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Author Topic: Mic cable picking-up handling noise?  (Read 801 times)

Steve Litscher

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Mic cable picking-up handling noise?
« on: March 14, 2020, 05:05:25 pm »

Got a really strange one here (at least to me)...

Rig:
A&H dLive C1500 console v1.84 firmware (current)
A&H dLive CDM32 Mixrack v1.84 firmware
A&H DX168 stage box

Console connects to Mixrack via known good Cat5e Ethercon. DX168 connects to MixRack via known good Cat5e Ethercon. Everything plugged into same electrical circuit (testing this in the home studio).

I made some XLR drum looms for an upcoming (and subsequently canceled) tour, and was testing them for noise, etc.. I noticed that while using PAFL (solo) on the dLive, that I could hear myself handling the mic cables. If I thumped/tapped on the cable housing, I could hear it clearly in my headphones. So, I unmuted the PA and brought the channels up - sure enough, I could hear any tapping, thumping, sliding, or stepping sounds through the cables.

I didn't have mics on the other end.

Figuring my cable build may be dodgy, I grabbed some brand new (still in the packaging) XLR cables (Rapco Horizon, Whirlwind, EliteCore) and sure enough - all of them exhibited the same behavior... audible noise in the PA when being handled or stepped on.

I tried it with a M32 console, and it doesn't pick-up/amplify the handling noise.

Strangely enough, the noise is more prevalent in the DX168 stage box.

I set all of the preamp gains to 25dB (a normal operating range on the dLive for vocals), 0 digital trim added/subtracted. So, it's not like the gains are cranked and it's exaggerating things. I eventually connected SM58s to the cables and I could still hear handling noise from the cables.

Any ideas? Anyone ever experienced something similar? I've contacted A&H for suggestions/info, but am waiting to hear back.

Chris Hindle

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Re: Mic cable picking-up handling noise?
« Reply #1 on: March 14, 2020, 05:17:05 pm »

Plug in some loads, and see if the problem is still there?
Any chance the pre-amp doesn't like un-terminated inputs?
Chris.
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Frank Koenig

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Re: Mic cable picking-up handling noise?
« Reply #2 on: March 14, 2020, 05:22:09 pm »

Beat me to it. Try plugging a dummy mic (~100 Ohm resister between pins 2 and 3) into the mic end of the cable and see what you get. That will be more representative of the cable's noise with a mic attached. Once a real mic is plugged in it might be harder to separate cable microphonics from what the actual mic picks up. --Frank
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Steve Litscher

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Re: Mic cable picking-up handling noise?
« Reply #3 on: March 14, 2020, 05:23:15 pm »

Good call on testing it with a resistor... what wattage would be appropriate? Looks like I'll have to order them.

« Last Edit: March 14, 2020, 05:26:04 pm by Steve Litscher »
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Ike Zimbel

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Re: Mic cable picking-up handling noise?
« Reply #4 on: March 14, 2020, 05:50:14 pm »

Good call on testing it with a resistor... what wattage would be appropriate? Looks like I'll have to order them.
1/4 watt or 1/2 watt is fine. 150 ohms is standard dummy load value. Another thing to try is tightening the screws that hold the xlr's in the stage box. I saw some weird noise behavior on a Midas XL-8 that I traced back to those screws once.
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Dan Mortensen

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Re: Mic cable picking-up handling noise?
« Reply #5 on: March 14, 2020, 08:43:09 pm »

I noticed that while using PAFL (solo) on the dLive, that I could hear myself handling the mic cables. If I thumped/tapped on the cable housing, I could hear it clearly in my headphones. So, I unmuted the PA and brought the channels up - sure enough, I could hear any tapping, thumping, sliding, or stepping sounds through the cables.

I didn't have mics on the other end.

Figuring my cable build may be dodgy, I grabbed some brand new (still in the packaging) XLR cables (Rapco Horizon, Whirlwind, EliteCore) and sure enough - all of them exhibited the same behavior... audible noise in the PA when being handled or stepped on.

I tried it with a M32 console, and it doesn't pick-up/amplify the handling noise.

The surprising part of this is that you didn't hear it with an M32.

I noticed this some years ago, too, and it seems to be a function of the fact that the unterminated cables are acting like condenser microphones, where the unterminated wires are moving in relation to each other and changing the capacitance and induction, causing a signal that can be amplified and heard.

I've always heard that phenomenon called "microphonic cable", i.e., the cable is acting like a microphone.

Don't handle unterminated cables connected to an amplifying device (you can hear it connected to power amps/speakers, too) with the system powered and gained up, and you'll never hear it again.
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brian maddox

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Re: Mic cable picking-up handling noise?
« Reply #6 on: March 14, 2020, 11:21:09 pm »

....
Don't handle unterminated cables connected to an amplifying device (you can hear it connected to power amps/speakers, too) with the system powered and gained up, and you'll never hear it again.

"Doctor it hurts when I do this"

"Well then, don't do that.  Make sure to check out up front with the receptionist."

 ;D ;D ;D ;D ;D
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Eric Snodgrass

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Re: Mic cable picking-up handling noise?
« Reply #7 on: March 15, 2020, 01:23:09 am »

Did you have phantom power engaged on any of the channels that the drum loom was plugged into? 
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Tim Weaver

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Re: Mic cable picking-up handling noise?
« Reply #8 on: March 15, 2020, 11:15:25 am »

This happens to one of my CL5/Rio3224 setups too. I also have an X32 Rack with an SD8 on it for a classroom that will do it.

Both are "simple" systems meaning, desk>switch>stagebox and that's it. If I have mic lines sitting around with no mic or DI plugged in they will pick up the noise every time you move them around.

Not sure if adding other surfaces and stageboxes, etc stops this phenomenom, but I don't have it on any more complicated systems.
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Ike Zimbel

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Re: Mic cable picking-up handling noise?
« Reply #9 on: March 15, 2020, 12:18:08 pm »

This happens to one of my CL5/Rio3224 setups too. I also have an X32 Rack with an SD8 on it for a classroom that will do it.

Both are "simple" systems meaning, desk>switch>stagebox and that's it. If I have mic lines sitting around with no mic or DI plugged in they will pick up the noise every time you move them around.

Not sure if adding other surfaces and stageboxes, etc stops this phenomenon, but I don't have it on any more complicated systems.
If you are having it on some set-ups but not others with identical equipment try tightening the screws that hold the XLR's in the stage box / chassis. Why? These screws are an integral part of the grounding scheme and the solution to the "Pin-1 Problem". Typically, you will get about a 1/4 turn on each screw, which is enough to make a good connection to the metalwork and eliminate any resistance that has built up.
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Re: Mic cable picking-up handling noise?
« Reply #9 on: March 15, 2020, 12:18:08 pm »


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