Question about combining two mic signals live.

[Blakemore Effects]

So, I have a bit of a minor problem. In the band I play with, I'm running two guitars amps at the same time. I don't need the guitars panned left and right, since I'm not looking to get a stereo spread or anything, I just like the way they sound together. So far at shows, it hasn't been a problem for the sound guy to mic both of my amps and run them together, but at the last show, the sound guy said they were running low on channels on the mixer, and they almost couldn't mic both of my amps. I was wondering if there is any way I could buy something that would make it possible to combine the signals from the mics that are on my amps, so the sound guy would only need to take up one channel for both of my amps? I figure this would make things easier for him, since he doesn't have to worry about two separate channels for my amps, plus I figure it's better for me since the sound guy can't screw up my tone by accidentally making one of my amps way louder than the other one. Is there any cheap solution to this problem that you guys can think of? Thanks in advance!

[Mogwix]

Short of buying your own mixer (which is kind of a dumb idea), you can buy a little XLR y-adapter. It'll work fine for your application but there is a chance of some combing and interference from mixing two low-impedance sources. Perhaps it'll be better to just mic up one cab, as what sounds like night and day to you on stage is an inaudible difference out front.

 

Either that or come up with an input list for your band and provide that to any new venues, promoters, or organizers you may be working with so they're prepared for what you need.

[Blakemore Effects]

I had been looking at XLR y-adapters, but I read somewhere online that for some reason, summing two mic signals into one like that was a bad idea? Something about the two low impedance signals doing something or other. I don't remember for sure. That was basically what I thought though, was that I could either go with a mixer, y-cable, or just mic one cab if I had to, but I thought y cables were a bad idea, but if they're fine, that might be my best bet. If I only miked one cab though, why do you say it would be an inaudible difference out front? I'd only be getting half of what my normal signal is, so I'd assume it would drastically different out front.

[Mogwix]

You can try a y-adapter, pick one up for a few bucks. At your next show try it out. Mic up both cabs as you usually would, with mics going into seperate channels on the board and stand out front while a friend plays through your rig. Then connect a y-adapter into a single channel and see how that sounds. If it sounds drastically different to you then maybe it's not a good idea.

 

As for just miking one cab, I say that because you have to realize it's all about perception, and how things like two cabs with separate mics don't really make much of a difference. Again, I'd recommend really going out front to listen to how your rig sounds in the house, with one cab and with two, then consider that sound in the context of the band. My guitarist uses two half stacks on stage, and while the difference is awesome when you hear the two amps, out front nobody really cares AND that little difference gets lost in the context of the band. Not that I'm against using two amps, because I play with a pair of half stacks on stage when I play guitar in bands, and would prefer each to be mic'd and mixed up front, but if channels are tight or for some reason I can't mic both cabs, then I just deal with using one in the house mix and keep both amps on stage for my own enjoyment.

 

That's a nice rig you got there, by the way. Every time a guitarist makes a big deal about micing BOTH of their amps on stage, they've always got a pair of DSL's or better yet, MG's, with the gain, lows and highs cranked, and mids scooped on both amps.

[jgthatsme]

Horizon used to make a mic combiner.

 

http://www.gigcables.com/CNdevices.html

 

I have a couple which I needed to use many years ago.

[davidss1]

if u intend to use a Y cable,u must consider the problems encountered when similar signals have different arrival times.imagine the same scenario micing both sides of a drum,,,if using a Y cable with both legs wired the same,,,u will have phase cancellation,,,one of the signal legs needs to be reversed to get summation of the 2 signals.

in ur proposed situation, if the mics have varying distances to the source,u will have some degree of phase mismatch which can cause phase shift and/or cancellation

even if u can match the phase for both mics,the foh guy will eq the resultant signal and thus negate any tonal differences u might be useing on ur amps for ur stage sound.

i would tend to agree with micing one cab,unless u have specific left right effects that need to be translated to foh,and if that was the case,u would need 2 seperate lines to foh.

a wall of quad boxes (if they are even plugged in)is fed to foh from one mic an one speaker,,,,because thats usually all that is needed

[Blakemore Effects]

 

Horizon used to make a mic combiner. http://www.gigcables.com/CNdevices.html I have a couple which I needed to use many years ago.

 

 

That looks like exactly what I may be needing. Why did you say they "used" to make one though? Do they not still make them? It looks like that website is pretty up to date, so it looks like they still sell them. Either way, that may be perfect for me, assuming they still make it. Thanks for your help!

 

 

 

Any other suggestions though?

[Blakemore Effects]

 

if u intend to use a Y cable,u must consider the problems encountered when similar signals have different arrival times.imagine the same scenario micing both sides of a drum,,,if using a Y cable with both legs wired the same,,,u will have phase cancellation,,,one of the signal legs needs to be reversed to get summation of the 2 signals. in ur proposed situation, if the mics have varying distances to the source,u will have some degree of phase mismatch which can cause phase shift and/or cancellation even if u can match the phase for both mics,the foh guy will eq the resultant signal and thus negate any tonal differences u might be useing on ur amps for ur stage sound. i would tend to agree with micing one cab,unless u have specific left right effects that need to be translated to foh,and if that was the case,u would need 2 seperate lines to foh.

 

 

That is a very good point that I didn't think of. Did you see the Horizon Mic Combiner that the poster before you linked to? If I used that, but made sure I had two of the same length mic cables going into it, then I wouldn't get phase cancellation, right?

[Mogwix]

 

If I used that, but made sure I had two of the same length mic cables going into it, then I wouldn't get phase cancellation, right?

 

No, cable length has nothing to do with it, and what he's describing has more to do with using multiple mics on the SAME audio source, in which case it doesn't matter where you sum the signal, they'll still be out of phase if you don't align them right. Either way, you may run into problems with the Y-cable... maybe not. As I said in my first reply, the easier solution is to just make sure ahead of time that they're prepared to mic both your cabs.

 

This here will work better for combining two mics... but IIRC it's about $100.

[Dogoth]

As long as you are using the same type mic (the idea being the same output and tonal balance) and they are both dynamics. there is no problem with passively combining them with a simple XLR Y cord (I've done it many times). You lose about 3db total signal but at guitar amp volumes this shouldn't be any problem at the console at all. Make sure all of your connections are polarity correct (if the output from the amps' speakers is inverted, sound guys would have mentioned having to reverse phase so it doesn't sound like a problem).

 

It is true that it's a bad idea to passively combine active circuits (like line driven mixer outputs, playback devices or anything with active electronics in it (you can trash the output stage doing this) but with passive mics it's no problem.

 

If you're using different mics or condensers then you're opening a can of worms - Don't do it.

[Blakemore Effects]

 

As long as you are using the same type mic (the idea being the same output and tonal balance) and they are both dynamics. there is no problem with passively combining them with a simple XLR Y cord (I've done it many times). You lose about 3db total signal but at guitar amp volumes this shouldn't be any problem at the console at all. Make sure all of your connections are polarity correct (if the output from the amps' speakers is inverted, sound guys would have mentioned having to reverse phase so it doesn't sound like a problem). It is true that it's a bad idea to passively combine active circuits (like line driven mixer outputs, playback devices or anything with active electronics in it (you can trash the output stage doing this) but with passive mics it's no problem. If you're using different mics or condensers then you're opening a can of worms - Don't do it.

 

 

Yeah, no one has mentioned reverse phase issues with my amps, so I don't think it's an issue. I'd just be using two SM57's on my amps, I would assume though, or at the very least, two dynamic mics. I doubt any of these venues have extra condensers just lying around haha.

 

You said that you've had a y-cable work for you though, which is reassuring, but I did notice most of them are only 6-12 inches long, which could create some difficulties, since the mics will likely be placed farther away than that. I'll ask you too, what do you think of this suggestion that a previous poster mentioned? http://www.gigcables.com/CNdevices.html

 

Thanks for all the help so far!

[jgthatsme]

 

That looks like exactly what I may be needing. Why did you say they "used" to make one though? Do they not still make them? It looks like that website is pretty up to date, so it looks like they still sell them. Either way, that may be perfect for me, assuming they still make it. Thanks for your help!

 

 

I'm not sure they still make it, and Horizon doesn't exist as Horizon any longer. They merged w/ Rapco and are now called RapcoHorizon:

 

http://www.rapcohorizon.com/

 

I just looked on their site and they do list the combiner:

 

http://www.rapcohorizon.com/products/devices/media_devices/Default.aspx

 

And for what it's worth, the top dogs on this site who really know their stuff would urge you not to use a Y-cable to combine two signals. It's fine to use a Y-cable to split signals, but not to combine them. I don't recall the technical reasons why, but Aged Horse or WMHellinger would certainly be able to explain it in a very easy to understand manner.

[Craig Vecchione]

Rolls has just the ticket:

 

http://www.rolls.com/product.php?pid=MX54s

 

[Dogoth]

 

You said that you've had a y-cable work for you though, which is reassuring, but I did notice most of them are only 6-12 inches long, which could create some difficulties, since the mics will likely be placed farther away than that. I'll ask you too, what do you think of this suggestion that a previous poster mentioned? http://www.gigcables.com/CNdevices.html Thanks for all the help so far!

 

 

You get a Y cable and add two 6' or 12' or 20' extensions to get the cables to your amps. Y cables come in different XLR genders. what you need is a (1 male to 2 female) cord (I like the sound of that cord myself :>) and two appropriate length mic cords.

 

The transformer iso box isn't a bad idea but in this instance IMO isn't necessary. There shouldn't be any need to isolate the two passive devices running to the same channel.

 

Are you depending on the venue to provide the mics? If so make sure you advance the info that they MUST be identical dynamic mics (most places should have a pair of 57s but assumtions are what bit you sometimes).

[dboomer]

I'd recommend a combiner or the Rolls unit that Craig mentioned. You "can" do it with a Y cable (as long as the mics are the same polarity). You don't need to have the cables be the same length. If you have "Phase" issues it's much more likely that they are caused by bleed from one amp the the other mic.

 

Now if you are using a pair of dynamics and a Y cord ... you should wire the Y cord in series rather than the normal parallel cable that you are likely to buy off the shelf. The problem with using Y cords to combine (rather than splitting ... which is their proper use) is that it is likely that you'll load down the mic and will change the frequency response. If you try it with a regular parallel cable and the sound doesn't bother you then you don't need to worry further.

 

To me it looks like the Rolls unit or similar offers the greatest flexibility as you are sure to run into this problem of too few inputs again.

[TimmyP]

 

Short of buying your own mixer (which is kind of a dumb idea), you can buy a little XLR y-adapter. It'll work fine for your application but there is a chance of some combing and interference from mixing two low-impedance sources. Perhaps it'll be better to just mic up one cab, as what sounds like night and day to you on stage is an inaudible difference out front.

 

 

This should be no different (combing wise) than running through two channels - if the channels are not panned, they will sum the same whether it is in the console or in a wye cable, summing cable, or transformer mic combiner.

 

However a summing cable (or box) would be better than a wye cable, as otherwise the mics will load each other and affect the performance. To build a summer, see http://www.rane.com/note109.html

[Blakemore Effects]

This should be no different (combing wise) than running through two channels - if the channels are not panned, they will sum the same whether it is in the console or in a wye cable, summing cable, or transformer mic combiner. However a summing cable (or box) would be better than a wye cable, as otherwise the mics will load each other and affect the performance. To build a summer, see http://www.rane.com/note109.html

 

Wow. Thanks a lot for the help. Good stuff.

[Shaster]

 

Perhaps it'll be better to just mic up one cab, as what sounds like night and day to you on stage is an inaudible difference out front.

 

 

Quite true IME.

 

Guitar players often live in a fantasy world where they're positive that their golden tone will be transferred directly through the PA to the audience's ears (I play guitar, been there). But as Mogwix has noted, sound engineers deal with the reality of placing the guitar into the big picture - a good overall mix.

 

To that end I would suggest that if you go with the Rolls or something similar, you only use it when you have to. I would suspect that the typical sound tech listens to your two guitar amps fiddles a bit, and then might even just pick the one he/she likes. If you're always combining the two amps you're taking away that possibility (maybe that's what you want to do), which means that the amps better combine very well together. Otherwise the tech will have to fiddle with the volumes up on stage (versus at the board).

 

Just a thought.

[agedhorse]

Good grief there's some bad info here...

 

Combining 2 like dynamic mics with a Y cable is not a problem (for most practical applications anyway).

 

Transformer combiners are not required as many dynamics (like 57's) have transformers inside them. Also, the voice coil and magnet of the capsule look just like a transformer anyway. There are some minor resonance and impedance curve effects that may alter the tone alittle bit, but pretty small stuff. You could use 150 ohm buildout resistors in the Y cable to eliminate most of this effect if it was that important.

 

Phase/polarity makes no difference in this case when combining, you would NOT want to reverse the polarity of one mic because the signals are different, and in fact it would be a problem because of the bleed. This suggestion is a classic misunderstanding of basic principles.

 

Summing a signal with a mixer or passively makes no difference with regard to phase or polarity. A mixer allows buffering of the signal and isolation between sources, higher load impedances, (make-up) gain, etc.

 

Doesn't matter about the length of the cables, the signal moves at the speed of light. Remember the guy here a few years ago who said he (and his clients) could tell the difference between a 25' and 50' mic cable on arrival times? Craig snuffed him good after his a-hole side emerged when presented with the fact that signal travels through a mic cable at the speed of light and there is less than 0.00001 degrees of phase shift due to the extra 25' of cable. Of course we were all wrong in his mind, but often bull{censored}ters believe their own dung.

[Craig Vecchione]

 

Good grief there's some bad info here... Combining 2 like dynamic mics with a Y cable is not a problem (for most practical applications anyway). Transformer combiners are not required as many dynamics (like 57's) have transformers inside them. Also, the voice coil and magnet of the capsule look just like a transformer anyway. There are some minor resonance and impedance curve effects that may alter the tone alittle bit, but pretty small stuff. You could use 150 ohm buildout resistors in the Y cable to eliminate most of this effect if it was that important. Phase/polarity makes no difference in this case when combining, you would NOT want to reverse the polarity of one mic because the signals are different, and in fact it would be a problem because of the bleed. This suggestion is a classic misunderstanding of basic principles. Summing a signal with a mixer or passively makes no difference with regard to phase or polarity. A mixer allows buffering of the signal and isolation between sources, higher load impedances, (make-up) gain, etc. Doesn't matter about the length of the cables, the signal moves at the speed of light. Remember the guy here a few years ago who said he (and his clients) could tell the difference between a 25' and 50' mic cable on arrival times? Craig snuffed him good after his a-hole side emerged when presented with the fact that signal travels through a mic cable at the speed of light and there is less than 0.00001 degrees of phase shift due to the extra 25' of cable. Of course we were all wrong in his mind, but often bull{censored}ters believe their own dung.

 

 

That was Nick..."where02190" (among his dozen or so be-back accounts), and he claimed Tony Bennett was the client who insisted his sidefills have identical cable lengths. Taking all factors into consideration, moving his head or the mic position a few inches would make more of a difference than the cable length, since sound travels much slower than electrons. I wonder how they "centered" him...maybe a laser rangefinder and transit...

[Craig Vecchione]

 

That looks like it may be a bit more than I need, isn't it? I don't really need to mix the mics, and I don't need stereo outputs. I just need a way to sum the two signals, but that does look really nice. ... Isn't the Rolls unit a bit beyond what I need though? For as nice as it looks, I can't help but feel like it might be a bit overkill, right?

 

 

There may be an even simpler unit in their list of products. Have a look. I figured this was a good choice because it has good basic controls. It's only $120, and if it's like other Rolls products it's sturdy if not glamorous.

[The Real MC]

 

Remember the guy here a few years ago who said he (and his clients) could tell the difference between a 25' and 50' mic cable on arrival times? Craig snuffed him good after his a-hole side emerged when presented with the fact that signal travels through a mic cable at the speed of light and there is less than 0.00001 degrees of phase shift due to the extra 25' of cable. Of course we were all wrong in his mind, but often bull{censored}ters believe their own dung.

 

 

I rebuked him here

 

 

It takes one nanosecond (0.000000001 milliseconds) for an electron to travel fourteen inches of a conductor. The smallest delay that the human ear can perceive is 20-30 milliseconds. In order for the human ear to hear the perceived delay in two non-equal cables, it would require one cable to be 4,419,191 miles longer than the other. 0.000000001 milliseconds = 14 inches Multiply both sides by 20,000,000,000 20 milliseconds = 280,000,000,000 inches = 23,333,333,333 ft = 4,419,191 miles You'll never hear the delay of even a 50 ft difference in cable length.

 

 

I don't miss people who are incapable of admitting they are wrong.

[Craig Vecchione]

Good times.

[Dogoth]

That was Nick..."where02190" (among his dozen or so be-back accounts), and he claimed Tony Bennett was the client who insisted his sidefills have identical cable lengths. Taking all factors into consideration, moving his head or the mic position a few inches would make more of a difference than the cable length, since sound travels much slower than electrons. I wonder how they "centered" him...maybe a laser rangefinder and transit...

 

Quick get out the survey crew, Here comes the star!

 

Actualy I've read a couple of articles from Tony Bennett's FOH guy. He seems very down to earth and intuitive. Mostly I liked his message: "It's about the music and nothing else" (if I recall, one article was about deeper & more acurate bass rather than just more of it :>)

[Bobby1Note]

 

I rebuked him here I don't miss people who are incapable of admitting they are wrong.

 

 

That math is off. Milliseconds, is thousandths of a second, not millionths. That's a microsecond.