FV12 is not a flat sub. Take a look at an old graph I found. The spike is around the 50-70.
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I can adjust the Bass Extension settings to High to flatten this out. It is set to low and 14 hz. Setting switch for bass extension are composed of 2 switches. One switch has: Low, Mid, High the other has 14hz, 20hz and 28hz. This might help. I have had other subs in thi same position...it is honestly not a bad one. This one just tends to be boomy and with it forward firing port it can exaggerate frequencies easier. Ports tend to do this. Not to mention most movie effects soundtracks lean heavy in the 40-70hz range because of the impact side of things.