144 BELL SYSTEM TECHNICAL JOURNAL 



telephone line a system is provided whereby a speaker can address 

 an audience at a distant point. Also with a complete public address 

 system at the point where the speaker is located, connected by lines 

 to receiving elements of the public address system located at one or 

 more distant points, the speaker is enabled to address a large local 

 audience and to be heard simultaneously by audiences at one or more 

 remote points. This last arrangement was first used on Armistice 

 Day, 1921, when audiences at Arlington, New York and San Fran- 

 cisco joined together in the ceremonies attending the burial of the 

 Unknown Soldier at the National Cemetery at Arlington, Virginia. 



By means of the public address system, the meeting of this Institute 

 at New York, at which this paper is presented, is attended and par- 

 ticipated in by Institute members at a meeting in Chicago. This is 

 the first occasion on which complete public address systems installed 

 at meetings in two cities have been connected together by telephone 

 lines so that speakers at each meeting address the local and distant 

 audiences simultaneously. 



With the transmitting element of the public address system work- 

 ing into the radio transmitter of a broadcasting station and with the 

 receiving elements of the system connected to the output of radio 

 receiving sets, a system is provided whereby a number of people can 

 be reached by each radio receiver. 



The combination of these wire and radio communication channels 

 with the elements of the public address system is, therefore, without 

 limit in the number of persons who may be reached simultaneously 

 by one speaker. Such combinations may prove extremely serviceable 

 for occasions of nation-wide interest and importance. 



The public address system apparatus has been used not only for 

 transmitting speech sounds but also for music, both vocal and instru- 

 mental. The paper 2 describing the public address system has pointed 

 out that the requirements for such a system are that for a wide fre- 

 quency range it be practically distortionless, that is, transmit and 

 reproduce with equal efficiency all frequencies in that range. This 

 requirement must apply likewise to lines which are used with the loud 

 speaker system. It has been found that a circuit which transmits 

 without material distortion the frequency range from about 400 to 

 2000 cycles, can be used with the public address system to reproduce 

 speech sounds which are fairly understandable under favorable con- 

 ditions, although sounding unnatural. In general it is important to 

 extend this range at both ends in order to improve the intelligibility 

 of the sounds and increase the naturalness. For vocal and for some 



2 Green and Maxfield, "Public Address System." 



