I'm often old school/low tech on this...setting up an SM58 out in the room about 7-8 feet in the air pointing directly up. I then go through the spectrum from LF to HF with a GEQ boosting each band in turn to identify any problem areas/room modes. For precision (with time) I'll then use the GEQ results as a starting point to go through and set more precise, narroer PEQ filters.
This takes as much or less time as any other method and does not require any noise or even much "feedback" as one can hear the onset of any ringing at a very low level. Lather, rinse and repeat to taste.
back before I got my first rta, long before digital processors were popular, I'd set up a '57 in the room and do the same thing, It was amazing how much I could tell about the room by raising each frequency until it started feeding back. After doing that, anything on a '57 or '58 sounded really good!