Yes carpet only absorbs the highs 1000hz up. Panel absorbers will absorb from around 200hz down. (if in fact those panels work as low frequency panel absorbers).
It's the frequencies in between 200 - 1000hz that are your probelem frequencies.
Sean, if you've mounted thin panels directly on the framing studs, you've created panel absorbers whether you meant to or not. If you've instead mounted paneling OVER sheet rock, then you've pretty much just changed your visual aesthetics. This is because the sheet rock has much more mass than a thin panel, so the addition of the panel over the rock won't change the wall dynamic very much.
If you've carpeted the entire room, I'd be very careful about using much more absorption that reaches into the high freq range or you may end up with a dead sounding room. Having to artificially replace highs that are lost to absorption is NEVER as good as not losing them in the first place; first, you introduce phasing problems with EQ, and second, when you turn up the treble you turn up the hiss.
If you want to know what your room is REALLY doing, here's an interesting site