With respect to tuning, can you elaborate or point me on where to learn more? On the amp I just purchased, the only variables I see are front and rear gain controls. Those I believe work in unison with the volume control...
You can read up an car audio tuning for days so I'll just nutshell it here.
Audio travels in a sine wave. The more power you put into it the more distorted(called clipping) that wave gets. By tuning a system you set the volume of the deck and then the gain of the amp to the point just under the clipping point.
A proper way to do this is with an oscilloscope. This method allows you to see a visual representation of the sine wave. As you increase volume you'll see the wave clip. Most guys don't have this so you tune by ear.
Just cause a deck goes to 40 doesn't mean that it's a clean signal all the way to 40. More often then not even good decks will clip in the 80% of max volume range. So we need to find the max volume setting the deck can handle before clipping.
Starting with just the deck and speakers hooked up to power. Play some really bass intensive music, or get specific tuning frequencies online, and turn up the volume till you hear the music distort. Back the volume down and note the number. Let's say the deck goes to 40 but in this case it clips at 35. 35 is your max volume for clean music.
Now you simply hook up the amp, turn the amp gains all the way down and set the deck to 35. Play your bass heavy music, I prefer Slayer, and turn up the gain until the music clips. Do this for both front and rear. Now your gains are set. You now have the most clean power for your set-up. Most guys will leave it like that but we'll go another step since you have front and rear gains,
When tuned properly you get what's called a sound stage. It's a fancy ass word for music that sounds like it's in front of you. Sit in the rig with the doors closed and listen closely to music you prefer. It doesn't need to be bass heavy for this. You want it to sound like all the tunes are coming from the front. Since those Polks carry some serious punch you'll probably find that it's centered slightly behind you. Now you turn the rear gain down slightly until it centers in front of you.
That's tuning a system in a nutshell. I've done a lot of systems over the years. When I did the one in my rig I tuned it by ear. A few weeks later I took it to a buddy with an oscilloscope. It was set almost perfect by ear. lol
EDIT:
On those pair of Polk Audio DB651 6.5s I found in the garage... I just realized that I fab'd something in my other car for them, so I'd like to keep them for that ride...
So, I'm in the market for four 6.5" speakers. Just get the same Polks? 56 bucks a pair at Amazon:
https://smile.amazon.com/gp/product/B000P0PF9G/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Anything comparable or better for the price? $112 for four speakers seems like a pretty good deal...
Put those Polks in the rear. For the price they're the best coaxial speakers on the market. Get some components for the front. You'll be replacing the factory tweeter that way. The new crossover box can be mounted between the window and the interior sheet metal of the front doors. I use these and highly recommend them if there in your price bracket:
https://www.amazon.com/gp/product/B007SNMQDQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
