[AreYouElite]

Do you believe it might be possible that the frequency band of human speech is not determined by such factors at all but more of a function of height? kids have higher voices adults have deeper voices. Similar to stringed instruments: viola high pitched and bass low pitched.

I'm no expert in these matters just speculating...

[fwip]

It's not height, but vocal cord length and thickness. Longer vocal cords (induced by testosterone during puberty) vibrate more slowly, with a lower frequency/pitch.