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Gear / Technical Help => Cables => Topic started by: Elana on March 29, 2010, 11:44:13 PM
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I was always curious if you could take an XLR Y cable and plug it into a microphone to split the signal to two different sources without any noticeable signal degradation. So I figured I may as well ask here :-) And if it's possible would you only need phantom power from one of the two sources?
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I was always curious if you could take an XLR Y cable and plug it into a microphone to split the signal to two different sources without any noticeable signal degradation. So I figured I may as well ask here :-) And if it's possible would you only need phantom power from one of the two sources?
Possible, yes (some comps posted here were done that way). Whether there is signal degradation is another question. Run P48 on just one source though.
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Yeh, I figure it would be a good way to do comparisons... unless noise is introduced or other problems occur.
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I know Smokinjoe tried this out and was less then thrilled with the results. Although, He & I have had good results when using a y cable for a soundboard feed.
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Yeh, I figure it would be a good way to do comparisons... unless noise is introduced or other problems occur.
I made a set a few years ago..
There is some uncertainty in regard to how the various components will interact in terms of impedance. So that makes the accuracy of the results a bit of an unknown.. I had one result with inexplicably diminished bass, and lost my confidence in that method of doing comps.
I have heard conflicting opinions on whether one or both 48v sources should be on. You're driving two mics on each circuit, and there may not be enough output with only one source. Voltage will drop lower than with only one mic. You may end up testing which mic handles below spec 48v best?
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I know Smokinjoe tried this out and was less then thrilled with the results. Although, He & I have had good results when using a y cable for a soundboard feed.
Agree with Ted.
There is another thread somewhere about this, and the recommended approach is a little box with transformers in it to avoid potential ground loops.
In particular, I used simple splitter cables to run Mics > splitters > both the Transparent/Vintage channels of my Busman Hybrid R4. There shouldn't be any ground loop issues here, because they are both in the same box. Yes, only phantom power from one source. My thought was that rather than decide "do I run Transparent or Warm channels today", I do both and decide later which I prefer.
One day (2008 Ratdog/ABB tour) I ran the splitters for the first set, and no splitters the second set. Hardly a solid A/B comparison, but my opinion was that the second set sounded better so I said "don't do that splitter thing any more". As Freelunch suggested I think I lost some bass response, and I was running Earthworks hypers which are thin on bass anyway, so I didn't want to lose any more.
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With a quality recorder and normal Phantom powered mics -- it will work perfectly. No degradation of the signal whatsoever is to be expected. I have done this often enough to know. Of course, both recording inputs has to support 48V phantom power. Turn on phantom on only one of them but nothing but will be destroyed if both has power on by mistake.
Now for the problems you might encounter in exceptional circumstances. Remember, these are exceptions.
1) Ground loop.
This is mostly a problem if the two inputs are far from each other. Like on a large stage where one mixer on stage feeds the foldback to musicians and another mixer sits out in the audience and feeds the main PA. There might even be a third feed to a recording van outside and perhaps a fourth feed to the video people in their own van. Solution for this is a transformer splitter if you have boxes far from each other. A cheaper solution on this rare problem if boxes are closer to each other is to snip of the ground connection in one of the XLR connections (pin 1 used for shield in most cases). This isolates ground from that box and also means that that box cannot supply phantom power.
2) Slightly lower input impedance
Most microphones has a very low output impedance and the preamps a high impedance. This means that the sound will not be modified by having two inputs. Notable exception from this rule are especially band microphones (that generally do not like phantom power) and a few microphones here and there. Modern phantom powered mics should not be an issue at all in this respect but do check the manufacturer figures. The Earthwork omni mics are known to be slightly special in this respect, beeing among the very few mics that actually require the full 10mA the 48V phantom spec says the preamp should be able to supply. Remember that on large stages all mics are fed to two mixers, and maybe to even more without the people beeing concerned.
Side not: there are a few high price studio microphone preamps where you can select the input impedance as a way to modify the sound. These move well outside the loading given by two normal mic preamps. The effect is generally only noticeable at all on dynamic microphones and condensor microphones with transformer outputs (genarally meaning expensive) and is never very prominent.
3) Home quality equipment
There might be a problem with some of the home quality equipment. Those that cannot supply full 48V phantom might not stand it on the input side (due to selecting smaller or cheaper components). There might even be mics that has really high output impedance. I would be especially vary and test ahead when running micro mics through an XLR converter. Still, most mics no issues at all and no degradation in sound. With normal brand name condensors there is no problem whatsoever.
What you probably will find running Y-cables is that the difference between modern recording boxes is smaller that you expected in a typical taper situation. Here we work with high output levels and a very dynamic range ( dynamic range = difference between most quiet and most loud sound ). Contrast this with other situations that might have different scenarios. Example might be recording a full symphony orchestra that might range from hardly hearable to almost full metal rock concert. Or if you preferr that, going outdoor on a summer day recording nature sounds at a very low volume. In my experience a lot of the difference in recording stems from exact microphone placement. Sometimes moving a foot can make a quite large difference.
// Gunnar
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In particular, I used simple splitter cables to run Mics > splitters > both the Transparent/Vintage channels of my Busman Hybrid R4. There shouldn't be any ground loop issues here, because they are both in the same box.
The thing is that this actually is a ground loop, although maybe not a ground loop problem.
The ground connection goes from ground inside the box, out from one channel, round the Y-cable and back in to the other channel and then to ground in the box again. This is actually a ground loop per definition. It will act as an antenna and sniff up all sorts of frequencys.
Most recorders are designed to suppress the kind of noise this connection creates, and suppress it really well. But if by mistake you did place this loop on top of a high amperage power cable this could induce enough noise to create an issue. In a performance situation the worst cables are those that carry lights, high amperage and switching creates a very disturbing environment. A badly placed cell phone might induce quite a bit of noise as well.
Professional type equipment often has loads of extra components inside to protect against all kinds of interference, but with consumer type equipment you cannot really know. And with modifyed stuff all bets are off really, unless you know that the modifier does test against EMI interference.
// Gunnar
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Sorry mshilarious.
It would help if we knew each others background a bit more. I am not sure what kind of experience you have from electronic circuit design. As for me I have been working and hobbying in and around electronics since the 70-s.
Not trying to start a flame war, but I have to slightly object to your wordings. Regardless, in a typical Y-cable this should not be a problem unless you happen to end up in special circumstances. I remember visiting an electro steel plant, where the currents are several thousand amps, people with pacemakers were not allowed and it was suggested that we would leave our wrist watches outside as they might be magnetized and stop working. A ground loop there would probably fry just about any kind of equipment.
... It's not really, it's just a extra wire from the same ground point to the mic. Since there is no difference in potential with one lead or two, it wouldn't matter.
Actually, difference in potential is not the point with a ground loop. Magnetic fields induce a current going through the loop. This current can in turn influence other parts of the electronics inside the box.
... Besides, the job of the shield is to collect RF and dump it to ground.
Sort of the opposite. The main purpose of the shield is to stop RF from reaching the signal conductors, not necessarily to dump it to to ground although to a certain degree that is happening as well.
... If the two lead shields had a substantially different ground point in the box, you would have a point, but they shouldn't.
It sort of depends on the box. I´ve looked inside quite a few. Some boxes has different paths for the ground inside the box, some are carefully layed out to not have different paths. And the problem is that a large enough induced current going inside the box might in turn induce a signal to other circuits. Now, to be clear again, this is normally not a problem with a Y-cable at all but if it ever occurs, try breaking the ground loop by cutting the pin1 / shield at one of connectors. Often enough DI-boxes and such used on stage has a breaker for this called "ground lift". It is very common to have ground loop problems on stage and the universal solution is DI-boxes with transformers. The problem is that cheap boxes has cheap transformers that modify the sound in a non-likeable way. Expensive transformers often only sounds good although you do get increased distortion ( as measured by instruments ) towards lower frequencys.
So it depends on the purpose of splitting the signal. If you want to split a microphone signal to many outlets the best solution is an active splitter. This has electronics inside. This might happen at, say, a press conference where dozens or reporters should get a split of the podium mic. In a controlled stage situation the standard solution is splitters with transformers. The sligth degradation of the sound is not noticeable. If you want to really compare two mic preamps side by side I would say that a Y-splitter is the solution as long as you check the output impedance of the microphones. It is also the quick and cheap solution.
// Gunnar
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.. That's because the magnetic field created by a 1000A current is huge. Not sure what the relevance is here.
It does matter if you plan on recording sounds there. Sorry, agree non relevant.
... Which expresses as a difference in potential across a resistance. If the resistance between the two shield terminations in incredibly low, then the potential is extremely small. If pin 1 is immediately linked to chassis, no interference signal should trouble the audio signal path.
Note, I said that ground loop is an exception when we talk about short Y-cables.
There is an additional component called magnetic inductance that may interfer with things. I agree with you ( as stated several times ) that in a short Y-cable this is not an issue. A long loop acts as a loop antenna, the lower the resistance the higher the current.
http://en.wikipedia.org/wiki/Loop_antenna
Difference in ground potential is a quite different problem, severe enough in itself but it does not need a ground loop to induce disturbances or even destroy electronic equipment.
// Gunnar
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Again, I maintain that if that scenario causes interference, even if the recordist does something silly like make a nice loop out of the cables, the design of the recorder is ultimately at fault.
That's a good point that I don't think many folks think about.... Especially unbalanced mic cables.
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Wow, this discussion just went way over my head :) I don't even know what a ground loop is.