Taken from the thread I started here:

Thinking About Upgrading Your Sound System? Do It!

Here's my complete sound overhaul - on a modest budget. I just finished installing sound deadening on the front doors and new Infinity component speakers up front powered by a modest amp. I knew the stock speakers were pretty awful since I've swapped speakers in other cars before but this is the first time I've gone a more serious route. Here's what I've done:

Installed Alpine head unit for BT & USB - $99
Alpine CDE-143BT CD receiver at Crutchfield.com

Installed Alpine power pack, 45RMS x 4 (a bit higher since the Infinitys run at 3 ohms, not 4) - $100. Best part? NO EXTRA WIRING NEEDED!
Alpine KTP-445A Power Pack Compact upgrade amplifier for your Alpine receiver ? 45 watts RMS x 4 at Crutchfield.com

Installed 6 1/4 in. Infinity Reference X Components - $105
Reference 6500cx - Infinity US

Sound deadening on front doors as well as on the center console and transmission tunnel - $395 total spent in materials for the entire vehicle from RAAMaudio - Automotive sound deadening products Also, they have a GREAT how-to article for newbies like me, not every surface needs to be plastered with the stuff for great results. I ordered an additional amount, now up to $395. Wanted more foam and mat materials to do the entire cargo area since it's so noisy compared to the front end now.

6 1/4 in. Coax Infinity Reference X speakers on rear doors (current ones are completely blown out) - $70
Infinity Reference X REF-6502ix 6-3/4" 2-way car speakers — also fit 6-1/2" openings at Crutchfield.com

Sound deadening in the rear cargo area, it's noisy.

Powered Blaupunkt 10" subwoofer - $216
Blaupunkt Blue Magic XLb 250 A Single 10" subwoofer enclosure with 250-watt amp at Crutchfield.com

Wiring kit from Crutchfield, 10 gauge - $40 Don't get this one: http://www.crutchfield.com/p_142PA8B...t.html?tp=2919, the RCA's failed in a week. I'm so bummed. Get the Kicker or higher quality ones that have RCA's made with copper for more strength.

After doing the front end of the vehicle, it is a HUGE improvement in sound, at least to me. I still get a lot of road noise from the rear of the vehicle but the speakers sound awesome. I tested it along the way to hear improvements to see what was most effective:

1. Adding the amp brought it to life. These Infinitys really shine with an amp, but I knew that already. Clear highs and good bass, almost feels like I have a small sub tucked away somewhere!
2. The sound deadening quieted down the cabin and increased bass response but more importantly, took away all the rattles I had in the door panels.
3. Just swapping the speakers did very little to improve sound, even though Infinitys are good quality. Would have been a waste of the speakers if I stopped there.

Now that I'm really going at it, an amp and sound deadening or some sort of insulating foam is a must. Those showed way more improvement than just swapping speakers.

Also, no more distortion at low frequencies that was hurting my ears Did I mention I did not have to do any wiring for the amp? That was the best part, it's literally plug and play. Only tricky part was where to mount it, I ended up putting it right below the head unit but far enough away that heat would not be an issue. I'm all for easy routes, and besides a new head unit plus a new amp for $200 is a complete steal. Crutchfield sells open packages for cheap, and Amazon and Ebay will have steals if you watch long enough.

I've put in about $900 to do the whole 4Runner, but it could be done for less if you're not so picky about sound. There are some decent Alpine or Pioneer speakers out there for much cheaper, I just love the sound of the Infinity Reference X line. Decent bass but the mids and highs just sound sooo good to me. Highly recommend going to Fry's or a car audio store to listen to speakers before you buy, they really do sound different when compared. If you guys want some photos I can take some of the next parts of the installs, such as my plan on how to fit 6 1/4 in the 5 1/4 openings on the rear doors and such. I was really cramped for time over the past week so I didn't have any time for photos of what I did up front but could take off the door panel if you really, really want me to. I've put in about 10 hours total so far with the install, it's slow going especially when I have to solder new wiring but not hard at all.

UPDATE: Just finished the deadening and wow, what a difference. The rear cargo really is the problem spot in our vehicles. There's still engine noise but there's nothing coming from the back of the 4Runner anymore. All the sounds are still there but reduced, if that makes sense. Also pretty much all high-frequency sounds are gone. I can hear my wife talk to me much, much better than before.

If you wanted to go one step further, do the front floor, that's the next spot that would need it. I'm not going to though, I'm happy with what I've got.

Anyway, hope this helps someone looking to plan their next sound upgrade on their 4Runner! Here's the photos for reference (I adjusted my crossover settings so had the door panel off this evening):

Tweeter:



That's right, I glued it, just like how the stock ones were. The ones I have are in a solid casing, there's no magnet to move like the woofers. The component set had three different mounts but there's not enough space to fit it behind the grill (the stock tweeter is very thin, probably why it sounds bad!). Gorilla Glue and a clamp and we're done! All you audiophiles are probably cringing right now

Here's a few more photos for kicks:

Crossover location inside the door above the support bar (not deflecting any sound waves and not blocking the window operation):



New speaker on the old mount I did use the supplied mount provided in the kit for a more secure fit:



Finished product. Not pretty on the outside but it sounds awesome and nobody sees it anyway!



Also put foam on the inside of the door panel, took away a lot of rattles. I used twice as much foam as I did sound deadening:




More photos, updated 9/8

Routed the power wire for the amp through the firewall plug (poked a hole with a screwdriver)



And then ran it under the trim to the back. Also ran my RCA's on the OTHER side to remove any risk of sound contamination.



Installed the volume control knob in the pocket under the head unit using Velcro. Great location and easy to remove if I ever need to. If you haven't bought a large supply of Velcro yet... it makes life so much easier.



Stripped the interior (which is a whole lot easier than it looks, took all of an hour) and added sound deadening. I ran out though so waiting on some more to come in.



Took out the plastic pocket and glued some carpet in there instead. Now my storage is 3x what it used to be! No more rattles either. Shout out to @BrianSD_42 for his photos that gave me the inspiration.



Bonus pic of the other side in progress.



All I have left to do is finish the floor of the cargo area and I'm DONE!

Post #2:

Ok, had some time last week to do the rear doors as well as some of the interior panels, I took a few photos that I hope will help some people. I will also show how I mounted 6 1/4 in speakers in the rear doors. It was a pain, but doable.



First, how I mounted the speakers in the rear doors. I took the existing plastic mount, trimmed it flat and traced it on 0.22" MDF board that I picked up at Home Depot. This thickness was perfect, not too thick but still rigid.



Then I cut out the opening by tracing the mounting bracket supplied by Infinity. I have to say, that bracket was super helpful since it had hole alignments that fit perfectly for a Toyota. I did have to trim off some very long screw mount holes, but nothing terrible. I ended up putting screws straight through the bracket, MDF and into the door panel in the stock holes, except for one. If this is not an option for you, you'll have to cut out a second "ring" for a mounting bracket and then either glue it to the MDF board or sink the mounting screws so they don't stick up, and then put in more screws to hold the speaker to the ring.

Wiring was simple, no crossover to deal with.



The harder part was trimming the door panel. This does cut into the inside of the pocket, but there's extra space in there so you don't notice it. Even with taking 2" off the side there's no chance of anything falling inside the door. If you take off the panel you'll see what I mean.



Also stuffed the center pillar behind the door with foam and coated over some of the holes in the metal. No more echoes. BE CAREFUL WITH THE CLIPS! These metal ones tend to bend and break, one snapped off and was lost in the pillar. No need to detach anything above the removable panel, that's where I went wrong.

My Infinity's sound AWESOME now that they are tuned a bit to my liking. They actually have really good mid-bass now that the doors are done and essentially act as custom enclosures. With the 10" sub it sounds fantastic. Went with this one since it's easy to wire, just run power, ground and RCA's. Amp and sub come pre-loaded in the enclosure. No remote wire needed!