PUBLIC ADDRESS SYSTEM AND LONG LINES 145 



types of instrumental music the melody can be reproduced with the 

 above frequency range, but these tones also are lacking in naturalness. 

 Since some of the musical instruments are used to produce tones three 

 and even four octaves below middle C, it is evident that the proper 

 reproduction of music requires a further extension of the lower limit 

 of the transmitted band than does speech. While the fundamentals 

 of the higher musical tones lie in general in the range mentioned above, 

 it is the harmonics in musical tones which distinguish those produced 

 by different instruments and which give what musicians term "bril- 

 liance." The true reproduction of many musical selections requires 

 the distortionless transmission of a frequency band of from about 16 

 cycles to above 5000 cycles. Many musical selections, however, 

 employ only a part of this range and accordingly can be satisfactorily 

 reproduced by systems not transmitting the whole range. Also, even 

 with slight distortion obtained with somewhat narrower ranges, re- 

 productions may be given which are agreeable to many popular 

 audiences. 



Line Requirements 



In general the same line requirements which make for satisfactory 

 transmission of speech over commercial telephone circuits also make 

 for satisfactory transmission when telephone circuits are associated 

 with loud speakers. There is this difference however. The loud 

 speakers tend to make the line distortion much more noticeable and 

 serious. Speech transmitted over a particular telephone line is, in 

 general, more difficult to understand when listening to loud speakers 

 than when listening to telephone receivers. 



In commercial telephone service the main requirement is intelligi- 

 bility while, with the loud speaker, the naturalness of the repro- 

 duced speech sounds is very important. People are accustomed to 

 hearing transmission through the air with very little distortion and 

 naturally expect the same result with loud speakers. 



The above constitute the reasons why, for transmitting voice cur- 

 rents over telephone lines with loud speakers, it is necessary to pay 

 unusual attention to the electrical characteristics of the lines. Evi- 

 dently when music is to be transmitted, particularly music of a fairly 

 high grade, it is necessary to place even more severe electrical re- 

 quirements on the lines. 



An analysis of what constitutes the electrical requirements of a 

 telephone line which make for good transmission, particularly when 

 loud speakers are employed, will now be given. 



In the first place, as explained above, it is essential that a suffi- 



