Mixing Live Sound

Lesson 4 of 17

Grounding and Ground Loops

 

Mixing Live Sound

Lesson 4 of 17

Grounding and Ground Loops

 

Lesson Info

Grounding and Ground Loops

Now we want to talk about it something super important that everybody always talks about everybody tries to figure out it's maybe one of the biggest problems with mixing live sound um and that is ground loops if you guys know what ground loops are ground loops are basically situations where well, first of all, before we talk about ground let's, just talk about what a ground actually is. So in every circuit like I said, you have in a in a single face system you have too hot a neutral on the ground and what the ground is built in for is it's made as a path of least resistance for electricity so that if there's any extra electricity that doesn't get used up in the circuit that electricity goes back into the earth. If that wasn't the case and you had anything with a conductor like a medal chassis on a microphone or anything and there wasn't a proper ground, any extra electricity in the circuit can actually go through your hand if you're touching the body or the external part of the microph...

one or whatever it is and through your feet into the ground because electricity eventually wants to go the path of least resistance it wants to make it into the ground um so typically in your house when you see the bottom plug, that ground actually goes into the circuit breaker and then goes into the actual earth and that electricity just gets dissipated so because it's the path of least resistance if there's a ground on the circuit that electricity that gets left over in the circuit that's not being used finds its way to the earth ground, it goes all the way into the earth. What can happen sometimes is if you have two parts of the sound system that are on separate circuits and they're both grounded, then essentially what happens is you've created antenna because you have one ground appear that has electricity coming through and another one here that has electricity come through and those two can meet up in the ground they khun basically create a magnetic field through being connected up top on being connected to the bottom, and you've basically created kind of a radio antenna under the ground, and what that ends up happening is that sometimes create a magnetic interference on anything plug into that circuit and that turns into what you hear is like a low frequency hum. So if you've ever, like, plugged in something and you hear that like fifty or sixty hertz hum come through the sound system um it's most commonly associated with the ground loop, so, uh, how can you avoid ground loops? How can you make that happen? There's sort of two different ways? One way to avoid the ground loop is to make sure that anything that's connected to itself with signal, for example, microphone cable or guitar cable everything that's connected is on its way on the same circuit. This could be kind of tricky, especially if you're running multiple circuits, but if you have a large amperage circuits, but if you have your front of house mixing console and your stage boxes on separate circuits, you have the potential for creating ground loops. If they're on the same circuit, then it's off, then you they'll have the same ground, the same shared ground. It'll end up going back to the same spot, so if you could imagine in your head you basically have a device like a microphone, and that microphone has aground on the actual xlr cable and that's going to the front of house mixing console into the pre amp than that ground, then goes through the pre amp into the what's called the icy plug or the power plug, and that ground goes into the circuit, which then gets plugged into the ground. So if there's any electricity in that entire connection, it can make its way all the way to the ground now here's an example of where that can get a little tricky let's say you have a bass guitar on stage and the bass guitar, bass guitar, amp the bass guitar has a direct output so the direct output is plugged into an xlr cable that goes to your front of house mixing console, and that is grounded through the mixing console. But then the amplifier itself has its own ground that's plugged into a separate circuit on the stage. So now you have two grounds that air going into two separate ground circuits, and they're connected with that xlr cable in the middle, and that can often create what's, called a ground loop. So there's, sort of two ways that you could go about fixing that, like I said, one way would be to put them on the same circuit, and the other way would be to use what's, called a ground lift. Its very important understand when to use ground lifts, and when it's dangerous to use ground lifts, if both the circuits are properly grounded. So if you have a, um, amplifier that's grounded, and you have the consul, this grounded, you can lift the ground between them, because they'll both be grounded separately. If, however, the amplifier is not grounded and you lift the ground, when it's connected back to the front of house, you could potentially create a very dangerous circumstance for whoever is on stage to get electrocuted and the way that they would get electrocuted. Follow through this with me a little bit, if the amplifier is not grounded all like let's say for some reason the stage circuits on stage are not grounded which they absolutely should be but for some reason they're not or the ground gets messed up somehow hours there's lifted then if you connect the guitar players amp to an ungrounded circuit and his microphone is connected to a grounded circuit when he's holding his guitar and his hands on the guitar string and he goes up to the microphone if his lips touched the microphone now his guitar amp is going to be grounded through the microphone because if there's no ground for his guitar amp that electricity we'll travel up the guitar cable through his guitar strings and then if your lips touch his lips touch the microphone will find its way through the microphone out through the sound system and then to be grounded by the front house console. Obviously that is an incredibly dangerous situation, so it's very important to understand that if for any reason something on stage is not grounded, you should not lift the ground um of that specific signal another example would be in the way that this happens sometimes you'll have like hand wired guitar to bands that will have a ground left switch on it so you've got the amplifier and its buzzing a little bit so you flipped the ground left switch on the buzz goes away but now that amplifiers not grounded anymore it's, no longer reaching the ground on stage. A lot of like, you know, custom to banks will have that switch. If then the guitar player starts playing and, like I said, somehow comes in contact with the grounded circuit that is connected to the front of house console, then his guitar amp will now ground itself through that physical connection. It happens too often, you should make sure that that you're very careful about that, thea other situation would be if you have a piece of gear that's not properly grounded like a sometimes bands will show up with, like a handmade guitar pedal or something. I mean, a pedal shouldn't be that big of a deal, but maybe a hand wired, and that they didn't include a ground in it. In which case, if that happens, then also you have to be very, very careful, because if there's no ground for the amplifier, the electricity will find its own ground whenever it's connected to a circuit that's grounded. Um, and then the ultimate worst scenario is if it's, a really shady place, and there is nothing is grounded in the circuit except the front of house counsel than anybody on stage could actually be electrocuted if they touch any part of the circuit, because all of their anything there touching then becomes sort of a natural ground, so you have to make sure that you're you're avoiding ground loops, you're eliminating ground loops by lifting grounds and not duplicating ground. So you create that ground loop circuit, but at the same time, you also very clear to understand exactly how that works so that you don't create a situation where someone could get hurt or could get electrocuted, those air sort of the two things to balance, and we've got some questions, so I'm gonna jump in and look at these first question joe says, what causes you to get shocked by a microphone? Does it have to do with grounding? Yeah, so I kind of just answered that that's that's, basically, what happens is if the guitar amp or whoever is on stage playing has something that they're touching, that is not properly grounded and they touch the microphone that is properly grounded, then whatever they're playing on stage will find its way to the natural ground connected to front of house. Um, how can I test if I'm being supplied a proper ground for my circuit? That's a good question. The best way to find out how to test for a proper ground is to have an electrician's teo test on the actual circuits, and I know that's not the best answer, but that's the absolute, safest way. There are devices that you could buy that test circuits to see if they're properly grounded, and sometimes those could be accurate. But the only true way to know is to actually have an electrician's come out and make sure that the circuits properly grounded. If you plug that there's a lot of signs that that show you that something is not properly grounded. If you plug something into a circuit and it's sort of, like lightly shocks you or you, you know you can sort of sense that there's extra electricity it's not being grounded. You can sometimes see that or figured out on your own, but usually that's kind of a dangerous situation, too. So the rial safest way is tohave an official electrician's. Make sure that a circuit is properly grounded, dave jay asks when you talk about lifting grounds, are you referring to lifting the audio ground connection or the power ground connection that's a great question, so the answer is sort of twofold. If you were connecting a audio ground connection, so say you have a d I box that's plugged into a that's plugged into a keyboard onda also plugged in with an xlr cable to your front of house counsel. The d ay box will have a signal ground lift, and what that does is it basically disconnects the ground from the dicks connects the ground in the signal path on the xlr cable from the keyboard to the front house console so those air now no longer connected ground circuits they're too isolated ground circuits the a c ground lift is sometimes included in guitar amps and like I said, that's typically a dangerous situation because if you're lifting the ground on the circuit then it's not properly grounded by itself and if it's not physically connected with an xlr cable for example to another ground then it's not grounded at all? Um, there are situations when you can lift a ground safely, but most of those situations are not on stage because there's too many opportunities like, for example, accidentally touching a microphone on a separate circuit that can create potential problems. Sometimes you'll see people sort of make a homemade acey grounds lift and they'll take the three pronged break off the bottom prongs so that's sort of like your your homemade ground lift again that's that shouldn't be used for anything on stage because anybody on stage that's physically touching another microphone could if you lifted that ground then could be the ground connection between whatever you ground lifted a c ground lifted and a grounded circuit okay, another great question when you're using a generator how is the ground created so there's sort of two parts there's two types of grounds one is called a chassis ground and what is called an earth ground so typically, generator's actually do have a steak that you put in the ground that actually creates a physical ground. A lot of times, you'll also have chassis grounds, which basically means that the ground circuit touches enough of the chassis that the electricity has dissipated across the entire circuit. That's typically not with generators that's, usually with things like car stereos or obviously, you can't ground your car because your car would be able to go anywhere s o most things in your car chassis grounded the ground is actually connected to the frame of the car, which is metal, and so that's enough of a dissipated space to dissipate that electricity, but typically, um, that's kind of how that works with that there's sort of a difference between a ground left in the chassis, your ground earth ground in a chassis ground um, how does the ground lift work on a d I box just got that question that's actually very, very simple aground lift. So if you look at it xlr cable, you have, um, the positive, the negative in the ground. Basically, all a d I box does with ground lift is it disconnects the ground pin on the xlr cable, so the two grounds on either side are no longer connected that's the ground left switch

Class Description

Mixing Live Sound can be one of the most daunting tasks for any engineer. In this class, Zach Varnell will walk you through the entire live sound production workflow, from loading in a PA and rigging and flying speakers to soundcheck and mixing on the fly.

In this class, you will get to see an entire day of load-in from Seattle's Capitol Hill Block Party along with a complete breakdown of a live sound production workflow and interviews with some of the country's top touring live sound engineers. You will learn:

  • Scaleable components of a live sound PA
  • Power distribution and management
  • Tuning speakers with a SMART system and FFT analysis
  • Mic Placement and tips for an effective soundcheck
  • Mixing front of house
  • Mixing for stage monitors and in-ears

We'll also walk through a live mix setup and interview with two touring engineers from their FOH mix position: Adam Jackson and Andy Frost (FOH and Monitor engineers for Christina Perri) and Shane Bardiau (Twenty One Pilots).

Whether you are a working live sound engineer and just want to brush up on some core concepts or you are a new engineer looking to get into live sound production, this is the place to learn all about live sound in one location.

Reviews

user ee67bf
 

A very good overview of live sound presented by a professional sound technician. Good supporting video of a real event that Zach worked. He explained everything very well and I enjoyed the split screen views of his console work. Good job.

PGApromike
 

Was fortunate to watch this live. Zach clearly is a master of his craft. I am a home studio drummer but learned allot about mixing and sound. Thank you Creative Live and Zach Varnell.

Cary Knoop
 

Extremely useful class and great presentation!