Here's my problem :

I can only get decent output from my subs if I maintain a low pass filter setting below 40Hz

At 50Hz low pass they perform ok at moderate volume, but at 60 Hz + LPF they produce a SERIOUS rattle (i.e. the subs sound like they are about to self destruct).

Here is the setup :

1 off Directed 1100D amp
2 off Earthquake Magma subs (3.2 ohm DVC subs) paralleled up to give a nominal 0.8 ohm load.
Common sub enclosure so both subs occupy the same volume. Enclosure volume optimised as per manufacturers recommendations.

Thinking the problem was enclosure resonance, I went to the trouble of fitting various M8 threaded rods to brace the enclosure. This had negligable effect (after trying to convince myself otherwise).

Any thoughts suggestions ? Are the magma's not capable of driving over 50 Hz ?

Thanks,

John