Big dip at 120Hz, reason why?

[HendersonD]

I have a dedicated home theater that is 18'1" x 13'8" x 6'11" for about 1,700 cubic feet of space. The room is well treated on all walls with a carpeted floor. Purchased new components:

• Seven RSL CG25s for the base layer, all in the vertical position. They are rated at 53-35,000 Hz ± 3dB
• Four in ceiling RSL C34E MKIIs for Atmos layer. They are rated at 65Hz – 20,000 Hz. Realistically it looks like they do about 90-35,000 Hz ± 3dB according to the frequency response curve
• Denon AVR-X6700H receiver
• Two SVS PC-2000 subs

I ran Audyssey using the iOS App and it set all 11 of the RSL speakers to small which is correct. Here are the crossovers it set with all numbers in Hz

• Fronts - 120
• Center - 90
• Surrounds - 150
• Back surrounds - 120
• All in ceiling speakers - 200

These all seem low, I would expect all the CG25s to have a crossover no higher than 80Hz and the ceiling speakers having a crossover no higher than 120Hz. I then fired up REW and took a measurement of the left speaker and used 1/6 smoothing. Sure enough there is a big dip at 120Hz. Any idea why? The speakers as measured by the company and Audioholics have quite flat frequency response down to about 60Hz. Is my room really causing this?

 

[HendersonD]

I am thinking this is Speaker Boundary Interface Response (SBIR) cause by the drywall ceiling in the room which is at a height of 6'11". Having Audyssey set the crossovers a bit high seems OK as long as the sub can handle the frequencies up to 120Hz for left and right, 150Hz for surrounds, and 200Hz for in ceiling Atmos. My two SVS PC-2000 Pro subs an certainly handle these frequencies and with two of them my hope is I can get smooth response up to those frequencies from the subs