Bizarre SQ trick you would never expect to work
 

Okay, so I have a full set of speakers up front with passive crossovers and a subwoofer in the trunk facing towards the back of the car to make use of the trunk as a chamber to enhance the bass. As you might expect, it was a little muddy, demonstrating the classic symptom of when someone is talking there is an annoying rumble that just doesn't belong. So I did the old trick of reversing the polarity on the subwoofer and it got a lot better, but still wasn't as good as I liked. I had pretty much given up and decided I was going to have to invest in something for time alignment. So during lunch I went over to my favorite local sound shop (919 Motoring if you live in the Raleigh area) and told him my problem and what I had done so far. Now the owner knows I'm tight with a buck so before I can ask about bargains on product, he stops me and says, "I have a trick you can try before installing more equipment. It only works on setups like yours that don't use rear fill and it sounds insane, but it works quite often." Turns out he had been at the JL Audio facility and was talking about product with Lucio Proni (the L in JL) and the subject of time alignment came up. Proni told him this trick (which he was very doubtful of) and then showed him in a test car that it really works. It doesn't sound as great for the passenger, but it is amazing from the driver's seat if it works for your setup. He told me to put the subwoofer back to normal polarity and reverse the wiring on the passenger side. He also suggested doing it after I had been out of the car for a while so my ears would be fresh. So I went back to work and, at the end of the day, before starting my car to go home, I swapped the wires around. The difference is amazing. The funny thing is that with the mud gone, I found that I needed to turn down the tweeters in my crossovers, which was great, because they had been a little harsh coming off the glass.
I thought it sounded good before, but now it's what I would expect from a nice set of Hertz speakers.

Well.

FYI. Time alignment is just adjusting phase. So, you're adjusting it, by 180 degrees. A full 180 degrees at all frequencies. This is why Subwoofers often invert phase for non-time aligned systems, as it's moving the woofer's phase relative to the other speakers. (Among other effects that may or may not be wanted depending on system design)

If this works for your setup, great. It's not something I'd do in my car as opposed to time alignment. 3Sixty.3's aren't that expensive on Amazon these days.

I know that. I just thought it was really odd that reversing one side of the front corrected the sub in the back.

The title of this thread reads like some of those internet ads you see.

"USE THIS ONE WEIRD TRICK TO SAVE THOUSANDS ON YOUR MORTGAGE"

so does this mean you're not running a crossover on the front speakers?

As indicated in the rather long first post, they use a passive crossover. The amplifier, of course, has a high pass crossover. I reversed the passenger side at the input to the passive crossover so all three speakers were reversed.