Originally Posted by KevinG
Fair enough, but if the panels are already placed at the observed (using a mirror) FRP, what am I looking for? And, furthermore, does it make any sense to measure a given speaker (let's say front left) when only the left wall has been treated (still to come is the right wall, and the ceiling). Should I take the panel off the wall, measure, put the panel back, measure, and then compare the ETC? Is that the best way to show the results of what I am trying to achieve? I assume this is more about ETC then in is about FR. Right?
It's all about the ETC.
Since you're using the mirror method, you should have the locations for the treatments nailed. If you can remove the panels easily, I would do so, so you have a baseline measurement with no treatment.
What makes sense for the measurements, depends on how willing you are to understand the effects the panels have. If you run a measurement now, you can at least confirm your placement of the panels.
The general consensus is to have all unwanted
reflections at -20dB as soon as possible in the time domain.
Here is a random ETC from google.
And my own.
I'm a little overboard with my treatments, but you can see in the above graph, there are a few reflections above -20dB.