The method is to wash the room with pink noise... you'll need a live EQ/Analyzer and a microphone. This technique is primarily used for rinsing out rooms at live venues to knock out any potential feedback problems.

1. Wash the room with pink noise and slowly turn up the gain on the microphone.
2. As you turn up the gain the modes of the room will start to appear.
3. If you have a feedback destroyer you will notice the peaks start to appear.
4. These frequencies can then be knocked back.

The main use, like i said is for feedback destroying, something you dont want to do in your studio room as the only way you can impliment your findings is through an EQ. but it does tell you where the standing waves are or modes are in your room and which frequencies are exaggerated or nullified.

Behringer do a great piece of equipment called the Ultracurve which is an amazing piece of kit for this task. I recommend buying one if you want to do this task. But then you only need to do it once in a static studio situation.