I used to compete in IASCA Car audio and built several systems. From my experience with factory systems is that they are usually a budget line that won't handle the power of the audio manufacturers normal line and the amps gains are usually turned down and sealed so you cant adjust them. In the car audio world, having access to the gains has always been critical to part of the tuning process. Crank them up when the speaker starts to pop at a heavy bass track and then turn them back just a bit until the speakers stop popping to keep them at peak performance. They now have amps that "automatically" supposedly adjust the gains for you. I'd rather tune my own.
I listened to a variety of music from some old comp bass tracks
Spooked by Bro Safari & DJ Craze
Lost in the Crowd by Bassnectar
Hellraiser by Blanke
Feel that way by BYOR
I love big speakers by bassboy & Techmaster P.E.B.
Frequencies of the Future
These bas tracks had alot of bass but no solid umpf of a hard kit. It seems like a port is necessary to get the tight snap for these.
Some rock/bluesy tunes
Celador by Bill Fisher
Dirty Finger by Texas Hippie Coalition
Thats the working man by Shotgun Sawyer
Wisco Disco by 20 Watt Tombstone
Heavy Honey by Left Lane Cruiser
Back on It by Mount Caramel
Before the Flood 7 Horse
Sixty Eight by Slow Season
Graveyard Earth by Cobra Thief
Again these all had decent bass but not quite the snap
When I got into some old hairbands era music and Ride the Stash by Backyard BBQ it's like the bass is almost non existent. Some country tunes that were more pop seemed to have decent bass while others than should have a good snap do not. Metal was very similar. Metallica One just clearly did not have the hard hitting snap it should.
What I think they did in this is chose to tune the system more toward pop country, dance, rap. I've experienced this when building systems. To correct I would normally predict to correct are several things. I normally liked to run Rockford Fosgate 10' subs 1 cubic inch smaller than the 1 cubic foot recommended. I would also tune from there by adjusting the gains and if still not hitting hard as I wanted to either port the box or if I thought it seemed it was too tight and wasn't getting into the low deep frequencies like its in a small enclosure to stuff angel hair (Synthetic pillow stuffing) into the box to slow the airflow and trick the sub into functioning like it's in a bigger box for deeper bass. Can you do this in the our ZR2's? I don't know, I have not had the ambition to pull it apart to see what the box and amp is like.
Swapping speakers for other speakers is kinda pointless unless you are swapping the amp as well. These factory amps are probably running pretty safe and cool at a 4 ohm load if not an 8 ohm load. You can drop the load at the speaker by bridging a second sub at the same ohm rating in half. Example two 8 ohm speakers will be 4 ohm bridged mono and will see twice the amount of power of that single 8 ohm speaker. Two 4 ohm speakers will be a 2 ohm bridged mono and will see twice the amount of power that a single 4 ohm speaker. However, the amp only sees half the load and you have to remember this or you can overheat or fry your amp. So a 4 ohm load at the amp is a 2 ohm and a 2 ohm load is 1 ohm. You do not want to go lower than what the amp is rated for. If it says it runs 750watts at a 2 ohm load, a 4 ohm load is what you do not want to drop below. It's confusing as hell I know, I fried an amp once wiring up four 10' pro subs into a .5 at the amp load. She hit hard as hell for about a mile down the road before we started smelling burnt electronics. This is where I should have wired the 8 ohm speakers in pairs in parallel and then bridge the two seperate groups mono so the load was 4 ohms load and 2 ohms at the amp.
So, I'd say if your going to swap speakers, pay attention to the ohm ratings and how you want to wire it. Select an amp that has a subwoofer channel rated for 2 ohm and at the RMS rating for your sub and buy a sub that will use that power at 2ohm. Usually those amps are big enough and have enough power in their other stereo channels to really push some nice mids and tweets and make all the difference in the world to the clarity, (and volume) of your experience for better result.
