Tools to measure in room response

To do this properly you will need software (RoomEQWizard works fine for "snapshopts", but I prefer TrueRTA as I can see the changes visually as I move things around), and a properly calibrated microphone along with a mic preamp.

If you are taking this project seriously, don't use the RS SPL meter, as it is well known that it is not accurate.

I use a portable phonic PPA3 RTA and achieve consistently good results.

Its built-in microphone is calibrated, you can store the data in your computer through an USB port and calculate the average of several room response graphs (just like John Atkinson does in Stereophile room response meausurements).
It comes with 31 band spectrum analyser, SPL reading, EQ setting calculations/suggestions, RT-60 calculator, phase checker, a built-in test tone generator and a test CD.
Last time I saw it cost U$ 500, a great investment if you really want your system to shine.

The learning curve is quick, in 30 minutes you are set to go.
In most systems I can find a much better loudspeaker positioning after 3-4 readings.
Usual disclaimer...

I tried the PAA3 and I currently use Fuzzmeasure. I find the sweep of PAA3 takes too long and very susceptable to ambient noise. Fuzzmeasure allows 1/3 octave to 1/48 octave smoothing with RT60 calcutalions at 1/3 octave. The sweep time and freq range is also adjustable. The curves from each measurement can be superimposed on the same grap so you can see the result of each change you do to the room/speaker.

PAA3 is useful in other ways and very portable. But for frequency response curve and reverb measurements, Fuzzmeasure is more precise and informative

Glai:
Thanks for the info. I will look up Fuzzmeasure.