Since I am from SW Michigan where Electro-Voice currently resides, the story we heard was that Knute Rockne (legendary ND Football coach and professor of Chemistry) needed a device that he could use during practice so that the team members could clearly hear him.  

This company (then in South Bend, Indiana I believe) built him a PA system that Knute referred to as his "Electric Voice".  At least that's the story as told around that part of the country.  That was back in the 1930s so some embellishment of the story since then is quite possible.  Some say that there were also some ties to the Heath Company but I could never substantiate that.

Scott Robbins, W4PA Ten*Tec Amateur Radio Product Manager, adds:

That story is correct.  The PA system referred to was set up by Al Kahn (K4FW).  Mr. Kahn grew up in South Bend and started Electro-Voice there in the 1920's and the story of how he named his company has been accurately repeated to you.   After selling E-V in 1968, Mr. Kahn bought a 15 acre piece of land and had a two story building built right across the street from the Electro-Voice plant in Sevierville, TN., and named his new company Ten-Tec.

Mr. Kahn was also directly involved with Heathkit's beginning's in Benton Harbor, MI in the late 1940's (just down the road from Buchanan).  Mr. Kahn "donated" a train car load of war surplus electronic parts to Heath, and that load of parts became the foundation of the O1 oscilloscope, Heathkit's first electronic project. 

As of January 2001, Mr. Kahn continues to be the chairman of the board of Ten-Tec, is still active daily on HF CW and at age 94 is enjoying his
well-deserved retirement in southwest Michigan.