ELEMENTS OF ACOUSTICAL ENGINEERING 



CHAPTER I 

 SOUND WAVES 



1.1. Introduction. — A knowledge of the elements of acoustics is be- 

 coming increasingly important to any profession depending in any manner 

 upon acoustics. Modern civilization is becoming more critical of sound 

 reproduction. The radio receiver, phonograph, sound motion picture or 

 sound re-enforcing system of a few years ago is not acceptable to-day. 

 Auditoriums and studios must exhibit proper acoustic qualities. Reduc- 

 tion of noise in all types of machinery and appliances is demanded by the 

 consumers. Acoustics is one of the oldest divisions of physics. A few 

 years ago it appeared to be a decadent science. To-day acoustics is an 

 important and necessary branch of Applied Science and its application to 

 every phase of modern civilization is in its infancy. 



The widespread interest in the phonograph, radio broadcasting, sound 

 motion pictures, sound re-enforcing, architectural acoustics and noise 

 problems has stimulated research and developments in these fields. During 

 the early stages progress was made by the trial and error method. Later, 

 by the extension and application of scientific knowledge, results have been 

 obtained that could not have been accomplished by other means. A major 

 portion of the problems in acoustics is concerned with vibrating systems. 

 Comparisons between these problems and those of electricity considered 

 from a dynamical viewpoint have led to impedance methods in acoustics. 

 By a judicious application of dynamical theory and experimental research, 

 the science of acoustics has developed into a wide field of interesting phe- 

 nomena and with countless useful applications. 



In this book, the author has attempted to outline the essentials of acous- 

 tics from the standpoint of the engineer or applied scientist. The book 

 has been written and illustrated so that the derivations may be taken for 

 granted. The concepts of mechanical and acoustical impedance have 

 been introduced and applied so that anyone who is familiar with electrical 

 circuits will be able to analyze the action of vibrating systems. 



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