First reflection formula?

Formulae are useful for all sorts of things. For example, they can tell you at what frequencies standing waves will occur. As far as determining where the first reflection is located, I don't know if there is a formula. However, it's not necessary. Use your "mirror on the wall" technique. If your ears and speaker can "see" each other, it's a reflection point. Measure the distance from the speaker to the mirror and from the mirror to your ears. Add the two figures together. No need for a formula; it's just arithmetic. Whichever reflection has the shortest total distance from speaker to ear is the closest reflection.

By the way, the mirror should be placed on the ceiling and floor as well as the wall. The first reflection is likely to be from the floor in front of the speaker.

I asked the same question over on AA a little while back. I had seen the formula somewhere, then when I needed it I couldn't remember what site I saw it on:

http://www.realtraps.com/art_room-setup.htm

It's down near the bottom of the page.

If you really want to try something interesting, read this review of Eighth Nerve products, which also discusses Nathan Loyer's speaker positioning method. While I just started using his products, I also use absorption panels (not on first reflection points) and after following his method, the improvement in clarity was quite noticeable.

http://6moons.com/audioreviews/8nerve/8nerve_2.html

ever try the tin foil and a light bulb on your wall?, the foil will allow you to see reflection points very well.