Springs under turntable

Uberwaltz, you measure it!  Check out this https://www.parts-express.com/dayton-audio-omnimic-v2-acoustic-measurement-system--390-792. My room control system essentially does the same thing. It measures each individual speaker. The frequency response above 10 kHz is significantly different in my right ESL than in the Left one. The only difference is the right one has a window in front of it on the side wall. The system corrected it but beforehand the window was smearing the image.
To produce the best image the frequency response of both speakers has to be identical or the image will smear to the side that is louder at any given frequency. There are always differences from one speaker to another of the same type not to mention that the speakers occupy different positions in the room. If you measure your system you will be amazed if not terrified at the variations in frequency response particularly below 100 Hz. The curve will look like a profile of the alps. 
It is a lot of fun to measure other people's system and show them how bad things are. 

So, Uberwaltz, do not downplay those windows. More than likely they are having a significant effect on the sound. But, it is hard to predict how. If you want to know measure it. But if you are not planning to get a room control unit don't bother. Ignorance is bliss. 

Mijo
I KNOW the windows are having a huge effect, hence the semi treatments to all of them.
Wood blinds on all of the side and back windows usually at 2/3 closed position.
Recent addition of heavy blackout curtains behind my gear and speakers on the large glass doors that open into the room, that had an even bigger impact than I expected.
But no I have no intention of getting any type of room control unit for this room atm.
I can live with ignorance is bliss because right now my listening experience is pure bliss!
Could it be better?
I am positive it can but small steps.

Every electronically-based room equalizer that I have ever heard does far more damage to the sound than it does good for the sound. So I agree with your strategy of altering the room, rather than the signal to give you your desired response at your listening seat.

Traffic though the tunnel created very low frequency rumble exciting the panels cracking them.

The failure was in the epoxy holding the panels. They didn't crack due to rumble. 

Every electronically-based room equalizer that I have ever heard does far more damage to the sound than it does good for the sound. So I agree with your strategy of altering the room, rather than the signal to give you your desired response at your listening seat.

Tonal timbre accuracy is too complex to be measured by computer program for sound....It takes ears to correct the room...

I correct mine with an astounding success on all counts by ears on a many months of experiments listenings, with TONAL TIMBRE accuracy, not frequencies of the bass... Now my bass are so intense and clear you will not believe what i take to reach that....(7 inches driver i hear with my stomach)

The important point, no ready made formula correcting frequencies can beat your ears to establish the best room possible for perception of timbre....

The same room is different for different ears, then also the fact that it must be FOR YOUR EARS that you work a room treatment not for a program or for another person.... 

All people speaking about bass are beside the point for me....

I dont need a woofer nor bass traps....Not even a program...

All treatment and controls cost peanuts....

:)

« The room is the third ear »-Groucho Marx