[GR86Talk]

Disclaimer/warning: Always have negative terminal of battery disconnected at all times when working on electrical.

Special thanks to @removedonut for his inspiration and replies to my questions about his install (his is JBL).

Due to the limited space in the truck and lack of real spare tire, I added a spare tire amplified subwoofer. I ended up going with a Rockville Rockghost 8” amplifier subwoofer. I chose this one because it is lower cost, had all the wiring included, and it has a ported design. The SNR is >90db too, which is higher than the JBL, which means more volume per watt. Rockville has a 90 day return policy and free shipping. It shipped fast too! It doesn’t hit low like a sealed 1000 watt 12”, but it definitely is worth the $185 (includes wiring). I have a few tips and suggestions for anyone installing one.

Rockville Rockghost:

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The base doesn’t have an amp and in order to get input, you have to tap the front speakers. While you can do this from the kick panels, it is cleaner and easier to use a harness at the head unit. You don’t cut any factory wiring and you get a remote turn on from the head unit. Thia is what I got. I modified the one end that goes into the head unit. The seller has instructions. You basically shave/sand off 1/8” hump near rear of connector. I neglected to take a photo as I did it last minute. I have arrows showing area. Maybe I could have pushed harder but it worked for me after removing some of the plastic humps. I set the pots on the converter to max. Originally I had them at the default of middle, but the input gain on the amp had to be set all the way up and still needed more. After changing the converter pots to max, all the way clockwise, I have the subwoofer gain at a little past halfway (1-2 o'clock). Having more input voltage going to the sub is probably better anyways as it can mute out noise.

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I used this video to remove the head unit. If you find the cables behind the head unit have no slack, they may be wedged under the metal round bar/frame. If that is the case, use a stickor something to free them.

I ran the power cable from the battery using the top terminal of the positive terminal (as this is the one OEMAudio+ showed in their video). I ran the power wire through the firewall using a factory hole that was plugged. This hole could easily fit an 8 gauge or possibly a 6 gauge, but mine was only 10 gauge. The firewall grommet they gave me fit right in. I added some electrical tape to thicken the cable to keep it snug in the grommet. You have to poke a hole through the sound deadening padding on inside of firewall too. I also made a cut on the positive cover to allow the cable to have room with cover on.

I ran the power cable down the passenger side in the actual plastic channel parallel to factory wires.

I ran remote turn on and low level RCA cables down driver side in the plastic channel parallel to factory wires.

I used wire wrap/conduit from Harbor Freight (1/4“ for power and 3/8” for RCA, remote turn on, and remote control cable) for all wires other than what was run in the plastic channels on side. To get to the trunk I followed the factory wire bundles on both sides all the way to the sub/spare tire area. This makes it super easy to route into the thin back trunk panel and between trunk foam inserts and into the spare tire area, bypassing interference with rear seats.

CONTINUED….

 

[GR86Talk]

For the ground, I used the strut bolt in the trunk. It is closest location and right next to a low channel I could feed it down to the sub. I added some copper to fill in a gap around bolt and sanded down the paint with a Dremel. I bought slightly larger 10ga eye terminals for ground and power that I got from Walmart. The ones that came with it were a little thinner and I needed 10ga barrel connectors to connect sub harness to power and ground 10ga cables. These all came in a pack for less than $4. These barrel connectors are hidden in the black wire wrap conduit.

I used a hacksaw to cut the mounting bolt to size. Basically screw it in until you hear it hit the shield under the car, back it off a few turns, measure distance between round black hole on top of sub and base of wing-nut. I cut off about 2.25”.

I put some rubber foam tape around the whole base of the sub. The sub sits at a slight angle and I don’t want extra vibration.

I also added some on car body at front and rear ends where the sub rests on. The side closest to the front has a little bump so you can be creative and put down a layer on each side of it then one strip across it all, making it even.

I even modified the factory storage foam block so that I have solid support in the trunk (in case I want to throw some bags of gravel in there lol). This was tedious but well worth it! I even cut out an area for the ported vent. It still sounds good with this in and I even have the tire repair kit in there!

The foam block bottom is cut out so you can pull it off, but I have it so you have to disconnect the sub harness first since I have the harness cables in small channels on the top side (look at photos). Just take your time and measure thrice and cut once. I used a serrated knife and a little hacksaw blade to do most of the modification. I used a nail in the center circle on bottom and attached string/marker with a measured radius to get the main cut roughly marked out. the top T section was left by measuring space between top of sub and top of other side foam blocks to the right and left of the center foam block. It didn’t cut too deep when cutting the center out, giving me extra material to take off a little at a time. Take your time so you don’t damage the T foam. If you do it right, the whole thing will still be one piece. Use a yard stick/flat edge laying on the right and left foam locks and measure up from the top of the installed sub at front and rear of sub top to get how much space should be kept on the T. The foam T is not the same hight at front and back, as the sub is at a 10 degree angle as the sub doesn’t sit straight. If you take a little off at a time, you will get there. Just shave off 1/8 inch at a time. If you do it right it will fit like a glove on top and let the trunk liner lay perfectly flat. Worst case is you mess up and have to pay $75 for a new foam spare wheel insert.

For the remote control, I have gain a little past halfway (1 o’cloc) with line converter at max, bass boost (45Hz fixed) at about 9db (3/4), and crossover at about 70-80Hz (1/4 the way up from min). I also have phase at 180 as it seems to produce cleanest sound (cuts down overlap).

 

[GR86Talk]

If you have any questions, please ask. Drop a like if you want more posts like this.

PS. This is a base but I updated my door sills to the premium ones as you may have noticed in the photos.

 

[Karlosak]

Very clean installation with even room to spare, the Rockville sub is not that big. Thanks for another great set of instructions @GR86Talk ! How is the sound? I'm not a bass head myself, I just need to feel the bottom end of the music with nice progression to the upper lows, does it fill that role nicely?

 

[GR86Talk]

Very clean installation with even room to spare, the Rockville sub is not that big. Thanks for another great set of instructions @GR86Talk ! How is the sound? I'm not a bass head myself, I just need to feel the bottom end of the music with nice progression to the upper lows, does it fill that role nicely?

It sounds great for $185 (includes all wiring too), and for fitting in wasted empty spare tire space. The trunk is so small, so I needed to save that limited space for cargo, so this is a great compromise. It is a donut 8” woofer. It has a subsonic filter at 20Hz, but anything under 30Hz is not very strong. Like I said, it doesn’t hit super low like a heavily amplified 12” would. I suspect the JBL spare tire sub may hit a tad bit lower but it is over twice the cost and that doesn’t include amp power, signal cables, fuse, etc! There is a remote control to make adjustments and you can fiddle with that in the listening position which is nice. The bass boost frequency is set at 45Hz and can add up to 12db. Overall I am very happy with it. I like bass and it does the job for such a small unit/woofer, but you won’t feel it in your chest or win competitions if that helps.

 

[Karlosak]

Thanks for the feedback! Looks like an easy and cheap upgrade

 

[GR86Talk]

Thanks for the feedback! Looks like an easy and cheap upgrade

Cheap, but I wouldn’t say easy. It is more time consuming than anything, as you have to remove a lot of panels and such, especially if you do the line out converter from the head unit and feed the cables like other factory cables. The foam block modification takes a lot of patience but it turned out great.

 

[Master Jedi]

Great write-up! good job.

 

[Ginge's 86]

Cheap, but I wouldn’t say easy. It is more time consuming than anything, as you have to remove a lot of panels and such, especially if you do the line out converter from the head unit and feed the cables like other factory cables. The foam block modification takes a lot of patience but it turned out great.

I have to know, i'm installing mine as we speak. How did you go about modifying the foam block? Did you do a cutout of the bottom of the block so the whole block can be pulled off the sub?

 

[GR86Talk]

I have to know, i'm installing mine as we speak. How did you go about modifying the foam block? Did you do a cutout of the bottom of the block so the whole block can be pulled off the sub?

Yes, the bottom is cut out so you can pull it off, but I have it so you have to disconnect the sub harness first since I have the harness cables in small channels on the top side (look at photos). Just take your time and measure thrice and cut once. Lol. I used a serrated knife and a little hacksaw blade to do most of the modification. I used a nail in the center circle on bottom and attached string/marker with a measured radius to get the main cut roughly marked out. the top T section was left by measuring space between top of sub and top of other side foam blocks to the right and left of the center foam block. It didn’t cut too deep when cutting the center out, giving me extra material to take off a little at a time. Take your time so you don’t damage the T foam. If you do it right, the whole thing will still be one piece. Use a yard stick/flat edge laying on the right and left foam locks and measure up from the top of the installed sub at front and rear of sub top to get how much space should be kept on the T. The foam T is not the same hight at front and back, as the sub is at a 10 degree angle as the sub doesn’t sit straight. If you take a little off at a time, you will get there. Just shave off 1/8 inch at a time. If you do it right it will fit like a glove on top and let the trunk liner lay perfectly flat. Worst case is you mess up and have to pay $75 for a new foam spare wheel insert. Good luck!

 

[Ginge's 86]

Yes, the bottom is cut out so you can pull it off, but I have it so you have to disconnect the sub harness first since I have the harness cables in small channels on the top side (look at photos). Just take your time and measure thrice and cut once. Lol. I used a serrated knife and a little hacksaw blade to do most of the modification. I used a nail in the center circle on bottom and attached string/marker with a measured radius to get the main cut roughly marked out. the top T section was left by measuring space between top of sub and top of other side foam blocks to the right and left of the center foam block. It didn’t cut too deep when cutting the center out, giving me extra material to take off a little at a time. Take your time so you don’t damage the T foam. If you do it right, the whole thing will still be one piece. Use a yard stick/flat edge laying on the right and left foam locks and measure up from the top of the installed sub at front and rear of sub top to get how much space should be kept on the T. The foam T is not the same hight at front and back, as the sub is at a 10 degree angle as the sub doesn’t sit straight. If you take a little off at a time, you will get there. Just shave off 1/8 inch at a time. If you do it right it will fit like a glove on top and let the trunk liner lay perfectly flat. Worst case is you mess up and have to pay $75 for a new foam spare wheel insert. Good luck!

This is going to be such a clean setup, thanks for the inspiration!

 

[Neptune86]

This is an awesome writeup! I'm definitely considering doing this along with the speaker upgrade you did in my base, along with possibly adding some sound deadening while in the doors/trunk.

 

[Wayward67]

Test fit is a success. Pretty sure the JBL and Cerwin Vega are rhe same unit

 

[Lucyt]

Quick question: how did you get the original firewall grommet out? I’m having a bit trouble getting mine out.

 

[Wayward67]

Quick question: how did you get the original firewall grommet out? I’m having a bit trouble getting mine out.

I drilled a new hole.

 

[Lucyt]

For the blue remote turn on wire, did you just connect it from the sub to the blue wire on the wiring harness or did you connect it straight from the sub to the head unit?

 

[GR86Talk]

For the blue remote turn on wire, did you just connect it from the sub to the blue wire on the wiring harness or did you connect it straight from the sub to the head unit?

I used the included blue turn on wire attached to the harness and attached it to the lead of the subwoofer harness. None of the car’s wiring was modified or spiced into.

 

[DirtyDustin]

Do you think one of these could fit in that space above the rear wheels in place of the rear speakers? I was considering a custom box but this would be much simpler. Thanks for both of your audio posts.

 

[Wayward67]

An 8/6.5 inch sub or the spare tire kit?

You could definitely put small subs in that spot with some modification. But it would require a custom box and some cutting.

 

[GR86Talk]

Do you think one of these could fit in that space above the rear wheels in place of the rear speakers? I was considering a custom box but this would be much simpler. Thanks for both of your audio posts.

Nope, not even close. There is actually not a lot of space in there. Not only does it lack space, you have to have this sub mounted tight against the body for good performance and limit rattle/vibration. OEM Audio Plus has some kit for a sub that fits on one side of the trunk. It is kind of pricey. Best location with limited hassle and space savings is the spare wheel well.