Basic Subwoofer Connection Question - AVS Forum
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post #1 of 38 Old 07-30-2012, 02:07 PM - Thread Starter
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My current subwoofer has only one input connecting to the subwoofer output of my avr. I am looking at replacing the sub with a better one and noticed that some have a single cable input (like my current one), some have R/L inputs, and some have both. The HT system is used for tv and movies only (BD/DVD, streamed etc). Which input type is recommended to be used for my setup and why?
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post #2 of 38 Old 07-30-2012, 02:14 PM
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It doesn't make much difference in most cases.

If your receiver only has one output for subwoofer and the subwoofer has L and R inputs, you will normally want to get an RCA Y-connector to put at the subwoofer end so the one cable connects to both of the inputs.
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post #3 of 38 Old 07-30-2012, 03:31 PM
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Quote:
Originally Posted by Otto Pylot View Post

Which input type is recommended to be used for my setup and why?
The receiver LFE output is summed to mono, that's why there's only one output jack. Subs with two inputs allow left/right input from a receiver that doesn't have an LFE output, the summing to mono is done in the sub amp. Since you have an LFE you don't need dual inputs.

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post #4 of 38 Old 07-30-2012, 06:39 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The receiver LFE output is summed to mono, that's why there's only one output jack. Subs with two inputs allow left/right input from a receiver that doesn't have an LFE output, the summing to mono is done in the sub amp. Since you have an LFE you don't need dual inputs.

Thanks. So if the sub has both types of inputs, just use the LFE. If it only has the R/L inputs, then use an RCA Y connector or just plug the receiver cable into either one because its mono and doesn't make a difference which channel it goes into?
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post #5 of 38 Old 07-30-2012, 07:16 PM
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Quote:
Originally Posted by Otto Pylot View Post

If it only has the R/L inputs, then use an RCA Y connector or just plug the receiver cable into either one because its mono and doesn't make a difference which channel it goes into?
If the source is an LFE output you only need to connect it to one of the inputs, it doesn't matter which. There's never a need to use a Y connector.

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post #6 of 38 Old 07-30-2012, 07:27 PM
 
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Get a "Y Splitter" at Amazon like one of these.

415HRUI1LSL._SL500_AA300_.jpg

Attach the two RCA mono plugs to the sub and via a 2 male RCA plug cable like this to the AVR's sub-out connector and you'll be good to go.

31YLKvWteuL._SL500_AA300_.jpg

Not to argue while arguing, Klipsch says with their products, there will be an increase in output level when covering both RCA inputs. confused.gif

I'm using a pair of these subs; Klipsch, SW12 II. See pg 8.

http://mediacdn.shopatron.com/media/mfg/3579/media_document/live_1/SWIIManual.pdf?1288057259

The Shack has a six foot audio Y-Cable so you don't have additional connections; part # 4202539, for $10.49 plus sales tax.

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post #7 of 38 Old 07-30-2012, 10:10 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

If the source is an LFE output you only need to connect it to one of the inputs, it doesn't matter which. There's never a need to use a Y connector.

Thanks. That's sort of what I thought but confirmation is always nice to have. Is it safe to assume that if a receiver has a single sub output, that output is an LFE (receiver docs aren't always clear on the specifics)?
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post #8 of 38 Old 07-31-2012, 06:30 AM
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Originally Posted by BeeMan458 View Post

Not to argue while arguing, Klipsch says with their products, there will be an increase in output level when covering both RCA inputs. confused.gif
There may be an increase in the input voltage sensitivity, depending on how the amp is configured. There will be no increase in the available amp power, as that's limited by the amp power supply, nor any increase in the speaker output, as that's limited by the driver excursion.
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Is it safe to assume that if a receiver has a single sub output, that output is an LFE (receiver docs aren't always clear on the specifics)?
Yes.

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post #9 of 38 Old 07-31-2012, 06:54 AM
 
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Quote:
Originally Posted by Bill Fitzmaurice View Post

There will be an increase in the input voltage sensitivity, 3dB to be exact. There will be no increase in the available amp power, as that's limited by the amp power supply, nor any increase in the speaker output, as that's limited by the driver excursion.
Yes.

My response was to your comment as there was no mention of Amps in your comment when you posted: "If the source is an LFE output you only need to connect it to one of the inputs, it doesn't matter which."

In this world, it's seems if you're not ready to split hairs, then you're asking to mess the sound quality of your system up. Boo, hoo, hoo. tongue.gif

It's hard with online communication as comments left out make things a bit confusing. Referencing your 3dB comment, that's why I found the "Y" splitter that I did as it eliminated a connection. My understanding is, each connection creates a 3dB drop and it's all cumulative in nature.

Me? My dilemmatic question? Other than the version I posted, I can't find a decent audio "Y" splitter that's not much more than the equivalent of a nine inch jumper cable so to have matched cables of similar lengths, I have to add in a connection which in my understanding, creates a 3dB drop in sensitivity.. I can't find 10' mono RCA mono cables either. I can find 6', 8', 12' and 15' but no 10's as I'm getting one heck of a pile of wire going on behind the entertainment center. Why a 10' "Y" splitter? Because the sub on the right needs a 10' connection where as the sub on the left can use a 6' connector. The sub on the right has an extra connection and is using two cables as to get 10's, I had to use an available stereo cable where as the sub on the left is connected by a contiguous six footer with no additional connectors. All this who-ha, not to mention then fear of magnetic interference building up with all that electricity going every which way, in all those cables behind the entertainment center.

Oh, the nuance of it all.

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post #10 of 38 Old 07-31-2012, 07:37 AM
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Ever notice how some members appear to be doing nothing more than sucking the oxygen out of as many threads as possible by creating issues where none exist?
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post #11 of 38 Old 07-31-2012, 08:27 AM
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The connections DO NOT cause a 3db drop. That is nonsense.

Putting in a Y connector causes the same signal to go to both subwoofer inputs and that causes the subwoofer amplifier to have 3 db more input than if you just connected it to a single input with no Y connection.

For the Y-connector, go to Amazon and search for the Tsunami RCA701-Y1 connector for $4.55. (1 female to 2 male).

Search for 3-METER RCA cables, which is the same as 10 feet.

Quote:
Originally Posted by BeeMan458 View Post

My response was to your comment as there was no mention of Amps in your comment when you posted: "If the source is an LFE output you only need to connect it to one of the inputs, it doesn't matter which."
In this world, it's seems if you're not ready to split hairs, then you're asking to mess the sound quality of your system up. Boo, hoo, hoo. tongue.gif
It's hard with online communication as comments left out make things a bit confusing. Referencing your 3dB comment, that's why I found the "Y" splitter that I did as it eliminated a connection. My understanding is, each connection creates a 3dB drop and it's all cumulative in nature.
Me? My dilemmatic question? Other than the version I posted, I can't find a decent audio "Y" splitter that's not much more than the equivalent of a nine inch jumper cable so to have matched cables of similar lengths, I have to add in a connection which in my understanding, creates a 3dB drop in sensitivity.. I can't find 10' mono RCA mono cables either. I can find 6', 8', 12' and 15' but no 10's as I'm getting one heck of a pile of wire going on behind the entertainment center. Why a 10' "Y" splitter? Because the sub on the right needs a 10' connection where as the sub on the left can use a 6' connector. The sub on the right has an extra connection and is using two cables as to get 10's, I had to use an available stereo cable where as the sub on the left is connected by a contiguous six footer with no additional connectors. All this who-ha, not to mention then fear of magnetic interference building up with all that electricity going every which way, in all those cables behind the entertainment center.
Oh, the nuance of it all.
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post #12 of 38 Old 07-31-2012, 10:25 AM
 
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Quote:
Originally Posted by commsysman View Post

The connections DO NOT cause a 3db drop. That is nonsense.;

I don't know if it's nonsense or not as that's what I was told by others; every additional connection gives a 3dB drop in signal strength.

---snip---

Quote:
Search for 3-METER RCA cables, which is the same as 10 feet.

I'll give the 3m search suggestion a try as I'm sure coming up short using 10' as a search requirement.


Addendum; I ended the angst by buying a pair of audio "Y" connectors and a pair of 15' shielded subwoofer cables. With two-day Prime shipping, they'll be here Thursday and I won't have to drive anywhere.

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post #13 of 38 Old 07-31-2012, 11:23 AM - Thread Starter
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Wow. I didn't think that my simple question would create such a discussion. My current sub has an LFE input only, to which I have a 10' shielded MediaBridge cable connected. If the new sub has only R/L RCA inputs, then the "Y" connector seems to be the way to go for the reason pointed out above. If the new sub and an LFE input, no brainer. I will only be using one sub as the current one (with speakers) will go to my daughter.
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post #14 of 38 Old 07-31-2012, 11:48 AM
 
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Say hi to San Jose as we left San Jose a couple years ago. Lived by Meridian and Hillsdale on Foxworthy for over thirty years. Great place to raise a family and enjoy your career. Lot's to do to keep the family entertained on the weekend while waiting for the next work week to begin. And when you retire, it's a great place to leave. smile.gif

I'm sure you'll be very happy with the shielded MediaBridge subwoofer cable/Audio "Y" splitter combination. It's a solid, good looking combination.
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Originally Posted by bfreedma View Post

Ever notice how some members appear to be doing nothing more than sucking the oxygen out of as many threads as possible by creating issues where none exist?

Ever notice how everywhere you go, there's always a "Debbie the Downer," waiting for a chance to put somebody down?
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post #16 of 38 Old 07-31-2012, 12:01 PM
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Quote:
Originally Posted by Otto Pylot View Post

If the new sub has only R/L RCA inputs, then the "Y" connector seems to be the way to go for the reason pointed out above. .
The reason pointed out above is fallacious. The only purpose for having two inputs is to sum to mono two outputs from a stereo source. Since an LFE output already sums to mono a Y connector is superfluous.

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post #17 of 38 Old 07-31-2012, 02:18 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The reason pointed out above is fallacious. The only purpose for having two inputs is to sum to mono two outputs from a stereo source. Since an LFE output already sums to mono a Y connector is superfluous.

Ok. That's where this got a little confusing with two opposing views. If the sub does not have an LFE input, then the LFE output from the receiver can go into either the R or L channel without any noticeable loss. The use of a "Y" connector in that case does not offer any real noticeable benefit over just using one of the inputs. However, if one was to play music from a stereo source then there may be some benefit to using the R/L inputs (but of course not using the LFE sub cable)?
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post #18 of 38 Old 07-31-2012, 02:29 PM
 
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Originally Posted by Otto Pylot View Post

Ok. That's where this got a little confusing with two opposing views. If the sub does not have an LFE input, then the LFE output from the receiver can go into either the R or L channel without any noticeable loss. The use of a "Y" connector in that case does not offer any real noticeable benefit over just using one of the inputs. However, if one was to play music from a stereo source then there may be some benefit to using the R/L inputs (but of course not using the LFE sub cable)?

And then to mess up the salad, Klipsch subs have both style connectors so if your receiver doesn't have a sub-out you can use the speaker connects but advises using both L/R sub-in if your receiver has a mono sub out. So you could read for yourself regarding what I was sharing, I posted a link to the Klipsch site with the page number for ease of locating the information then you can make up your own mind as to what's the best route to go.

In the end, if it don't matter, then it don't matter.
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post #19 of 38 Old 07-31-2012, 03:20 PM
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Quote:
Originally Posted by Otto Pylot View Post

Ok. That's where this got a little confusing with two opposing views. If the sub does not have an LFE input, then the LFE output from the receiver can go into either the R or L channel without any noticeable loss. The use of a "Y" connector in that case does not offer any real noticeable benefit over just using one of the inputs. However, if one was to play music from a stereo source then there may be some benefit to using the R/L inputs (but of course not using the LFE sub cable)?

Bill is giving you very solid and accurate advice. Don't let the attempts to confuse the issue make it more complicated than what he's suggesting.

The only common reason to consider a "Y" cable on the LFE input would be if you use a sleep mode on your sub and the signal from the AVR isn't strong enough to "wake" it. Sometimes the extra 3db in the signal from connecting a "Y" to both inputs will provide enough output to trigger the sub to turn on.
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post #20 of 38 Old 07-31-2012, 03:42 PM - Thread Starter
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^^^^^ Thanks. Good advice to follow.
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Originally Posted by bfreedma View Post

Don't let the attempts to confuse the issue make it more complicated than what he's suggesting.

Knock it off. There's no attempt on my part to confuse any issue and a "Y" splitter, isn't complicated. It seems the problem here is some don't like what Klipsch has to say on the matter and they have to have things done their way and nobody else can share.

It's real simple, do it the left way or do it the right way as either way is the okay way.

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post #22 of 38 Old 07-31-2012, 04:22 PM
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Regarding the 3db loss per connection issue, I think some clarification is in order. When 3db per connection is mentioned, it doesn't mean every time you connect one cable to another using a butt connector, you lose 3db. It's 3db for every device the cable is connected to.

I read the page in the Klipsch manual, and it doesn't make sense to me why they say it would result in increased power out. If a signal at 0db is split into two lines and connected to a L and R input, each signal would then be at -3db, or half power relative to the single line. However, the sub only has one speaker. So what does it do with the L and R inputs, each at -3db? It sums them, and we now are back where we started at 0db.

Now, if you are running two subs off one LFE output, each of them will be getting a signal which is -3db relative to having only one sub hooked up. This will likely not be an issue as this can be compensated for both by adjusting the LFE output signal in the receiver itself, and by adjusting the volume on the sub. As long as you can play a reference test tone out of the LFE output and get both subs set to your desired output level, you're golden. However, if your LFE channel is turned all the way up in your reciever, and your subwoofer is turned all the way up, and you still can't hit 75db (or however hot you calibrate) using a reference level test tone, then you have a problem.

This problem is most likey to occurr if somebody is running 4 or more subs off of one LFE output. But as far as the OP is concerned, the simplest thing to do is hook up a mono RCA cable to one of the subs inputs. As long as you can calibrate to reference, there's nothing else to do.
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Thanks for weighing in with your insight.
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Originally Posted by DanLW View Post

So what does it do with the L and R inputs, each at -3db? It sums them, and we now are back where we started at 0db.

Sounds like a speaker version of "Who's On First?"

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post #24 of 38 Old 07-31-2012, 04:55 PM
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Originally Posted by DanLW View Post

If a signal at 0db is split into two lines and connected to a L and R input, each signal would then be at -3db, or half power relative to the single line.
That's not the case. The signal is a voltage source. If split to two parallel loads the voltage to each remains the same.

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post #25 of 38 Old 07-31-2012, 07:54 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

That's not the case. The signal is a voltage source. If split to two parallel loads the voltage to each remains the same.

Okay, I guess I should have thought out the reasoning better. Since this signal isn't driving a low ohm load, but rather a high impedance input, the current delivery and resulting power output is essentially a non issue unless we try to run 7 or 8 line inputs off one output. So while it's technically true that the power delivered to each input is half, it is not an issue since we are amplifying the voltage.

And so back to the sub in question, I could see how it could be 3db louder with both inputs hooked up. As such I would provide an addendum to my original response and say if you can't obtain your reference level using one input (assuming the receiver's LFE output level AND the sub are turned all the way up), then go ahead and obtain a Y splitter and see if that gets you where you need to be. But if you can get to where you need to be with just one input, save the time, gas, and money and use just one cable.
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Originally Posted by DanLW View Post

But if you can get to where you need to be with just one input, save the time, gas, and money and use just one cable.

FWIW, if one has an Amazon Prime membership, there's no time, gas or postage and if one simply throws a "Y" splitter on as suggested by the manufacture, all the rest is moot. Win lose or draw, unless one has a subwoofer cable handy in their pocket, one still has to buy the subwoofer cable and doing so is going take as much time to order or buy as anything else. Yesterday I ordered a pair of shielded subwoofer cables and a pair of audio "Y" splitters from Amazon, two day postage included and they'll be here tomorrow. Took me less that a minute to complete the order. Over the last couple of days I've ordered from Amazon, White, CL2 12AWG wire, shrink wrap tubing of various inside diameters, shielded subwoofer cables, audio "Y" splitters and speaker wire pants; not to mention a bunch of unrelated stuff to audio speakers. With the internet, it's a different day and age.

I guess it would be wrong of me to ask, why do all the manufactures I've seen from Klipsch to HSU and many in between, put a pair of L/R hookups on the back of their subs unless they feel there's a need? Doing so just because doing it makes buyers feel all warm and fuzzy inside is not a good reason. As an old guy, I've found life is much easier if I simply take time to read the manual. What's that acronym again? eek.giftongue.gifsmile.gif

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post #27 of 38 Old 07-31-2012, 09:31 PM - Thread Starter
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Quote:
Originally Posted by BeeMan458 View Post

What's that acronym again? eek.giftongue.gifsmile.gif
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RTFM wink.gif I just wanted to know why because some subs have both, LFE and RCA R/L, as well as speaker R/L input/output. The manuals, at least some of the ones I've seen, don't really go into enough detail as to why and when to use the various inputs, and when to use or not to use the audio settings on the subs.
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post #28 of 38 Old 07-31-2012, 10:02 PM
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Quote:
Originally Posted by BeeMan458 View Post

I guess it would be wrong of me to ask, why do all the manufactures I've seen from Klipsch to HSU and many in between, put a pair of L/R hookups on the back of their subs unless they feel there's a need? Doing so just because doing it makes buyers feel all warm and fuzzy inside is not a good reason. As an old guy, I've found life is much easier if I simply take time to read the manual. What's that acronym again?

They do that to be backwards compatible with older receivers that don't have an LFE out, but rather have stereo pre-outs. Another setup I can think of is a 2-channel music setup with a L/R line out and no mono sub out. Newer subs are designed so that you only have to plug into one of the inputs. In the replacement amp I bought for my sub, you can plug a mono source into EITHER input. In the current lineup of Klipsch subs, you plug a mono input into the left line input and leave the right one disconnected.

If one already has an RCA cable of appropriate length lying around, try it as mono first. If it doesn't work, then order from Amazon and wait two days. Or if you don't want to wait two days, drive to the electronics retailer of your choice and get a Y splitter. But it would be silly to do either of these if you already have an RCA cable of appropriate length lying around.
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post #29 of 38 Old 08-01-2012, 06:53 AM
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And so back to the sub in question, I could see how it could be 3db louder with both inputs hooked up..
Again, depending on the topology of the summing it could have higher sensitivity. But as for how loud it will play that's determined by the amp power supply rail voltage and driver excursion limit, and neither is altered by how many inputs are used.

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post #30 of 38 Old 08-01-2012, 11:53 AM
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Again, depending on the topology of the summing it could have higher sensitivity. But as for how loud it will play that's determined by the amp power supply rail voltage and driver excursion limit, and neither is altered by how many inputs are used.

This is true, and is why I think a Y-splitter is an unnecessary expenditure. But since we're all geeks here, and since I'm stuck in Djibouti with nothing better to do, let's explore this further.

IF somebody experienced an issue where they turned up their LFE channel all the way up in their receiver, and they turned their sub all the way up, and their sub had an amp which would be at -3db with just one input (which is a poor design, and explains why the newer subs aren't like this), and they ended up 1-3db shy of whatever level they were trying to calibrate to, then a Y splitter might seem like the answer.

However...

I still wouldn't recommend a Y splitter. If they have to turn both the LFE channel and the subwoofer all the way up, and they are still 3db shy, the sub is way too small for the room. If they did get a Y splitter to get to that target, that sub would not have anywhere near the headroom to play any louder. A larger sub is the answer.

Now, let's say that we ended up in a situation where our sub does calibrate fine, but we ran sweeps, and found that we are only attaining 112db peak loudness, instead of the 115db which is the loudest peak we're ideally supposed to have in a calibrated setup. (although depending on bass management, and how well/poorly a movie is mixed, our peaks could theoretically be higher, but that's a different debate in a different thread) Should we use a Y splitter to get to 115db (again assuming the poorly designed sub amp)?

I would again have to say no. If we added a Y splitter and gained 3db, when we run our calibration we would have to turn our sub back down by 3db, and we'd be where we started. The issue this time is availabler headroom - our sub does not have the oomph to hit 115db. So like in the last scenario, a larger sub is the ultimate solution.

Now, if one were to not calibrate their setup, and they did nothing else but add a Y splitter, and they had the amp in question, they would experience a louder sub with a Y splitter. But in that case, adding the Y splitter had the same effect as turning up the LFE channel, or the sub's master volume.

All that to say I agreed - while in some instances a Y splitter would provide the amp 3db more signal, it would be essentially the same thing as adjusting either the LFE out on the receiver or the master volume on the sub. But ultimately, it would have no effect on the absolute loudness of the sub unless something else was drastically wrong.
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