Need help understanding SUBWOOFER options with pre-wired home - AVS Forum
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post #1 of 14 Old 10-17-2013, 09:31 PM - Thread Starter
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I'm hoping I'm in the right forum... if not, please tell me where to go.

We just moved into a home, and already have 2 giant headaches related to the home theater.

If you're going to tell me to run new wires, then just don't bother.. It's NOT happening, I don't have the money to destroy everything.
The walls are filled with Polyurethane Foam Insulation, and the labor is through the roof (lowest quote I've found for running the HDMI again over 60-70ft is just shy of $3k).

Again. NOT GOING TO HAPPEN!

1) The HDMI cable tip is broken... I'm in the process of splicing that, with fingers crossed.... This isn't what this thread is about (duh, we're in AUDIO), but geez what a headache that has been so far.

2) The real issue I'm here... My Receiver (Onkyo TX-SR605) came with a powered sub (Onkyo SKW-705), which has a preamp out for the LFE sub. Ok. Great.

EXCEPT! The house was pre-wired with standard speaker wire, even for the subs (the idiot ran 2 speaker wires to the EXACT SAME SPOT for "7.2", IN THE REAR.. so irritated, but that's another issue for another day)!
I've looked and looked, and I might be just slightly over my head in understanding what's required to make this work. From what little I understand, I need to use a few resistors in series to reduce the output and reduce hum. But that doesn't make 100% sense to me.... Simply lowering the input, effectively the amperes, seems like a good start, but it needs to be clean input still, right? We're talking low/high pass filtering to an LFE, seems like it's as close to digital over analog as you can get... Again, unless I'm completely misunderstanding it.

I already tried taking an RCA cable and splicing it to the speaker wire... I simply used the outer wires as one channel, and the inner sheathed wires as the other channel (assuming it kinda works like stereo).
Without the other end hooked up to anything (so literally just plugged into the sub and that's it), the sub hums like crazy... Obviously not right.

Maybe I don't know what an LFE cable looks like inside, but outside it looks like a standard RCA (the one that came with the speaker does anyway, and I'm not ready to cut it open to see what's under the sheathing).
But I'm pretty sure they're basically the same...

Is there a device I can get to go from LFE to Speaker? or is my only option to get a new setup (a new receiver/sub combo, which obviously I don't want to do).
I've seen "Line out converters," but they're always assuming stereo. Could I still use one of these, and just use a single channel?

I really want to make use of the prewired 7.1 cabling, and have my full 7.1 system back (our old house we were able to run cabling for a proper setup, and LOVED it).

HALP! I'm confused, poor, irritated, and I want my theater system back up and running! eek.gif

Thanks in advance guys!



**EDIT**

After researching new receivers on Amazon, Newegg, etc... It looks like everything is now LFE or stereo RCA... neither which will work with my setup... ****!

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post #2 of 14 Old 10-18-2013, 06:10 AM
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http://www.bestbuy.com/site/rocketfish-wireless-subwoofer-transmitter-receiver-kit/6965266.p?id=1218817520479&skuId=6965266

http://www.svsound.com/subwoofers/subwoofer-accessories/sub-link-24-ghz-wireless-subwoofer-system-dsl-xr#.UmEyVXDMCSo

http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-580

http://www.snapav.com/p-920-es-sub-wireless.aspx
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post #3 of 14 Old 10-18-2013, 08:22 AM - Thread Starter
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Huh.... That could be an option.... Kinda makes me wanna do this for ALL my speakers now.

Anyone tried that? If you have too many going, will there be interference with each other, or other devices? Will you get the cancers? :P

Thanks for the response - very interesting product.

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post #4 of 14 Old 10-18-2013, 09:57 AM
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The real issue I'm here... My Receiver (Onkyo TX-SR605) came with a powered sub (Onkyo SKW-705), which has a preamp out for the LFE sub.

Looks like your receiver has a line level output for the sub.

Google doesn't find anything for SKW-705....is that the correct model number?Does it have an amplifier built into it?
Quote:
I already tried taking an RCA cable and splicing it to the speaker wire... I simply used the outer wires as one channel, and the inner sheathed wires as the other channel (assuming it kinda works like stereo).

Where are you getting two channels from? The receiver only has one LFE output.
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post #5 of 14 Old 10-18-2013, 11:31 AM - Thread Starter
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Quote:
Originally Posted by SAM64 View Post

Looks like your receiver has a line level output for the sub.

Google doesn't find anything for SKW-705....is that the correct model number?Does it have an amplifier built into it?
Where are you getting two channels from? The receiver only has one LFE output.

My apologies -- bad typo there: SKW-750

And yes, it absolutely does have line level output (LFE), and it is powered/amplified.

As for the channels, I'm just calling it that. The RCA cable had loose strands of wires surrounding another shielded set of strands. I figured it one wired to the center plug of the RCA, and the other to the outer ring portion (see example of this female side - http://yorkspace.files.wordpress.com/2007/10/img_94751.jpg). So to get both signals back to the reciever across the house, I figured I'd need both, so I put one on the + and one on the - of the some speaker wire....

So I stripped it back enough so that I could wire them to banana plugs; but as soon as I put the RCA end into the sub, the sub just hums like it's picking up ambient EMF. I'll have to take a pic later tonight when I"m back home (currently at work).

I was hoping someone would be able to tell me if one of those line level converters would work, but (as you had mentioned) using just a single channel instead of stereo (I've yet to find one specifically FOR a sub/LFE cable).

The wireless adapter that RATMAN suggested would likely work, but it's a bit pricey for what I was wanting to consider. That and there will likely be lag.

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post #6 of 14 Old 10-18-2013, 12:46 PM
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Quote:
Originally Posted by KillerSpaz View Post

The wireless adapter that RATMAN suggested would likely work, but it's a bit pricey for what I was wanting to consider.

$60 w/free shipping? Pricey?

http://www.ebay.com/now/p.html?_flppid=34266290&_store_id=14005&_epc=94043

IMHO, a small price to pay for a convenient workaround.

EDIT:
That Best Buy link is bad (from previous post).
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post #7 of 14 Old 10-18-2013, 01:42 PM
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And yes, it absolutely does have line level output (LFE), and it is powered/amplified.

It has a line level input.
Quote:
The RCA cable had loose strands of wires surrounding another shielded set of strands.

An 'RCA' cable has two conductors. two conductors are required to complete any simple circuit. it only carries one channel of audio, and in this case, you only need to carry one channel...the LFE.
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So I stripped it back enough so that I could wire them to banana plugs;

Why? Your receiver has a line level LFE output on an RCA connector.
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I was hoping someone would be able to tell me if one of those line level converters would work

You don't need one, you have a line level source feeding a line level input.

Take an "RCA' cable and cut it n half. Connect the shield and center conductors to the two conductors of the speaker wire, do this at both ends of the speaker wire. plug one RCA connector into the LFE output on the receiver, plug the other RCA connector into the LFE input on the subwoofer.
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post #8 of 14 Old 10-18-2013, 07:57 PM - Thread Starter
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Quote:
Originally Posted by SAM64 View Post

It has a line level input.
Yeah, my bad... it has the input, the receiver has the output... Misworded.
Quote:
Originally Posted by SAM64 View Post

An 'RCA' cable has two conductors. two conductors are required to complete any simple circuit. it only carries one channel of audio, and in this case, you only need to carry one channel...the LFE.
Why? Your receiver has a line level LFE output on an RCA connector.
You don't need one, you have a line level source feeding a line level input.

Take an "RCA' cable and cut it n half. Connect the shield and center conductors to the two conductors of the speaker wire, do this at both ends of the speaker wire. plug one RCA connector into the LFE output on the receiver, plug the other RCA connector into the LFE input on the subwoofer.

Heh, again, slight misword, or different terminology. I used the term "channels" not in terms of audio channels, but circuitry channels (but conductors is the better word to use).

So yeah, I did that, but before I was able to do the other end at the receiver-side, I plugged in the RCA portion to the subwoofer and it just hums pretty bad.



I tried it with and without the banana plugs; I only had the banana plugs on there because I had already put a banana plug face-plate on the wall already and was anticipating it working in my favor (which clearly it isn't).

The only part of your post I don't 100% understand what you're meaning is:
Quote:
You don't need one, you have a line level source feeding a line level input.

I don't "need one" of what? (Sorry, simple misunderstanding I'm sure, just not getting the context)

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post #9 of 14 Old 10-19-2013, 05:49 AM
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Quote:
Originally Posted by KillerSpaz View Post

So yeah, I did that, but before I was able to do the other end at the receiver-side, I plugged in the RCA portion to the subwoofer and it just hums pretty bad.

Most all subs will do that. You have to plug in BOTH ends of the cable and the hum should cease.
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I don't "need one" of what? (Sorry, simple misunderstanding I'm sure, just not getting the context)
A "line level" converter.
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post #10 of 14 Old 10-19-2013, 11:21 AM - Thread Starter
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Ah ok, I'll build out the other side and see what happens.

For the record, when I plug in my RCA that came with the sub, it doesn't do the humming unless I touch the center post, so that's why I was concerned. Maybe it's the closed circuitry that will ground it.



I'm about to splice some stuff, so I'll test it out before the day's end to see how it goes.


BTW, thanks for all your input so far!

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post #11 of 14 Old 10-21-2013, 05:03 PM - Thread Starter
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So I built out the other end, and like you said it stops humming, but only when the receiver is on. I like to turn it off at night to avoid overheating for whatever reason, and to save electricity....

Any idea how to solve the off state? I'd hate to have to unplug the sub every night :/

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post #12 of 14 Old 10-21-2013, 05:14 PM - Thread Starter
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FYI, I successfully spliced a new end on my HDMI cable routed through the wall. My guess is it's a 50 or 100 ft cable, but I used around 8in off a 6ft cable. Talk about needing patience!

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post #13 of 14 Old 10-21-2013, 08:11 PM - Thread Starter
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Ok, after a bit more searching, it looks like I need to now try a ground-loop isolator, or worse case a power conditioner (expensive!)

Since it's only doing it when the receiver is off, I'm going to rule out any other components causing the issue; also to consider - I noticed the hum before ever plugging in anything to the receiver (sub included).

The sub itself doesn't have a ground pin on the plug, which made me think it could be power --- but I see people online talking about using a 3 to 2 prong adapter, ultimately removing ground. Originally it seemed like backwards logic to me - I would expect grounding to fix the problem, not add a problem. But now I realize that the two devices are defining volt-levels for what "ground" is, and they're not matching (they are, after all, across the house).
But either way, I don't have ground on the power cable, so that clearly isn't directly my issue.

Also, I see a ton of talk about COAX, but I'm not using that at all, and my receiver doesn't even support it directly anyway (duh). And I'm not using a power strip with a coax connection either, it's plugged directly into the wall. For the record, I've also tried a high quality surge protector to no avail.

I'm thinking of trying an inline ground-loop iso first, otherwise I'll have to keep searching for options.

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post #14 of 14 Old 10-22-2013, 07:32 AM
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But now I realize that the two devices are defining volt-levels for what "ground" is, and they're not matching

No, you're really stretching.
You're LFE output is going into a high impedance state when the receiver is turned off.
The sub input is high impedance and is susceptible to induced hum.
Try a 600 Ohm resistor across the sub input.
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I see a ton of talk about COAX, but I'm not using that at all, and my receiver doesn't even support it directly anyway

All those RCA connectors are coaxial connectors, they can use coax cable.
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