Acoustic panels - how high?

"stay at your listening position and have a friend move a mirror along the wall until the speaker sound emitting areas are centered in the mirror. This center point can then be used as the center point of the absorber panels."

The problem with that technique (using a mirror) is that speakers do not have uniform dispersion patterns thus making it difficult to visually obtain optimum results (using a mirror). This is especially true if you are listening to all panels at once initially when trying to make judgements. Not to mention all speakers actually have different dispersion patterns, making generalizations about location of panels kind of irrelevant. If you could obtain the dispersion pattern for your particular speakers you can do the geometry calculations and figure out exactly where the panels should go a priori.

oh, and another thing. not all panels are effective to the same degree and some panels do more harm than good. I wont mention any names but one of those that are ineffective is SONEX. it all kind of depends on what happens to the wave as it passes through the panel material twice.

It is possible since there was no difference in sound that the room is fine without them.
Another + for Elwood though. I used to have a few roomtunes etc..until I rebuilt the room with Crown moulding and added art to the walls.

Regardless of a speaker system's dispersion pattern, sound waves travel in a straight line and their angle of reflection will equal their angle of incidence. Thus, an easy way to find the first reflection point, of the waves that will actually reach your ears, is via the method mentioned by Elwood. (http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reflec.html) Yes- a panel that will disperse or absorb those reflections must be chosen.

Further info, here: (http://realtraps.com/rfz.htm) & (http://www.gikacoustics.com/video-early-first-reflection-points/)