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BELL SYSTEM TECHNICAL JOURNAL 



In one case no baffle or reflecting surface of any kind was used at the 

 pipe opening. In the other cases it was terminated (1) in a repHca 

 of a human head molded of soft rubber (2) in an 8-inch square baffle. 

 The fourth type used was the artificial mouth with acoustic resistance 

 shown in Fig. 2. The variation in pressure measured for these various 

 conditions is shown on Fig. 7. It will be noted that except for the 



500 1000 

 FREQUENCY IN CYCLES PER SECOND 



Fig. 7 — Effect on station transmitters of variation in size and shape of 

 artificial mouth. 



extreme condition of the pipe without termination, good agreement is 

 obtained for the various response-frequency characteristics, indicating 

 that the shape of the artificial mouth is not critical provided the 

 opening is of the proper order of magnitude and is effectively in a 

 baffle commensurate with the size of the human head. The measure- 

 ments described above were made with the plane of the mouthpiece of 

 the instruments in a representative position with respect to the plane 



