What happened to my room acoustics

Is this even the right forum? It seems like you are replying to a thread from a different web site.

You might want to clue us in on what speakers you are even talking about.

Measure 1 speaker at a time.

That dip you see around 12 kHz can very possibly be a reflection issue. If ithe frequency response dips change frequency as you move the microphone closer to the speaker that’s your clue.

Generally speaking, if all you have for room treatments is the bass traps and single curtains you are not going to have enough.  Treating the room to be more absorbent in the mid to treble regions (including the ceiling) will let the bass emerge from underneath. 

Another approach, of course is to move the speakers closer to the rear wall until you get the balance you are seeking, or just use tone controls. :)

Is this even the right forum?  It seems like you are replying to a thread from a different web site.

I really do not know what are you talking about.  I am addressing my message to the Audiogon forum.

My speakers are Burchardt S400 II as said in the chart.

Thank you for the clue about the 12khz dip being possibly due to reflection.  I will investigate this furhter.

FWIW, my room is about the same size as yours (19.5x13.5x9), but my set up is a tad different. I use the triangulated set up with my speakers 4' off the wall behind them, 9' apart, sharply toed in (axis crossing slightly in front of my head). My chair is about 4.5' off the back wall and placed to avoid a bass node at about 60hz. I have no special room treatments but I do have window coverings (heavy drapes), book cases, and soft furniture. 1st reflection points have been dealt with. My sound stage is excellent in that it allows very specific instrument placement over the entire wall behind the speakers. I measured my room, speakers etc endlessly (it seems) but ultimately it was tuned by ear.

The point of my saying all of that is to suggest that your chair might be too far back from the plane of your speakers which might just be a bit too close to the wall behind them and your low and midrange node may be the result of a room node which will change with moving your speakers forward. The HF dip could be the result of the off axis output of your speakers (but not so much reflections, I think).

BTW, FWIW, I know nothing special about your speakers. Also, for the most part, the measurement that really matter are those made with the mic at the listening position. Measuring your room or trying to duplicate the speakers spec's is really meaningless, interesting perhaps. Regarding sound stage, with my present system, the difference between my present system set up and one with the chair further back toward the rear wall was that the sense of depth diminished and there was some loss in specificity.  Those issues disappeared when I moved my chair forward (towards the speakers) to something closer to an equilateral triangle.