Black guy voice, is it different from others?

I noticed it too. Based on my sexual experience, I can assure you it's the race, even when it's a mestizo, the smell is quite different than the races they are mixed up from.

It is a cultural thing.  The more inclined they are to segregation the more likely a distinct manner of speaking is to be handed down.

American immigrants are often more "American" than the native population.  I've had opportunity to see immigrants to the United States that enthusiastically take full advantage of their opportunity during the formative years to embrace vibrant new culture.  Naturally it is possible if someone assimilates well that they would incline themselves to learn the peculiarities of their English speaking from a native accent, and that contributes to generating opportunity (Americans love immigrants) which in turn contributes to efficiently attaining a great level of refinement. 

If a child or young adult was not familiarized heavily by a Spanish speaker and they immigrated for say, education, where they were somehow immersed in black culture, they might come to speak similarly while thinking in English with only slight or occasional hints of their native tongue.

The opposite is also true.  I've seen old families that hand down their black ethnicity migrate to places that they got along very well with, and their children or grandchildren developed the native accent of their peers because there was no segregation about the community.

That has been my experience.  Of course, individually, your voice has that inherent influence by your direct family.