dbstedt

It definitely sounds like something was defective OR maybe you were driving the cab(s) into heavy distortion at "75%" and up. Any details on the hardware you were using? Box, amp, etc.

Does anyone have contact info for Ricci?

Dual opposed will reduce the majority of cabinet vibration due to the drivers moving mass acceleration but it shouldn't affect the output response unless the distance between drivers is 'large' or the frequencies you're running at are 'high'. I would start by putting your largest sub in the corner (highest low-fq output) and work from there. Please send updates or measurements if you have them and best luck in handling your room modes.

Thanks for the update and info! Did you end up using any flare or round-over on the inner end of the ports?

Maybe some of this would be helpful? The Subwoofer DIY Page - Sealed Systems http://www.diysubwoofers.org/sld/

I think if I was a vendor of drivers I'd look for interesting ways to promote the sale of more drivers. 😏