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Rear speakers, amplifier, and subwoofer

Building a Mobile Listening Lab: part 7

Now that the front door speakers were in — and we could ably demonstrate the difference between the front aftermarket and rear factory speakers — it was time to install the new rear speakers. Matt and I decided that this next phase would be big; not only would we be mounting JL Audio C2-525X full-range speakers in the rear doors (initially we tried the 6-1/2" version, but it didn't fit), but we would be installing JL's magnificent new HD 900/5 5-channel amplifier under the rear seats, adding a JL ProWedge 10" W7 boxed subwoofer, and wiring the whole system with Streetwires 12-gauge speaker wire. While threading the 12-gauge wire into the rear doors would prove to be challenging, the rest of the installation went quite smoothly — thanks to the acres of room afforded the backseat area by GMC.

Choosing rear speakers

Since I do all of my listening from the front seats, and since our goal is to create a truly high-performance system without using top-of-the line components exclusively, we decided to put a set of mid-level, full-range speakers in the Yukon's rear doors. Since we went with JL Audio C2 components up front, it was a no-brainer to voice match the rear speakers as much as possible. A quick check of our installation database confirmed that the C2-525X models would fit.

At left, the Yukon's factory rear speaker; at right, the JL Audio coaxial:

The larger magnet structure, better basket construction, and superior sealing of cone to basket flange give the impression that the speaker on the right will perform better when mounted in a door panel:

We knew we would have to run the speaker wire through the existing wire looming from the body of the vehicle into each door:

door loom

Exposing the flush-mounted wiring harness in the door jamb:

So we pull out the harness and discover that there's precious little room to run any additional wire, to say nothing of high-performance, 12-gauge speaker cable. Oops? Well, almost — the brilliant Matt Freeman peeled back StreetWires' clear jacket and wrapped the positive and negative strands on either side of the plug, in the plastic grooves:

Major installation hurdle negotiated, the harness is once again in place and yes, we struggled (successfully) to wrap the looming back on top:

I should note that when screwing in the speakers, I had to be careful not to overtighten, as the bolt head seemed to stretch the speaker surround quite easily. Another small issue with the speaker design were the connecting posts — they were thin and pliable and weren't stiff enough to scrape through some stray solder on the speaker wire's spade connectors, forcing me to re-attach new spade terminals. Neither of these were issues with the higher-end C2s up front. Relatively small concerns, as the speakers sound smooth and sweet in the back seat.

Choosing amplification

When we started this project at the beginning of the year, we didn't anticipate using JL's killer 5-channel amp, which wasn't to be on the market for several months. And we figured we'd be working slightly quicker than at the snail's pace into which we've seemed to settle. The original plan was to connect a four-channel amp to the main speaker system and use a mono or bridged-to-mono stereo amp for the subwoofer. By the time we were ready, however, the HD 900/5 was in house and seemed the perfect choice for our project. Audiophile-grade and Class D means efficient high-fidelity. These things run cool, never shut down, and control your speakers effortlessly. I've wanted one of these amplifiers ever since I heard them demoed at CES 2008 (Consumer Electronics Show – our industry's biggest trade show, held in Las Vegas every January). JL had a Beetle wired up for true high-fidelity, and these amps were at the core of a mind-bogglingly accurate car audio system.

Amplification was the one gear category where we knew from the outset that we would go top of the line. That's because the power source is the heart of an audio system. When we later fired up the system, the difference the amp made was obvious; an amplifier is the force behind your speakers, similar to the way a musician "powers" his or her instrument. We put the Keith Jarrett Trio's latest disc Yesterdays in, and the tonal complexity, warmth, and level of detail was so pronounced it just made us laugh. I think the harmonic richness of Gary Peacock's upright bass is what hit me first, followed quickly by the delicate sparkle of Jack DeJohnette's ride cymbal dancing around Keith's resonant Steinway articulations. You're never really ready for that kind of experience in a car.

(A note about the power wiring: Since we realized that we would be powering the entire system with this super-efficient, low-profile technological marvel, we realized that we wouldn't be needing the 1/0-gauge power wire coming off the battery into a distribution box with multiple fuses, outboard capacitor, etc, and running individual 4- or 8-gauge power leads to each amp. All we needed was one length of StreetWires 4-gauge to stretch between the battery and the amp. So, we disconnected and removed the StreetWires PowerStation capacitor, pulled the 1/0 cable we had used to pre-wire the vehicle, and ran the smaller wire in its place. Sure, that was a bit of a drag — unnecessary step — but at least it was easy. We simply tied the new wire to the old wire and pulled the new 4-gauge through as we removed the 1/0-gauge cable. Such are the vicissitudes of spending a year on a vehicle overhaul.)

Running RCA patch cable from the rear panel of the radio...

... rightward behind the glove box ...

... down behind the right front kick panel ...

... along the floor trim ...

...and to the amp location, joining the power and speaker wiring (speaker wire not visible in this picture):

The controls are easy to access under the seat (and are nicely hidden behind an elegant, removable metal plate) and they give me total flexibility over each set of outputs. High- and low-pass selectable, continuously variable filters with adjustable slope, multiple channel configuration, input sensitivity, subsonic filter, etc.

Listening, evaluating, and making these kinds of adjustments is nothing but fun for me. It's like tuning a fine musical instrument.

Just after I made all the adjustments. Flip the seat down, turn on the stereo, and it's ready to pump:

Choosing a bass speaker


With respect to the subwoofer, I considered a few options. I gave very serious thought to replacing my front, between-seat console with a JL Audio Stealth Box™ but ultimately decided against the idea as I would have lost my rear A/C ducts and front seat cup holders. The cup holders could have been remade with fiberglass, but sacrificing rear seat climate control was too steep a price to pay for low-frequency high fidelity. If this vehicle wasn't also the family road car, I would have done it in a heartbeat. A Stealthbox would have been a true hi-fi solution, as they're designed specifically for a vehicle's physical and acoustical environment, utilizing a high-end 10" W3v2 subwoofer in a super high-quality, handcrafted enclosure (which would be located in the listening area of the vehicle's cab).

So, what could be our great-sounding alternative? Matt and I explored the driver's side rear quarter panel factory subwoofer location to see if a stealthy replacement could be managed. We could have installed an entry-level 8" sub of some kind, but the results would have been less than ideal: moderately deep bass physically separated from our listening area. We decided to go with a high-quality loaded sub enclosure and position it right behind the rear seats. When I have passengers in the back, the woofer fires into the seat back; when I don't, I pull the seat back down and enjoy unobstructed low end. It takes time to gradually break in a new woofer, and this one sings a little sweeter with every passing day. I love it.

So, here again, we really are going top of the line with a JL Audio ProWedge™: solid-as-a-rock cabinet construction loaded with the best subwoofer they make. From symphony music to slamming electronic beats, this woofer fills my enormous vehicle with bass energy — and barely breaks a sweat doing it.

Note: while the picture below looks nice, it's not set up optimally. For safety, the enclosure should be secured to the floor. I've also discovered that if I position it in the middle of the left-hand seat back and turn it around to fire into the seat, the response tightens up considerably. And if no one's occupying the spot, the seat back can be folded down for greater clarity:

Next up: applying more Dynamat to previously untouched surfaces and Alpine IMPRINT™ signal processing. Stay tuned.


Read the entire Building a Mobile Listening Lab series:

  1. Laying the Foundation, Part 1
  2. Laying the Foundation, Part 2
  3. Laying the Foundation, Part 3
  4. Dynamat installation and pre-wiring for amplifiers
  5. Installing the front door speakers
  6. Video: factory vs. aftermarket speakers
  7. Rear speakers, amplifier, and subwoofer
  8. Report on the Yukon system's performance
  9. The ultimate in system tuning
  10. Video: Alpine's IMPRINT signal processing in action
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