I see gain (Input sens.), LP filter (LowPass), and Bass boost on the picture if found, I also see a bass ****.
what is feeding your amp the signal.. Aftermarket HU or Factory HU? your settings will depend on this. are you using RCA cables or just tapping into the factory wires.
The LP crossover should be set anywhere around 80 to 180Hz, dial it up and down until it blends with your main speakers without sounding muddy or too thin.
keeping the low-pass crossover too low will defiantly cause a lack of bass.
this should be done with the bassboost off. the bass boost is the important control to keep low.
after you figure out the crossover setting and gain is set right, then you can boost the bass a little bit, but if you hear any distortion when doing it, then you need to drop the gain a little bit and try again.
If you have a aftermarket headunit then you might have a highpass crossover that you can turn on that will cut some bass from the front speakers to allow for the subs' crossover frequency to be raised even more without being muddy. this will lighten the load on the small main speakers and place more of it on the sub. this will allow you to turn the overall volume up even more. and will feed a stronger signal to the amp.
But let me know what headunit you have.
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