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established statistical methods (Beers, 1957) to fit func- tions to deal with datasets that previously were far too cumbersome for casual application. Also in the 1980s, pro- tocols were developed to connect personal computers to the digital instrumentation used in acoustics laboratories and for field experiments (e.g., multimeters, spectrum ana- lyzers, function generators, thermocouple readers, sound level meters). Hunt (1978) cautioned that it would have been wrong “to ignore the profound changes in the scope of acoustics that have occurred [since 1950].”
With such important changes in the substance and prac- tice of acoustics, it may be valuable to reflect on how little of the content and methods taught in the funda- mental textbooks have changed over the last century. By the dawn of the twenty-first century, it was possible to generate numerical solutions to the complex coupled nonlinear differential equations that describe the ther- mokinetic behavior of vibroacoustical systems (Penelet and Garrett, 2019) and produce solutions to acoustical boundary-value problems for objects that did not have a shape that could be expressed in any of the 11 coordi- nate systems in which the wave equation was separable (Eisenhart, 1934).
The Dominance of the “Morse/Kinsler and Frey” Approach
The Source
The nineteenth century closed with the publication of the second edition of a monumental two-volume summary of the entire field of acoustics as it was understood at that time. It was written by the Nobel Prize-winning physi- cist John W. Strutt (also known as Lord Rayleigh). The first volume of The Theory of Sound (published in 1877) was written on a houseboat on the Nile while the author was recovering from rheumatic fever, so it contained few references. It focused on general theorems govern- ing vibrating systems and the mathematics required for their description. Volume I addressed the dynamics of simple-harmonic oscillators and vibrating strings and the vibrations of thin bars, stretched membranes, plates, and curved shells.
The second volume was dedicated mostly to sound in fluids, with particular attention given to fluids contained within resonators. That volume contains many references, particularly for published experimental results. The first edition of both volumes was followed by a “revised and
enlarged” second edition (Strutt, 1894). Rayleigh’s choice of topics and his sequence of presentation, starting with simple vibrators, progressing from one-dimensional con- tinua (i.e., strings and thin solid bars) to two-dimensional continua (i.e., membranes and plates) before addressing waves in fluids, is still how acoustics is organized for presentation to students of science and engineering in their introductory coursework, usually taken by upper- division undergraduates or first-year graduate students.
The part of Rayleigh’s perspective that was not per- petuated in subsequent textbooks was his dedication to the experimentalist’s perspective. In 1868, Ray- leigh purchased laboratory apparatus that he set up in his baronial mansion, Terling Place, in Essex, UK (see bit.ly/3xm4VjR). This was because at that time there were no university laboratories. Indeed, little of the historic experimental work in the United Kingdom before Rayleigh’s, by the likes of Young, Davy, and Fara- day, was performed in a university. It was not until 1871 that Cambridge University established the Cavendish Professorship in Experimental Physics. When Rayleigh succeeded Maxwell as the second Cavendish Profes- sor, in 1879, a substantial part of his effort and £1,500 of university funds (then equivalent to $7,280 and now worth about $3M) were dedicated to creating laboratory courses for large classes in heat, electricity and magne- tism, elasticity, optics, and acoustics.
Rayleigh’s 1904 Nobel Prize in Physics was awarded for his discovery of argon. He noticed that the mass of nitro- gen gas prepared by a chemical reaction differed from the nitrogen extracted from the atmosphere by an amount that was small but larger than his estimated experimental uncertainty. The balance he achieved between theory and experiment was (unfortunately) not reflected in the text- books that followed. Both Lamb (1925) and Morse (1948) focused on theory and ignored considerations related to experimental techniques and data analysis
The First Textbook
The first acoustics textbook of the post-Rayleigh era was written by Horace Lamb. Lamb made the same contribu- tion as Rayleigh but to the field of fluid dynamics, with the publication of his book, A Treatise on the Mathemat- ical Theory of the Motion of Fluids, published in 1879. Later editions were entitled Hydrodynamics (Lamb, 1932). Lamb’s acoustics textbook, The Dynamical Theory of
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