542 BELL SYSTEM TECHNICAL JOURNAL 



gible when there are only a few lamps as, for instance, at highway 

 intersections. 



Sound Picture Recording and Reproducing Characteristics}^ D. P. 

 LoYE and K. F. Morgan. In the improvement of sound motion 

 pictures, the trend has been to make the response of all parts of the 

 recording and reproducing circuits as nearly "flat" as possible. In 

 some cases, however, this has resulted in unnatural sound, and there- 

 fore certain empirical practices have been adopted in the studios and 

 theaters to make pictures sound best. 



This paper describes the results of a study the purpose of which has 

 been to evaluate the factors which afi^ect the quality of speech as 

 recorded and reproduced, from the vocal cords of the actor on the 

 sound-stage to the brain of the listener in the theater. The character- 

 istics of the various factors have been determined and combined with 

 dialog, voice efifort, and other equalizers designed to produce an overall 

 characteristic " subjectively flat " at the brain of the theater patron. 

 These factors, as well as others which are now in the process of being 

 studied, are presented in this paper. 



One of the most important characteristics studied is that of the 

 change in voice quality with a change in the efl^ort on the part of the 

 speaker. This is described in detail in this paper. The stage and set 

 acoustic characteristics, microphone characteristic, and dialog equal- 

 ization to compensate principally for the hearing characteristic of the 

 average theater listener, are among the factors described herein. 



A Dynamic Measurement of the Elastic, Electric and Piezoelectric 

 Constants of Rochelle Salt}^ W. P. Mason. The elastic, electric and 

 piezoelectric constants of Rochelle salt have been measured at low 

 field strengths by measuring the resonant frequencies and impedance of 

 vibrating crystals. It is shown experimentally that the resonant and 

 anti-resonant frequencies of the crystal are both considerably below 

 the natural mechanical resonant frequency of the crystal in disagree- 

 ment with the usual derivation of the frequencies of a piezoelectric 

 crystal. By assuming that the piezoelectric stress is proportional to 

 the charge density on the electrodes rather than the potential gradient 

 as usually assumed, theoretical frequencies are obtained which agree 

 with those found experimentally. This theoretical derivation to- 

 gether with the measured frequencies supply values for the piezoelec- 

 tric constants. The elastic constants measured dynamically show 

 some differences from those measured statically. A large difference is 



10 Jour. S. M. P. E., June 1939. 



11 Phys. Rev., April 15, 1939. 



