You can import that .zma into PCD or WinPCD or the like. Then you can just look at the impedance plot and find the lowest point of the valley between the two peaks.
I'm just guessing, Ani, but, to me, those plots look like you have air leakage somewhere, which is causing the system to unload and not resonate at the proper frequency.
That can be the issue, they are not fully finished, though the inside has a thick coating of duratex acoustic paint, and I don't have any sealing on the baffle...
Comments
Here's a MLTL sim and an actual sweep after the build. Tuning at 26Hz (lowest point in the valley between the two peaks).