left/right subwoofer output - AVS Forum
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post #1 of 12 Old 05-03-2014, 04:12 PM - Thread Starter
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I'm doing some rewiring of a car stereo and am a bit confused on the subwoofer output from my head unit.  It is a single cable that splits into left/right RCAs.  Does that mean it's actually a 2-channel subwoofer out?  I can't think what else left and right would indicate in this case.  The diagram shows the RCA patch cable connecting to left and right inputs on an external amp.

 

I was originally trying to tie it into the OEM subwoofer, bypassing the OEM amp, but wasn't having any luck figuring out how to step down from 2x RCA (which equals 4x speaker level) to 2x speaker inputs (+/-) for the sub.  I have it working with an aftermarket amp, with the RCA patch cable connected to the left right inputs and the output bridged, but I'm still hoping to get the OEM one working so I don't blow the sub immediately.  :)  I don't even know if I have that set up properly with the two inputs.

 

I suppose I could try connecting just one of the RCAs to a speaker level adapter...

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post #2 of 12 Old 05-03-2014, 04:24 PM - Thread Starter
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I've found a few things that suggest the left/right sub outputs can be combined into a single RCA cable via a y-adapter, and that would provide pretty much the same signal to the amp, albeit with possibly a bit less signal strength.  Normally, splitting signals is okay but combining them is bad, so that must mean that the left/right outputs are identical?  In which case, I could try connecting just the left one to the OEM amp's speaker level wires.

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post #3 of 12 Old 05-05-2014, 09:25 AM
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Your RCA outs are not going to run a speaker. They are low level outputs used for sending the audio signal to an amplifier. Do not attempt.

You either need to :

A. Connect the RCA's to the factory amplifier driving the subwoofer.

or

B. Use another amplifer that you have or purchase to drive the subwoofer. You use the head units RCA subwoofer outputs to supply signal to the amplifier.

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post #4 of 12 Old 05-05-2014, 10:18 AM - Thread Starter
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Sorry, I didn't word that clearly.  I wasn't attempting to connect the RCA outs to the sub directly, rather to connect them to either the OEM amp (line level inputs) or aftermarket amp (RCA inputs).

 

After having looked stuff over more, I think my problem with getting a single side of the left/right RCA outs to power up the OEM amp is that lots of the OEM harness was cut and there may be an interruption of the signal there.

 

I'm okay on how to connect the head unit to an amp.  :)  I'm just not/wasn't clear on what the left/right RCA outs indicate.  It seems like they're just a way of getting higher voltage out of a mono signal?

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post #5 of 12 Old 05-05-2014, 02:23 PM
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My bet is its just a mono signal split into two RCA lines. Home audio usually just has the one out put/input but car audio has not gotten that far. You can "Y" it into one or since most all aftermarket amps have a "left and right" input (even the monobloc ones) it will work fine.

Now the OEM amp may be a different story. You may just require a spare set of RCA cables and cut the ends off and splice into the OEM amp.

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post #6 of 12 Old 05-05-2014, 03:38 PM - Thread Starter
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Yeah, one of my next attempts was going to be running a RCA-to-speaker line from the sub-out to the OEM amp, but I'd still have to:  a) ensure that it's receiving power, and b) that I know which ones are it's input lines on the convoluted harness.

 

Home audio is my greater area of familiarity by far, so like you, I was thinking of it in terms of a mono signal.  I think if I were to "Y" it into a single line prior to the amp, all it would accomplish is dropping the voltage level, but I should (?) still be able to bridge the two channels for output to the sub.

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post #7 of 12 Old 05-05-2014, 03:50 PM
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I have never seen a drop in output voltage "Y"-ing together a left/right output. Only when splitting a single to two

Without knowing the make of the vehicle, you might want to look into what the OEM amp is receiving. is it receiving a balanced input? Or is it something else entirely like what... I think Merceses does. It's some bus network set up thing that can be a real PIA. I would start wit hthe old google searches or crutchfield. There may be an adapter. I know for the Suburban, I used the OEM amp to drive everything including the factory sub. I had changed the headunit and the front and rear signals from the head unit were full range. I used the head unit sub out to feed another amplifier driving the subs in the back cargo area (first was for wife then son added to it.)

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post #8 of 12 Old 05-06-2014, 12:25 AM - Thread Starter
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I've never measured the voltage difference, just going on what I've read.  I think I see your point, though.  The dual signal increases voltage, so that increased voltage is still there if you "Y" them back together.

 

I've followed the DIY guides for the vehicle, so the wiring should be right.  That's why I think it's either a blown OEM amp (3 of the 5 speakers plus the fuse for an aftermarket amp were blown) or cut wiring harness causing the lack of signal.  I prefer the significant power increase of an aftermarket amp, but it would be nice to stick with the stock setup to keep everything hidden from the eye.

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post #9 of 12 Old 05-06-2014, 10:00 AM
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Well depending on how much power you are wanting to add, then there are several companies that make some very small easy to hide amplifiers. obviously, if you have your heart set on rocking 3 kilowatts.... Hiding becomes a bit more difficult.biggrin.gif

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post #10 of 12 Old 05-06-2014, 10:30 AM - Thread Starter
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I was looking at some of the Rockford Punch series amps for options that would fit in the stock location, but I just now pulled the OEM amp out, figuring it would be easiest to use its mounting holes to shape a board to mount my aftermarket amp to, rather than trying to pigeon hole something into the rear deck holes available.  There should be plenty of room if I go that route.

 

In pulling out the OEM amp, I saw on the label that it's designed for 1 ohm loads.  That explains why the guys at the car stereo shop that helped troubleshoot a few things were thinking the sub might be dead, reading such low resistance.  My aftermarket amp is rated for 2 ohm into two channels, 4 ohm bridged, so that could be a problem.  Does that force the amp to work too hard?  (I have the gain very low, since it exceeds the OEM sub's power by 2-3x.)  I may need to drop an aftermarket sub in to match the amp's range...

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post #11 of 12 Old 05-06-2014, 12:38 PM
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That DCR of the OEM sub might cause you or rather the aftermarket amp some problems. What is the resistance of the OEM sub? Instead of bridging the aftermarket amp to a mono configuration, try it stereo just connecting one channel to the OEM sub. Whilethe DCR of the sub may be ~1 ohm, there should be some rise. And the amp you have can tolerate a 2 ohm load running stereo. Plus that may not overpower the OEM sub so badly.

It would let you better determine whether the OEM sub is workable.

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post #12 of 12 Old 05-06-2014, 01:37 PM - Thread Starter
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That's exactly what I was thinking after my last post, just haven't had a chance yet to reconfigure things.  That should extend the life of both the aftermarket amp and the OEM sub, and I can always go back to bridged mode later when the OEM sub kicks the bucket.

 

The picture I've seen of the OEM sub out of the car (too tight of a space to see it when installed) is stamped with 1 ohm on the bottom of the magnet, so that matches the OEM amp.

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