He was responsible for sending coded messages for the German Army during World War II.

[1] Sennheiser went into business for himself, and achieved early success with a tube voltmeter and microphone, both of which were purchased by Siemens.

By the time of his death, the family-owned business employed 2,100 people with manufacturing facilities in Germany, Ireland and the United States and had sales of $500 million in 2008.

[1] Sennheiser died at age 98 on 17 May 2010 (eight days after his 98th birthday), and is survived by his son, daughter, three grandchildren and seven great-grandchildren.

[1] The Academy of Motion Picture Arts and Sciences recognized Sennheiser in 1987 with its Scientific and Engineering Award for the development of the MKH 816 shotgun microphone.