volume drop after ~15 minutes , no sub

Thanks for the concern, but I don't know what else to try. It isn't like I have spare amps or speakers laying around to try out, so I'm kind of stuck. The only thing I was able to rule out was the HU. I just won a new amp on ebay, $100 Massive Audio NX4 100w rms x 4 @ 4 ohms. Guess when it shows up, I'll either have more power than I need by bridging both it and the kenwood into two channels each (kenwood for front/MA for rear) that I won't have to worry about heat before my speakers pop. I'm hoping a few more watts out of a seemingly stable amp will either help find my problem, or eliminate it. Will keep you posted as to what I find out when this thing shows up.

Really wish this thing let me edit my posts... or that I use the preview post button instead... lol Had meant to say either bridging the amps I will have or hopefully the MA amp on it's own will just eliminate my issue. Then I have a kenwood sitting on a shelf in case I want to bridge it to 1 channel and run a single sub. Surely it could handle that...

Well, got the new amp installed. Can't believe how much smaller this thing is than the kenwood I had. Literally half the size. I also didn't notice that there isn't a built in fuse in this amp... Massive Audio NX4 is the amp I have now. Will run it hard on my way to work Or my way home... or both (1 hour commute), tomorrow to see how it does. However, the ambient temps outside are now in the 40's, guessing that will affect any thermal issues I may have. Anyone know how to tell what amp output an alternator puts out? I tried google'ing until I was blue in the face and didn't find anything concrete. Is it stamped on the alternator or something? My car is a 2007 mercury grand marquis.

The NX4 also thermals out on me, just takes a bit longer. Turned down the input gains to almost 0 and it still shuts down after about 30 minutes of hard run time. Since I like the size of the amp and realizing that without spending another decent chunk of $ for an amp that puts out at least 150W RMS for 4 channels, I'm thinking of an alternate approach of just getting another MA amp and bridge the 4 channel to 2 (200W RMS x 2 @ 4 ohm). That said, I don't want to have to buy more cable and have 0/1AWG power wire installed, which I think I'd have to do to run two NX4's bridged. So, I'm thinking of getting an NX2 (120W RMS x 2 @ 4ohm) for my fronts and bridging the NX4 for the rears. Then I'd have nearly twice the max RMS rating for my front and exactly twice the max RMS for the rears. That should give me plenty of power to drive the speakers, but yet keep amp temps/clipping well within safe ranges at a volume I want. 2 days later... Not sure what the deal is with the NX4, but honestly, bridged or 4 channel sounds almost the same in volume to me. In bridged mode, it overheats and shuts down faster. So... the money on that amp appears to have been a waste already. The kenwood however, did push the fronts bridged far better than it did in 4 channel mode. I have no idea what the issue is... Seems that the polks want big name brand power that I guess I'll have to cough up the $ for just to push them. What's funny to me is that I bought them due to them being reviewed as "factory replacement" speakers. Figured a lower wattage amp would push them fine. I guess it's either my bad luck, or polk's way of getting people to buy their stuff... then buy more to run it. Or, do I just ditch the polks and go with something that has a lower RMS rating so I can run them with my NX4? Which is another thing I don't quite understand. MA sells 6x9's, but they are only rated 30W RMS less than my polks. Seems to me, the NX4 wouldn't push those either...

I gave up and got another amp. Seems like the new amp holds up. It's an old rockford fosgate punch 800a4. I ran it hard for an hour and it just kept going. Will need to do some research though as it sounds a bit muddy compared to the other two amps. The MA was almost too bright on the highs (easily toned down via the EQ in the HU). The kenwood I had was pretty good on mids/high's, but lacked the power to drive the lows. The rockford pounds hard on the lower frequencies, relatively mild highs (not shrill, but still pretty clear). The midrange is the muddy area. Hoping I'll find the right balance on the EQ of my HU to get the mids sounding better. Definitely seems able to drive my speakers though. Gets warm to the touch, but not so much that you can't keep your hand on it.