Acoustics is one of the youngest classical sciences, with the theoretical foundations being formulated by Lord Rayleigh in 1877. In the period between 1898 and 1905, Wallace Clement Sabine advanced the application of acoustics to architecture. But it was the development of the vacuum-tube amplifier, loudspeakers, and noise-free microphones in the second quarter of the 20th century that allowed the amassing of enough accurate data to make acoustics an effective engineering science. Before electronic equipment was invented, acousticians lacked both the means to produce specific types of sounds and to then measure the strength of them. Before these tools existed, designers of music halls could learn about acoustics only by observing other halls, speculating about which factors were responsible for glorious sonorities in one place and muddled cacophony in another. The information herein applies to any concert hall or opera house, the result of hundreds of interviews with opera and symphony orchestra conductors, performers, and music critics; of listening to music in some sixty different halls; of collecting precise acoustical measurements, accurate architectural drawings, and photographs of said halls. The story of the acoustics of many of the world's greatest halls is told as simply as possible, while maintaining technical accuracy.