Speaker Placement or Room

While it may be obvious, what the hell!

Don't forget that where your listening seat is located can play a huge difference. Especially if you've got it sitting in a null. Play with both speakers and listening position. For example, with your test disc playing, stand at the present listening position and when a 100hz signal (or any signal) plays move the meter back and forward a foot or so and see what happens. You might be surprised. Take your time, make lots of notes and graphs as you go.

BTW, FWIW I find it easier to use a disc with pink noise such as those available thru Stereophile than the Rives disc with its 'constant tone'. I just factor in the corrections for the errors in the RS meter.

FWIW, The Cara program on Rives site is an excellent starting point, it hit my speaker locations perfectly, but missed my listening position by a foot or so.

Ecruz, Glad it helped. FWIW, and perhaps its just me, but I find the pink noise in the Stereophile disc to be more constant and easier to track. The tone on the Rives disc did not seem as constant and it also seemed more beamy, especially in the higher frequencies. But, then, maybe I've just got unsteady hands and one needs to hold the SPL meter steady, like on a tripod (actually I did just that) when using the Rives disc. Anyway, what ever works best for you. The're cheap anyway, waste a acouple of bucks and see for yourself which you prefer. :-)
Oh, the other thing I liked about the Stereophile disc was the assending order of the frequencies. Makes a bit more sense to my poor brain, and I also like that they have a 1k hz reference tone at the beginning so you don't have to mush arouand in the disc to find one.