Originally Posted by dragonfyr
A couple thoughts.
Don't band limit. Just run a full out broadband sweep.
In the limits, try a setting of ~ X(time)-axis: -.2 -> 50 ms; Y(gain) axis: max 2-> min -35 dBfs.
As 50 ms corresponds to ~44.25 feet of travel, that should be fine to encompass the preponderance of the behavior in the space. that should 'zoom' in and window the display in a much clearer and more detailed POV for you as a good place to start.
The repeating spike intervals tend to suggest flutter echo Especially since you are running surround speakers (as opposed to a strictly 2 channel setup) you might consider applying a bit of absorption to the front wall and see if that does not mitigate that behavior. (Ordinarily I would use diffusion for flutter echo which only requires that the parallel surfaces be rendered 'less parallel' to stop the behavior as well as to retain the energy; but in this case the front wall may benefit from the absorption in order to also help damp early reflections from the surrounds. Note, this can all be determined with more certainty by running ETCs of all of the sources individually.)
Oh, and one more comment about the time scale.
Be careful in assuming that the time/distance, as displayed, corresponds to the actual time/distance of travel. The reason is that the direct signal arrive in the IR has been set to 0s. This translation of the axis neglects the time of flight (TOF) of the signal from the source speaker to the mic - in other words the TOF of the direct signal arrival has been effectively discarded - and it is a very real
part of the time/distance of travel! Thus I would not opt for the 'set IR peak to T=0' option.
Hope that helps a bit...
Appreciate the help, some background on this purpose of this thread:
-For myself and others to learn and apply ETC, hence the title
-using my HT as the initial poster child for this - learn by doing, trial/error, hopefully with constructive feedback/guideance for experts in the field
-summarize my experiences as cliff notes, to re-enforce what I learned and help others start off more quickly to grasp the concepts and apply them
>>This thread is not just for me, I encourage others who are into the acoustic journey to do same in their HT/listening space and post their learnings/"light turned on" moments<<
My room layout and current treatments:
The big 130" screen is made from DW laminate, a acoustic reflection source.
The rear walls are not treated - yet, that is my first priority before I dig into the minute of fixing specific reflections.
I need to get rid of the front sound stage <> rear wall <> screen reflections, for now since I own OC703 that will suffice (in appropriate placement).
If as I gain knowledge, some of my RFZ goes from OC703 to other type of treatments, I'll cross that later, for now the treatments are paid and made, hung on the wall/ceiling, and doing some "good".
I'm focusing on the front soundstage LH/CTR/RH for now, one speaker at a time. Later, I'll do same for the side/rear surrounds.
I crossover the LH/CTR/RH at 80hz, so next time I'll run the sweep at 80-20khz as you suggested. The IB sub handles LFE.
Also, I'll look into "set IR peak to T=0" setting in REW tonight, I do understand your point.
Later, I will post the readings I took last night.