204 BRLL SYSTF.M TliCIIXICAL JOURNAL 



(irouncled Xeutrals." This report includes a detailed discussion of the 

 factors invoked and describes methods which have been developed 

 for control of the triple-harmonic residual currents and voltages which 

 occur with this method of operation. 



The results of the work done by the subcommittee on a surxey of 

 room noise in telephone locations were described in a recent paper.''' 

 While this was an incidental phase of the general study on effects of 

 noise on telephone transmission, it was felt to be of timely value, 

 particularly in respect to the methods of measurement employed. 

 Using the results of the data obtained in surveys of wave shape on 

 operating power systems and analyses of noise current on telephone 

 circuits, a paper ^^ was prepared on the frequency response character- 

 istics of telephone transmitters and receivers. This paper indicated 

 that there appeared to be no advantage, in reducing effects of noise, 

 in shifting the resonance points of telephone transmitters and receivers 

 from their present region, as the frequency distribution of the noise 

 currents was such as to give a minimum in this resonance region. 



At the time that the joint work was started the need arose for con- 

 siderable special apparatus to make the measurements which were 

 required. Some of the important pieces of apparatus for the work in 

 the voice-frequency range were sensitive single-frequency voltmeters 

 and ammeters. These needs were taken care of by the development of 

 sensitive analyzers whereby single-frequency voltages or currents could 

 be selected from complex wave shapes on either power or telephone 

 circuits. One form of this apparatus has been described in a paper 

 before the Institute ^^ and another in a serial report ^^ of the National 

 Electric Light Association. 



In connection with the survey of room noise, a room noise meter was 

 developed. This was described in the paper ^^ previously referred to 

 which presented the results of this survey. 



Further Work of the Subcommittee 



When the subcommittee started its work there was before it an 

 accumulation of technical problems which had arisen as the arts devel- 

 oped without such close cooperation as now exists. The statements 

 given above regarding various phases of the subcommittee's work on 

 noise-frequency induction indicate the substantial progress which has 

 been made in the solution of these accumulated problems. They con- 

 vey also a general picture of the work which the subcommittee has 

 immediately before it. 



It must not be thought, howe\-er, that when these accumulated 

 problems have been solved the work of the subcommittee will be com- 



