566 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



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Fig. 2 — An early photo of a sound field in which 

 the scanning strokes were too coarse. 



Fig. 3 — Finer grained scanning produces a smooth pattern 

 of the 10'' acoustic lens of Fig. 2./ = 9 KC (X = 1.51"). 



loud speaker which supplies a single frequency sound field. The Polaroid- 

 Land camera in the background has been favored because its short develop- 



