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Linear Acoustic Theory

1961; Springer Nature; Linguagem: Inglês

10.1007/978-3-642-45956-6_1

2197-4195

Philip Μ. Morse, K. Uno Ingard,

Scientific Research and Discoveries

Acoustical motion is, almost by definition, a perturbation. The slow compressions and expansions of materials, discussed in thermodynamics, are not thought of as acoustical phenomena, nor is the steady flow of air usually called sound. It is only when the compression is irregular enough so that over-all thermodynamic equilibrium may not be maintained, or when the steady flow is deflected by some obstacles so that wave motion is produced, that we consider part of the motion to be acoustical. In other words, we think of sound as a by-product, wanted or unwanted, of slower, more regular mechanical processes. And, whether the generating process be the motion of a violin bow or the rush of gas from a turbo-jet, the part of the motion we call sound usually carries but a minute fraction of the energy present in the primary process, which is not considered to be acoustical.KeywordsIncident WavePartial WaveAcoustic PressureScattered WaveRoughness ElementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.