Sub ported to 18 Hz - where to set rumble filter?

[Bent]

My sub's amp (ADA 1200) has provisions to adjust it's low cut-off (rumble filter).

it is set at 1.8 Hz from the factory, and taking into account the fact that there is a likely roll-off to the rumble filter, which I don't know... can anyone suggest what freq. I should shoot for as a rumble filter frequency to allow best use of my enclosure's tuning frequency of 18 Hz, but not so low as to allow to much acoustical "unloading" of the driver below that frequency?

[ThomasW]

14Hz-15Hz

[Bent]

And once again, I thank you.
Now to call adire and find out resistor and cap values.