So today I learned my sub has been out of phase...for like 7 years.

I'm dumb sometimes...hope this might help someone.

So way back in 2014, I bought my second new Tundra, a '14 SR5. Since then, I've owned a '16 Pro, '17 SR5, '19 Pro and '21 TRD Sport (it's a long story).

In every single one of those trucks, I've elected to keep the factory system and add the same Alpine MRV-250 amplifier and JL Audio 8" subwoofer enclosure (CP108LG-W3V3) behind the passenger side rear seat. I've always installed it the same way with clean input from before the factory amp, and always utilized the Alpine RUX knob to control the subwoofer level so it can blend in with my wide variety of music correctly. I'm a simple guy with hearing that is already destroyed by military and gov service, so this setup suits me pretty well (and will apparently last forever).

So with my most recent truck (and others, now that I think about it), I noticed that whenever I rolled on the subwoofer via the crafty little knob just a tiny bit, the front door speakers would lose a ton of lows and just sound weird until the sub started to pick up those same frequencies. I never paid it too much attention until today, when I elected to do some research and found out that what I've been hearing this whole time (and likely in every other GD truck this has been installed in), is the sub cancelling out the bass from the fronts due to phase interference, likely muddying up the sound like crazy in the process and making my brain hurt.

5 minutes later, I swapped the output wires at the amp, and all is well with the world. I wish I had been paying attention for...you know....like, the 4 previous trucks.

I'm sure you all know about these things and could have diagnosed it immediately had I asked, but oh well...NOW I know!

 

Glad you figured it out...
But I can do you one better, I'm buzzed tonight, so here goes...

I have a non-JBL 2014 SR5 double cab.
I bought a twin 10" $1K JL Audio Stealthbox and an Alpine PDX V 5 channel amp in 2015.

Tried an AC LC6i and a JBL MS-8 to work with the stock Entune.
They both sounded like sh!te..
Well, not sh!t, but not what I paid for for better audio.
I never got a good calibration from the MS-8.
Sold it to a forum member and he stated it worked for him.

Replaced the HU with aftermarket, 3 times.
Sounded better but never got the bass response I wanted out of the Stealthbox.

Last year really started researching what the problem was.
It was this;
The Stealthbox (2 8 ohm DVC subs) was supposed to be wired to 2 ohms (according to JL Audio), it measured into the 9s.
I finally took it apart and found it wired in series.
I rewired it to parallel and brought it down to 1.9 ohms.

Lowered the amp gains and this thing rocks.

So I went over 4 years listening to subpar, lifeless, muddy bass, when the problem was the Stealthbox wiring from the factory..
It never should have been wired in series, it should have been factory wired in parallel.

I have the same bass knob, but installed it at finger tip position as I drive.
Adjust it for almost every different music genre...

 

Oh man...I likely would have suffered for a while with that one, JL usually does it right. 9 ohms would require one hell of a sub amp to run correctly!

Thats a perfect spot for the knob, I may move mine.