All- I go back and forth on this quite a bit likely due to the square nature of my room (20x20x10) and it just dawned on me that when I use the Rat Shack SPL meter to calibrate, I should not worry about the 75db output between the two setting as that is simply a function of the volume setting HOWEVER, is what I should be doing looking at how much the needle moves back and forth within that range? What I mean is the Trim setting that stuck the closest to 75 DB w/o "going back and forth" as much during the test tone would be the best setting right?

Thanks as always guys.

Darth,

I'm not sure if I am understanding your question Are you using the analog RS SPL meter, and you are you are running through a frequency sweep?

Generally speaking, you want to choose the trim setting that will give you the best frequency response. So the setting that stays close to 75dB would be desirable.

However, keep in mind that if you want to me more exact, you will have to use some correction factors. At lower frequencies, the meter understimates SPL.

That is a pretty big room, according to the pamphlet you normally want to use Flat for large rooms and Full or Half for small to medium sized rooms.

If you are doing full frequency sweeps, then choose the setting (flat/half/full) that gives you the flatest response curve. Then after making your choice, re-calibrate to 75 dB with the SPL meter.