Marjatta Nybom was broken off in 1912. Sound-on-film prototype After returning to Finland, he continued his experiments and succeeded in building a prototype of sound-on-film technology ("talking movies"). Tigerstedt then returned to Germany in 1913 and founded a company with the Swedish merchant Axel Wahlstedt and the Swedish engineer Hugo Swartling. This was the first in a series of unsuccessful business ventures. Although Tigerstedt was able to complete his work with the sound-on-film technology, the partners' laboratory was eventually confiscated due to unpaid rent. They managed to reclaim their laboratory, but it was then destroyed in a fire. The cooperation between Wahlstedt and Tigerstedt became strained and in January 1914 they dissolved their company. After breaking off their commercial partnership, Wahlstedt returned to Sweden, while Tigerstedt stayed behind in Berlin, more or less broke. Demonstration of sound-on-film Tigerstedt continued working on his sound-on-film technology and made progress in solving a major technical problem, that of how to amplify film audio sufficiently to fill a large theatre or hall. He did this by making major improvements to the vacuum tube design of Lee de Forest, increasing the amplification capacity substantially. In February–March 1914, Tigerstedt demonstrated his sound-on-film technology to a small group of scientists, using his own film Word and Picture. 1914-1917 After being expelled from Germany in July 1914, Tigerstedt returned to Finland, but he moved to Sweden a few months later and then to Denmark in 1915. After another unsuccessful business venture, Tigerstedt once more returned to Finland. In 1917, he moved back to Denmark and founded yet another company, which was then sold. After that, he participated in the founding of the Norwegian company A/S Anod, in which he held a 45% stake. Finnish Civil War of 1918 As a Finnish citizen, Tigerstedt was called back to take part in the Finnish civil war of 1918, and on 14 February 1918 he was on his way back to Finland. After the cessation of hostilities, he participated in the victory parade on 16 May 1918, but then returned to Denmark, where he married Ingrid Lignell in 1919. Their son Carl Axel Waldemar was born in 1921. However, their marriage soon began to deteriorate, and they separated not long after the birth of their son. Loss of German patents During World War I, Germany invalidated all of Tigerstedt's patents. After the war, he received compensation from the German government, but