sound+of+one's+step
131Unusual types of gramophone records — The overwhelming majority of records manufactured have been of certain sizes (7, 10, or 12 inches), playback speeds (33⅓, 45, or 78 RPM), and appearance (round black discs). However, since the commercial adoption of the gramophone record, a… …
132Underwater acoustics — The field of underwater acoustics is closely related to a number of other fields of acoustic study, including sonar, transduction, acoustic signal processing, acoustical oceanography, bioacoustics, and physical acoustics.HistoryUnderwater sound… …
