THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

8 1. A Capsule History of AcousticsWorld War I ended before underwater echo-ranging could be fully deployed tomeet the German U-boat threat. The years of peace following World War I witnesseda slow but nevertheless steady advance in applying underwater sound todepth-sounding by ships. Improvements in electronic amplification and processing,magnetostrictive projectors, piezoelectric transducers provided refinements inecho-ranging. The advent of World War II heightened research activity on bothsides of the Atlantic, and most of the present concepts and applications of underwateracoustics traced their origins to this period. The concept of target strength,noise output of various ships at different speeds and frequencies, reverberation inthe sea, and evaluation of underwater sound through spectrum analysis were quantitativelyestablished. It was during this period that underwater acoustics becamea mature branch of science and engineering, backed by vast literature and historyof achievement.The invention of the triode vacuum tube and the advent of the telephone and radiobroadcasting served to intensify interest in the field of acoustics. The developmentof vacuum tube amplifiers and signal generators rendered feasible the design andconstruction of sensitive and reliable measurement instruments. The evolution ofthe modern telephone system in the United States was facilitated by the progressof communication acoustics, mainly through the remarkable efforts of the BellTelephone Laboratories.The historic invention of the transistor (1949) at the Bell Laboratories in MurrayHill, New Jersey, gave rise to a whole slew of new devices in the field of electronics,including solid state audio and video equipment, computers, spectrum analyzers,electric power conditioners, and other gear too numerous to mention here.Experiments and development of theory in architectural acoustics were conductedduring the 1930s and the 1940s at a number of major research centers,notably Harvard, MIT, and UCLA. Vern O. Knudsen (1893–1974), eventually thechancellor of UCLA, carried on Sabine’s work by conducting major research onsound absorption and transmission. The most notable of his younger associateswas Cyril M. Harris (b. 1917), who was to become the principal consultant onthe acoustics of the Metropolitan Opera House in New York, the John F. KennedyCenter in the District of Columbia, the Powell Symphony Hall in St. Louis, and anumber of other notable edifices.Sound decay, in terms of reverberation times, was discovered to be a decisivefactor in gauging the suitability of enclosed areas for use as listening chambers.The impedance method of rating acoustical materials was established to predict theradiative patterns of sonic output, and prediction of sound attenuation in ducts wasestablished on a scientific footing. The architectural acoustician now has a widearray of acoustical materials to choose from and to tailor the walls segmentwisein order to effect the proper acoustic environment.Acoustics also engendered the science of psychoacoustics. Harvey Fletcher(1884–1990) led the Bell Telephone Laboratories in describing and quantifyingthe concepts of loudness and masking, and there, many of the determinants ofspeech communication were also established (1920–1940). Fletcher, now regardedas “the father of psychoacoustics,” worked with the physicist Robert Millikan at