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2019 Forester Limited CVT
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Discussion Starter · #1 ·
12" JL Audio subwoofer install in a custom built sealed enclosure under cargo panel!

It's been a while since being active here, but I'm excited to share with the group my custom subwoofer installation! I'm an audiophile guy, and installed aftermarket speakers and a 6 channel AudioControl amp in my 2019 Limited as soon as I bought the car. I've been very happy with the setup, but I don't get good bass. Since the pandemic I've been driving much more than before, between upstate and the city, and I decided to add a subwoofer to make my listening more enjoyable :)

I spent a lot of time figuring out how to do this - I wanted high quality bass response, which needs a good size speaker in an enclosure with some volume, but I didn't want a box taking up valuable cargo space. So using the recommendation of the audio shop that installed my system - who said to put the sub sitting on the spare tire under the cargo panel; and with TONS of design help from experts on the DIYMA forum, I put together an enclosure that fits really well and is large enough to hold a JL Audio 12-TW3 D4. I got an AudioControl LC1.800 monoblock amp to power it.

And WOW I am thrilled with the bass! I was grinning from ear to ear on my first 3 hour drive, cranking up some tunes (probably louder than I should). Here's pics I took putting it together. It's an odd shape: a shallow trapezoid (so that the top panel becomes level), with a cutout extension on the bottom that sits in the well of the spare. This was needed for the speaker to fit and to give some additional volume. The speaker is also recessed quite a bit to allow for speaker movement without the risk of it getting too close to the grill.

This was totally a passion project of mine, something I can now check off my bucket list! Well...not quite yet check it off, cause now I realize that the sound coming out of the factory head unit is kinda crappy and I need to figure this out...but that is for another thread!
IMG_6485.jpg IMG_6491.jpg IMG_6498.jpg IMG_6505.jpg IMG_6510.jpg
 

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'14 Forester XT Touring
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657 Posts
Well done, it looks great.
Not sure why you didn't use MDF wood, but eh it does the job. Looks like you .75 cubic feet out of it right?
Hope to read your next thread on solving that audio problem.
 

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2019 Forester Limited CVT
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Discussion Starter · #5 · (Edited)
Where did you keep the spare?
Didn't lose the spare! The sub is sitting right on it. That's why the box is so shallow. I put a quick disconnect on the speaker wire in case I need to pull it out.
Not sure why you didn't use MDF wood, but eh it does the job. Looks like you .75 cubic feet out of it right?
Well from what I learned, even though baltic birch is not as dense as MDF the sound of the sub is not gonna be different. The birch is lighter and easier to deal with. Also my friend who cut the wood in his shop uses it all the time and basically threw it in for free. Yeah the volume is very close to .75 cuft, I added some polyfill as well which makes it seem a little bigger.
Hope to read your next thread on solving that audio problem.
What happened was in the process of tuning my audio I discovered the right side speakers connected to the head unit are polarity reversed (front out only). The speaker wiring is fine so I had no idea what was up with that. Turns out Subaru factory head units have a built in all pass filter on the fronts (not rears). I think the intention is to correct phase for the front passengers. But the result is a sound that is pretty processed. This is in addition to high pass filters to protect the OEM speakers. So the low end is seriously removed. Not great when adding a subwoofer!
 

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2005 Subaru Forester XT
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Nice job, very jealous. the 'sub' that comes stock on the 05 XT has blown on my forester and i am still working out the possible solutions. This looks good; making it removable is an attractive option, as i sometimes use it for carrying a lot of stuff.
 

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2019 Subaru Forester Limited CVT
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64 Posts
I was thinking about doing something like what you did but I ended up taking the easy way out and got a spare tire sub. It sounds pretty good but I really, reeeely miss that sealed box sound. It's kind of boomy and loose sounding. I had to add an additional adjustable crossover to it to make it sound a little better.
PXL_20210419_193608629.jpg
That's interesting that the polarity was reversed on your front speakers. Mine was correct on my Forester. I wonder what's up with that? My rear speakers are also crossed over pretty sharply. No bass at all. I found a way around that and now the new rear spks. play full range.
I believe the rear speakers are crossed over for the potential of the Rockford fosgate upgrade so you don't shred those fragile factory paper cones to bits! If that's not the reason I have no idea why Subaru would do that.
Very nice work on that box! I bet with those awesome audio control amps your system sounds amazing!
 

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OuchDamn, Another options to the "spare tire subwoofer" you have there is to do a "sonotube" subwoofer box. The cardboard tubes come in all sizes and you can easily fit an 8 and even some 10s into a lot of spare tires, giving you that "sealed box" sound you want. FYI!
 

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Discussion Starter · #10 ·
@OuchDamn,
Yeah I was considering the CV at first, but was quickly talked out of it by my installer friend :) He said I would not be too happy.

As for the reversed polarity - that's very interesting that yours is correct. What did you use to check, did you do a speaker pop test? I'm running a speaker pop file and checking + or - results on my AudioControl app.
 

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2019 Subaru Forester Limited CVT
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@citysoundman

I have a very old realistic polarity tester from radio shack. It's about 35 years old lol! Still works great though. I checked all four at the doors and they were correct. The dash speakers were correct also. I was trying to double check and see if the wiring diagrams I downloaded were accurate to my model Forester. That's really puzzling about your polarity. I wonder what happened and where in the harness/wiring cluster your polarity swapped?
The CV sub isn't bad. It does make a surprising amount of bass for what it is. I'm not trying to bash on it too hard. It sounds just like a ported/slotted subwoofer enclosure. Kind of loose and boomy. I prefer either sealed boxes or ones with passive radiators.
I never imagined actually building a small box on top of the spare tire. That's seriously genius. You literally get the best of both worlds. A sealed box plus your cargo space!
Curious what are you planning on doing with the hole you cut in the cargo liner panel?
 

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2019 Forester Limited CVT
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Discussion Starter · #12 ·
The cut out in the panel is basically my speaker hole. I have a protective grill on the sub that comes up flush with the panel, and I added that fabric to keep out dust and stuff.

I forgot to mention - even though these front speakers on the right side show negative polarity, they sound in phase. This is what's perplexing. I did some very careful listening to be sure. When I reverse the speaker wiring to give me a positive phase test result, the sound is out of phase. This leads me to believe that something like an all pass filter on the fronts, which was posted by one of the top DIYMA guys (I'm not at all familiar with these filters) may be the cause. At first I thought it was a wiring problem due to my installation (tapping in to the stock head unit to send signal to my amp). And maybe I do have a wiring issue, I'm just not sure what's going on.
 

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2019 Subaru Forester Limited CVT
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The head unit certainly leaves a whole lot to be desired. It's pretty laggy and I agree the sound isn't that great. Unfortunately it costs so much right now to replace it with the price of a decent new head unit plus a maestro control device It's out of budget for me for the time being.
I saw somewhere on a different forum where somebody replaced the head unit with a really interesting looking one. Never heard of the brand name before. I'm going to try to dig up a picture of it. Here it is.
subaru_xv_android_headunit__entertainment_system_1572075421_7c3a630b_progressive.jpg
Here's a video of it working. Seems kind of cool.
 

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2019 Subaru Forester Limited CVT
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64 Posts
Kicker makes a device that removes the phase shift of an all-pass filter if you were interested.
 

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60 Posts
Discussion Starter · #15 ·
Wow that's a seriously large screen!
Thanks so much for the Kicker info, that may be just the ticket, will definitely look into it (y)
 

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Discussion Starter · #17 ·
Kicker makes a device that removes the phase shift of an all-pass filter if you were interested.
Just ordered the Keyloc! I think this is going to work... :)
 

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2019 Subaru Forester Limited CVT
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I sure hope it does! I spent a chunk of the afternoon learning about all pass filters out of curiosity. I read the other post on the other forum. It is a very confusing topic. Then I watched a couple of YouTube videos with side-by-side comparisons and it made a little more sense. That's where I learned about the keyloc. I'm curious why my polarity checker passed the test but it is old and it may be confused with a 90° phase shift on some frequencies. I really wish automakers would just leave that garbage out of their head units. Since all radios now are just basically computers we should be able to select what we want and what we don't.
I hope more familiar electronics makers decide to manufacture a full panel head unit like the one I showed you earlier. I would definitely upgrade to a full screen unit if it was a good brand name who made it. I researched a couple of them and was leery of the weird brand names and that you could only order them from Alibaba.
I really hope that keyloc works for you!
 

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Discussion Starter · #19 ·
I'm with you on this, it's incredibly difficult to grasp - maybe working with the filters directly makes it sink in.
I was also wondering why we both don't get the same polarity results, and the big difference is I have the AudioControl amp. Pretty sure you have no external amp? So my signal is boosted or more present or something. And yeah I'm also not comfortable going with an off brand like that one.
I'll let you know how things go once I get it installed, thanks so much for you help!
 
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