Frequency Response Errors have accumulated

I recently ran a pink noise frequency response test of my living room system as shown above and was very disappointed.

Frequency response is something I consider very important.  This system is corrected to be flat with a slight bass boost below 30Hz, through the use of a Tact 2.0 RCS preamp with user room curve settings.  I remember pink noise measurements in the past (taken in the same way) which were virtually flat (unfortunately, I have no permanent record of them anymore).  The above curve was taken with pink noise from Stereophile Test Disc Two and the iPhone application called RTA by Studio Six Digital.

But not this time.  Now I am showing 20dB of response variation from the highest highs to the lowest lows, with mostly a gradually rising response from lows to highs, but very low response in the bass below 100Hz where the subwoofers are playing.

So what happened?

Possibly somehow my Tact has gotten messed up.  With the room correction set to bypass, I get more sub 30Hz bass than with correction turned on.  Possibly the Tact lost its memory in a power surge, or possibly the changed response was a result of the accumulation of small changes.

Funny how I have made small changes over the year, now ending up with this, clearly not what was intended.  I would have not expected much different from flat response.  Seems like a quarterly frequency response test is in order to avoid drifting away from desired frequency response through seemingly limited corrections.

Back in mid 2010 when I was playing the Santana "Supernatural" album and concerned about way-too-much-bass, I discovered that right subwoofer level had possibly been tampered with, turned straight up, which was not what I remembered it should be.  So I found a reduced level I thought was better, combined with less bass boost used in my room currection curve.  I figured 3dB reduction in bass, tops, and I was simply restoring the original corrected response.  It sounded much better on Supernatural without any bass cut, and I didn't notice any problem with other recordings later.

To restore frequency response, I will begin with no correction, and set driver levels and crossover points for a fairly decent overall response.  Then room correction measurement and room curve adjustment will be performed.

Room correction measurement is a complicated process, and I haven't bothered since early last year.