Speech volumes on bell system message circuits

The volume of message signals at various points in the telephone network is of utmost importance to those who design and engineer telephone systems and equipment, and ultimately, of course, to the listener. This volume is influenced not only by the speech pressure produced by the talker and his habits in using the telephone set, but also the characteristics of the set, the battery supply and loop resistance, and the electrical loss, or gain between the set and the point at which knowledge of the level is desired.