I just installed a Kenwood X500-1 amp and 2 Kenwood KFC-XW10 10 inch subs in a prefab sealed bassworx box. I have a stock HU and I'm using a line-out convertor. I used an O-scope to set the gain and have the bass boost all the way down and the crossover set at ~100Hz.
My problem is that when I have the volume turned up about half-way to 5/8 on the HU, when the the music comes to some lower sustained notes, the subs don't seem to be very loud, and they sound sloppy. Sloppy as in you have a POS factory speaker and you turn the bass, on your head unit, all the way up and crank up the volume. But it sounds okay any other time.
The screws, that hold the subs in the box, a few of those aren't very tight because the holes have been somewhat stripped, could this be the problem?
Could it be that the crossover on the amp isn't set properly?
Also, the line-out convertor has adjustable levels and they're turned up about 3/4 of the way; could it be the LOC? I'm planning on eventually getting a better one that'll put out a better signal. I've used this LOC with a different amp, but had the LOC levels all the way up (it was also just one sub and a different one).
I've checked the resistance of both subs and each one is stable at ~4.1-4.3 ohms, so they're not blown.
I've checked the ground and all wires for the amp, all of those are good. I'm using 12 gauge speaker for the subs.
I'm lost on what to do; it sounds bad and I want to fix it. Any tips/advice on what to do?