Tater, the idea is to have surround effects coming from above ear level, and 2-3' above is a common suggestion. If your room doesn't allow for this, a foot or so less won't be critical.

More significantly, your front speakers should have the tweeters at ear level, if possible, so I'd think that about 36" would be better. Consider an upside-down positioning if you want the speakers higher in the wall.

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Enjoy the music, not the equipment.