Abstracts of Technical Articles From Bell System Sources. 



An Efficient Loud Speaker at the Higher Audible Frequencies} L. G. 

 BosTWiCK. This paper describes a loud speaker designed for use as an 

 adjunct to existing types for the purpose of extending the range of 

 efficient performance to 11,000 or 12,000 cycles. A moving coil piston 

 diaphragm structure is used in conjunction with a 2000-cycle cutoff 

 exponential horn having a mouth diameter of about 2 inches. Mo- 

 tional impedance measurements on this loud speaker indicate an aver- 

 age absolute efficiency of about 20 per cent within the frequency range 

 from 3000 to 11,000 cycles. The variation in response within this 

 band does not exceed 5 db. By using a high-frequency loud speaker of 

 this type the efficiency and power capacity of the associated low-fre- 

 quency loud speaker can be improved and a uniform response-fre- 

 quency curve from 50 to 12,000 cycles can be obtained. 



Results of Noise Surveys. Part I. Noise Out-of-Doors? Rogers 

 H. Galt. The purpose of a noise survey of a locality is to study the 

 space and time distribution of noise intensity, the frequency composi- 

 tion of the noise, the contributions of various noise sources, the relation 

 between the annoyance effect of the noise and its physical and auditory 

 characteristics, and the effectiveness of methods of noise reduction. 

 The extent to which each of these phases of the noise problem has been 

 investigated heretofore has depended upon the point of view of the 

 investigator and upon the apparatus employed. From one standpoint 

 or another, any audible sound may fall within the category of noise; 

 hence the variety of possible noise surveys is almost unlimited. Not 

 many such surveys have been carried out, however, partly because the 

 appropriate apparatus is of recent development ; nor has any extensive 

 comparison been published between the results obtained in different 

 places and with different instruments. It has therefore seemed worth 

 while to assemble such previously published results as are available, 

 and certain new observations, in the present series of papers, of which 

 this paper deals with noise out-of-doors. 



Microphonic Action in Telephone Transmitters.^ F. S. Goucher. 

 This semi-technical article gives a brief resume of the theories of micro- 

 phonic action and describes the results of some experiments on the 



1 Jour. Acous. Soc. Amer., July, 1930. 

 ^ Jour. Acous. Soc. Amer., July, 1930. 

 3 Science, Nov. 7, 1930. 



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