- Wiring the speakers out of phase when they should be in phase, or vice-versa.

I think the latter is the most likely culprit, since you said that removing the filters made it the loudest. Having speakers in the wrong phase most commonly results in lowered bass response.


To test for/fix this: switch the + and - wires on one of the subs (are they single or dual coil subs?)

Wiring problems, such as wiring the speakers in parallel when they should be in series, or vice-versa.

Wiring stuff in parallell when it should be in series is most likely to send the amp into protection (or smoke signalling mode if it doesn't have protection circuits) , but wiring in series when it should be in parallell will lead to less power produced by the amp.

What is the lowest Ohm load the amp is stable down to?

What are the impedance of the subs and are the single or dual coil subs? (if dual give the impedance of a single coil)

Can you describe how they are wired now? For schematic examples, look at this page.

/Michael