SOUND WAVE AND MICROWAVE SPACE PATTERNS 



577 



cause the amplitudes of the two signals are unequal when their distances to 

 the point of interference are unequal. Perfect cancellation can then not oc- 

 cur. It is interesting to compare this photograph with the contour curves for 

 this case as calculated from diffraction theory^ and shown in Fig. 18. Al- 



Fig. 18 — Calculated radiation pattern for two non-directional sources separated 3 

 wavelengths. (After Stenzel.) 



Fig. 19 — The pattern of Fig. 17 except that the sound sources have opposite phase. 



though the contour plot gives more quantitative information, the photograph 

 allows one to grasp the qualitative effects more quickly. Figure 19 is similar 



^ Heinrich Stenzel, "Leitfaden zur Berechnung von Schallvorgangen," (Julius Springer, 

 BerUn, 1939), p. 59. 



