source <cite><a href=httpspatentsgooglecompatentUS1713039Aenoq=1713039>Phonograph Recording and Reproducing<a><cite> US Patent 1713039 by Lloyd Espenschied<br>恐らく世界初の電気録音に関する特許に登場する図版
US Patent 1,713,039 “Phonograph Recording and Reproducing” Figs.1-3 (Espenschied, filed 1919)