I don't remember the exact frequencies of speaking, but I know they're
right in the middle of our 20 to 20,000 Hz perception range when you plot
the log frequency.
An interesting question to me is the relation between the range of spoken
frequencies and the range of frequencies to which our ear is most sensitive.
The two ranges don't quite overlap, I don't think, but one might ask if
there's a cause/effect relationship in either direction: How did one
influence the other?