Mixing Live Sound

Lesson 5 of 17

Powering Speakers

 

Mixing Live Sound

Lesson 5 of 17

Powering Speakers

 

Lesson Info

Powering Speakers

Let's, talk a little about powering speakers so typically with speakers once you get electricity to all of your circuits, you finally have all of the electrical figured out you're ready to start actually plugging amplifiers into speakers s so I should clarify just really quickly there's something there's sort of a difference to different types of speakers, there's, passive speakers and active speakers passive speakers are just literally the speaker with a driver in an enclosure with two connections on the back, and typically what you have to do with passes speakers is provide an amplifier that actually takes the signal on dh amplifies the power by creating a buy by increasing the actual wattage of the signal to be able to push those speakers back and forth for a variety of reasons which will get into the second. A lot of speakers for front of house applications are now being self powered, which means or active speakers, which means that the amplifiers are actually built into the speake...

r itself. So if you look at the back instead of having just a positive and a negative speaker cable connection, you could actually just plug your sound system right into the back of the speaker and all of the power handling has done for you if you're actually connecting speakers to amplifiers, you need to understand about that what the amplifier load is and what the speaker can handle and to make sure that your matching the resistance across both the output of the amplifier and the input of the speaker so we're going to get into a little bit of that here we're going to talk about power handling, sort of how you match power between an amplifier and a speaker. We'll talk about impedance matching we'll talk about siri's versus parallel wiring bridge mode of amplifiers we'll talk about how you can accidentally damage speakers, and then we'll go through some really just basic connection types um, so speaker power handling there's typically and fires are rated on how much output power they have s o if you look at a typical amplifier used for for for a public address system for speakers, you'll see that it will typically be a stereo amplifier, meaning it has two channels and a channel on b channel, and you might see something like six hundred watts stereo amplifier, three hundred fifty watts at each for each channel at eight homes so you might see something that says something like that it's important to understand what that rating is actually telling you, is it giving you the continuous wattage, the program wattage of the peak power wattage? This is very similar to sort of the amperage that you're drawing from a circuit the continuous means without the speakers actually making any noise and the amplifier actually pushing any signal if it's just sending out power how much power will be coming out without any actual program material program what it shows you that at typical volume you'll have power coming through the amplifier on and this is about how much power will actually coming through overtime um over a consistent long period of time and then the third one is peak power and the peak power basically shows the maximum amount of electrical power that the amplifier could push up to at any one time even if it was just for a second so it's understand it's important to understand that you don't have to actually use the peak power like you would for amperage looking at the programme power and then giving you a little bit of headroom for wattage when you're matching it to a speaker is important power is affected by impedance so remember the relationship between electrical power and resistance on a circuit so if I reduce the resistance I will increase our sorry if I reduced the resistance I will decrease the amount of power that gets created in vice versa eso if a speaker is rated at eight homes for example and I connect that I'm sorry if I an amplifier it gives me a power rating at eight homes and I connected to a speaker that's forums then the power is going to increase because it's pushing through a smaller tube imagine that that a dome water pipe gets turned into a four on water pipe in the same model water's coming through the water pressure is going to go up because you're putting more resistance back on the amplifier. Typically, amplifiers will give you a rating for all for multiple resistance is so it will say something like three hundred watts of eight homes, six hundred watt stereo amplifier at eight homes, eight hundred watt stereo at four owns, so if you're connecting it to a nato speaker, you'll end up with six hundred watts, but if you connect it to a forum speaker, you'll have more power, you'll have eight homes, so you need to both know the impedance of the speaker and sort of the maximum power rating that they can handle. Um, big question is what's more dangerous, overpowering a speaker or under powering a speaker? This may seem counterintuitive, but it's actually more dangerous for the speaker toe under power than it is to overpower it. If you connect a five hundred watt speaker amplifier to a four hundred watt speaker, all you have to do is turn down the output of the amplifier, and you'll have plenty of signal to work with. However, if you have a two hundred watt amplifier and you're connecting it to a four hundred watt speaker than if you're trying to push the level from your console into the amplifier and there's not enough power to drive it you can end up distorting or clipping the signal and that clip signal running through the speaker can actually doom or damage even at low power than a higher power over powered signal coming through typically if you overpower a speaker it'll just get loud and distorted and you won't be ableto you'll lose clarity, but if you try to drive the line level output of your console into a power amplifier that's under powering a speaker you could end up distorting the signal and that distorting signal causes the speaker cone to sometimes get damaged um so impedance matching you should always match the impedance if you haven't a home output on amplifier connected to a nato speaker it's just that simple think about the water pipe analogy the relationship between resistance and power parallel versus siri's wiring so this is less important now that people are not hand wiring speakers typically you'll have, um connections but you khun daisy chain speakers that will change this so there's sort of three ways toe wire speakers to a two on amplifier and how you connect them changes the net impedance across the entire speaker system s so let's say for example that you run them in siri's this is super uncommon it usually was done when you actually had physical wire that you were actually connecting the positive the negative teach cable connecting them in serious would be that instead of daisy chaining them, you actually connect the positive to the first one, then the negative of that next speaker to the positive of the next one on the negative of that speaker to the positive, the next one, and then the end of the chain would go back to the negative of the other speaker. So in that situation, if you're connecting them in syria's, the signal's flowing all the way through the speakers, and all the way back to the beginning on dh, if you connect the speakers that way, what ends up happening is every the impedance of every single speaker in the chain just gets added, so if you have, for example, three speakers at eight homes and they're connected in siri's, then you'll end up with twenty four homes across the entire circuit, which makes sense because what would happen if you have twenty four homes across the circuit that's actually supposed to be driving a tomes, obviously it's a much bigger pipe? The load is much smaller to push because it's being distributed across three speakers and so the power is going to drop dramatically eso connecting three speakers in siri's, you'll end up with a pretty big drop in the electrical power that'll come on the outside, um connecting them in parallel, however connects all of the positives together and all of the negatives together on the same exact circuit, so they're all parallel connected and typically how you decide this. The net impedance across the parallel circuit of speakers is you'll have if you have three speakers at eight homes, you take eight homes divided by three, so you end up with lower power. It actually increases the amount of the load that is pushing because it's, pushing all three speakers at the same time instead of dividing it across the entire circuit, sort of a way to get around both of these is that you can create a giant network of syrup speakers and what's called siri's parallel, where basically you have three separate sets of speakers in siri's, and each of those sets are connected parallel, so the decrease in impedance across each of the siri's is counteracted with the parallel nature of all three, and you set up with the net. The net impedance across the whole circuit is actually the same as just one speaker that's the best way to start it evenly distributed load across the entire set of speakers. Um, again, there's a lot of information on how to get into this specifically in the yamaha sound reinforcement guy definitely check that out. It has tons of diagrams that goes through and explains siri's parallel and serious parallel wiring if you have wired up guitar cabinets like a four by ten guitar cab, for example typically you'd want a wire those four speakers in siri's parallel that would allow you to distribute the load across all four speakers evenly back to the original amplifier. So look at some of those diagrams looks some of that up online we'll put up some links on the course page later on today is that you can see those on get some more information on that stuff. But understanding the basic thing is understanding that how you connect speakers to an amplifier is affects the sort of overall load and then finally most after fires have what's called bridge mode and what bridge mo does his bridge mode basically allows you to take both sides of the amplifier and combine it into one amplifier. So if you have an eight hundred watt stereo amp which is four hundred watts per channel you khun bridge the two together to create an eight hundred watt single channel amplifier and typically how this happens is both sides of the amplifier will have one hot and one neutral one hot one neutral and what it does is it takes both hearts and puts them together so that you have twice as much power with no neutral it's very similar to the way that single phase power actually works on bridge mo typically have an answer for how you would set it up there's usually a switch on the back that you just switch it into bridge mode and then there's usually a separate output that you plug the speakers into that's now the bridged output so that's that's sometimes helpful to know to again this is all on lee applying to speakers that are passive that you're connected to amplifiers um so like I talked about damaging speakers you can sometimes damage speakers with harmonic distortion below is a picture of a clip sine waves so if I'm driving into the amplifier too hard the signal can get clipped at the top because there's not enough power that I'm pushing out and that clipping well instead of the speaker moving back and forth evenly and smoothly when it gets to the top jolts back to the bottom and back to the top again and that jolting movement can sometimes cause damage to the speaker cone or to the driver so under powering a speaker can actually cause that damage from that distortion more so than overpowering speaker um okay I'm gonna answer some questions here let's see so as long as the base sam going back to grounding as long as the bass amp in front of house border on the same circuit the direct out of the amp can be plugged into the board with no loop many times when my board is on fire wire mode I'm having luke home issues yeah so the idea is if both the d id signal like your laptop, for example, and the front house counsel, if they're on the same circuit, they should be able to be connected without getting a ground loop because they're being grounded by the same circuit. Um, sometimes you can try lifting the ground as long as both of them are grounded properly to the same circuit, and that can sometimes resolve the issue. But most of the time, a ground loop is caused by the source and the destination being grounded on separate circuits, and so they're in there connecting, creating a magnetic field to connect underneath in the ground. Did you use earth ground at capitol hill? Block party? Yes. So the generator is grounded with the earth. We didn't show up, but the generator actually has a stake that goes into the earth. So it's very important that everything, especially the festival like that. Where there's a lot of bands coming on enough stage that everything is properly grounded. So all of the front of house actually gets power, gets run backstage over the snake. So all the power's coming from one location it's, all coming from the generator box and all of that is properly grounded, so there's, very little chance for people to get shocked. There was an example where a band showed up with a guitar amplifier that didn't have a proper ground in it. It was buzzing, and so we flipped the ground, and the singer actually could feel getting slightly shocked by the microphone because his guitar amp wasn't grounded wasn't grounded properly. And so when he connected to the microphone, he now became the ground connection to front of house, so we made sure not to lift the ground on his amplifier so that that wouldn't happen, and we just had to deal with the buzz because it's more important that actually people are safe, obviously, than trying to get rid of a buzz that's coming from his amplifier, which isn't properly grounded. So, um, last question, how do you make sure the lighting rig doesn't interfere with the sound rig? That's actually, a great question, so if you're working in a live sound situation, a lot of times you'll have lighting text there, right? And they'll have lighting boards, it's becoming less and less common now that people are using led and digital lights led lights, typically with older lights, you have huge dimmer packs or dim iraq's that actually have transformers inside, and those transformers resist the amount of electricity that gets sent to the to the lights. And by doing so, create, you know, a dimming effect that electricity then gets pushed back into the ground. And if the dimmer pack is on the same circuit is your audio pack, you're forcing a lot of low and sixty hertz. Extra electricity into the same ground circuit is your audio equipment, and it can often cause buzzing or ground loops. It's very important to make sure that your lighting rig is on a separate circuit than the south. If you saw in the video, we had completely separate distribution boxes for lighting and for audio, because we keep them absolutely completely separate in situations where they're led. Lights it's less important, it's. Less common that you'll see ground loops. But as good practice, it's just always better to make sure that the lighting and the electricity and the sound are always complete on separate circuits.

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.

Cary Knoop
 

Extremely useful class and great presentation!