For those interested, I made some progress with the ETC measurements. Guess what? It works!
As an experiment, I decided to track down the largest reflection in my ETC measurement of my front right speaker, which was measured at 2.22ms or 2.5 feet after the initial direct speaker signal. The direct speaker signal is normalized at T= 0 on the x axis, with the spike measured at the 2.22 ms later as shown following:
Next I needed to do some simple calculations in order to use the "string method" to find out specific areas to check where the actual reflection surface is. First I measured the distance from my Radio Shack SPL meter to the actual acoustic center of the speaker being measured. That distance was 12' (as best as I could measure). The reflection being measured takes an additional 2.5' to arrive, which means that the total distance of the reflected signal is 12' + 2.5' or 14' 6".
The concept of using the string method is that you take a length of string which is equal to the distance traveled of the signal (in this case 14'6"), tie off one end to your measurement mic, and the other end to the acoustic center of your speaker. If you have helpers available, they can hold either end. In my case I didn't so I had to gin up tie offs. You then take up (I just slid a finger along the length) the string slack between the mic and speaker extending it in all axis's and note what boundary surfaces it touches.
In my case, it touched the ceiling about 1/2 way between the mic and speaker. Following are a few pic for clarification.
Mic at measurement position with one end of string tied off:
Other end of string tied off at speaker:
Location on ceiling where string touched:
Visual of overall string path with my "treatment stick" holding it up:
I next took another measurement while holding that insulation batt to the ceiling. Following is that measurement with time reference noted. Notice that the spike has been attenuated. Original measurement shown directly following again for ease of comparison.
I have the same spike occurring on the left speaker at similar time, so appears that a ceiling panel is in my future.
The other thing I noticed and was able to measure was the amount of reflections coming off of my front row seating surfaces. I measured with and without blankets on the seats, and the results were significant.
During my investigation, another member who has been helping me pointed out some strange anomalies occurring with the direct signal, which brought into question the quality of the speakers being used. My fronts are very old (1988 or so) American Acoustics (was under Mitel) that I have been using just because I had them available, with intent to upgrade at some point. With Christmas just around the corner, I foresee two new fronts in my future, and I suspect Santa will be arrive early this year
Also, I have been questioning my FR and FL positioning since I built. If you look at the speaker location, you'll notice that it is sitting on the floor with a portion of the bottom woofer blocked by the stage, with the second one having my screen framing in the way (should have did Big's minimalist style). I can't believe this is having any positive contribution to my audio response, especially where I have a lot of anomalies in the crossover range. So, planning on bookshelves to replace those. I can sit them on stands just above the bottom screen frame and take all that mechanical interference out of the picture.
So, I won't be doing much more with this effort until those arrive.
Hopefully this has demonstrated how ETC can be used to locate reflections, and verify effectiveness of treatment. It's really not that complicated.