Acoustic panels - how high?


Is there a rule of thumb on how high an acoustic panel should be hung? I have a number of 2'x4' panels I want to hang behind my speakers and at first and second reflection points. My walls are 8ft tall.
Do I center the panels vertically on the wall or, since the top of my monitor speaker is only 4' high, do I lower the panel and center it on say the center of the speaker cabinet ?
rockyboy
I treated the top five feet of the wall behind my listening position with 2" Auralex Studiofoam Wedges, with LENRDs in the corners and accomplished the same effect. An added benefit is being able to listen at realist levels, without overloading the room. Happy listening!
Take Elwoods advice re the mirror and if you wish to maximize your efforts on first, and second,reflection,go floor to cieling with panels in those locations. You cannot go wrong with this simple solution,and it will benefit you. Good luck and let us know your results :) Pete
Eleven little Zilplexes will greatly exceed any benefits of acoustic panels.
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Hi Rocky,

One thing I have found is that acoustic panels improve imaging in the dimension you lay them out.  That is, if you don't find very deep imaging, put more behind the speakers. If you find the image is in a line between your speakers, put more dampening above and below the speakers, that is on the floor and ceiling. 

Of course, getting rid of primary reflections is the first thing you do, I just thought this might help.