1160 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



high-frequency loss is due to spacing. This would imply that, under the 

 conditions of this experiment, self-demagnetization has a negligible effect 

 on frequency response. 



In any case it seems clear that the intimacy of magnetic contact between 

 the reproducing head and the medium can have a very pronounced effect on 

 high-frequency response. The condition of the surface of the reproducing 

 head (and of the tape) may have more effect on high-frequency response 

 than any other single factor. 



In a very fine piece of pioneering work Liibeck found empirically that a 

 term of the form e~^^^^ was needed to account for the shape of measured 

 response curves. Guckenburg^ has recently written more on this subject. 

 Both authors have assumed that this term has to do with self-demagnetiza- 

 tion and that Xi is determined by the magnetic properties of the recording 

 medium. The experiment just discussed and the theory presented in this 

 paper suggest, on the other hand, that Xi is not a function of the magnetic 

 properties of the recording medium but rather is determined by the intimacy 

 of magnetic contact between reproducing head and medium. If this is the 

 case then Lubeck's Xi is related to the d of this paper through the equation 

 Xi = Iwd. 



Guckenburg reports Xi = lOO^u for the best available medium. This cor- 

 responds to d = 0.625 mil and yields a response curve a little better than 

 the poorest measured curve of Fig. 9. The best measured curve of Fig. 9. 

 corresponds to Xi = 37//. 



ACKNOWLEDGEMENTS 



The author wishes to express his appreciation for the encouragement 

 and guidance of Mr. R. K. Potter, Mr. J. C. Steinberg, and Mr. W. 

 E. Kock. 



APPENDIX I 



THE FIELD DUE TO A FLAT SINUSOID ALLY MAGNETIZED 



MEDIUM 



The Field in Free Space 



It is convenient to begin by evaluating the field inside and outside the 

 recording medium when the medium is in free space. By making use of the 



•H. Ltibeck, "Magnetische Schallaufzeichnung mit Filmen und Ringkopfen," Aku- 

 sticheZeit., 2,27$ (1937). 



' W. Guckenburg, "Die Wechselbeziehungen zwichen Magnettonband und Ringkipf 

 bie der Wiedergabe," Funk und Ton, 4, 24 (1950). 



