From Lehrbuch der Stimm und Sprachheilkunde (“Textbook of voice and speech therapy”), Chapter 1, “Die stimm und ihre Storungen” by Prof. Dr. R. Luchsinger, Published by Springer-Verlag, 1959, page 10. Manufacturer was not named.
From Lehrbuch der Stimm und Sprachheilkunde (“Textbook of voice and speech therapy”), Chapter 1, “Die stimm und ihre Storungen” by Prof. Dr. R. Luchsinger, Published by Springer-Verlag, 1959, page 10. Manufacturer was not named.