I question the wisdom of a professional install. - AVS Forum
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post #1 of 23 Old 08-21-2013, 12:38 PM - Thread Starter
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I'd like some opinion on the logic of this part of an install, done by an AV company. They just finished the install, and we get almost no bass from the supplied subwoofers.
If you need additional picture I can get them. I do video production (think HD-SDI and XLR) not home theater, so my knowledge level is not at the level of you guys. I am prepared to be wrong wink.gif .

Receiver--- 100ft---Powered subwoofer

He seems to have run an unbalanced output over coax cable 80-100' to each powered sub. At the powered sub he then converts RCA to a 1/4 adaptor (not sure if it's 3 or 2 pole it wont come out) and it goes into a balanced XLR/1/4" jack.

#1 Surely you want to go balanced over distances like that?

#2 How is he going from 2 conductor coax to 3 conductor XLR/1/4" (he's not right?)

#3 Can I call the installer out on this?



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post #2 of 23 Old 08-21-2013, 01:10 PM
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not sure what amplifier you have there but you may have a issue with input signal not being strong enough from the pre to the amp. it looks like your pre amp has xlr's so i wonder why they wouldnt just use them?

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post #3 of 23 Old 08-21-2013, 01:11 PM
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The installers did the right thing, but 100 feet is a lot of distance if you go unbalanced especially in case of subs. Your sub has only balanced input, if um not wrong. Whereas your avr has no balanced output for the sub. Hence they had to use a converter to terminate rca end into balanced input of your sub.

But having said that, your sub still gets unbalanced input. The converter itself cannot transform an unbalanced signal into a balanced one. You are getting very weak signal on the sub end.

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post #4 of 23 Old 08-21-2013, 01:17 PM
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Sorry, I think you do have XLR outs on your AVR. If there is one for the sub; use a balanced cable for your sub. That's the only connection you can go with if 100 feet cable is to be used.

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post #5 of 23 Old 08-21-2013, 01:20 PM
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Quote:
Originally Posted by braveheart123 View Post

Sorry, I think you do have XLR outs on your AVR. If there is one for the sub; use a balanced cable for your sub. That's the only connection you can go with if 100 feet cable is to be used.

or use a bump box, but XLR cable is cheap so i still dont understand why they dont use it.

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post #6 of 23 Old 08-21-2013, 01:30 PM
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Quote:
Originally Posted by brian6751 View Post

not sure what amplifier you have there but you may have a issue with input signal not being strong enough from the pre to the amp. it looks like your pre amp has xlr's so i wonder why they wouldnt just use them?

+1

The AVR PreAmp clearly has XLR out for Subwoofer1 and Subwoofer2:



I just cropped and lightened your first photo to make it easier to see.

Is it possible that your installer just took the easy/cheap route by pulling RG6 instead of pulling you a proper XLR line?
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post #7 of 23 Old 08-21-2013, 03:20 PM - Thread Starter
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Sorry, I subscribed but wasn't getting notified of the replies, or I would have been back sooner. Thanks for all the input.

Yes there are XLR outs on the receiver. Why he didn't run XLR I don't know, just one of the many mysteries on this install.



The amp is built into the sub, and is a Bag End minima one.
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He's done a similar thing on some of the main speakers (while the rest are all XLR).
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Short of re-running cables, I wonder what the solution here is.
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post #8 of 23 Old 08-21-2013, 09:51 PM - Thread Starter
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I think he used a TS plug into the subs, but it's going to want a TRS plug.

The unbalanced outputs would be -10dBu while the balanced ones will be +4dBu right, so my thinking is to put XLR-RCA adaptors on both ends, and see (hear) what happens. I don't think he can re-pull the cables easily.

It would look like this:

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post #9 of 23 Old 08-21-2013, 11:39 PM
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Why he didn't run XLR I don't know, just one of the many mysteries on this install.

After knowing that your AVR does have a balanced output; the installers didn't do the job right. Just get a balanced XLR cable for the hookup. No need for a bump box. The impedance on both ends of the 100 ft cable would be the same.
Don't think too much smile.gif

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post #10 of 23 Old 08-22-2013, 12:54 AM
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Quote:
Originally Posted by rally1 View Post

I think he used a TS plug into the subs, but it's going to want a TRS plug.

The unbalanced outputs would be -10dBu while the balanced ones will be +4dBu right, so my thinking is to put XLR-RCA adaptors on both ends, and see (hear) what happens. I don't think he can re-pull the cables easily.

It would look like this:


Bad idea. XLR termination does not mean balanced signal. It has to be balanced along the entire run of the cable. RCA cable is not balanced.

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post #11 of 23 Old 08-22-2013, 08:44 AM
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Quote:
Originally Posted by rally1 View Post


#1 Surely you want to go balanced over distances like that?
Not necessarily, especially with a sub. Any EMI/RFI picked up is in the high frequencies, not the lows. Balanced does make it a lot easier to avoid the usual problem with subs, that being a ground loop.
Quote:
#2 How is he going from 2 conductor coax to 3 conductor XLR/1/4" (he's not right?)
Right.
Quote:
#3 Can I call the installer out on this?
Yes. By not running balanced into the sub amp you lose 6dB of input sensitivity.
Remember that to claim to be a 'professional' installer he doesn't have to know what he's doing, he just has to know more than you do. He should have run XLR balanced on both ends, and as the AVR has XLR balanced outs there's no conceivable excuse for not doing so.

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post #12 of 23 Old 08-22-2013, 11:45 AM - Thread Starter
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Because I like to prove the point without a doubt.... I plugged his unbalanced line into a mixer with test tone on the LFE channel, then with same settings I plugged in the balanced connection (even though it goes over unbalanced cables)

His way:
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My way:
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The 6dB gain is pretty evident. And as the subs are only looking for balanced levels, he needs to rerun the cables (or at the bare minimum use the adaptors).
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post #13 of 23 Old 08-22-2013, 12:06 PM
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I would tell them that the subs are playing way too low and let them figure out what to do. It's their job to figure it out. You shouldn't have to. The problem may not be the way they wired it.

Why are your subs 100' from the pre-amp? Is it a huge room?
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post #14 of 23 Old 08-22-2013, 01:07 PM - Thread Starter
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AVR and amps are in a server room, the one sub is in the back of a theater. The screen is 19' so you get an idea of the sizes/distances involved. Thanks.
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post #15 of 23 Old 08-22-2013, 04:46 PM
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Originally Posted by rally1 View Post

Because I like to prove the point without a doubt.... I plugged his unbalanced line into a mixer with test tone on the LFE channel, then with same settings I plugged in the balanced connection (even though it goes over unbalanced cables)
The 6dB gain is pretty evident. And as the subs are only looking for balanced levels, he needs to rerun the cables (or at the bare minimum use the adaptors).
OK, if you're from Missouri, but the simple answer is that balanced versus unbalanced has twice the voltage swing. Double the voltage is 6dB, every time.

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post #16 of 23 Old 08-22-2013, 10:20 PM
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And as the subs are only looking for balanced levels, he needs to rerun the cables (or at the bare minimum use the adaptors).

If you use balanced adaptors; your entire effort is pointless then. If balanced is the approach, it must be along the entire length.

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post #17 of 23 Old 08-23-2013, 12:21 PM - Thread Starter
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I understand that they need to be switched to balanced cables, but I am not going to pull new cables for the guy to prove a point, so I simply used the adaptors at each end to quickly demonstrate the level difference.

I am not sure what the Missouri reference means.

He's got a similar level issue here too right? He's running an unbalanced output to a balanced input.

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post #18 of 23 Old 08-23-2013, 12:24 PM
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I understand that they need to be switched to balanced cables, but I am not going to pull new cables for the guy to prove a point, so I simply used the adaptors at each end to quickly demonstrate the level difference.

There will be zero difference. Both are unbalanced approach. Been there; done it!!!

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post #19 of 23 Old 08-23-2013, 12:34 PM
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Quote:
Originally Posted by rally1 View Post

I am not sure what the Missouri reference means.

Missouri is "the show me state." The reference was to the fact you went to the trouble to verify and show the 6db change even though it was expected because of the balanced vs. unbalanced connection.

http://www.sos.mo.gov/archives/history/slogan.asp


This is trivia for the day... nothing more.

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post #20 of 23 Old 08-23-2013, 12:35 PM - Thread Starter
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The cable is unbalanced yes (in the sense they dont reduce hum etc), but the levels are now correct because I have plugged into the balanced output on the AVR.

Appreciate the trivia, I am not up on my state slogans wink.gif With this installer I have to prove everything, his ignorance is masked by his ability to talk his way out of anything!
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post #21 of 23 Old 08-23-2013, 02:07 PM
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Originally Posted by rally1 View Post

The cable is unbalanced yes (in the sense they dont reduce hum etc), but the levels are now correct because I have plugged into the balanced output on the AVR.
That depends on how you did so. To get the full voltage swing pins 2 and 3 must both be employed. Most converters use pins 1 and 2, which means the voltage swing remains half that of pins 2 and 3. Explained here:
http://www.rane.com/note110.html
You might want to print off a copy for your 'professional installer'. rolleyes.gif
If it is louder using only pins 1 and 2 it would be because the XLR outs are at +4dB, not consumer -10dB, so even though 6dB down from +4dB that's still -2dB, 8 dB hotter than the 2 conductor outs.

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post #22 of 23 Old 08-23-2013, 02:35 PM - Thread Starter
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Printed, thank you.
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post #23 of 23 Old 08-23-2013, 04:00 PM - Thread Starter
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That was fun call. A couple quotes.
"I have been doing this 14 years"
"those subs can take balanced or unbalanced, they have an XLR and 1/4" "
"I'll turn up the levels when I calibrate it"

It's obvious he has a fundamental lack of knowledge on the subject, and that he didn't like be called out on it.

I am not the owner/client, I just happen to work here and see what he did wrong, my hands are tied on what I can actually make him do.
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