Dual subwoofer phase issue


Standard Member
Hello people!

After a lengthy time and fix for my previous thread named 'In need of 20hz and below subwoofer' I now have to open a new thread for a new problem.
I have a BK Monolith Plus FF and a Klipsch R-12SW.

Here are the frequency response graphs using REW of my two subwoofers and then combined response.

I also included an ALL SPL without EQ.

Is the Klipsch holding back the Monolith?
Why do I suddenly have a dip between 50hz and 70hz that just isn't present in the singular measurements? I have had a different dual setup here before and it had it's problems but I worked them out. One sub (discarded one) was at the front of the room and one was at the back. This time around both are at the back.

Now I suspect this has to do with phase, positioning (which I cannot do anything about) or time alignment which looks to be correct. The Monolith gives me a better measurement than both which is strange to me. I understand that dual subwoofer setups can have their challenges as I have come across them before and won, but this time it's more scientific (physics based) and I don't have the knowledge base to overcome it on my own.

I am stumped. Can someone with more knowledge of REW help me here or is the problem more straight forward?

Subs are not in symmetry so are at different distances but both are back of the room. Using MiniDSP to time align. The Monolith is at Phase 180 degrees and Klipsch at Phase 0 degrees. This was done because it sounds better at the listening position. It's odd because I'm losing slight SPL with both. PHASE! PHASE!. But I can't correct it.

Any other information someone might need I am trying to think of everything to help you help me here.

Thank you in advance.


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