Is there any difference between a single RCA sub in and a L/R RCA sub in? - AVS Forum
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post #1 of 58 Old 09-18-2011, 09:28 PM - Thread Starter
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Just like the title says...is there a reason some subs have a single RCA port for the sub in and some subs have a L/R that require a splitter/Y-adapter?

Wouldnt it just be easier to have the single line in?
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post #2 of 58 Old 09-18-2011, 11:46 PM
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Use the single RCA when you have a "sub out" on your AVR, etc. There is no point whatsoever in y-cording a single sub out to L/R connectors - it is already done inside the AVR!

Use the L/R when there is not a dedicated "sub out" on your receiver.

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post #3 of 58 Old 09-19-2011, 07:26 AM
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Quote:
Originally Posted by Test123455 View Post
Just like the title says...is there a reason some subs have a single RCA port for the sub in and some subs have a L/R that require a splitter/Y-adapter?

Wouldnt it just be easier to have the single line in?
Subs differ in this regard in that some subs will have higher ouput with any given sub level setting if you use both the L & R inputs. Note though that the presence of L&R inputs doesn't mean you are supposed to use both.

Normally this makes no difference as the AVR will have ample output using only one output.

There are people who for one reason or another choose to use both the L&R inputs.
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post #4 of 58 Old 09-19-2011, 07:28 AM
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Supposedly using a Y-splitter will cause you sub to turn on quick over just one input, that's the theory at least. I've heard other people claim it gives up to a 6db boot depending on the sub, but I've verified none of this so I cannot speak for the accuracy. I planned on doing some totally unscientific testing once my A2-300 gets here.
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post #5 of 58 Old 09-19-2011, 07:55 AM
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Quote:
Originally Posted by gid View Post
Supposedly using a Y-splitter will cause you sub to turn on quick over just one input, that's the theory at least. I've heard other people claim it gives up to a 6db boot depending on the sub, but I've verified none of this so I cannot speak for the accuracy. I planned on doing some totally unscientific testing once my A2-300 gets here.
Even if it doubles the signal strength, when you recalibrate the sub to the system you're back to where you started.
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post #6 of 58 Old 09-19-2011, 11:27 AM
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Rythmik subs provide an extra 6 dB of gain if you use a Y and run both L and R inputs from the same source.

Other subs include an internal summer circuit that combine both signals but without the gain (effectively inserting an attenuator).

I have an older sub that "required" you to use just one input for sub/LFE, no idea why. It did sum the inputs if both were used so I suspect marketing mistranslated engineering.

If you are using the subwoofer output from your AVR chances are the quetion is moot; just run a single line from sub out to either input and call it a day.

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post #7 of 58 Old 09-19-2011, 11:30 AM - Thread Starter
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Just curious because the sub i was GOING to get had a L/R and the sub im getting now only has a single RCA in. I bought a Y-adapter for nothing, i guess.

...looks like im gonna have to get a second sub to put it to good use.
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post #8 of 58 Old 09-19-2011, 11:43 AM
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Quote:
Originally Posted by gid View Post

Supposedly using a Y-splitter will cause you sub to turn on quick over just one input, that's the theory at least. I've heard other people claim it gives up to a 6db boot depending on the sub, but I've verified none of this so I cannot speak for the accuracy. I planned on doing some totally unscientific testing once my A2-300 gets here.

Not sure about 6db but there was definitely a noticeable difference in output and accuracy with my Velo when i got a y-splitter.

I had it connected with just the left RCA in for several months after getting it and finally decided to try using a splitter, instantly after turning it back on there was a very noticeable increase in the tightness and i would estimate atleast a 2-3db output gain.


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post #9 of 58 Old 09-19-2011, 11:47 AM - Thread Starter
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so if theres only a single RCA input, that means it is already summed?
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post #10 of 58 Old 09-19-2011, 11:50 AM
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I cannot imagine why accuracy would increase. Or decrease, for that matter. However, the gain I can easily explain, as summing two identical voltages should provide 2x the voltage (6 dB in voltage).

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post #11 of 58 Old 09-19-2011, 12:27 PM
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Quote:
Originally Posted by Dasteru View Post

Not sure about 6db but there was definitely a noticeable difference in output and accuracy with my Velo when i got a y-splitter.

I had it connected with just the left RCA in for several months after getting it and finally decided to try using a splitter, instantly after turning it back on there was a very noticeable increase in the tightness and i would estimate atleast a 2-3db output gain.

This doesn't make any sense. You were probably fooled by the increase in output. Using both inputs can't possibly increase the sound quality of the subwoofer.

If what you are saying made any sense, everyone here would be using both inputs.........
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post #12 of 58 Old 09-19-2011, 12:57 PM
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Quote:
Originally Posted by Dasteru View Post

there was definitely a noticeable difference in [...] accuracy with my Velo when i got a y-splitter.



"Accuracy"?? Compared to what, exactly?!

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post #13 of 58 Old 09-19-2011, 01:02 PM
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Quote:
Originally Posted by DonH50 View Post

I cannot imagine why accuracy would increase. Or decrease, for that matter. However, the gain I can easily explain, as summing two identical voltages should provide 2x the voltage (6 dB in voltage).

Don-what you're saying about the dB increase makes sense to me, but I've also heard others here say that using a Y-splitter is basically the same as bumping up the gain level, and that you're really not increasing the overall dB. I've used a Y-splitter since day 1 with my Rythmik but have always been curious about this.

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post #14 of 58 Old 09-19-2011, 01:03 PM
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I have an unopened Lava LSP08 sitting at home and its manual mentions this exact issue. Check out page 2 of this PDF:

http://www.lavasubs.com/instruction_manual.pdf

It says that once you have the gain set to the max, you'll get an extra 3-6db by splitting the mono cable using a Y cable. Not sure what it does to accuracy and sound quality, though... I'll do some unscientific testing and report back.

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post #15 of 58 Old 09-19-2011, 01:03 PM - Thread Starter
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Quote:
Originally Posted by Test123455 View Post

so if theres only a single RCA input, that means it is already summed?

Anyone?
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post #16 of 58 Old 09-19-2011, 01:08 PM
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Quote:
Originally Posted by Test123455 View Post

so if theres only a single RCA input, that means it is already summed?

Is "WHAT" is already summed?!?!

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post #17 of 58 Old 09-19-2011, 01:15 PM
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Originally Posted by jackbuzz View Post

Even if it doubles the signal strength, when you recalibrate the sub to the system you're back to where you started.

What aren't "some" of you getting? Unless you don't have enough signal to match the sub output to system, adding a second line won't do anything but add a few db to output, at which point you now have to recalibrate/trim level back down.
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post #18 of 58 Old 09-19-2011, 01:20 PM - Thread Starter
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Quote:
Originally Posted by cavu View Post

Is "WHAT" is already summed?!?!

The signals. Is it just both of the RCA l/r ports combined?

Everyone went all crazy when some guy claimed his accuracy increased lol, I wasn't even wondering that since I know it's ridiculous, I just need some clarification on the question I originally asked. Thanks.
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post #19 of 58 Old 09-19-2011, 01:39 PM
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Quote:
Originally Posted by cavu View Post



"Accuracy"?? Compared to what, exactly?!

There was less residual after a note.


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post #20 of 58 Old 09-19-2011, 01:45 PM
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Quote:
Originally Posted by Test123455 View Post

so if theres only a single RCA input, that means it is already summed?

Well, let me try to decipher your incomprehensible question:
Quote:
so if theres only a single RCA input

As you are referring to an "INPUT", I will ASSUME you are referring to an input on the subwoofer. Subwoofers are MONO. They only provide a single sound source. An "input" on a subwoofer cannot guess what kind of signal it is being fed but, if you are hooking it up to a multichannel source, I am certain the designer of the subwoofer expected that you have already combined all of the necessary sources together when you plug something into its single input.
Quote:
that means it is already summed?

If you are referring to a single RCA "OUTPUT" on an AVR, yes - the multiple channels in the AVR are already summed together at the single output to the subwoofer (dependent on the bass management settings in the AVR).
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post #21 of 58 Old 09-19-2011, 01:47 PM
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Originally Posted by Dasteru View Post

There was less residual after a note.

And, if that were true, this would make it more accurate, how?

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post #22 of 58 Old 09-19-2011, 01:57 PM
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Originally Posted by cavu View Post

And, if that were true, this would make it more accurate, how?

Common sense will answer that question. If someone hits a drum do you feel it would be more accurate to hear the initial hit reverbing for several seconds after?

http://dictionary.reference.com/browse/accurate


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post #23 of 58 Old 09-19-2011, 02:48 PM
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Originally Posted by Dasteru View Post

If someone hits a drum do you feel it would be more accurate to hear the initial hit reverbing for several seconds after?

A drum does reverberate for a period of time. It doesn't emit a single, one-shot waveform. Whether or not the reverberation time you hear is "accurate" or not is wholly dependent on what exists in the original recording/sound source. You can't arbitrarily declare it accurate without specific knowledge of and comparison to the original.

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post #24 of 58 Old 09-19-2011, 02:55 PM
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Originally Posted by cavu View Post

A drum does reverberate for a period of time. It doesn't emit a single, one-shot waveform. Whether or not the reverberation time you hear is "accurate" or not is wholly dependent on what exists in the original recording/sound source. You can't arbitrarily declare it accurate without specific knowledge of and comparison to the original.

Maybe accurate wasn't exactly the right word then. It was tighter though, notes come to a stop alot faster.


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post #25 of 58 Old 09-19-2011, 08:18 PM
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Quote:
Originally Posted by holt7153 View Post

Don-what you're saying about the dB increase makes sense to me, but I've also heard others here say that using a Y-splitter is basically the same as bumping up the gain level, and that you're really not increasing the overall dB. I've used a Y-splitter since day 1 with my Rythmik but have always been curious about this.

It depends on how the summing is implemented, but all it can do is to increase the input (stage) signal level; it cannot increase the sub's total output if that is what you mean by "overall dB". For practical purposes it looks like a gain increase, but it probably* does not actually increase the gain of any single stage, it just doubles the input signal amplitude after the summing circuit.

HTH - Don

* There are circuits that would double the gain of the summing stage if both inputs are driven. I do not know what Brian (Rythmik), or anybody else, has actually implemented in the sub. Regardless, the output is not increased.

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post #26 of 58 Old 09-20-2011, 09:05 AM
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Quote:
Originally Posted by DonH50 View Post

It depends on how the summing is implemented, but all it can do is to increase the input (stage) signal level; it cannot increase the sub's total output if that is what you mean by "overall dB". For practical purposes it looks like a gain increase, but it probably* does not actually increase the gain of any single stage, it just doubles the input signal amplitude after the summing circuit.

HTH - Don

* There are circuits that would double the gain of the summing stage if both inputs are driven. I do not know what Brian (Rythmik), or anybody else, has actually implemented in the sub. Regardless, the output is not increased.

OK, thanks for clearing this up, Don.

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post #27 of 58 Old 09-20-2011, 09:32 AM
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Quote:
Originally Posted by Dasteru View Post

Maybe accurate wasn't exactly the right word then. It was tighter though, notes come to a stop alot faster.

This is an electrical impossibility as the output from each end of the Y connector carries exactly the same signal.
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post #28 of 58 Old 09-21-2011, 09:00 PM
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Here's my actual experience with this:

I have a receiver with a mono sub out (but it's not an LFE out). My sub is a Lava LSP08 which has LFE and R/L RCA jacks. When I connect the cable to just the left RCA jack, the sub is indeed quieter (leaving the gain knob alone) than when I split the cable into the right and left RCA jacks with a Y cable.

So there: at least in this instance, even though each half of the Y cable is carrying only half of the signal, the sub plays louder at the same gain setting when both channels are used.

Make of it what you will.

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post #29 of 58 Old 09-21-2011, 09:52 PM
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Quote:
Originally Posted by JBWIII View Post

even though each half of the Y cable is carrying only half of the signal, the sub plays louder at the same gain setting when both channels are used.

That's just a repeat of what others have said. The point is ... so what?!

If your sub output level was calibrated with one connection and you add another with the y-cord, the output level jumps 3dB "at the same gain".

Now, in order for you to maintain calibration, you have to turn the gain down by 3dB so that the sub output is the same as it was before you added the y-cord.

How are you ahead??!!

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post #30 of 58 Old 09-22-2011, 06:03 AM
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Quote:
Originally Posted by JBWIII View Post

Here's my actual experience with this:

I have a receiver with a mono sub out (but it's not an LFE out). My sub is a Lava LSP08 which has LFE and R/L RCA jacks. When I connect the cable to just the left RCA jack, the sub is indeed quieter (leaving the gain knob alone) than when I split the cable into the right and left RCA jacks with a Y cable.

So there: at least in this instance, even though each half of the Y cable is carrying only half of the signal, the sub plays louder at the same gain setting when both channels are used.

Make of it what you will.

Nothing unusual there. When you split the cable and plug into both the R and L RCA inputs, the signal being sent to the sub is increased. Hence the sub plays louder.

You get the same effect if you just turn up the volume knob on the sub.
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