i have 2 adire shivas in a sealed box with an mtx 8001 powering them. right now the subsonic filter is on. it seems they are not hitting the really low notes when i have it on. im afraid to turn it off cuz idont want to damage my speakers. is the subsonic filter just for ported boxes, or do i need it for sealed too?
a sealed box offers damping or suspension for the driver at pretty much any frequency, so no filter is required. a ported box loses driver control below the tuned frequency of the ports, thus the filter is there to prevent the system from trying to produce any notes below that point, that might cause the sub to over-extend due to loss of suspension, and damage the drivers.
only ported or bandpass enclosures really need anything more than a normal LPF.