262 



BELL SYSTEM TECHNICAL JOURNAL 



Under the worst conditions encountered, a margin of at least 15 db 

 is realized with this structure which effectively eliminates howling as a 

 limiting factor in the general use of the handset. 



Determination of Dimensions 



Particular effort has been made to proportion the handset so that the 

 transmitter mouthpiece may be as near as possible to the lips of the 





Fig. 1 1 — Distribution of the head measurement data. 



talker, thereby avoiding unnecessary transmitting loss. Care has been 

 taken also to provide adequate clearance between his hand and cheek. 

 In determining the proper dimensions of the handle and assembly, 

 about 4000 measurements of head dimensions were made. The 

 subjects selected for these measurements included both sexes and the 

 various races in about the proportion indicated by the census figures. 

 The head measurements were made with a special gauge as shown in 

 Fig. 10. The receiver cap was held to the ear and the pin placed in 

 contact with the cheek. The slider was moved along the calibrated 

 bar until it touched the lips. A record was made of the dimensions 

 which determined the position of the center of the lips relative to the 



