fi btl blown?

Yes.  Tuned to the specifications.

This is why I ask.

What is the model # of the HiFonics amp being used (so I can see if it has a subsonic filter)? What is the box tuned to (if you don't know, please provide the link to RE's site that states this)?

But, yes, it's a knob with different frequencies... It'll either be called a subsonic OR an infrasonic filter. It needs to be set to right below the tuning frequency of the enclosure.

Are you using the low-pass filter on the amp, or do you have a separate active filter BEFORE the amp that cuts the midrange and treble frequencies? The reason I ask is if the amp doesn't have a subsonic filter, you can actually use the amps' high-pass filter as a subsonic filter (as long as the amp is recieving a low-pass signal already AND the high-pass filter on the amp goes down to below the tuning frequency of the enclosure -which is iffy).