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Mic Splitter volume issues

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Mic Splitter volume issues

Postby sacriseverence » Mon May 20, 2019 4:15 pm

I've got a live in-ear monitor rig for my band, only for vocals. We have three mics. At the smaller venues we've played some sound engineers have had issues saying our signal is too low, and that when they try to get the mics loud enough they have feedback issues.The engineers don't have a problem with the other bands, even if they have three vocal mics as we do.

I tested the rig at home going into my PreSonus Studio 1824 interface to make sure the levels are comparable: both the mics (all SM58) going directly in, and then the mics going through our rig (the way they would go to Front of House). I'm not noticing ANY signal loss!

My setup is as follows:

SM58(x3) -->MXL369PatchBay-->Galaxy JIB/Y splitter(x3)-->MXL369PatchBay-->Front of House


(Galaxy JIB/Y splitter(x3)--->MX821S mixer --->Galaxy AS900T In-Ear Transmitter)

My only thought is somehow the JIB/Y splitters aren't up to the task? Is it possible that going into some smaller PAs there is an impedance issue that's not present at both the bigger venues and when plugging into my PreSonus interface?

Thanks so much
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Re: Mic Splitter volume issues

Postby Hugh Robjohns » Mon May 20, 2019 4:37 pm

sacriseverence wrote:...some sound engineers have had issues saying our signal is too low, and that when they try to get the mics loud enough they have feedback issues.

All passive splitters will introduce some attenuation to the mic signal -- so the outputs will be slightly quieter than the straight mic would be. Exactly how much attenuation is dependent on the quality of the splitting transformer. The loss is normally only a dB or two, though, so barely audible in most cases.

If the feedback issue is normal acoustic feedback, that's simply a problem of mic placement relative to the monitor speakers (if present and used) and/or the main FOH speakers. It won't be anything to do with your splitter rig.

However, are you completely certain your SM58s are genuine SM58s? There are a lot of fake ones about -- especially on ebay! If they are fake, you could well have substantial problems with both the output level and the polar response, potentially causing all the feedback problems you've complained of.

There are several resources on the interweb that advise on how to determine if an SM58 is the real thing... or not.

A quicker way of checking, though, would be to temporarily replace your SM58s with some known to be genuine examples from the sound team at a venue to see if that improves the situation.

Can I check which splitter output you're using to feed the FOH? The phantom-blocked one, or the straight-through on? Only the straight-through connection passes a ground to the mic. So if the FOH has the phantom-blocked feed and your local IEM setup is ground-free (as many such systems tend to be), you could be missing a solid ground which might potentially affect gain levels and electrical coupling.

And that's another consideration -- when using splitter transformers there is also the possibility of electromagnetic coupling that could cause electrical feedback... It sounds like you've got the splitters and IEM system in some sort of rack arrangement, so it might be worthwhile temporarily moving the splitters out and apart, to see if that makes any difference.

Is it possible that going into some smaller PAs there is an impedance issue that's not present at both the bigger venues and when plugging into my PreSonus interface?

Not very likely. If the splitter output feeding the FOH was being loaded in a weird way, you'd hear some effect (such as a lowered level) on your IEM system.

H
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Re: Mic Splitter volume issues

Postby AlecSp » Mon May 20, 2019 4:52 pm

As with so many of these other questions,, you will only be able to identify the guilty component(s) in the signal chain by trying each part in isolation - simple fault-finding!

My first bet is on the mics, if your rig has lower gain before feedback than others in the same venue. But, obviously, you need to do some testing to see where the problem really is.
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Re: Mic Splitter volume issues

Postby sacriseverence » Mon May 20, 2019 5:56 pm

Hugh Robjohns wrote:Can I check which splitter output you're using to feed the FOH? The phantom-blocked one, or the straight-through on? Only the straight-through connection passes a ground to the mic. So if the FOH has the phantom-blocked feed and your local IEM setup is ground-free (as many such systems tend to be), you could be missing a solid ground which might potentially affect gain levels and electrical coupling.

Aha! The phantom-blocked signal is the one going to FOH right now. I can swap them no problem, but I'm not sure I have a way to test if there's a difference before the next gig. I have a fairly cheap PA I can try it out on and see if there's any difference. Is this the kind of issue that would only pop up with certain engineer's boards?

The mics are actually 2 genuine SM58's and one Samson Q4 (I'd forgotten they weren't all Shures until just now). There's no question they're genuine - one is from a reputable chain and the other is a replacement directly from Shure. I'm fairly certain the Samson isn't an issue, it behaves identically to my Shures.

The monitors at the venues aren't causing the feedback - I always have the engineer turn them off. And as I mentioned, they're getting feedback issues from us when they don't have the same problem (or the need to have the mic levels so high) with other bands on the same nights, often with as many mics.
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Re: Mic Splitter volume issues

Postby Hugh Robjohns » Mon May 20, 2019 8:09 pm

sacriseverence wrote:The phantom-blocked signal is the one going to FOH right now.

If you have a digital multimeter, it would be work checking whether pin 1 of the mic's XLR has continuity to the earth pin of the mains plug of your IEM rack system. If it does, great. If not, I'd swap the splitter outputs over so that the FOH gets the direct feeds, rather than the phantom-blocked outputs.

The mics are actually 2 genuine SM58's and one Samson Q4 (I'd forgotten they weren't all Shures until just now). There's no question they're genuine - one is from a reputable chain and the other is a replacement directly from Shure. I'm fairly certain the Samson isn't an issue, it behaves identically to my

Fair enough. Good to rule the fake mic idea out.

The monitors at the venues aren't causing the feedback - I always have the engineer turn them off. And as I mentioned, they're getting feedback issues from us when they don't have the same problem (or the need to have the mic levels so high) with other bands on the same nights, often with as many mics.

Hmmm... So that leaves the distinctbpossibility that you (and your colleagues) simply aren't working the mics close enough and/or loud enough.

Actually, that is not an unusual situation when using in-ears as they make it so much easier to hear things... So maybe try turning down the vocal contribution into the in-ears to encourage closer/louder working through the mics.
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