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Shielded xlr cable/connector

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Mark DAgostino
Shielded xlr cable/connector
on Dec 9, 2016 at 6:19:36 pm

I'm looking for recommendations for shielded xlr cables for handling EMI. I appreciate any suggestions.

Mark D'Agostino
Video Producer
Creative Media Productions - Exelon
Baltimore, MD
MacPro,2.7 Ghz 12-Core Intel Xeon E5, 64GB 1866 Mhz DDR3 ECC, AMD FirePro D700 6144MB, AJA Io XT, Yosemite 10.10.1


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Richard Crowley
Re: Shielded xlr cable/connector
on Dec 9, 2016 at 11:36:44 pm

Neutrik makes a special connector with extra RFI/EMI shielding built-in.
Male: http://www.redco.com/Neutrik-NC3MXX-EMC-EMI-Protected-Male-XLR.html
Female: http://www.redco.com/Neutrik-NC3FXX-EMC-EMI-Protected-Female-XLR.html

Any cable with FOIL shield has 100% coverage. But foil shield cables are typically best for fixed installations.
The more common mic cables with braided or wrapped shields which may have only ~85% coverage.
There are some cables with double braided shield with nearly 100% coverage.

Redco will make custom cables with your choice of wire and connectors, and for a very sensible price.
http://www.redco.com/Custom-Cable.html
I have no connection with Redco other than a satisfied, paying customer.

Note, however, that the cable (and connectors) play only a partial role in solving RFI/EMI problems.
So don't assume that even the very best cable and connectors will solve any RFI/EMI interference issue.

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Ty Ford
Re: Shielded xlr cable/connector
on Dec 10, 2016 at 1:59:59 am

Hello Mark and welcome to the Cow Audio Forum.

What kind of EMI are you experiencing?

One simple way would be to ground the XLR shells at both ends of a cable. This is not necessarily recommended for live sound work because XLR cables (and connectors) are sometimes dragged over other conducting surfaces.

I have tried the Neutrik connectors Richard mentions and have found them partly effective. That is to say, they help in some but not all situations. We also found that you really only needed to use the female end plugged into the mics. Using the special male XLR connector didn't really do that much more.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Richard Crowley
Re: Shielded xlr cable/connector
on Dec 10, 2016 at 5:58:15 am

Indeed, as Ty said, grounding (or AC coupling with a small capacitor) the XLR shell would be an easy first step to closing up some of the holes where interference is creeping in. Most modern XLR connectors have a separate internal tab for the shell. Simply solder a short, straight piece of wire between the shell tab and pin 1 ground. In cases where that causes a ground loop, then use a small capacitor (~0.01uF) instead of a piece of wire.

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Ty Ford
Re: Shielded xlr cable/connector
on Dec 10, 2016 at 4:07:14 pm

Richard,

As always, you're there with the right stuff.

I really appreciate that you spend time here helping people.

You are both wise and kind.

Season's Best,

Ty

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Mark DAgostino
Re: Shielded xlr cable/connector
on Dec 13, 2016 at 2:35:40 am

Since moving to a new job in Baltimore a few years ago I kind of drifted away fro the Cow. I have benefited greatly from both of you, Ty and Richard, in more situations than you could imagine. I am truly thankful for your generosity over the years sharing your knowledge. In this case, you given me some great ideas toward a possible solution and understanding that the cable may not be the only issue here.
I'm getting a fairly loud hum and can easily trace it to the communications snake in the conference room tables in the brand new corporate office. I'm the first one to shoot in there. I've dealt with this many times over the years and always solved it by moving my cable. One cable definitely failed in this situation. The other was far better when I moved it away from that source, though not completely quiet. This is why I figured better shielded cables may do the trick. Worth a shot.

Mark D'Agostino
Video Producer
Creative Media Productions - Exelon
Baltimore, MD
MacPro,2.7 Ghz 12-Core Intel Xeon E5, 64GB 1866 Mhz DDR3 ECC, AMD FirePro D700 6144MB, AJA Io XT, Yosemite 10.10.5


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Ty Ford
Re: Shielded xlr cable/connector
on Dec 13, 2016 at 3:15:47 am

Hello Mark,

I was on a video shoot right when Excelon, BGE and Constellation merged. We spent at least one day up in the Pratt Street building shooting. I think the company was from NYC. The picked me up to do sound.

Anyway, keeping your audio cable from being parallel with power and other data cables is a "best practices" approach.

Regards,

Ty Ford,
Cow Audio Forum Leader

PS: Yes Richard's pretty great!

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Alan Lloyd
Re: Shielded xlr cable/connector
on Dec 13, 2016 at 7:36:16 pm

Have to agree, especially if there's any dimmers involved. Audio interference and massive hum bars in the video signal to boot.

Also, HD-SDI over non-spec cabling can cause interesting results with wireless audio. (Personal experience - it drove a couple of us, including a rental vendor, crazy tracking that source of interference down.)


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Richard Crowley
Re: Shielded xlr cable/connector
on Dec 15, 2016 at 5:20:51 am

Your symptom of "fairly loud hum" suggests a broken shield or a ground loop, etc. That is a rather different kind of problem than "EMI". "Hum" is typically mains frequency (50Hz or 60Hz) and overtones (100Hz, 120Hz, etc.) While "RFI" is most often higher frequency buzz or even faint radio sounds (broadcast, police, etc.) Posting a sample of the interference would be very helpful in offering analysis and suggestions for resolving the problem.

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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John Fishback
Re: Shielded xlr cable/connector
on Jan 6, 2017 at 6:08:51 pm

In the recording studio using a star-point grounding scheme is often preferred. I learned this years ago when John Storyk designed our studio. His tech people explained star-point grounding. This is where there is only one ground point (the star-point) in the facility. In our studio the star-point is the patchbay. All shields are connected at that end, and all shields are open at the device end. Each device in turn is grounded through its a/c third pin to the star-point. This ensures no ground loops. BTW, you only need the shield grounded at one end. You may have noticed in hospitals, data centers and other installations where quality grounds are essential, that the a/c outlets are colored orange. This indicates the orange outlet is connected to the star-point.

Modern buildings follow a similar plan. Power comes in from the street, usually passes through an isolation transformer and it is at that point a star-point is created and ultimately run through the building. But, the fact that there are different phases in power distribution opens up lots of room for bad grounding and hum in a building. If the power in the room you are shooting is on one phase, and you're you're using a snake or wall-mounted outlet connected to a device on a different phase, that can open a can of worms re hum. Sometimes a simple ground lift in an a/c plug and/or xlr connector) can fix a thorny hum situation like that. When we shoot, we only have one power strip to which all audio & video gear is connected. This useful in reducing the possibility of hum, though not always. As mentioned by those above, there are many and varied good ways of attacking hum in the field.


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Mark DAgostino
Re: Shielded xlr cable/connector
on Jan 13, 2017 at 4:45:11 pm

Thanks, all for your kind advice. What I've come to realize is that each room, each situation has it's own solution and there is not a one-fits-all solution. Sticking to the basics of good cabling, keeping cable away from and not parallel to potential sources of "hum" and understanding and respecting grounding and ground-loops are a necessary base of knowledge for anyone trying to record professional audio. In my case the issue appears in only one room in a large office building That at least leads me to a room issue rather than a gear issue...I think:)

Mark D'Agostino
Video Producer
Creative Media Productions - Exelon
Baltimore, MD
MacPro,2.7 Ghz 12-Core Intel Xeon E5, 64GB 1866 Mhz DDR3 ECC, AMD FirePro D700 6144MB, AJA Io XT, Yosemite 10.10.5


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Ty Ford
Re: Shielded xlr cable/connector
on Jan 13, 2017 at 5:11:43 pm

Connecting all sorts of gear these days can result in some interesting audio by-products.

At one facility here in town, the stage is usually electrically quiet. On one shoot, I was getting hum back in my headphone return. We isolated the problem to one of the big screen video displays on a BNC from one of the cameras. Take it out. No Hum. Put it back. Hum.

The video gear was all plugged into the same stinger. My presumption was that it was an isolated incident and was due to a dirty power supply in the video display.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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