Thanks Andrew. I am attaching preferenes->Analysys. The decimate checkbox is already checked. Next time I will do full range sweep of 0 to 20khz for subwoofer alone , left speaker alone and sub+ left speaker. I will continue researching to understand.Timing reference set up is correct. Sub + Left timing is consistent with Just Left Speaker. But Sub alone timing is not. Two more variables to eliminate: First is the Decimate IR setting in Preferences, Analysis tab. Decimation changes sample rate used internally by REW in handling data, based on bandwidth of measurement sweep. So for sweep to 200Hz, REW is doing sample rate conversion from 44100 samples per second to 2756 samples per second. 44100/16 = 2756.25, so REW isn't doing an integer value sample rate conversion. I have not studied how well REW converter works, and eliminating it as a variable is easier.
Yes more details... It will cause files to be slightly larger without the decimation.
The 2nd variable to eliminate is to use same full range sweep for all measurements, this will ensure timing characteristics across all measurements, simplifying analysis.
And, all that really matters is how system sounds to listener(s). Chances are if system doesn't sound right, or clearly isn't performing relative to other listening experiences, then an underlying measurable difference with remedy exists. Typically the smoother a sound systems response, the greater the agreement is that the system sounds good.
I'll look into Anthem correction.
chinni123: post#33, Yes that is result of process I describe. If you display a left/right pair of as Left alone with Right alone or pair with subs, and zoom in close you will see peeks are separated by about 700u (that's 0.7 milliseconds) which works out to about 9.5 inches. Left peak is trailing, so real center line between speakers was about 4.75 inches left of microphone.
Andrew,Based on limited measurements, a dip in response exists in 200Hz region. Pinning down absolute source would require yet more measurements. More important perhaps is apparent channel imbalance of Left and Right speakers, both in general amplitude, and in frequency response, assuming that levels were not changed during measurement set. Impulse responses indicate microphone was several inches closer to right speaker. This could also impact 200Hz response dip to some degree, but is more likely do to asymmetry in placement of Left and Right speakers in distance from front wall, and in distances from left wall and right wall; or if left and right front corners of room have large feature differences such as furniture, proximity to doorways or closets. These impacts are greatest upon front speaker sound stage width, depth, detail, and coherence, with music being most affected. Small tweaks in speaker location can have big effects, as can fairly small movements in head position of listeners.
Andrew, I did use 0 degree calibration file for ECM 8000 microphone. I did not use Anthem microphone since calibration is their propriety.Getting peak performance from great stereo recordings demands much from playback system. Linkwitzlab.com is extensive resource covering this topic. Excellent speakers set up in reasonable listening space, that typically doesn't require extensive treatments, will produce sound image where both the speakers, and the room itself disappear. The basic trick is getting the spatial cues contained in the recording into the mind, and adding minimal distractions such as reflections differing in spectral content compared to direct sound. This is where highly symmetrical room and speaker placement come into play.
Anyway, when looking at overlay of left and right speaker impulse responses after offsetting back to t=0 as you did for post #33, zoom in real close and you see right speaker with peak at t=0 and left with peak at 0.749m, which is 749 microseconds (749u):
View attachment 37448
Plot results are not normalized, and it is easy to see that peaks are two very different levels. Same conclusion if viewing ETC.
Microphone primarily has different high frequency response when on axis (0 degrees) and pointing straight up (90 degrees). Calibrations for both positions are possible. I don't know about Anthem's microphone. I understand it is USB microphone. When plugged in does it show up in windows as sound device? Can you see it in REW preferences?