Problem with Infinity 1242W

[Exist_ential 10+ year member]

This may not actually be an issue with my sub but that is where i am starting.

i have an Infinity 1242W in a sealed box running off an Alpine VPower MRP-M350. i also have a 1.5 hour drive to work. i have all my gains and HU set properly with a DMM. Out of a max 40 volume i never listen above 20.

When i start up the car and set my volume everything sounds great, nice and loud plenty of bass decent lows (for what the setup is of course). After an hour of driving my sub starts to sound like A$$. it actually sounds blown. the bass is really low (as in quiet) and REALLY distorted.

i thought i was overheating the amp but nope, its actually still cool to the touch as is the dustcap on the sub. the sub still sounds like a$$ after sitting for a few hours, however if i leave it sitting overnight without running the sub AT ALL it sounds great the next morning.

WTH is wrong with this setup?

i do not have another sub or amp to test with by the way.

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[infamous_e46 5,000+ posts]

Battery , alt, ,headunit or loc might be taking a dump

 

[Exist_ential 10+ year member]

brand new HU, no LOC. i guess it could be the batt or alt. but i have never had issue starting the car keeping it running and a recent test says it still has about 38 months life left.