File:Bell telephone magazine (1922) (14776597173).jpg

Identifier: belltelephonemag19amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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ed the turntable stopped and a lamp lighted toindicate that everything was ready for another test. At the New York Fairthere were eighteen of these machinesand at San Francisco there were four.To assure a constant output level,the machines were checked carefullyeach day with a special test record,and all the telephone receivers weretested periodically. Listening testswere also made daily by the engineersin charge and by the attendants. Ihe walls of the booths where thetests were made were covered withsound-absorbing material and thefloors were carpeted. This assured alow noise level in the test booths.The masking .effect of outside noise,as calculated, was less than 5 deci-bels at the lower frequencies andzero at the higher ones. As a furthercheck, members of the Bell Labora-tories staff who had taken the test atthe Fair were retested at the Labo-ratories under conditions free fromdisturbing noise. The average im-provement was about 3 db at 440 cy- 270 Bell Telephone Quarterly OCTOBER
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Source of the Tests The test tones and numbers were reproduced Jrom hill and dale phonograph records through amplifiers to assure constant quality and control of intensity cles, 1 db at 760 cycles, and the differ-ences were negligible for higher fre-quencies. Part of this improvementmay have been due to repetition, butit indicates the maximum effect ofsurrounding noise. Findings from the Tests 1 HE actual losses in db for bothmen and women for the next to thelowest and next to the highest fre-quency tested are shown on page 273.Women 55 years old heard the 800cycles-per-second tones 3 db less well than men, but 3520 cycles they heard7 db better. For the 10-20 yeargroup there was practically no differ-ence at the lower frequencies and notmore than 3 db at the highest fre-quency. The hearing of the young-est group was found slightly poorerthan that of the next older, but it wasbelieved that this was principally dueto difficulty which the younger chil-dren had in understanding the testpr

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