THE TIME FACTOR IN TELEPHONE TRANSMISSION 



57 



ture has been taken liy means of artificial delay circuits. One method 

 has been to loop back and forth loaded conductors in a cable until the 

 desired delay was obtained Another method has been to record the 



Fig. 1 — Acoustic delay circuits. 



talkers' waves on a phonograph and pick up the impressions with a 

 second needle, displaced the desired amount from the first so as to 

 introduce delay into the conversation. 



HIGH QUALITY 



^^-''^ LOUDSPEAKER UNITS "^^ 



TRANSFORMER 



TRANSFORMER 



Fig. 2 — Acoustical delay circuit showing two high-quality loudspeakers with one 

 connected to each end of tube forming delay circuit. 



Considerable use has also been made of pipes or "acoustic" delay 

 circuits. Fig. 1 shows an illustration of a brass pipe delay circuit 

 used in experimental work. Fig. 2 shows the circuit in schematic 

 form. In addition to the pipe, w^hich is looped back and forth to 

 conserve space, the circuit involves telephone receivers at the two 



