ABSTRACT
There is, in principle, a perfect solution to this type of noise problem. If the sound that is produced has the pressure pattern p(t, x, y, z) as a function of time t at the location x, y, and z in three-dimensional space, and if we could generate the sound pressure wave - p(t, x, y, z), then the simple superposition of the two yields
p(t, x, y, z) + [- p(t, x, y, z)] = 0, that is, total suppression. We may speak of - p(t, x, y, z) as antinoise to the noise p(t, x, y, z). This possibility for suppressing noise has been known for years, but no effective use of it was possible because of the great and unpredictable complexity of the sounds resulting from turbulent flows. It was, of course, apparent that if the following three conditions could be met, the idea could be implemented:
1. One must have detailed measurements of the sound as it is being produced.
