Large peak/dip in unity horn Akabak sim

I have been trying to sim a unity horn in Akabak but I'm getting a large peak and dip in response at just over 200hz. I have been moving things around to try and get rid of it.

The dip is the same frequency as a peak in the radiation impedence and a dip in the electrical impedence

Could this be an issue with the model in Akabak? How would I get rid of it?

I am using four B&C 12NDL88 drivers in this sim.
 

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    Response.png
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    Unity Horn.png
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  • unity horn 2.png
    unity horn 2.png
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