What is the purpose of rca two inputs on sub - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 18 Old 04-26-07, 06:03 AM
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Re: What is the purpose of rca two inputs on sub

Quote:
doreytp wrote: View Post
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.
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post #12 of 18 Old 04-29-07, 08:01 AM
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Re: What is the purpose of rca two inputs on sub

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.

Ed Mullen
Director - Technology and Customer Service
SVS

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post #13 of 18 Old 02-23-09, 10:06 AM
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Re: What is the purpose of rca two inputs on sub

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Ed Mullen wrote: View Post
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?
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post #14 of 18 Old 02-23-09, 11:32 AM
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Re: What is the purpose of rca two inputs on sub

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blued888 wrote: View Post
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.

Ed Mullen
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SVS

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post #15 of 18 Old 02-23-09, 01:00 PM
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Re: What is the purpose of rca two inputs on sub

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.
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post #16 of 18 Old 02-23-09, 01:18 PM
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Re: What is the purpose of rca two inputs on sub

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aNomad wrote: View Post
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???
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post #17 of 18 Old 02-23-09, 01:37 PM
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Re: What is the purpose of rca two inputs on sub

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salvasol wrote: View Post
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???
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.

Ed Mullen
Director - Technology and Customer Service
SVS

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post #18 of 18 Old 03-06-13, 04:11 PM
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Re: What is the purpose of rca two inputs on sub

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.
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