Acoustic panels on ceiling

Jetter it is a bit difficult on ceilings but you have to find the early reflection point. To do that you sit in the listening position and have somebody else hold a mirror against the ceiling and walk slowly between you and each speaker. when you can see the speaker's reflection in the mirror that would be that speakers early reflection point. Then do it for the other speaker and place one panel for each speaker centered on those points. The trick is to find a way for that person to do that. Either a ladder that you have to keep moving or a mirror on a long handle. The mirror has to be flat against the ceiling. The other way to do it is with a laser. You shine the laser on the mirror and when it hits the speaker you have it. Have fun!,
Mike

One more point just for future reference. Line sources or linear arrays the best of which extend from the floor to the ceiling do not send almost any energy to the floor or ceiling. If they are dipoles they don't send almost any energy to the sides either. The only reflections you have are to the front and rear walls and only the reflection off the front wall is early enough to matter. 

thyname, thanks for the link.

mijostyn thank you for the explanation.

I can see the obvious physical problem of holding and moving the mirrors while sitting in the listening position.  It does seem that having a ladder and friend (or wife/significant other), LOL, to hold the mirror would be pretty essential.  

The mirror technique will work if you can MacGyver a way to hold it and move it.  If it were me, I'd start approximately half way between ears and front plane of speakers, and then explore a little fore and aft.

The scientific way to do this is locate the sound pressure peaks greater than 6 dB above the average sound pressure in the room using a SPL meter and appropriate test tone. Otherwise, it’s like shooting blanks in the dark. It’s like trying to solve x simultaneous equations in x+n unknowns.