Headunit: 1 Subwoofer out RCA=Amp: 2 Subwoofer in RCA

[b0r 10+ year member]

I've searched high and low, this forum, that forum and all in between and have YET to find an actual definitive answer, so let's see if we can just get the correct answer out there and be done with it.

My $400+ dollar Headunit (New in 2011) has a black RCA line out that says "Subwoofer" on it. Obviously, RCA's come in pairs. My amps input has 2 RCA's. This is the "dilemma" or the question:

What is the 100% "book" way to make this connection? Do you put a Y splitter RCA into the headunit subwoofer out and run it as normal, or do you just connect ONE of the RCA's to both the headunit and the amp because the amp "knows it's mono anyway and only needs one"

The general consensus basically leaves 2 answers that make sense, but nothing definitive, and 1 answer that's just asinine.

1. Plug 1 RCA into the headunit and 1 into the amp. The amp handles the signal internally, and there is no need for a splitter or any other alterations.

2. Use a Y-splitter. The problem with this is you will split the signal and only get half the voltage which you can make up with the gain setting.

3. Buy a better headunit loser. One that has 2 outputs.

All 3 of these are what I have come across on multiple forums. The 3rd one is retarded, because my headunit was $400 and does not need to be upgraded to accomplish this connection.

Maybe someone's search/googleFU is better than mine, and I apologize in advance if this has been discussed in depth as I have not been able to find it.

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[Side Show 10+ year member]

buy a y-splitter or a nice DD amp, some of those only have a single rca input for the sub. (some other high-end amp do also)

 

[Jepalan]

Use a Y-Splitter. This is the *only* way to be 100% sure the mono HU output will work with *any* amp without knowing the make/model of amp you are using and how the output is wired (bridged or normal).

Your assertion about half voltage is WRONG. The HU RCA output is low impedance and the amp inputs are high impedance. (Very close to) the same voltage will be present at both amp inputs as would have been present at one input.

Most manufacturers will tell you in the manual the best way to connect a mono sub signal for that particular amp. It varies. But if in doubt, just use a Y-splitter.

I won't profess to be an absolute expert, but I have been an electronic design engineer for 25 years and a car audio enthusiast for longer than that. I am very open to hear other opinions on this one.

 

[b0r 10+ year member]

Use a Y-Splitter. This is the *only* way to be 100% sure the mono HU output will work with *any* amp without knowing the make/model of amp you are using and how the output is wired (bridged or normal).
Your assertion about half voltage is WRONG. The HU RCA output is low impedance and the amp inputs are high impedance. (Very close to) the same voltage will be present at both amp inputs as would have been present at one input.

Most manufacturers will tell you in the manual the best way to connect a mono sub signal for that particular amp. It varies. But if in doubt, just use a Y-splitter.

I won't profess to be an absolute expert, but I have been an electronic design engineer for 25 years and a car audio enthusiast for longer than that. I am very open to hear other opinions on this one.

Nice. Again, not *MY* assertion, the internets. Even on this forum, people say splitting it will cut your voltage and that you shouldn't. My amp is a Rockford Fosgate T1000-1BDCP and I have a Sony XAV-70BT 7 inch in dash.

 

[Side Show 10+ year member]

if you don't split it, your only sending half the signal to either the left side or right side, by splitting it you atleast have the full signal coming out of your headunit going into your inputs on your amp.

 

[Jepalan]

I looked at the amp's manual. It shows stereo inputs and says nothing about mono inputs. It looks like a basic 2-channel amp that is internally bridged to make it "monoblock". In order for a bridged output to work properly, there has to be a signal present on both L and R inputs. I highly recommend you use a Y-Splitter into this amp.

Y-SPLITTING DOES NOT CUT THE VOLTAGE IN HALF - read on, the example is typical:

Use this calculator to figure it out.

http://www.sengpielaudio.com/calcula...agedivider.htm

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Vin = Enter HU output voltage

Z1 = Enter HU output impedance

Z2 = Enter Amplifier input impedance

Zload = Enter Amplifier input impedance.

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Example.

Vin = 5 volts

Z1 = 200 ohms

Z2 = 20,000 ohms

Zload = Don't enter anything, default is 1 megaohm.

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The HU outputs 5V, but with amplifier connected, the loading effect of the amp causes

the voltage to be 4.95 volts.

If you connect another amp, lets say it also has 20,000 ohms input impedance,

the calculator says;

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Vout = 4.90 volts

With one amp, 4.95v

With two amps, 4.90v

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*What if*

Vin = 5 volts

Z1 = 2000 ohms

Z2 = 10,000 ohms

Zload = 10,000 ohms

With two amps, 4.54v

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