Signal and Power Cables

 

Mixing Live Sound

 

Lesson Info

Signal and Power Cables

There's a lot of different types of cable that used to plug speakers in one of the most common types of cables what's called en el cable. It looks like this that uses to speak on connector, and they plug into this, they lock and switch and you have to unlock them. They're really solid. And the cool thing about en el cable is that there's n l two and a four and a eight, you can actually send more than one signal through one speaker cable, which is really, really helpful if you're running really long runs from where your amplifier ax are eso with our speakers that we flew, they were all self powered, the amplifiers were built into the speakers themselves. Um, but with a lot of speakers, you have the amplifiers on this side of the stage, and then you have to run cable speaker cable up to the actual amplifier, and so in order to do that, sometimes you have separate amplifiers power in different parts of the circuit. We'll get this, then we'll talk about loud speakers, but sometimes you'll ...

have amplifiers just powering the mid range of the tweeters and separate amplifiers powering the subwoofers. So instead of having to run a separate cable from each amplifier to each type of speaker you, khun run l a cable, which actually sends four signals since eight total channels so positive and negative for four channels in one cable and then from that lake cable, you can split off the outputs to whatever speaker you're plugging into so you can run both the mid range, the tweeters and the subwoofers, all on one cable up to the top of the speaker and then down to and distributed down to whatever speaker you're plugging into. S o n o cables really, really helpful t do that with, um, make sure that speaker cable is typically heavier gauge than microphone or instrument cable. A lot of speaker cable has quarter inch connectors on it, so it can be it can sometimes look like a like a guitar cable, but speaker cable is usually like twelve or thirteen gauge actual copper wire, and that gauge allows you to have enough impedance have enough resistance to be able to teo pass high power, um, electricity down that cable, which isn't the case for like a guitar cable, which has a really, really high impedance or low resistance on the thickness of the actual copper s o make sure that when you're using a speaker cable, you're using an actual speaker cable the cable itself is high enough gauge to be used for powered situations, and you're not just substituting guitar cable. So a lot of times speaker cables will have a quarter inch connection just like it gets hard jack and then finally sometimes and this is much, much less common now, but you'll have banana plugs will you'll actually have just bare wire of positive and negative and you'll plug them into a plug or just wire them into the back kind of like you with your home stereo? Um so those the types of cables and connections um okay, one more thing about power and this is going to get a little bit geeky but it's important to understand we're not going to dive into this a ton again. I really recommend the yamaha sound reinforcement guide if if you want to look through there this goes into great detail to explain how powers measured we're going to talk about this unit of measurement called the decibel so what is a decibel? A decibel is actually a unit of measurement to measure electricity and you might be thinking like that's weird because I swore that a decibel was supposed to measure how loud something is that's how typically people use it on dh that's true one type of a decibel is what's called a dbs pl which does measure sound pressure measures how loud something is and we'll get to that but that's not actually where it comes from the original use of a decibel was using to measure electricity um this is what's interesting about a decibel it's not an absolute measurement it's a relative measurement which means that if I say something is like seventeen volts that's an absolute measurement I know exactly how many volts something is it's seventeen votes because I know how much one volt is a decibel measurement is a relative measurement which means it's not actually accurate to say like this is fourteen decibels if you were to say this is fourteen decibels that actually makes no sense at all a desk a relative measurement is a way of comparing two different measurements so if I was to say this electrical measurement is fourteen decibels mohr than this measurement then that's correct that's the proper way to use it you're basically comparing two things the other thing that they've set up they got used a lot with electricity is being able to compare decibels against what's called a zero reference value eso if I was to use a measurement like a dbm where a d b u d b m or d b v then I could say something is plus for de bu which we'll get to in a second because it means that it is four decibels mohr than zero reference value for d b u so I know it gets kind of complicated but it's important understand especially when you're mixing live sound because if you look at all of your favours they're all measured in decibels um and zero decibels is not no sound right? Negative infinity is no sound. If you look at a typical fader here, zero is, um no change at all to the sound. If I set the fader zero, it means that the signal coming into the pre amp is passing through to the other side with no change. Zero is no change at all. It's, not zero sound it's. No change. If I bring it down to negative ten. It now means that the output signal is ten decibels less than the input signal. If I bring it up to plus six, it means that the output signal is six decibels mohr than the input signal. So understanding the decibels are relative measurement is important to understand how they sort of interact. So what actually is a decibel and how is it measured? A decibel is technically considered one tenth of a bell. It was named after alexander graham bell it's, a relative unit, and the technical definition is a it's, a log arrhythmic ratio of to power quantities. So if I say one zero d b, our decibel is equal to ten times the log. A rhythm of pee one overpay to it means that if I'm comparing to power quantities, for example, the input of a fader and the output of a fader, the log arrhythmic ratio between those two power quantities is what a decibel is. I know that kind of gets a little confusing there's different ways to measure electricity obviously we could measure power or voltage d b u is a measurement of electrical voltage and zero d bu is actually point seven seven, five votes so if I say something is plus three d b you it means that it's three decibels mohr than point seven seven five bolts again that's not like that's not don't worry about the super technical side of that I'm just sort of giving you reference for what these are for measuring power dbm zero dbm is equal to one miller what so if I say something is like plus six dbm that it means that six decibels more than one million watts um d b v mdb capital vieira other ones that are used sometimes and dbs pl is probably the one you're used to so zero dbs pl which is a measurement of sound pressure in the air is immeasurable. Zero dbs pl is basically what's called the threshold of hearing so in the perfect, most quiet room in the world zero dbs pl is no sound there's almost nothing in your life I guarantee that zero dbs pl even like a neighborhood street at you know two in the morning that's perfectly quiet is still like you know thirty dvs pl on all the way up to like a rock concert is typically hundred dbs pl a jet taking off is one hundred twenty dbs pl um all those sort of spl measurements are relative to what people are used to hearing so it's a relative measurement it's also important understand that when you're using things like gain structure, deep decibels are measuring the relative value of two different of usually input and output. So if I say like a compressor is increasing something plus six d b, it means that the output is six decibels more than the input it's a relative thing, it doesn't mean that it's six decibels difference between really quiet and a little bit more quiet is the same as six decibels between pretty loud and really loud. Obviously the difference is going to be much greater, but it's still sixty b'more because it's relative to what's being pope what's coming in on the input so without geeking out too much about that that's just sort of the background of where dbs pl comes from it's used on recording consoles it's used in mixing understanding what a decibel is and how it's measured that it's a relative values really important without getting into the math specifically knowing that a decibel is a relative measurement and it's based on a log arrhythmic ratio typically plus three dbs pl is about twice a cz much power is something so if I increase something by plus three that usually means that I'm increasing it by um twice a cz much power if I increase something by um uh ten d b I'm sorry by sixty be that means it's ten times is loud so it kind of just depends on what signal you're starting with but understanding sort of what that means when somebody asked you to turn up something three decibels that usually means they would ask them to double how loud something is um those were just good things to keep in mind um okay so we're going to talk about patching and snakes when we come back from the break right now if you guys have any questions please send them over my way we're going to sort of recap all this stuff about power and electricity now that we know sort of the basics of how power works how we get electricity to our sound system and then how we distribute audio to the speakers and get them ready to fly on ready to start running sound we can start actually doing the fun stuff of actually plugging in microphones and setting up a stage and starting to mix which we're going to get into here in a second so let me answer some questions how can you tell the difference between instrument cable and speaker cable just looking at the cable without seeing the wires inside? Excellent question people ask us all the time the only way to tell the difference by looking at it is to look at the thickness of the cable you don't actually have to peel back the insulation but you can tell after a time you can tell you get the ability to tell just how thick a speaker cable is versus instrument cable sometimes they get tricky too because monster cables air you know like high end guitar cables can be extra thick and so it's it's confusing but typically you khun sense how heavy the cable is based on how much coppers inside the only way to really know is to know when you get the cable whether it's a speaker cable or what the gauges so there's no physical marking to tell people always I think that there's some trick there's not really a trick you just have to know what the gage thickness of the gauge of the wire actually is on the inside um what's d b v s o d b you just kind of answer this question and di b u was a measurement of voltage that was adopted by and this is the super geeky response but you asked for it it was adopted by the american engineering society it was set up to be the same zero reference value is dbm so when you ran point seven seven five volts of electricity into a six hundred home telephone line you end up with one mil a lot of power and that's why they used point seven seven five volts and zero d b and one mil a lot for dbm at the same time that the u s was doing that the european broadcasting union instead insisted on splitting the two and coming up with d b v which was reference value of one volt instead of sticking with point seven seven five volts so they sort of ended up with two different measurements that have still made their way through time so that's sort of the geeky response but basically it's the same unit it's just a different reference value that different sort of organizing bodies have adopted um is it advisable to bring your own to twenty box and use it instead of going through the house electric um your own to twenty box so I'm assuming you mean your own power distribution system on dh that is that's absolutely common there sometimes when you can pull from a especially like larger venues things like you know schools or churches or arenas or event centers a lot of times they will have an electrician's on site that they will allow you to patch all four of the single phase legs into your own two hundred twenty box or your two hundred twenty volt distribution box and a lot of times that's really easy because then you know exactly what you're getting you're getting four legs of clean single phase power and you're creating your own circuits and you don't have to worry about the circuits of the house it kind of depends on the situation there is definitely a lot of situations where showing up with your own um power distribution box just saves a lot of time and hassle because you know exactly what you're going to get but sometimes that could be harder if there's a venue where they don't they're not set up to give you those feeds then it's probably not possible it just kind of depends on what the venues like inputs and out uh tackiest asks input and output signal is the same as zero dbs but you have to consider the panning love the consul, right. Thanks for the seminar. Thanks so much for the question. Yeah, I mean, ideally I what I meant by that was just that the definition of a decibel means that zero d b is not changing. The fader itself is not changing the input for the opera section, depending on how that channel is bust. Um if it's bussed to a stereo output and its pants center obviously it's going to be different. What I was just using to illustrate is that the fader itself said it zero d b is meant to mean that that fader is changing it by zero decibels obviously just sending it zero doesn't necessarily mean that all the way from the input to the output of the master bus is going to be zero. It just means that that fader um zero d b is intended to me no change in the signal from the fader itself, josi asks, I see guys referencing d b f s quite a bit. Can you touch on that? Yes, absolutely I'm so sorry. I forgot to mention that that was the last d b reference value. So all of the d b decibel reference values that I've talked about so far all analog values, their measurements of electricity d b f s is actually a measurement of digital audio. It stands for d b full scale decibel full scale that the difference with d b f s than all other measurements is you can't go above zero zero is the absolute point at which the audio starts to clip it's the absolute maximum headroom of the digital audio converter. The negative point, like the lowest point in the signal, is actually a product of both the sample rate and the bit depth, so you could go down negative ninety six, for example, on a forty four one twenty four bit circuit or a twenty for bit abc, but zero d b f s is gonna be the loudest, so on a zero dbs full scale you start a zero at the very top and work negative down to there. That's. What zero d b f fs means.

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!