As a friend confirmed there is certain software available for a PC that will not only
work as an RTA but also for the very important in room impulse-response measurements.
To have a flat frequency response, in other words to prevent "colorations" (a coloration width of one Terz, which is 1/3rd of an Octave, is what I hear most often to be the smallest width the human ear is sensitive to), is just one aspect. The next step is still to listen to room modes and echos/high-reverb (impulse fall times), which tend to make a certain frequency last for a too long period in the room.
Another friend did have a very long, almost endless, reverb time in the low bass freqeuncies, due to his giant windows and old house construction. So everything worked like a passive membrane and kept "singing" for ever.
You want a flat frequency response coupled with a very fast stopping impulse response. I think a reverb (I always mix up the proportions) of 0,3 sec. is the goal over the entire frequency spectrum, which tends to become impossible in low frequencies (or you have alot of room or cash http://www.avsforum.com/ubb/wink.gif
[This message has been edited by Andreas (edited 05-15-2001).]