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Old 05-13-2013, 11:48 AM   #1
colorado_df
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Retrofitting Factory Sub in 2012 SE

Just sharing my bad luck so far. I picked up a used factory sub on e-bay and spliced in the speaker wires using the info I found here on the forum (thanks to the diligent work of so many of you!!).

The factory sub has two 2 ohm voice coils. I wired them in series for 4 ohms. Wired up a cheap Dual brand amp that had a low pass option, 12 volt trigger, speaker level inputs, gain dial, and dB boost switch. I tapped into the rear speaker wires and the 12 volt switched wire, I ran all my wiring to the back and hooked everything up and alas, as some others have found, the sound was crap. I used the speaker level inputs. I used the rear speaker wires since my front speakers also have the tweeters installed. I wasn't sure how the tweeters are wired and I didn't want to rob power from the front door speakers. The amp was triggering on and off as it should (it has a handy blue indicator light). When I used the high pass option and max gain, I could hear squawky voices coming through. Really couldn't hear anything on low pass.

I'll keep testing it. I might try some LOCs to see if the pre-amp inputs produce a better amped output.

One thing for those of you with the undersized spare, the dense foam platform isn't as thick as it is in the cars with full size spares. As such, your amp probably won't fit in a cutout area (the amp is too thick) and the top board will hump up. I'm going to mount mine in the vertical space beside the factory sub. Better for heat dissipation anyways.


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Old 05-13-2013, 11:36 PM   #2
colorado_df
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Well I checked the speaker voltage going into the amp and it's only .019 volts. Something tells me that's my problem. I tried using those tap connectors that straddle the wire. They must not be making good enough contact. Will have to try something more invasive. A couple photos of the project-

Rear speaker wires pulled to the left and single 12 volt accessory wired pulled to the right-
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Planned location of amp and stock location for sub-
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Modified platform installed-
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Underside view of platform cutout. I pulled back the top felt before cutting the board and then wrapped the felt under and used spray adhesive to hold it-
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Last edited by colorado_df; 05-17-2013 at 11:13 AM. Reason: Added picture descriptions
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Old 05-15-2013, 10:14 AM   #3
asting
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Hm cool write up so far.
Yeah a line out converter will likely help a bit.
How much did the stock sub run you?
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Old 05-15-2013, 03:56 PM   #4
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$124 delivered. Seemed like a fair price.

I'm going to attempt pulling off a rear door panel and take some speaker voltage measurements for reference and will report out if successful.
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Old 05-17-2013, 11:04 AM   #5
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I'm embarrassed to say I have a degree in EE, but it's been nearly 30 years since I've really used it and I've forgotten a lot. After researching audio electronics prinicples, I've remembered a few things. Measuring dc voltage at a speaker is only providing what's called "dc offset voltage". I kicked myself in the head (duh) because audio is multiple frequencies, hence ac voltage is what I needed to measure. Offset is essentially how far the sum of all your audio frequencies is shifted up or down from a perfect balance above and below an x-axis. Turns out, 20 mV, as I was measuring, is typical.

So...I pulled the rear door panel off and tried taking some measurements at the stock speaker. First, the dc offset at the door speaker was 20 mV. While not the measurement I really want, it does give me confidence that my wire taps are making good contact. I then took an ac voltage measurement and came up with zip. The reason is likely because the radio would be putting out a full range of interspersed frequencies and the meter would try to sum them into some sort of nonsense reading, and since the freqs are constantly changing in addition to the massive possible/simultaneous freqs between 20 and 20,000 hertz, my meter basically told me to f off. :) True voltage measurements can only be made by using a signal generator and a dummy load of 4 ohms (for a typical car speaker). Two things about that- a signal generator is most easily simulated by using a CD with various tones recorded on it that you play through the radio; and a dummy resistor is needed because speaker impedence changes according to freq. The standard measuring practice seems to be using a fixed resistance to benchmark systems.

Hope you audiphile novices find this info useful. My amp testing continues this weekend. Never give up, never surrender!

Last edited by colorado_df; 05-17-2013 at 11:07 AM. Reason: mistyped "single" for "signal"
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Old 05-18-2013, 01:09 AM   #6
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I am VERY interested in seeing how this goes.. Thanks for keeping us posted!
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Old 05-18-2013, 11:03 PM   #7
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Let me post the bottom line up front- the retro fit is working, sounds great, and I'm thinking the rest of the system may need upgraded now. I won't win any audio competitions, but dang! There's a lot of boom! I stuck with the cheapo 400 watt Dual amp from walmart after comparing it to an 800 watt Kenwood I picked up cheap on craigslist. Frankly, they were comparable given the dialing in capability of each. By the way, I called the local Ford dealer with the factory sub part number for a price- $309. I'm tickled that I paid $124 and it works great! I also stuffed the sub with poly-fill as I saw in another post. Can't say I can hear the diff.

Longer story-
Project finished and I found my simple mistake. Turns out all my problems were self induced. When a put the two voice coils in series inside the factory housing, I got the wire colors mixed up. There's a very subtle difference between the white/gray and (I guess) white/silver. After testing the amp with a subwoofer from my garage successfully, I continued digging into the factory sub and found my miswire. I swear it measured out at 4 ohms, but I must not have double checked my work. Anyhow, here's the wire coloring I tapped into and some more pics. By the way, I read somewhere a recommendation to remove the battery box to expose a place to pull a power wire through. I found the plastic plug inside the car (upper left of the brake pedal in an automatic) and fished through from inside the car and the probe appeared on the driver's side of the battery box. I was able to pull the power wire through without removing the battery. I ended up tucking the power down the driver's side under the door trim at the floor and the same for speaker wires and trigger on the pass side. Oh, and don't torque the nuts down too hard on the factory sub bolts. They're only spot welded in and I broke the vertical one off. I drilled through and screwed through the same spot and siliconed the screw from inside the wheel well.

Nice clean install in the end and I'm quite pleased with myself except for having about 12 hours in this when I should have 6 or less. Oh well! Hope this little story helps the next guy.
Wiring-
LR- Brown/yel
LR+ Brown/grn
RR- Brown/blue
RR+ Brown/wh
12 volt trigger Brown/red

Here are some more pics:
http://s1284.photobucket.com/user/co...2f18a.jpg.html
http://i1284.photobucket.com/albums/...pse1a6502c.jpg
http://i1284.photobucket.com/albums/...pse7d271b8.jpg
http://i1284.photobucket.com/albums/...ps9b84e01c.jpg
http://i1284.photobucket.com/albums/...psc9f99544.jpg

Last edited by colorado_df; 05-18-2013 at 11:05 PM. Reason: typo
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Old 05-18-2013, 11:16 PM   #8
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By the way, I don't know this for sure, but as I think about it, the advantage of using speaker level inputs to your amp is that you can adjust the base from your head unit instead of having to go back to the amp to adjust when you use preamp levels. I set my gain and filter on the amp to just under annoying, and then adjust my base on the head unit according to the song/style of music I'm playing. I think LOC's trim your speaker voltage down to a fixed level so you loose the functionality at your head unit. The bass may be cleaner, but you give up a convenient feature. Think about your old phono player on your home stereo. Preamp inputs into your receiver/amp. You don't make any level adjustments at the phono player, just at the amp. I think adding an amp to your radio and using preamp inputs is the same.

Last edited by colorado_df; 05-18-2013 at 11:19 PM. Reason: typo
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Old 09-19-2013, 12:51 PM   #9
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I'm going to attempt the same install this weekend. Has anyone else had good results? Any words of advice?
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Old 09-20-2013, 04:34 PM   #10
colorado_df
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Mine still works great, but the bass does wash out the mids and highs of the factory speakers in the doors. I have the separate factory tweeters in the front doors, too. I still plan to upgrade the door speakers one of these days. Good luck!!
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