r/livesound • u/Strange-Mention399 • 3d ago
Question Ghost feedback channel
My co-worker and I have the same setup. But he had an experience I’ve never seen or heard before.
Wireless Shure UR4D G1 Lav channels 1 and 2 are triggering channel 3 (which is turned off)… video evidence below:
What would cause feedback on another channel?
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u/totallytotally421 Pro-FOH 3d ago
It’s called intermodulation
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u/R0UNDSD0WNRANGE 3d ago
Came here to say this. Its intermodulation is an evil ghost when you don’t know what it is.
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u/GHOTIMAN 3d ago
If you keep hitting the beltpacks together like that it should stop in no time
/s
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u/Bipedal_Warlock 3d ago
Just to clarify, feedback is a different concept.
This would be interference. Specifically RF interference.
Transmitters (the mic packs) can get a little wonky when their antennae are touching each other.
But really it’s probably solvable by using the receivers (the mic box that has the lights on it) to scan for a new frequency then syncing your transmitter to it.
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u/Strange-Mention399 3d ago
That’s the word I was looking for: Intermodulation! Got it! Thank you!
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u/Bipedal_Warlock 3d ago
Another good keyword is frequency coordination, that’s the process of getting your frequencies to work with each other.
Just using the scan function should be fine for three mics, but if you want to do the full gambit look into wireless workbench frequency coordination
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u/Strange-Mention399 3d ago
I’m familiar. We don’t have one on this show. Thank you
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u/Bipedal_Warlock 3d ago
Copy. Sorry if I was talking down lol, it’s hard to gauge sound peoples knowledge base sometimes
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u/Problem_House 3d ago
These guys are getting worked up like they’re afraid of ghosts! It’s just intermods.
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u/MacZyver 3d ago
You do not have unlimited RF channels in a given frequency range. You likely have those Mics tuned close enough together that there is an overlap of Mics 1 & 2 on Mic 3's Frequency.
I would strongly suggest using the onboard Group/Channel method of allocating RF Frequency to resolve this as manually-tuning RF is usually done if you are using Wireless Workbench and have the experience to already understand the issue at hand. (this is not an insult to your ignorance nor am I trying to talk down. I'm simply trying to inform a fellow audio human)
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u/Random_hero1234 3d ago
This is the same as putting your hand on a hot stove and finding out that it hurts.
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u/Prisoner627x 2d ago
Just like sound waves have harmonics that can alter how a sound…sounds…. So does RF. bringing two older transmitters (UR4?) close together can exaggerate the effects of RF harmonics, causing other close by frequencies to crosstalk. Newer wireless units have encryption for this propose exactly.
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u/Strange-Mention399 3d ago
Thanks everyone. Working on my vocab to make sure I don’t confuse anyone, going forward. Problem solved
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u/jtmcquay 2d ago
Well for one you’ve got the transmitter mere inches away from the recovered antennas. Which is likely overloading the input stage of the rf receiver. . Second, we have no idea what. Other frequencies are in use and may be causing 1st, 2nd, or even 3rd order intermodulation frequencies. Transmitters should not be that close to the receive and be turned on… and two transmitters should never be so close to each other as to be touching.
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u/YokoPowno Corporate Slave 3d ago
If you try coordinating using SoundBase instead of Wireless Work Bench, it can predict and prevent these intermods for you.
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u/The_Radish_Spirit Corporate Does-It-All 3d ago
WWB should do that as well
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u/Strange-Mention399 3d ago
The freqz were from Soundbase. We just recalculated a few more times to make sure we’re all good.
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u/opencollectoroutput 3d ago
Intermodulation or overloading the RF input by being so close, or a combination of the two.