Is there any difference between a single RCA sub in and a L/R RCA sub in? - Page 2 - AVS Forum
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post #31 of 58 Old 09-22-2011, 06:07 AM
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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.

Let's use a car analogy. The max speed it is capable of is fixed. Using a Y-splitter is like pressing the throttle a bit harder; the car goes a bit faster but the max speed it is capable of doesn't change (as you said "you're really not increasing the overall dB").
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post #32 of 58 Old 09-22-2011, 08:51 AM
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Some subwoofers have Left and Right inputs (such as Velodyne) as not all systems have a LFE output. There are still many people who listen to music on two channel systems. Since there is no bass management in most two channel pre-amps, the Left and Right input on the subwoofer allow the use of the subwoofers crossover controls while maintaining stereo separation for the rest of the system.

When utilizing a subwoofer that has separate Left and Right inputs along with a home theater processor with a LFE output, a y-splitter is not necessarily needed. The subwoofer will sum the signal from the left and right inputs internally, however utilizing a Y-splitter will increase your signal input to the subwoofer. This occurs as you are connecting the inputs in parallel and the impedance is halved.

When in comes to audio there are seldom right and wrong answers.  The opinions of "experts" are just that, and should be used as a suggestion only.  Remember at the end of the day it is your money, your system, and you will need to listen to it.
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post #33 of 58 Old 09-22-2011, 09:17 AM
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Originally Posted by cavu View Post

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??!!

I didn't say that I was ahead. I just said that it was louder at the same gain setting, which I found peculiar.

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post #34 of 58 Old 09-22-2011, 09:41 AM - Thread Starter
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Is there a difference between a "sub out" and an LFE port (on the receiver)?
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post #35 of 58 Old 09-22-2011, 09:45 AM
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Quote:
Originally Posted by JBWIII View Post

I just said that it was louder at the same gain setting, which I found peculiar.

It's not peculiar because this:

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Originally Posted by JBWIII View Post

......even though each half of the Y cable is carrying only half of the signal................

.......is not correct. A Y-cable doesn't simply split the signal in half.

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post #36 of 58 Old 09-22-2011, 09:47 AM
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Quote:
Originally Posted by Test123455 View Post

Is there a difference between a "sub out" and an LFE port (on the receiver)?

Generally, no. 'Sub Out' is probably the more correct term as that output can carry, in addition to the LFE channel info, the rerouted bass from any channels that are being bass managed. But many manufacturers do incorrectly refer to it as the 'LFE' output.

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post #37 of 58 Old 09-22-2011, 09:51 AM
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Originally Posted by sivadselim View Post

It's not peculiar because this:

.......is not correct. A Y-cable doesn't simply split the signal in half.

Okay, I see now that this was my misconception. I've been reading up on the subject but just to make sure I understand: why not?

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post #38 of 58 Old 09-22-2011, 10:07 AM
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My RCA powered sub has L/R in. The owners manual says if your receiver has a single sub preout, connect to the left input. Some receivers have L/R preouts for dual subs. The manual says it sums both inputs internally for that type of receiver. I fell for the split adapter pitch, along with buying a unidirectional Monster sub cable. (It even has arrows on it )

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post #39 of 58 Old 09-22-2011, 10:09 AM
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Some subwoofers work better with a Y-splitter and some work better without.

When in comes to audio there are seldom right and wrong answers.  The opinions of "experts" are just that, and should be used as a suggestion only.  Remember at the end of the day it is your money, your system, and you will need to listen to it.
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post #40 of 58 Old 09-22-2011, 10:34 AM
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Quote:
Originally Posted by Rob Morse View Post

It is a discussion of the difference between a series and a parallel circuit.

IMHO, and no disrespect intended, if you are going to post over your company's signature, I sincerely recommend that you get one of your design engineers to screen your comments first.

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post #41 of 58 Old 09-22-2011, 10:43 AM
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Quote:
Originally Posted by Rob Morse View Post

Some subwoofers work better with a Y-splitter and some work better without.


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post #42 of 58 Old 09-22-2011, 11:23 AM
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Quote:
Originally Posted by JBWIII View Post

Okay, I see now that this was my misconception. I've been reading up on the subject but just to make sure I understand: why not?

The AVR looks essentially like a voltage source, so as long as the load (subwoofer input) is light (high impedance), the signal is not "split in half" -- the same signal is applied to both inputs. Twice the current is required from the AVR, but the current draw is small enough that there is essentially no change in voltage anywhere along the Y.

If you had a huge high-pressure water source (e.g. pressure tank the size of a house) and put a garden hose on it, then added another garden hose (a Y), both will be outputting the same flow because the source can provide more than enough pressure/flow for both hoses. Unlike my low-pressure well system, which burns me in the shower when my wifes flushes the toidy...

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post #43 of 58 Old 09-22-2011, 12:48 PM
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Originally Posted by DonH50 View Post

If you had a huge high-pressure water source (e.g. pressure tank the size of a house) and put a garden hose on it, then added another garden hose (a Y), both will be outputting the same flow because the source can provide more than enough pressure/flow for both hoses. Unlike my low-pressure well system, which burns me in the shower when my wifes flushes the toidy...

If you have two separate hoses coming out of the tank, then okay. You just doubled the flow capacity assuming there's sufficient pressure in the tank. But if you have a single hose, and then split that by putting a Y at the end, the two streams coming out of the Y together wouldn't fill a bucket any faster than the stream without the Y, would they?

I'm not sure that the water hose analogy really works because in that case it's the hose that's really the load; in the subwoofer case, it's the sub. Right?

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post #44 of 58 Old 09-22-2011, 06:02 PM
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True, I knew that was a bad analogy but it's hard to find good ones that are non-technical. Just think that the voltage is the same on the wires whether it is two or 20, so long as the source (AVR) has enough drive (low enough impedance) and/or loads are light enough (high enough impedance) so they don't drag down the source. Even that doesn't really matter for the Y cable itself as its impedance is in the mud compared to everything else. There is essentially no loss (or gain, at least as far as the cable is concerned) in adding a Y and driving two sub inputs in parallel.

Another analogy, also not without its problems, is an extension cord that you plug one or two lights into. Chances are they do not seem dimmer when you plug the second in (unless it's a small cord and very high wattage bulbs).

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post #45 of 58 Old 01-31-2013, 12:02 PM
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I just found this and am curious how this would be possible.

If you run a single LFE cable from the LFE output on your receiver, it is carrying a certain voltage and sound level. Splitting this signal into 2 would only cut the voltage / signal for each half of the Y adapter in half. So connecting both wouldn't magically double the input voltage or signal strength. Splitting 1 cable into 2 or just hooking up the single cable would deliver the same voltage / signal strength.

Even if the sub has a summation function where it adds the 2 together, I don't understand how it would make a difference? Let's say your receiver LFE is outputting 3 dB. If you hook this up to only 1 of the inputs on your sub, then the signal coming in is 3 dB. If you split it then each half of the Y adapter would be carrying 1.5 dB, so summing them together would bring them back to where you started, which is 3 dB.

Now if you were boosting the level of the signal coming into the sub then that would definitely result in it being louder. But I don't understand how splitting a signal in half makes your sub louder because the 2 inputs carry the same signal as if you hadn't split it in half in the first place?
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post #46 of 58 Old 01-31-2013, 12:48 PM
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Quote:
Originally Posted by bobby2478 View Post

I just found this and am curious how this would be possible.

If you run a single LFE cable from the LFE output on your receiver, it is carrying a certain voltage and sound level. Splitting this signal into 2 would only cut the voltage / signal for each half of the Y adapter in half. So connecting both wouldn't magically double the input voltage or signal strength. Splitting 1 cable into 2 or just hooking up the single cable would deliver the same voltage / signal strength.

Even if the sub has a summation function where it adds the 2 together, I don't understand how it would make a difference? Let's say your receiver LFE is outputting 3 dB. If you hook this up to only 1 of the inputs on your sub, then the signal coming in is 3 dB. If you split it then each half of the Y adapter would be carrying 1.5 dB, so summing them together would bring them back to where you started, which is 3 dB.

Now if you were boosting the level of the signal coming into the sub then that would definitely result in it being louder. But I don't understand how splitting a signal in half makes your sub louder because the 2 inputs carry the same signal as if you hadn't split it in half in the first place?

your opening assumption is incorrect. A parallel Y connection divides current (milliamps, here) not voltage. Voltage stays the same until you split among so many inputs that the input impedance gets so low the line out can't source anough milliamps to drive it. Given that we're likely talking about input impedances of 1000 ohms, it'll take a few splits . . . . So going into left and right then getting summed in the sub's little "mixer" does indeed increase the signal input level. Which makes zero difference as to how much you can get out of the sub, unless something is horribly misdesigned or malfunctioning.
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post #47 of 58 Old 06-18-2013, 07:58 PM
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I stumbled upon this tread today and it is truly great.

Does the term "ad nauseam" apply here? Probably, but educational anyway.

I have decided to not use a "Y" connector.

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post #48 of 58 Old 06-19-2013, 05:51 AM
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I stumbled upon this tread today and it is truly great.
Does the term "ad nauseam" apply here? Probably, but educational anyway.
Educational in that it shows what happens when those who have no level of expertise argue about what they do not understand, which is typical of the internet.
As to why to use both inputs on a sub amp, there are two reasons. One is if the source is not an AVR LFE, but rather a simple stereo source. If that's the case you may run an input from each output, typically the 'Tape Out' of a stereo receiver, and the low frequency information from each channel will be summed in the amp. With an LFE that's not necessary, as the AVR already does that.
The other reason is when the output level of the AVR is too low for the sub auto-on feature to detect. Some sub amps use a series configuration on the L/R inputs, and by using both with a 'Y' connector there is a 6dB boost in the input sensitivity, resulting from the doubling of the input voltage by series wiring the two input stages. Not all sub amps do this, some use a parallel input configuration, which does not result in any increase in sensitivity.

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post #49 of 58 Old 06-19-2013, 12:54 PM
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Originally Posted by gregavi View Post

Does the term "ad nauseam" apply here?

Yes, as in I am going to vomit. biggrin.gif

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post #50 of 58 Old 06-20-2013, 06:05 PM
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Using a Y adapter on most, but not all, subwoofers will increase the sound level from 3 to 6 db.

Aperion Audio Subwoofer Y Cable
"Why, oh why do you need a subwoofer Y cable? Most AV receivers come with a single sub output while most powered subwoofers come equipped with left & right inputs. By using a subwoofer Y cable for both the left and right subwoofer input, you can increase the bass output of your subwoofer by about 3dB."

HDMI cable for home theater and high-performace audio video cables.
"Attach this cable to an existing subwoofer cable to split the signal into two inputs.
Instantly improves your home theater or home audio experience.
Many subwoofers have increased clarity and bass response when both inputs are fed with a mono signal."

Wye Y Cable
"Typically, powered subwoofers will come equipped with either a single RCA connector, or double RCA connectors. However, both connections typically only require a mono (single) connection. Therefore, if you have both right and left inputs, a single cable connected to the "left" input will probably work just fine. However, you can get anywhere from a 3dB to 10 dB gain from your subwoofer by plugging into both stereo inputs. To plug into both inputs with a single cable, simply purchase our Y adapter Cable along with your subwoofer cable."

This is the science behind it:

There are two formulas used to find the db ratio between sound levels.

The first is used ONLY FOR POWER (watts): 10 . log (P2/P1). This formula is used when comparing Sound Intensity, measured in watts.

The second is used ONLY FOR VOLTAGES (and SPL levels): 20 . log (V2/V1). This formula is for voltage relationships and Sound Pressure Levels.

Using a Y adapter will add two correlated signals. When you sum two equal correlated audio signals (i.e., mono sources from sub output on the receiver/preamp), you will get twice the signal level (A1 + A2 = 2A1, since A1=A2).

Therefore , since V2 = 2 V1 and the log (2) = 0.30103, it follows

20 . log (2V1/V1) = 20 . log (2) = 6dB gain in voltage.

For power, it will be

10. log (2P1/P1) = 10 . log (2) = 3dB increase in power.

These are a few advantages (some real and some claimed) to using a Y adapter:
If you leave one of the RCA inputs open, dirt may get in there.
Using a Y adapter may add a few dbs to the subwoofers's output.
Some claim that the subwoofer works better at lower levels with the Y-cable.
The auto-off mode of some older subwoofers (e.g, Velodyne CH-12) may not come on at lower levels without the use of a Y-cable.
Some older subwoofers may actually need a Y cable because the left channel L may not default to mono signal.
Another benefit of using a Y-cable at the sub input jacks may be for reducing the amount of Radio Frequency (RF) and Electomagnetic (EM) interference, because you are not leaving the other input open and active. Subwoofers can be affected by annoying buzzes and hums.
Conclusion: Since Y adapters cost a few dollars and there is no significant risk involved, I would recommend using a Y adapter (2 male, 1 female) at the subwoofer's RCA input jacks. Make sure you use a good quality Y adapter that is shielded. Otherwise, you may hear hum and noises.

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post #51 of 58 Old 06-20-2013, 07:30 PM
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Quote:
Originally Posted by derrickdj1 View Post

Using a Y adapter on most, but not all, subwoofers will increase the sound level from 3 to 6 db.
Aperion Audio Subwoofer Y Cable
"Why, oh why do you need a subwoofer Y cable? Most AV receivers come with a single sub output while most powered subwoofers come equipped with left & right inputs. By using a subwoofer Y cable for both the left and right subwoofer input, you can increase the bass output of your subwoofer by about 3dB."
Only the input sensitivity will increase, by exactly 6 dB if the inputs are serial. There will be no increase in output, as that is determined by the amplifier output voltage swing, driver thermal capacity or driver excursion, whichever is the lowest, and none of those factors are altered by increasing the input sensitivity.
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post #52 of 58 Old 06-20-2013, 09:25 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Only the input sensitivity will increase, by exactly 6 dB if the inputs are serial. There will be no increase in output, as that is determined by the amplifier output voltage swing, driver thermal capacity or driver excursion, whichever is the lowest, and none of those factors are altered by increasing the input sensitivity.
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Agreed! I verified this by using a spl meter...with using the y I gained about 3db input gain, but the overall headroom or max output did not increase.

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post #53 of 58 Old 06-20-2013, 11:23 PM
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Originally Posted by basshead81 View Post

Quote:
Originally Posted by Bill Fitzmaurice View Post

Only the input sensitivity will increase, by exactly 6 dB if the inputs are serial. There will be no increase in output, as that is determined by the amplifier output voltage swing, driver thermal capacity or driver excursion, whichever is the lowest, and none of those factors are altered by increasing the input sensitivity.
Ready for a Pepto here as well. smile.gif

Agreed! I verified this by using a spl meter...with using the y I gained about 3db input gain, but the overall headroom or max output did not increase.

Tum...tum tum tum..Tums!! smile.gif




I gain 6 dB of signal level when I use a Y adapter on the inputs for all of my subwoofer equipment of various vintages. I do increase output level by the same amount as the input gain increase. I have to reduce the subwoofer gain structure by 6 dB to remain in calibration.

While you do gain input level and output level in equal amounts when you use a Y adapter, maximum output level does not change at all for the reasons that everyone has noted..
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post #54 of 58 Old 06-20-2013, 11:28 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by derrickdj1 View Post

Using a Y adapter on most, but not all, subwoofers will increase the sound level from 3 to 6 db.
Aperion Audio Subwoofer Y Cable
"Why, oh why do you need a subwoofer Y cable? Most AV receivers come with a single sub output while most powered subwoofers come equipped with left & right inputs. By using a subwoofer Y cable for both the left and right subwoofer input, you can increase the bass output of your subwoofer by about 3dB."
Only the input sensitivity will increase, by exactly 6 dB if the inputs are serial. There will be no increase in output, as that is determined by the amplifier output voltage swing, driver thermal capacity or driver excursion, whichever is the lowest, and none of those factors are altered by increasing the input sensitivity.




What the heck is a serial input circuit inside a subwoofer audio mixer? None of my equipment has a series circuit, and I do gain 6 dB with use of a Y adapter.
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post #55 of 58 Old 06-21-2013, 05:33 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post

What the heck is a serial input circuit inside a subwoofer audio mixer?
It's a variation of the same circuitry used to create a balanced line driver output, with one input pre inverted, the other non-inverted, with the two summed realizing a doubling of voltage for 6dB of gain. In this case rather than driving a line it drives the sub power amp.

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post #56 of 58 Old 06-21-2013, 04:52 PM
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I have used Y adapters with my powered sub since I have them lying around and they don't hurt anything. I paid $ 2.99 for them a while back. I agree that they will not increase the max output of a sub. In the end, you can choose to use them or just turn up the gain on the sub.

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post #57 of 58 Old 06-21-2013, 05:41 PM
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Quote:
Originally Posted by J_Palmer_Cass View Post

I gain 6 dB of signal level when I use a Y adapter on the inputs for all of my subwoofer equipment of various vintages. I do increase output level by the same amount as the input gain increase. I have to reduce the subwoofer gain structure by 6 dB to remain in calibration.

While you do gain input level and output level in equal amounts when you use a Y adapter, maximum output level does not change at all for the reasons that everyone has noted..

I this not what I posted or are you agreeing?
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post #58 of 58 Old 06-21-2013, 06:44 PM
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Quote:
Originally Posted by basshead81 View Post

I this not what I posted or are you agreeing?

He's just adding. To the nauseum. biggrin.gif

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
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