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Adding a subwoofer amp...lc2i or speaker level inputs?

SVT-DADDY

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I have a 12 speaker Shaker system. My car is a 2015 Premium convertible.

I've upgraded my center speaker(Polk db3651 and subwoofer (Polk db840dvc) speakers. The car now sounds more like I expected it to when I bought it.

I'd like to push that little 8" Polk a little harder. While I can rebuild a motor, my understanding of car audio is on a 4th grade level. So I'd like to keep things as simple as possible.

My synopsis of my options is this:

Option one- Take signal from one of the rear speakers, and run it to an amp that has speaker level inputs. However I don't have a rear deck with 6x9's just waiting for me to tap into. It's my understanding that I can't use the signal going into the subwoofer amp because it's different? Can someone confirm this?

Option two- Connect the output of the existing amp to an LC2i and connect the LC2i to the amp. Then the amp to the speakers.

These are the amps I am considering if it makes any difference:

https://www.crutchfield.com/Product...eItems=01|575P300X2&compareItems=01|575R250X1

My question is what are the pros and cons of each option. Again I am not an audiophile, so please feel free to break is down is 4th grader terms.

Thanks!
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stang1971

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I used a PAC audio sni-15 and works perfect
 
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If it has speaker level inputs you don't need the LC2i. But your not just tapping one speaker. You need to tap both rear speakers. I did something similar and bought these wire adapters on Amazon. The picture is not exactly what I received. The connector actually had four wires. I just cut the two wires that weren't being used and attached the speaker level inputs.

The second pic is the RCA to speaker level input.
Screen Shot 2017-09-12 at 3.44.36 PM.png
Screen Shot 2017-09-12 at 3.43.40 PM.png
 

2016Gruv

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Why can't the signal to the OEM sub amp be used?

The Polk sub is rated at 90wpc at each coil, so the Rockford Fosgate Punch P300X2 would be a good fit. I can't say whether it will get noticeably louder without knowing the rating of the OEM amp. It takes double the power to get a 3dB increase in SPL. If the Rockford Fosgate amp has 2x the power of the OEM amp, you notice a slight increase in output and probably better handling of low frequency transients.
 

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If it has speaker level inputs you don't need the LC2i. But your not just tapping one speaker. You need to tap both rear speakers. I did something similar and bought these wire adapters on Amazon. The picture is not exactly what I received. The connector actually had four wires. I just cut the two wires that weren't being used and attached the speaker level inputs.

The second pic is the RCA to speaker level input.
Thanks that makes option one a bit easier!

Why can't the signal to the OEM sub amp be used?

The Polk sub is rated at 90wpc at each coil, so the Rockford Fosgate Punch P300X2 would be a good fit. I can't say whether it will get noticeably louder without knowing the rating of the OEM amp. It takes double the power to get a 3dB increase in SPL. If the Rockford Fosgate amp has 2x the power of the OEM amp, you notice a slight increase in output and probably better handling of low frequency transients.
My limited understanding leads me to believe that some formating is done in the oem amp.
 

kingofsting

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I replaced the OEM sub with an 8" kicker sub powered by the JL HX 300/1 amp. I cut the wiring from the OEM amp to the OEM sub, daisy-chained the JL amp using speaker wire to RCA adapters, and ran speaker wiring from the JL amp back to the kicker sub. To be honest, I'm not sure what if any effect keeping the OEM amp in the loop has. I do notice that the sub output increases/decreases using the factory Bass setting control
 

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I replaced the OEM sub with an 8" kicker sub powered by the JL HX 300/1 amp. I cut the wiring from the OEM amp to the OEM sub, daisy-chained the JL amp using speaker wire to RCA adapters, and ran speaker wiring from the JL amp back to the kicker sub. To be honest, I'm not sure what if any effect keeping the OEM amp in the loop has. I do notice that the sub output increases/decreases using the factory Bass setting control
Would you happen to know the part number for that 8" sub
 

c_me_pass_u

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I've upgraded my center speaker(Polk db3651 and subwoofer (Polk db840dvc) speakers.
I was looking up Polk db840dvc but results kept pointing to polk db842dvc would either work?..I wanna upgrade my 8" oem sub
 

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Here's my set up. I replaced the 6.5" rear deck speakers with Morel Tempo Ultra 602's, speaker level inputs to an LC2i and pre-amp inputs into a Zapco ST-2D amp. After some adjusting of the pre-amp out puts on the LC2i and a slight bump on the gain on the amp I now have a balanced sound system and the fader works as it should. I left room on the plexiglass plate to add another amp that will power a proper 8" sub by-passing the factory sub amp.
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IvaPADWwWgwuUtyP1P5lRTzJeXpuc8k8AiZDt6OMtBr2j5ijuGM-ftLUwsXF1hiBrKQQtYQvBLnH9sUbA=w1418-h1063-no.jpg
UoBrg6kAOnU1YoXkfaMBX_zsFac04fk9I0ZWowQA5m7AZc4O8Ip4xrCSfXOgQUDBlG8T2wYqF_qIn6e6w=w1418-h1063-no.jpg
 

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I used the speaker level RCA connectors as above.
i used a Rockford P300 amp and a RF P3D2-8 sub.
35380230020_9eccb6922b_c.jpg
20170411_152007 by chefjpd, on Flickr
 
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I was looking up Polk db840dvc but results kept pointing to polk db842dvc would either work?..I wanna upgrade my 8" oem sub
That will work, I think it's just the latest model.
 

Vicr

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Did you you get it done and how does it sound? Sub replacement is my next sound mod after getting my Sportline springs installed.
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