THE ACOUSTIC ANALYSIS OF MATERIALS IN DYNAMIC APPLICATIONS,

The Sound Spectrograph, which plots a pattern showing signal energy level variation in both frequency and time, was utilized as the primary analysis equipment during this period. To produce a meaningful pattern, magnetic tape slow-down methods and special signal handling electronics were employed for spectrogram axis scale control and time-displacement referencing. Spectrographic patterns were made for comparative analyses of proper and defective tooth missing gear train operation. Significantly different patterns were obtained demonstrating that effects hidden in the waveform become very evident in the pattern. Sound Spectrography is exploited fully in the analysis of system characteristics where either fixed excitation is operated on by a time-varying transfer function, or controlled excitation having time-varying spectral content is applied to a fixed transfer function. The former class includes all rotational and reciprocating equipment and equipment powered by periodic excitation. The latter class includes all passive no moving parts devices excited by programmed forcing functions. Author