L. Wegel, "Theory of magneto-mechanical systems as applied to telephone receivers and similar structures", "Journal of the American Institute of Electrical Engineers", vol.40, pp.791–802, 1921.</ref>من أوائل التطبيقات لهذه الأدوات النظرية الجديدة كانت من خلال نسخ الصوت في الفونوغراف.
L. Wegel, "Theory of magneto-mechanical systems as applied to telephone receivers and similar structures", "Journal of the American Institute of Electrical Engineers", vol.40, pp.791–802, 1921.</ref>===Sound reproduction===An early application of these new theoretical tools was in phonographic sound reproduction.