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BELL SYSTEM TECHNICAL JOURNAL 



tuated. To reduce these effects as far as possible, the television booths 

 were made as large as other considerations would permit and all surfaces 

 were covered where possible with acoustic absorbing material. They 

 have a floor area of about 35 sq. ft. and are about 8 ft. high. Because 

 of the increased transmission required for the proper interpretation 

 of sounds in the presence of noise, the booths were made of heavy 

 masonry material to insulate the user and the microphone from 

 the noise incidental to the rotating parts of the television apparatus. 

 It was thus necessary to project the scanning beam and to view the 

 illuminated image through a window located in the front wall. The 

 microphone and the loud speaker were fitted into this wall, which was 

 then covered over with a thin screen to improve the appearance as 



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 FREQUENCY IN CYCLES PER SECONDS 



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Fig. 3 — Response frequency characteristic of microphone, amplifier and loud speaker. 



shown in Fig. 3 of companion paper, "Image Transmission System for 

 Two-Way Television." These means effectively reduced the noise in 

 the booth to an unnoticeable amount and reduced reflection effects to 

 the extent that the average speaker talking in a conversational manner 

 could be reproduced at a loudness best suited to the general effect. 

 The optimum loudness seemed to be about the same as would be ob- 

 tained from the speaker direct at a distance of about 10 feet, the ap- 

 parent distance between the image and the observer. At this loudness 

 the gain of the amplifiers was 12 db less than that required to cause 

 singing. 



While the system demonstrated was operated over a distance of only 

 a few miles, it will be appreciated that the same terminal facilities might 

 have been used over much greater distances. Thus for the first time 

 in the history of electrical communication it can be said that complete 

 freedom of exchange of both visual and aural expression between dis- 

 tant users of the telephone has been made possible. 



