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Author Topic: "Y" Cable Mic'ing  (Read 4734 times)

Jim McKeveny

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"Y" Cable Mic'ing
« on: March 22, 2013, 08:03:34 am »



Scenario: 2 identical mini-condensers identically mounted on 2 violins playing identical music. Ignoring the sacrifice of separate EQ and level, what downside differences are practically realized by "y"ing the 2 inputs to a single channel v. homerunning each mic to their own?

I have heard different opinions over the years. Like to hear more.. 
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Caleb Dueck

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Re: "Y" Cable Mic'ing
« Reply #1 on: March 22, 2013, 08:06:05 am »

What do you gain with a Y that independent channels can't do better? 
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Patrick Moore

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"Y" Cable Mic'ing
« Reply #2 on: March 22, 2013, 08:08:12 am »

Do not "wye" two mics to one input.  This could cause damage to your mics or console. 

http://rane.com/note109.html

John Roberts {JR}

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Re: "Y" Cable Mic'ing
« Reply #3 on: March 22, 2013, 08:33:19 am »

The general advice is to not short any low impedance sources together (good advice, it could damage the sources. The console input won't care).

In practice, it depends. Often active mics, use some modest build out resistance, so may not release smoke, but the two outputs will be fighting against each other. Just because they are trying to play identical notes, the signals will not be identical, so one can be zigging while other one zags. 

What's the worst case scenario... you damage mics.

Next worst case, distorted bad sound.

Best case, both sources sum passively and drop down -6dB in level.

Do you feel lucky.... well do you?

JR
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Jim McKeveny

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Re: "Y" Cable Mic'ing
« Reply #4 on: March 22, 2013, 08:57:18 am »

New wrinkle: each mini-mic has its own preamp before the "y".

FWIW - I have only ever experienced the passive sum and output drop.

Why would any zig v. zag = distortions potential not also present itself at after the channel inputs in summing?
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Jerome Malsack

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Re: "Y" Cable Mic'ing
« Reply #5 on: March 22, 2013, 09:31:28 am »

comb filtering and out of phase content as one is zig to the zag. 

There is a way to place two mic's in series, mic 1, pin 2 from mixer, pin 3 to pin 2 on mic 2 pin 3 back to mixer.  This is Ok for the dynamic but is not friendly to phantom power.  You would need to use phantom power after the combiner and before the mic.   The problem above will still be a problem.
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Jim McKeveny

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Re: "Y" Cable Mic'ing
« Reply #6 on: March 22, 2013, 09:35:08 am »

Would not the same comb filtering be evident in 2 home runs?

What I am saying is: Are we not simply using the console as an expensive "Y" in this scenario, or - other than the surrender of individual eq, and level - what are the problems?
« Last Edit: March 22, 2013, 09:41:33 am by Jim McKeveny »
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Matthew Knischewsky

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Re: "Y" Cable Mic'ing
« Reply #7 on: March 22, 2013, 09:36:12 am »

New wrinkle: each mini-mic has its own preamp before the "y".

FWIW - I have only ever experienced the passive sum and output drop.

Why would any zig v. zag = distortions potential not also present itself at after the channel inputs in summing?

I have used the circuit in Rane Note 109 many times when I need a cheap solution to sum 2 outputs together. The resistors will fit inside of XLR and TRS connector housings if you're careful. If you need to sum the outputs of 2 preamps together passively this is the way to do it. http://rane.com/note109.html

You can use this circuit for microphones too but you're going to loose a fair amount of output and in the case of phantom power it's going to drop some, but probably not enough to make a difference to the mic.

All that being said I'm not too proud to admit that I have y'd 2 mics together in a pinch. When the band keeps getting bigger but the console stays the same size you gotta do what you gotta do. Overhead choir mics and Crown PCC 160s are the most common things I have Y'd together, but I've also Y'd tom mics together (use placement to get the mix right, works best when the drums sound good and the person on the stool knows how to play).

This is fairly obviously NOT best practice, but it will work if you're really stuck. I have never had any mics get damaged from doing this probably because the current produced is too small to do any real harm.

Matt
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John Roberts {JR}

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Re: "Y" Cable Mic'ing
« Reply #8 on: March 22, 2013, 10:16:45 am »

New wrinkle: each mini-mic has its own preamp before the "y".
No, I factored in that mics were phantom power with active circuitry.
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FWIW - I have only ever experienced the passive sum and output drop.

Why would any zig v. zag = distortions potential not also present itself at after the channel inputs in summing?

The issue with zig/zag for passive sum after active circuitry is that the drive circuitry inside the mic is only designed to drive the nominal mic preamp input impedance (1.5-2k ohm) to ground. However two mics with say 150-200 ohms, build-out impedance, driving another similar source, could be like driving that 150-200 ohm load to ground (if other mic is perfectly opposite polarity).

This output stage running out of drive current, could be a relatively subtle overload distortion so not very apparent, but that doesn't mean it isn't happening.

The zig/zag issue is not about how the signals combine, but a local circuit drive current capability issue.

If the active mic uses lower resistor values this issues can be much worse. Dynamic mics will combine with different issues as one mic motor couples to the other.

JR
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Jim McKeveny

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Re: "Y" Cable Mic'ing
« Reply #9 on: March 22, 2013, 10:39:39 am »

JR-

So if the mic elements received a no-sag drive current, what other issues could there be?
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Curt Sorensen

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Re: "Y" Cable Mic'ing
« Reply #10 on: March 22, 2013, 10:46:34 am »

I worked a show with Chris Botti and a symphony where his engineer had us place DPAs on the bridges of the strings, and 'Y' each one with a condenser on a stand a foot or two away. We had something like 80 mics on a 48 channel desk. It broke several 'rules' I had in my head, but it appeared to work quite well for him. And I'm not aware of any damage to the hall's mic inventory. I'm not endorsing it, just passing it along. I've also used series wiring with dynamics and didn't hear anything disturbing. As far as what the difference between a 'Y' and a mixer, I'd say it really only matters if there's an issue with the electronics not liking the 'Y'. That said, I'd always prefer separate mixer inputs. It's pretty rare to see similar sources having truly identical settings such as a 'Y' would resemble.
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Curt Sorensen
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Jim McKeveny

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Re: "Y" Cable Mic'ing
« Reply #11 on: March 22, 2013, 10:52:58 am »

This has been my experience, except I have used Senni Mke2 Golds on MZA preamps.

A modern console's  front end is designed to  accept a range of load parameters, impedance, and current demands.

There are no doubt aberations at the fringes of the  twin-mic performance window, but not so much for SR practical demands. But I may be quite wrong. I am open to being otherwise coached.



« Last Edit: March 22, 2013, 11:11:35 am by Jim McKeveny »
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John Roberts {JR}

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Re: "Y" Cable Mic'ing
« Reply #12 on: March 22, 2013, 11:42:38 am »

JR-

So if the mic elements received a no-sag drive current, what other issues could there be?
Not to beat this to death, but it isn't a matter of sag... the mics all receive similar total power via phantom standard. The issue is more like connecting a 4 ohm sub up to a headphone amp, The HP amp is just not designed to drive that low of an impedance with any oompf (technical term). 

Now another consideration for anecdotal reports that it works fine. Mic designers who sell any number of mics to customers prone to experiment, will anticipate and protect against possible abuses. Along that line of thought, I recall old Peavey power amps being capable of working with loudspeaker signals plugged into their input jacks (don't try this with modern Peavey amps).

Ok, so back to the mics.. they may work, and may sound OK, or not sound overtly bad, however unless the mic manufacturer says "go for it", you are on your own, and it is not good practice.

This is a surprisingly common situation, for budget customers, and while at Peavey I came up with a conceptual design to use some of the phantom power available, to make a crude auxiliary sub-mixer/input-expander, with pad, polarity, and gain trims for each. This was  happiest with dynamic mics, but could probably work OK with modest voltage phantom powered mics. Mics that needed every drop of the phantom would not be happy. This never advanced beyond the "what-if" stage because the incremental cost to just buy a larger, new mixer was not so bad, and doesn't require pioneering a new product, for a tiny niche.

For another general observation be careful about extrapolating too much from anecdotal advice or experience. Because it worked for somebody somewhere, doesn't mean it will work for everybody every where. When in doubt, ask the mic manufacturer.

JR
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/
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