Yes, as Peter says, the human voice has a whole bunch of harmonics above its basic pitch, which varies roughly from 100-300Hz. The voice pitch of course can be varied, such as in singing, from a little below 100Hz to way above 300Hz. So far as the center speaker goes though, it's supposed to mainly be there to anchor speech to the TV screen, so output below 100 Hz isn't really important. What's more important is that the upper harmonics of the basic speech pitch which are what give speech its intelligibility(called the formant frequencies)running from about 500-4,000Hz and having most effect around 2,000Hz, are reproduced well.
The bottom line is that it wouldn't really matter if the center speaker had a slight depression in the 80-90Hz area. Use the 80Hz crossover.
