Quoted from jorant:
There are four iterations of the turtles and their voices (two cartoons and the two movies). Sadly this is stern's, thus a fifth. So like it or not, this is now how they sound.
Uh, there's actually 4 Cartoon Series and 6 Movies, all different actors, in the TMNT 2012 they even changed some inbetween seasons, so I don't give the slightest shit.