performance, as audiences have come to know it and sometimes to love it, adheres to a fairly rigid format. The music usually begins a few minutes after eight, listeners having taken their seats beforehand to peruse program notes or chat with neighbors. The evening falls into two halves, each lasting around forty-five or fifty minutes. An orchestral concert often proceeds from overture or short tone poem to solo concerto, and then to a symphony or some other major statement; a solo recital builds up to a big sonata or a virtuoso showpiece. The audience is expected to remain quiet for the duration of each work, and those who applaud between movements may face embarrassment. Around ten oâ€™clock, the audience claps for two or three minutes, the performers bow two or three times, and all go home. Opera has a slightly looser codeâ€”the length of the evening depends on the composerâ€™s whims, and the audience makes its feelings known with sporadic applause and very occasional boosâ€”but there, too, an atmosphere of high seriousness prevails.
Most people are aware that this clockwork routineâ€”reassuringly dependable or drearily predictable, depending on whom you askâ€”is of recent origin, and that before 1900 concerts assumed a quite different form. Itâ€™s always a shock, though, to confront the difference in all its particulars.