what is the rule of thirds?

I believe the former editor of TAS likes to take credit for identifying this concept but I think it has been known for some time, he was just the first one to publicize it. Other odd dimension fractions have been recommended as well - 1/5, 1/7, etc. Since another basic rule of acoustics is to avoid square rooms (equal dimensions maximize room nodes), assuming the room length and width are different, applying a fractional multiplier like 1/3 will result in different distances from the front and side walls which should also provide a benefit.

As Newbee points out, you should be just as concerned with your listening seat placement as with your speaker placement.

While the rule of thirds is a good starting point for most, that's all it is; a starting point. It assumes that one is using a desirable room w/o even multiple dimensions. And that might be the best premise of this guide, using uneven dimensions that don't have even multiples of any dimension. For example a rule of fifths might work in a desirable room or a combination of odd multiples might work better in a less than desirable room.

Pryso, you beat me to it.
I'm not sure, but I believe that Peter Walker of Quad fame might have been one of,if not the first to promote the "rule of thirds".
If at all possible, if one can avoid even multiples from ceiling, floor as well as length and width it might be beneficial.

fwiw the rule of thirds was the best setup for my Maggie 1.6s