# What is the purpose of rca two inputs on sub



## Guest

Hi: A bit of a dumb question, but why is there two rca inputs (left and right) on my sub ( 20-39 PC+)? I only use one of them (left) coming from a single sub-out on my a/v receiver! Do some receivers have left and right sub-outs? Why do I need two inputs for a single-driver sub? Give me some scenarios where I would use both rca inputs, also, how would I use the two rca outputs(left and right) please! Thanks, Keith:dunno:


----------



## brucek

> Do some receivers have left and right sub-outs?


Yes, certainly older analog systems.



> Why do I need two inputs for a single-driver sub?


You don't. Usually the left and right have one of them designated LFE for the situation when only one is used (which is most often the case). Some people like to use a Y splitter and feed the single signal to both inputs.



> Give me some scenarios where I would use both rca inputs


You have an older analog preamp that has left and right out and you want to split it and send it to a subwoofer besides sending it to a power amp.



> how would I use the two rca outputs(left and right)


Usually older analog systems that didn't have bass management on-board, would use the filtering in the sub itself to split the low and high frequencies. The outputs containing frequencies above the crossover set in the sub would be sent to a power amplifier

brucek


----------



## Guest

Thanks brucek..... again! Huck


----------



## lienly

tks Bruce.
this certainly clear my head for dual L/R jacks on sub but only 1 sub out on AV amp.:sweat: 
so just plug either L or R is enough.

will plug both jacks get better performance?


----------



## brucek

> will plug both jacks get better performance?


Usually, one is designated as the preference to use for a single LFE input, but it still leaves the other open circuit. Hopefully they've loaded the empty jack so as not to pick up noise. Personally, I'd use the splitter method and use both inputs even if I had a single mono input..

brucek


----------



## Guest

It is said using two L/R with a splitter wil give you a 3db lift ....

read it in my B&W sub manual


----------



## salvasol

lienly said:


> ....will plug both jacks get better performance?


Hi there!!! ..... I also had the same question, I read the manual for my Velodyne VRP 1000 online and it says to use a "Y cable"; but my Infinity TSS750 didn't said anything about it, so I send an email to Infinity's customer service asking if I can use a "Y" to connect L and R input from a single output from receiver :dizzy: ... and their answer was the following:

David,
Good evening and thank you for your inquiry. I can understand
the concern in this matter. If your receiver provides a single RCA
Subwoofer output, there are a few ways you can connect the subwoofer.
You can run a single RCA cable between the Sub output of the receiver
and the wither the left or right input on the subwoofer. Or, you can
connect the output of your receiver to the "Y" connector, then connect
this to the Left and Right inputs on the subwoofer. There is no
"better" way to connect this, as either way should work, with the one
that sounds best the one you should choose. 

I hope this helps.

SO, I'm using the "Y cable" :T :T :yes: :yes:


----------



## Guest

I had asked the fellas at SVS this before i bought my sub if i needed a y connector and they told me that I only needed to connect one of them because they are sumed internally immediately.


----------



## lienly

really? 3dB up if connect both L/R on sub....:raped: 
has anyone measured if it's true?:huh: 
remember SVS says just either L or R and no difference.:coocoo: 



doreytp said:


> It is said using two L/R with a splitter wil give you a 3db lift ....
> 
> read it in my B&W sub manual


----------



## Otto

lienly said:


> really? 3dB up if connect both L/R on sub....:raped:
> has anyone measured if it's true?:huh:
> remember SVS says just either L or R and no difference.:coocoo:


If so, I think this would be akin to turning up your receiver's sub output by 3 dB. I don't think you're actually getting any more power or headroom out of the amp.


----------



## Hakka

doreytp said:


> It is said using two L/R with a splitter wil give you a 3db lift ....
> 
> read it in my B&W sub manual


It depends on the sub, some give you a lift when you connect 2 rca's(B&W) some dont(SVS). As Otto said you can't get any more power or headroom, it just changes the input level by 3db, so now your sub will clip with the volume knob at a lower position than it was before.


----------



## Ed Mullen

Two RCA inputs can also be used to sum the L/R stereo outputs in a 2.1application where the customer only wants to use one subwoofer.

Adding a Y splitter doubles the drive voltage at the line level inputs. This results in a 3 dB increase in SPL since the inputs are internally summed. 

A Y splitter obviously can't increase the overall performance of the subwoofer - in this sense it is no different than bumping the sub level 3 dB in the AVR or pre/pro.


----------



## blued888

Ed Mullen said:


> Two RCA inputs can also be used to sum the L/R stereo outputs in a 2.1application where the customer only wants to use one subwoofer.
> 
> Adding a Y splitter doubles the drive voltage at the line level inputs. This results in a 3 dB increase in SPL since the inputs are internally summed.
> 
> A Y splitter obviously can't increase the overall performance of the subwoofer - in this sense it is no different than bumping the sub level 3 dB in the AVR or pre/pro.


This still depends on the construction of the subwoofer, right? Or *all* subwoofers have a 3dB increase if both line level inputs are used?


----------



## Ed Mullen

blued888 said:


> This still depends on the construction of the subwoofer, right? Or *all* subwoofers have a 3dB increase if both line level inputs are used?


It does depend on the construction of the amp and I was unclear/incorrect above and apologize for that. 

If the inputs are summed internally (and SVS are constructed this way), there is a 6 dB gain due to a doubling of the voltage.

I have seen other amps which only provide a 3 dB gain with a Y splitter, indicating there is not a voltage summer circuit.


----------



## aNomad

If the inputs are summed into an op-amp inverting input, the extra gain will be 6db. If they are summed passively, the gain can be ANY amount less than 6db, depending on the construction.

There is no benefit to splitting the signal into both inputs, unless you don't have enough gain using only one input. Adding extra items like Y connectors only add to unreliability.


----------



## salvasol

aNomad said:


> Adding extra items like Y connectors only add to unreliability.


Can you explain a little more???

What about if the manual suggest that you don't need but you can use a "Y" to improve/gain output??? :huh:


----------



## Ed Mullen

salvasol said:


> Can you explain a little more???
> 
> What about if the manual suggest that you don't need but you can use a "Y" to improve/gain output??? :huh:


If your auto-on circuit is sleepy, a Y splitter will wake it up earlier, but you can accomplish the same thing by upping the subwoofer channel level. 

I've found Y splitters to be utterly relibale when I've actually used them for test purposes, but either way (splitter or sub channel increase), you need to reduce the subwoofer amp gain in order to keep the overall subwoofer calibration level the same. Don't use a splitter to increase the overall subwoofer SPL.


----------



## Chilepastor

I know this is an old thread, but I'm adding a comment for any others who find this thread with search engine.

I've read all the previous comments and I don't see anyone with this use/info:

I have a sub (Infinity iL100) with left & right input & output as well as speaker cable in & out.

Briefly I used my sub as my amp for a 2.1 config! I used a y-cable connecting the headphone out of my iPod to the left & right rca inputs on the subwoofer. From the sub I ran two Klipsch quintet satellites.

I found a good baseline volume setting for the sub's volume knob, and used the iPod volume control to manage listening levels.

Even though the line inputs may be combined for the sub, I found it was still able to separate the left and right passed on to the satellite speakers. Not sure this would be the case for all brands/models.

Not ideal, but it worked, and I used this arrangement for 6 months!

I think this is more or less how many computer 2.1 speaker systems work.

Who knows, maybe someone out there will also take advantage of this option. Wouldn't have been practical without the volume control on the iPod.


----------

