JBL monitors - unbalanced out to balanced input - is my wiring OK? at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > All Things Audio

All Things Audio
Everything Audio, from acquisition to postproduction.


Reply
 
Thread Tools Search this Thread
Old October 27th, 2007, 10:41 PM   #1
Major Player
 
Join Date: Apr 2006
Location: Cedar Rapids, IA
Posts: 561
JBL monitors - unbalanced out to balanced input - is my wiring OK?

I just received my JBL monitor setup the other day. An LSR4312SP subwoofer and five LSR4326P, kind of an early Christmas present to myself, hooked up to my Macintosh through an M-Audio Firewire 410 interface. I have six cables going from the Firewire 410 to the subwoofer, and from there one additional cable to each of the other speakers. So far, so good.

Here is the problem. There is very noticable noise coming from all speakers. I have to lower the volume to -20dB before I don't hear it anymore. Here is a sample of what it sounds like:
http://www.mp-video.com/other/what_is_this_noise.wav
This is without any signal being sent to the speakers (i.e., with the computer and the Firewire 410 switched on but no sound produced).

This is the first time I am dealing with such an elaborate speaker setup, so I make no claim that I understand it well. The one area where I am a little suspicious about my setup is this: the Firewire 410 only has unbalanced outputs, whereas the subwoofer has balanced inputs. I am using balanced cables with a TRS on the Firewire 410 side and an XLR going into the subwoofer. I understand the basic difference between balanced and unbalanced audio connections, but not enough to analyze this mixed setup. The JBL manual has a section on using unbalanced inputs, but to be honest this exceeds my knowledge of audio wiring.

So this is my question to you: is the noise I am hearing the result of incorrect wiring? If so, what can I do to fix it (taking into account my very limitied electronics/hardware skills)? If not, what else might it be?

Thanks in advance for your help!

- Martin
__________________
Martin Pauly
Martin Pauly is offline   Reply With Quote
Old October 27th, 2007, 11:14 PM   #2
Major Player
 
Join Date: Oct 2007
Location: Houston, Texas
Posts: 262
JBL surround

There is a -10 /+4 switch on the back of the sub, this should be set to -10. Unbalanced audio has a reference level of -10 where as Balanced has one of +4. thats a 14db difference, which explains having to lower the volume -20. from looking at the manual there is a switch on the back of the sub that should handle this. your cable should be fine
Gerry Gallegos is offline   Reply With Quote
Old October 27th, 2007, 11:30 PM   #3
Inner Circle
 
Join Date: Feb 2007
Location: Fairfield, Dunedin, New Zealand
Posts: 3,634
Images: 18
Hi Martin............

Disconnect the cables from the 410 to the amp/ subwoofer, one at a time (at the amp end). If the noise dissapears, plug them back in and disconnect at the 410 end. If it doesn't dissapear, you have an amp/ subwoofer problem.

If, with the cables connected at the amp end but not at the 410 end, the noise is back, it's a wiring problem with the balanced/ unbalanced connections (probably). If the noise is gone it's a 410 or higher problem (probably).

If it is the unbalanced/ balanced problem, think you're either going to have to come to terms with that manual or post it here on DVinfo (just the relevant parts, perhaps).

The only way I can think of to eliminate the 410 is to, try another 410.


CS
Chris Soucy is offline   Reply With Quote
Old October 28th, 2007, 03:03 PM   #4
Major Player
 
Join Date: Apr 2006
Location: Cedar Rapids, IA
Posts: 561
Quote:
Originally Posted by Gerry Gallegos View Post
There is a -10 /+4 switch on the back of the sub, this should be set to -10. Unbalanced audio has a reference level of -10 where as Balanced has one of +4. thats a 14db difference, which explains having to lower the volume -20. from looking at the manual there is a switch on the back of the sub that should handle this. your cable should be fine
Gerry,

yes, that switch is sitting in the "-10" position on all speakers, because that's the level that the Firewire 410 outputs. But balanced/unbalanced and -10/+4 should be independent choices, right? While it is true that professional equipment tends to have balanced connections and also tends to use +4 rather than -10, there can be other combinations (such as balanced audio at -10).

- Martin
__________________
Martin Pauly
Martin Pauly is offline   Reply With Quote
Old October 28th, 2007, 03:23 PM   #5
Major Player
 
Join Date: Apr 2006
Location: Cedar Rapids, IA
Posts: 561
Quote:
Originally Posted by Chris Soucy View Post
If, with the cables connected at the amp end but not at the 410 end, the noise is back, it's a wiring problem with the balanced/ unbalanced connections (probably). If the noise is gone it's a 410 or higher problem (probably).

If it is the unbalanced/ balanced problem, think you're either going to have to come to terms with that manual or post it here on DVinfo (just the relevant parts, perhaps).
Thanks a lot, Chris. I unplugged the cables at the 410 and everything was fine (read: silent). Then I took just the cables for the left and right channels and plugged them into my TASCAM FW-1082, which has only two outputs, but they are balanced. Result: very nice stereo sound, no noise.

So if I interpret your message correctly, you would expect the problem to be in the Firewire 410 interface. I'd say that's possible, but I don't have access to another one (and bought this one pre-owned, so I can't just return it to the store). After reading about balanced wiring in the various audio books that I have, I am still not ruling out the wiring either.

While I read about some tricks one can use to connect balanced inputs to unbalanced outputs, it sounded like the only real solution would be to use transformers and balance those outputs. Or buy a better audio interface with balanced connections out of the box.

- Martin
__________________
Martin Pauly
Martin Pauly is offline   Reply With Quote
Old October 29th, 2007, 10:43 PM   #6
Major Player
 
Join Date: Sep 2005
Location: SLC, UT
Posts: 289
try changing your cables. use ts (tip-sleeve, 2 cond.) 1/4" instead of trs (tip-ring-sleeve, 3cond.). make sure the tip is connected to xlr pin 2 via the center conductor of the wire, and the sleeve connects to both xlr pins 1&3 via the wire shield. balanced ins are differential inputs (a plus and a minus). with your trs cable, the plus (tip>pin2) gets an input but the minus (ring>pin3) is not terminated resulting in residual noise. connecting pin 3 to pin 1 on the xlr takes this input to ground and should stop your noise. keep this cable under 20 feet, and away from other electrical wiring and rf sources.
Greg Bellotte is offline   Reply With Quote
Old October 30th, 2007, 07:37 AM   #7
Inner Circle
 
Join Date: Mar 2005
Location: Hamilton, Ontario, Canada
Posts: 5,742
You might try using the 1/4 jack on the speakers rather than the XLR. The manual seems to imply that's the preferred connection for unbalanced sources. For wiring the cables, take a look at page 35 diagram "C" or page 35 diagram "D".

-----------------------------
Revising my original post since the connections to the centre and surrounds are XLR only on the sub.

See the wiring diagram "B" on page 43 of the Subwoofer manual for JBL's recommended wiring of unbalanced 1/4 TS to XLR cables. Note that they suggest using the same shielded twisted pair cable that is normally used for balanced connections. Connect the TS plug tip to the XLR pin2 with one conductor, the TS sleeve to XLR pin3 with the other. Connect the cable shield to XLR pin1 but leave it unconnected at the TS end. This helps reduce ground loops yet still provides shielding. Those would be for the 6 cables from your Firewire interface to the sub. Use regular XLR/XLR balanced cables from the sub to the other speakers.

Bill - The JBL sub provides full bass management for the system. When you have a surround source with an LFE output it takes the signal sent to the LFE input and sends it to the sub only. Meanwhile it splits the bass from the signals going to the mains and the surrounds, sending the bass to the sub also while mids and highs go to the regular speakers.
__________________
Good news, Cousins! This week's chocolate ration is 15 grams!

Last edited by Steve House; October 30th, 2007 at 06:07 PM.
Steve House is offline   Reply With Quote
Old October 30th, 2007, 01:41 PM   #8
Trustee
 
Join Date: Jan 2004
Location: Scottsdale, AZ 85260
Posts: 1,538
Naw, sounds to me like you've got a simple ground loop.

I bet one or more of your powered speakers are plugged into an outlet on a different circuit and the ground potential difference is inducing 60hz hum into your audio.

Get a bunch of extention cords and power all the speakers (and the source of the sound) all from the same circuit leg and see if the hum disappears.

It also could easily be cable induced hum if you're running power cables parallel to and adjacent to your signal lines.

Ground loops are a VERY common pain in the butt when you're working with complex audio amplifier/speaker arrangements.

In my studio, I installed cable TV so I could watch stuff while I waited for long renders, and the long coax run from the house to the studio infected EVERY audio line with massive ground loop hum whenever it was attached.

Long cable runs, broken grounds, induced cable hum like I noted above, all of them can give you the low frequency noise you're experiencing.

It's fixable, but it's can be a pain in the butt to track down since it's related to the RELATIONSHIPS between all the powered components.

BTW, did you say you were running all 6 signals to the sub? That's weird. Any 5.1 system should have a dedicated output to the sub behind a low pass filter that ONLY sends the low freq info to that speaker. Running any full spectrum signal to a subwoofer just makes it try to reproduce frequencies that it's not built to handle - not very efficient. Feeding one speaker SIX simultaneous signals begs for phase problems and other bad stuff.

One feed per speaker ONLY please. If you need to enhance a stereo rig with a sub, you can split a single signal feed to both a full range speaker and a sub in a pinch, but running multiple signals into a single speaker is a kinda big no no.

Hope this helps.
Bill Davis is offline   Reply With Quote
Old October 30th, 2007, 04:14 PM   #9
Inner Circle
 
Join Date: Feb 2007
Location: Fairfield, Dunedin, New Zealand
Posts: 3,634
Images: 18
Hi Bill...........

It sounded to me as if the power amps for all channels were housed in the sub woofer box, hence the 6 feeds to that box. Did away with the need to power every single speaker from the mains.

Thus the only two powered units are the PC/ USB interface and the sub woofer/ amp box.

Hence why I ran Martin through the "disconnect here/ re - connect there" routine.

I could, of course, be completely in error.


CS
Chris Soucy is offline   Reply With Quote
Old October 30th, 2007, 05:38 PM   #10
Inner Circle
 
Join Date: Mar 2005
Location: Hamilton, Ontario, Canada
Posts: 5,742
Quote:
Originally Posted by Chris Soucy View Post
It sounded to me as if the power amps for all channels were housed in the sub woofer box, hence the 6 feeds to that box. Did away with the need to power every single speaker from the mains.

Thus the only two powered units are the PC/ USB interface and the sub woofer/ amp box.

Hence why I ran Martin through the "disconnect here/ re - connect there" routine.

I could, of course, be completely in error.


CS
Each speaker is powered on its own and has its own pair of power amps (they're bi-amped). The feeds all go through the sub first because it provides the bass managment for the system. I have a pair of the 8" version of the same monitors myself, will be adding the sub soon.
__________________
Good news, Cousins! This week's chocolate ration is 15 grams!
Steve House is offline   Reply With Quote
Old October 30th, 2007, 05:55 PM   #11
Inner Circle
 
Join Date: Feb 2007
Location: Fairfield, Dunedin, New Zealand
Posts: 3,634
Images: 18
Steve..........

You are, as per usual, entirely correct.

What a beast of a system.


CS
Chris Soucy is offline   Reply With Quote
Old October 30th, 2007, 10:46 PM   #12
Major Player
 
Join Date: Apr 2006
Location: Cedar Rapids, IA
Posts: 561
Quote:
Originally Posted by Steve House View Post
You might try using the 1/4 jack on the speakers rather than the XLR.
Tried that - makes no difference.

Quote:
Originally Posted by Steve House View Post
Revising my original post since the connections to the centre and surrounds are XLR only on the sub.

See the wiring diagram "B" on page 43 of the Subwoofer manual for JBL's recommended wiring of unbalanced 1/4 TS to XLR cables. Note that they suggest using the same shielded twisted pair cable that is normally used for balanced connections. Connect the TS plug tip to the XLR pin2 with one conductor, the TS sleeve to XLR pin3 with the other. Connect the cable shield to XLR pin1 but leave it unconnected at the TS end. This helps reduce ground loops yet still provides shielding. Those would be for the 6 cables from your Firewire interface to the sub. Use regular XLR/XLR balanced cables from the sub to the other speakers.
Interesting diagrams - this is where I wish I knew more about electrical engineering. It looks to me like in neither case (balanced or unbalanced connections) should the grounds of the two systems be connected, to avoid ground loops. This is different from what I picked up in Jay Rose's books, where I read that with balanced connections the grounds are connected even though they don't contribute to the audio transmission (and therefore cannot affect the audio).

Quote:
Originally Posted by Bill Davis View Post
Naw, sounds to me like you've got a simple ground loop. [...] Get a bunch of extention cords and power all the speakers (and the source of the sound) all from the same circuit leg and see if the hum disappears.

It also could easily be cable induced hum if you're running power cables parallel to and adjacent to your signal lines.
Tried both. I am powering all speakers and the audio interface using the same powerstrip - no change. There is some change in the noise as I am moving the audio cables around, but I cannot get it completely noise free.

Quote:
Originally Posted by Chris Soucy View Post
What a beast of a system.
Oh yes! A while ago I thought that my B&W speaker setup in my home theater was elaborate. I knew better when I unpacked the JBLs and found a CD-ROM for a firmware update. WHAT? Firmware in a speaker? Oh yes - these speakers are really sophistocated computers; they are networked amongst one another through CAT5 ethernet cables, they come with a remote control, and they have a USB connection to be controlled by a PC. This is not the system to just unpack and enjoy - what I am seeing is that there is a learning curve to understanding how these speakers are best used, and I am still very much at the beginning of this process.

There have been other issues. One of the LSR4326P arrived with a crack in the bottom of the speaker; I am working with B&H to exchange it. One speaker had a European power cord included instead of the North American type. Finally, I cannot switch off the speakers - sounds funny, I know. The way this is supposed to work is that you hit the power button on any one speaker, and the shutdown command is then sent via the ethernet cable to the other speakers. For some reason, two of my speakers always stay powered on. I contacted JBL; someone from tech support replied very quickly, but I need to find a time to call them sometime when I am actually in my little office during normal business hours.

Bottom line: I am working to resolve all these issues one at a time, and I have no doubt that these monitors will serve me very well once everything is in good shape. I am just not quite there yet!

Thanks for all your helpful comments!

- Martin
__________________
Martin Pauly
Martin Pauly is offline   Reply With Quote
Old October 31st, 2007, 04:40 AM   #13
Inner Circle
 
Join Date: Mar 2005
Location: Hamilton, Ontario, Canada
Posts: 5,742
Quote:
Originally Posted by Martin Pauly View Post
...
Interesting diagrams - this is where I wish I knew more about electrical engineering. It looks to me like in neither case (balanced or unbalanced connections) should the grounds of the two systems be connected, to avoid ground loops. This is different from what I picked up in Jay Rose's books, where I read that with balanced connections the grounds are connected even though they don't contribute to the audio transmission (and therefore cannot affect the audio).
While you are correct that with a balanced system the cable shield is generally connected at both ends, sometimes ground loops can creep in when you do that. It depends on the specific design of the devices at both ends - a complex topic relating to where and whether the various signal. electrical, and case grounds are tied together or not. If you're interested, the tech-notes on the Rane website includes a fascinating white paper on the whole issue. If noise due to a ground loop is present, breaking the connection between the grounds of the two devices by disconnecting the shield from ground at the signal destination end of the cable while keeping it connected at the signal origin end can help alleviate it.

Quote:
...Finally, I cannot switch off the speakers - sounds funny, I know. The way this is supposed to work is that you hit the power button on any one speaker, and the shutdown command is then sent via the ethernet cable to the other speakers. For some reason, two of my speakers always stay powered on. ...- Martin
Did you remember to termnate each end of the CAT5 daisy-chain? All of the speakers should be connected together in a chain using the supplied CAT5 or better network cables. That leaves an empty RJ45 jack on each of the two speakers at the ends of the line. JBL provides little terminator plugs that need to go in them - those plugs actually provide a resistive load on both ends of the network, they're not just there to fill the empty holes. I found some of the network functions that rely on the speakers being able to talk to each other get flakey if you omit the termination. If you've misplaced the JBL supplied plugs, you can make up your own by jumpering pins 4 and 5, the two centre connections, of a standard RJ45 ethernet plug with a 120 ohm resistor from Radio Shack. Alternately you can fulfill the same function by connecting the two speakers at each end of the chain to each other with an extra CAT5 cable so the entire system ends up connected together in a big ethernet ring.

Another hint for reliable communication in the network and with the computer control software is to make sure that the DIP switches on each speaker are correctly set to identify its position in the setup. First make sure its memory has been cleared by doing a factory reset. Disconnect the power cord and network cables from the speaker, put all switches in the on position (up) and reconnect the power cord. After the front panel stops flashing, power off, put all switches down except the one that identifies its position and reconnect the network cables.
__________________
Good news, Cousins! This week's chocolate ration is 15 grams!
Steve House is offline   Reply With Quote
Old October 31st, 2007, 01:58 PM   #14
Major Player
 
Join Date: Apr 2006
Location: Cedar Rapids, IA
Posts: 561
Audio Interface: PCI or FireWire?

Quote:
Originally Posted by Steve House View Post
Did you remember to termnate each end of the CAT5 daisy-chain?
Yes, I did - even though information on JBL's support website and their tech support representative that I talked to earlier today said it didn't matter whether the terminators are used or not.

Actually, the JBL guy figures it's due to incompatible firmware versions of the speakers. I had not even considered this possibility, since they are all brand new (had to wait five weeks to get them!), but sure enough, some of my speakers have an older firmware version which apparently is not fully compatible in terms of networking with the other speakers. This should be easy to fix.

Back to the noise problem. Given that my balanced Tascam outputs have produced great sound (but only in stereo), I am tempted to go ahead and replace the M-Audio 410 with a higher-end audio interface, one with balanced line outs. These beautiful speakers really should be treated to a great audio interface! I am not sure if a PCI card (this would be in a Mac Pro) or a FireWire-based interface would be best (did a search here on "PCI" and "FireWire", but did not see any useful hits).

I like the idea of PCI, because
- it frees up a FireWire port for other stuff
- I don't need mobility for this interface
- my experience with FireWire in the past has been less than excellent

But then I've never owed a PCI audio interface, so I am wondering if those have their own set of problems that I am just not aware of yet.

One interface that looks very nice is the Echo Layla 3G. Looking at the specs, it's worlds apart from the 410, assuming they are not overstating the performance. I've gotten recommendations in the past for the Echo AudioFire8, which also has great specs but uses a FireWire interface.

Unfortunately, I'm not enough of a handyman to try out all the suggested modifications to the cables in my existing system. I appreciate all your suggestions, but I am too scared of damaging my equipment by doing it wrong.

Any thoughts on the PCI vs FireWire question?
__________________
Martin Pauly
Martin Pauly is offline   Reply With Quote
Old October 31st, 2007, 03:09 PM   #15
Trustee
 
Join Date: Jan 2004
Location: Scottsdale, AZ 85260
Posts: 1,538
<< There is some change in the noise as I am moving the audio cables around, but I cannot get it completely noise free. >>

That statement alone increases my suspicion that what you're hearing might be radio frequency leakage into your lines somewhere.

Often, hums and buzzes that CHANGE as cables move come either from bad grounds or from inducted noise. If the cables are properly balanced, then RF and other "common mode" noise should be canceled by the balanced runs. But whenver the hum changes as the cable moves through space, I get suspicious that the cable itself is acting like an antenna.

If this is the case, you have two options. Address the issue at the cable (repair, replacement), OR (and generally better) eliminate the source of the RF.

Any AC motor driven appliances or fluorscent ballasts in the vacinity?

Just more thoughts along the way.

Good luck. Sounds like the system will be a joy to work with and listen to once you get these issues resolved.
Bill Davis is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > All Things Audio

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 03:12 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network