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Discussion Starter #1 (Edited)
The V3 CTS-V is an awesome machine. However, for audiophiles, the lack of low end bass might drive you a little crazy. While my wife wasn't thrilled that I was putting a 'boomy-box' in a car of this caliber, it didn't stop me. The install is a 10" Kicker CompC with a Kicker 43CXA3001 300W amp. The goal here wasn't to win SPL contests, but just to add that low end that the "subwoofers" in the rear deck just couldn't produce.

Step one was to strip the truck liners out and wrap my head around what we were dealing with. Over to the far right is the factory amp. More on that later. Not pictured is the crazy-ass magnets that GM used to secure the top of the trunk liner. In my situation, they don't vibrate but seriously... magnets?! My sub box is going in the well where you would normally find a spare tire. I'm a stealth-install kind of guy and besides the sound, I don't want anyone to know there's an aftermarket subwoofer in the car. Bonus of a car like this that the battery is in the back! Power and ground are super easy!

1 - Naked Trunk.jpg 1 - Naked Trunk 2.jpg

The toughest part of the box was the floor. There's a 'disruption in the floor of the nice 27.5" x 20.5" cavity. As you can see I just built a pocket in the bottom of the box to compensate for this brace.

3 - bottom.jpg

The factory Styrofoam has 3 mount points with a really nice set of fasteners. The goal was to use those fasteners to secure the box in the compartment. There are threaded studs that stick up through the floor. I drilled holes and built up the floor in those spots. Turned out my amp rack covered access to the rear hole. I wound up just screwing and gluing a piece of wood to the top of that mount point. You still need the mount point because of the threaded stud sticking up. With just the front two fasteners installed the box won't budge.

4 - bottom in car.jpg

The box is 6.5" tall. Here it is test-fit in the car with an integrated amp rack. Like a glove!

5 - test fit.jpg

Carpeted. The wood in the back is just to catch the floor. The floor needed raised a bit to allow for the added height of the box. If you get a shallow mount woofer, you can probably reduce the height of the box and just use the factory floor.

6 - carpeted.jpg

The factory 'fix-a-flat' sits in the container in the 'spare tire' well. I relocated it to the little compartment on the right of the well and made a small piece of wood to act as a retainer for the pump. The tow hook and fuel filler fit in there, too.

6a - tire pump.jpg

Finished product with amp and sub mounted. However... it didn't sound right. The box, all said and done, was about 1.37 cu ft. That's just too small for this woofer. I should have bought the CompR. This woofer wants a sealed enclosure of 1 - 2.6 Cu Ft. 1.37 is on the low side of what it would like. I have another box in another vehicle with the same sub that's 1.6 cu ft and it's perfect. But 1.37 was just too small for my taste.

7 - Finished Sub Enclosure.jpg

So... port it! Port is 2" round and 5.5" long. Tunes the box to about 35hz and it's perfect. There's a tiny bit of port noise, but it's in the trunk. I can't hear it in the cabin. This opened the woofer up and it's booms just right now.

8 - Ported.jpg

Because I built the box a little tall, the factory floor didn't quite sit flush. I neglected to account for some of the 'puffy' parts on the bottom of the floor. So... build an new floor. I didn't get pictures but the floor has aluminum mesh integrated in to it to allow the amp to breath and the woofer to fire through. The floor is just made out of 1/4" luan. There's a hinge in the middle to allow it to lift and give you access to the woofer/amp.

9 - New Floor 1.jpg 10 - New Floor 2.jpg

I added a hole in the floor to allow the port in subwoofer box to move air freely. You can't carpet over this hole because while carpet is invisible to sound, it does restrict airflow. That's a no-no for a port.

11 - floor with port.jpg

Finally, here's the real trick to adding a subwoofer to a modern car. I tapped high level inputs for the amp at the rear subwoofers. The amp only has one output for a sub. I assume it's just a mono signal, but just to be safe, I grabbed the signal at each subwoofer on the rear deck. It's already crossed over and is just subwoofer frequencies.

This is the biggie! The car has ANC (Auto Noise Cancellation). It's on all the time and you can't disable it through the radio. If you add a subwoofer to this system you're going to get a loud sound through the sub as soon as you close the door with the engine running. That's not a bad ground, it's the Bose system trying to cancel out low end noise and make the cabin quieter. It's a fantastic system but it ruins an additional sub. You've basically broken it when you added the sub. There's three mics mounted in the cabin that sample road noise and tell amp what to play. I disabled this by cutting the three return wires on the mics at the amp. This picture shows the pin-out for plug that has the ANC circuit in it. At first, since my system doesn't have the mid speakers detailed in this connector, I simply unplugged it. It worked perfect, except it broke Park Assist. I think that GMLAN low speed serial data is important. So, I cut the mic wires. I might have been able to just cut the crankshaft position wire. The wires will be very easy to fix if I ever want to. You could also put a switch on each one. I do notice a tiny bit more cabin noise without ANC functioning but hey... I paid for that big v8, it's actually nice to hear it!

ANC Circuit.jpg

Hopefully this helps someone looking to do the same! The sound is fantastic. I'd suggest getting a remote base knob to mount in the center console. It's nice to be able to manually adjust the bass. Especially when dealing with hi level inputs and factory systems. Without a Digital Signal Processor you're slave to what the factory system does with bass at higher volumes. This one isn't too bad but at higher volumes I like to bump the bass up a little.
 

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Nice write up, you hit pretty much all the questions I was thinking as I was going through it. Even the ANC levels with it being off and how noticeable it would be.
 

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Great write up and clean install reminds me of building boxes back in the day of soundquake SPL contest man I'm getting old :cool:
 

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Nice box/setup, but awesome post! Thanks for putting up a bunch of pics and the diagrams. I've thought about doing throwing the AVI 10in SQ sub I've got (loves a ~1.25cu ft sealed box) in the back there, but didn't want to deal with a line driver/etc.
 

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"Finally, here's the real trick to adding a subwoofer to a modern car. I tapped high level inputs for the amp at the rear subwoofers. The amp only has one output for a sub. I assume it's just a mono signal, but just to be safe, I grabbed the signal at each subwoofer on the rear deck. It's already crossed over and is just subwoofer frequencies."


I'm a little confused, can you please explain? Was the tapping done after the factory amp?
 

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Great write up Jfmoots!! Thanks to your advice i took the task on myself. Haven't cut the mic wires but I do have that "gruntle" from the sub when the music is off. Turning down my boost control kills that noise from my sub. Can i ask which plug is the one that has the mic wires? There are like 3 going to the amp any help would be greatly appreciated. Thanks.
 

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Discussion Starter #14
"Finally, here's the real trick to adding a subwoofer to a modern car. I tapped high level inputs for the amp at the rear subwoofers. The amp only has one output for a sub. I assume it's just a mono signal, but just to be safe, I grabbed the signal at each subwoofer on the rear deck. It's already crossed over and is just subwoofer frequencies."


I'm a little confused, can you please explain? Was the tapping done after the factory amp?
I actually tapped the signal on the rear deck speakers under the rear deck. The amp only has one pair of wires for the subwoofer. I assume they split somewhere in the harness because there's two pairs of wires connected to the rear deck speakers.
 

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Discussion Starter #15
Great write up Jfmoots!! Thanks to your advice i took the task on myself. Haven't cut the mic wires but I do have that "gruntle" from the sub when the music is off. Turning down my boost control kills that noise from my sub. Can i ask which plug is the one that has the mic wires? There are like 3 going to the amp any help would be greatly appreciated. Thanks.
Post pics! I'd love to see it.

If I remember correctly there's four connectors running down the left side of that amp (assuming I'm standing looking at it via the open trunk. I believe the connector is the 2nd up from the bottom. Review the PDF I attached in the original post. It's the only plug that has any of those color wires. The mic wires are in pairs right next to each other. Just cut the negative (or positive wire). Cut it far enough back so you have plenty of room to work to repair it if you ever need to. Honestly, I notice no interior noise level differences with the mics on or off. That system seems like a lot of trouble for very little benefit. You're going to notice your entire factory system sounds a lot better without all that out of phase ambient noise being pushed through it, too.

Best of luck!
 

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Thanks a bunch...Thought I had the worst ground ever....even though I took my time prepping it...
By the way on my 2016 it was the 2nd connector from the top...
TTD
 

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Nice set up!

was wondering where you ran the remote wire to from the new amp? I have a 2019 3.6L luxury and went with a full Rockford set up with the enclosed P3’s. Spliced the line out converter after the connector on the factory amp and cut the speaker return signal wires since mine doesn’t have the crank sensor wire. Lost park assist but oh well lol

Tested the set up with the remote wire at a constant 12v and everything worked, but I’m having problems finding 12v location to tap in to that's only when the car is on. On my 2009 cts 3.6L I tapped into the onstar power wire at the rear view mirror but I was hoping there was one I can tap into in the trunk for this go around.
 

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Nice setup. I used the same space with 2 10" Pioneer shallow mounts in a sealed fiberglass enclosure. I didn't bother finishing the fiberglass and left it naked which is just ugly. But since the whole thing is covered by the trunk liner anyway, I took the lazy way and left it. The extra mile on yours makes it much nicer to show off!
 

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Nice setup. I used the same space with 2 10" Pioneer shallow mounts in a sealed fiberglass enclosure. I didn't bother finishing the fiberglass and left it naked which is just ugly. But since the whole thing is covered by the trunk liner anyway, I took the lazy way and left it. The extra mile on yours makes it much nicer to show off!
What did you tap into for the amp remote wire?
 

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What did you tap into for the amp remote wire?
The amp I used doesn't need one if using speaker/high level inputs so I tapped into the rear deck subwoofer wiring (speaker level signal). The amp senses this and turns on automatically without the need for a switched circuit. If using low level preamp levels, I would have had to find a switched source which isn't easy on this car.
 
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