eventually granted a patent for this process. Communication device A pilot suggested to Tigerstedt that he should develop a device to facilitate communication between two pilots while seated one behind the other in an open biplane. Tigerstedt invented a device which had a very small earpiece that could be plugged into the ear. Tigerstedt spent considerable time on designing the earpiece. The device was also found to be helpful to people who were hard of hearing, offering a possible alternative to the large ear trumpets then in use as hearing aids. See also Tri-Ergon Phonofilm Vitaphone RCA Photophone Photokinema Fox Movietone Joseph Tykociński-Tykociner Sound film sound-on-disc List of film formats References http://www.filmsoundsweden.se/voxbilder/filmhist/tigerstedt_2.jpg is rather electromechanical amplifier Gerald F J Tyne: 'Saga of the Vacuum Tube' () A.M. Pertti Kuusela: "E.M.C Tigerstedt 'Suomen Edison'" () J Kuusanmäki, Kauko Rumpunen & Pertti Vuorinen: "AO Lisiä historiaan" () External links Virtual exhibition on Eric Tigerstedt by the Technical Museum in Helsinki (in Finnish only, opening spring 2007) Swedish article and diagram on Eric Tigerstedt's sound-on-film patent (German patent number 309.536 - July 28th, 1914) Reference to Eric Tigerstedt on "Virtual Finland" (Ministry for Foreign Affairs of Finland, Department for Communication and Culture) City of Helsinki Hochschule Anhalt (formerly Friedrich-Polytechnikum) City of Köthen 1887 births 1925 deaths Businesspeople from Helsinki Swedish-speaking Finns Finnish inventors Finnish electrical engineers Finnish expatriates in the United States 20th-century inventors 20th-century Finnish businesspeople Road incident deaths in New York City 20th-century deaths from tuberculosis Tuberculosis deaths in New York (state)