Mono vs. Stereo Sound System

Should you run your sound system in mono or in stereo? You want everyone to get the same mix, right? We'll go over the pros and cons of each, and even head into the Nerd Zone to find out what's really happening with multiple speakers in the same space.

Hey, if you're new here, my name is James and I help sound techs save the day by making things sound better and eliminating distractions. So if you're planning on running sound at the pub on Friday or church on Sunday, you're in the right place.

The Case for a Mono Sound System

Two goals that we have in live sound are consistency and intelligibility. We want everybody to get about the same mix, and we want it to be as intelligible as possible. Nobody leaves humming the kick drum, so we need to make our vocals loud and clear, even in our quest for mix energy.

We also want to deliver the best mix for every single seat in the listening area. The idea behind choosing a mono system is that people on the left side of the room want to hear the same thing as the people on the right side of the room. So if you have the same mix coming from a similar speaker to both sides of the room then, potentially, you're getting the most consistency from spot to spot. With a bigger room, if we pan something all the way to one side and all the way to the other, people on the opposite sides wouldn't hear that thing very well. It's not like in the studio where we have stereo and people are hearing both speakers equally. So in brief, that's the case for having a mono sound system.

Benefits of a Stereo Sound System

Now let's talk about the arguments for a stereo system. The most important input that we have is the lead vocal. So we have to make sure that the lead vocal is not covered up or masked by any other input. So that means that we need to pull it down either in level overall or with certain frequencies to make space for that lead vocal to sit on top of the mix, but not so far out in front that it feels like it's by itself.

With a stereo mix, we can move some things to the outside, or the sides of the mix, to make more room right in the middle for that lead vocal. Now that doesn't mean necessarily panning mono inputs hard left and hard right, but it includes some stereo techniques that we'll talk about more in just a second. In a studio environment, it's easy to pan mono sources hard left and hard right because we can assume that the listener is hearing both speakers wherever they're listening. Like we talked about a minute ago, people on the left side of your big room might not hear the right side of the P.A. or at least they're not going to hear it clearly.

Understanding Stereo Inputs

Now, I've talked about stereo inputs, but what do I mean by that? The stereo input is one that has different information on the left side and the right side, and it gives it some variation. It also is going to have some stuff that's in both channels equally. We call that the center channel and that's really what happens when we have two speakers or two sound sources that are producing the same sound at the same time. We perceive that as right in front of us if they're at equal level in timing. That's what's called the phantom center channel.

Technically speaking, it's all the stuff that's happening in both channels left and right, equally. So with the stereo input, some of these sounds and some of the tones are happening differently on the left side versus the right side. One good example of this that you might already have is a stereo keyboard with a stereo piano patch. A piano is a pretty large instrument, so there are different notes emanating from different parts of the piano. If we're close to it, we can perceive, “Okay, this note is coming a little bit more from over here. This is coming a little bit more from over there.” When we push up a stereo input, there’s less right in the middle that's competing for the space of that lead vocal, and the kick and the snare, if that's kind of what you're into.

Implementing Effects Using a Stereo System

Another cool thing about having a stereo P.A. is you get to use effects and some ear candy, or things that are really happening just on the left side, on the right side that aren't necessarily the critical backbone parts of your mix, but they add a little bit more excitement and a little bit more depth to the mix. Let's take toms, for example. If during a drum fill, the drummer plays the rack tom and then the floor tom, and that happens kind of left-to-right for the audience, that's going to give some “ooh” or interest to the listener. Even if they don't really notice it, they're going to notice that not everything is coming from exactly the same direction. In the effects realm, having a ping-pong delay, or a repeat of the vocal that happens on the left side and then the right side, can be a lot of fun to play with and it makes a lot of interest in your mix. It's especially helpful when you can highlight that one line of a song that needs to hang on just a little while longer. It's these little things that we can do as engineers that add that ear candy and creates interest for the listener. Again, we're just trying to amplify what's going on on stage and polish it up a little bit. This is one of those ways that we can put icing on the cake.

Experimenting with Panning

Another place we can have fun with stereo is with electric guitars, with two different delays on left and right. One standard one is to have an eighth note delay on one side and a quarter note delay on the other one. But things get really fun when we have a dotted eighth on one side and a quarter note on the other one. This adds some syncopation and some back and forth, and it really can be a lot of fun. It creates a soundscape rather than having everything coming from one direction. Now, if only there was a tool that could put sounds across the panorama of the soundscape. Maybe it's a potentiometer, so we can have a panoramic potentiometer. Oh wait, we do have a panoramic potentiometer! It's called the pan pot, or just pan for short. So now you know where that came from.

When you learn to drive, you are probably told to keep your hands on the steering wheel at ten and two. This gives you a good grip, and you can make turns and cross over and do all that fun stuff. You probably don't think about that a lot anymore if you've been driving for a while. But ten and two can be really helpful for our panning scheme as well. Let's take background vocals with the lead vocal, for example, and let's imagine that we have two of them or we have two different inputs that are balanced. This could be guitars, this could be keyboards, it could be background vocals, whatever you'd like. But ten and two is a good middle-of-the-road way to go. You can use panning as a tool to make your mix have more depth, and that includes for people on the left side and the right side.

The Nerd Zone - A Lesson on Pan Pots

Let's head to the Nerd Zone for just a little bit and talk about what the pan pot is actually doing. The pan pot is actually a logarithmic level control between left and right, where in the middle it's accommodating for how the sound is going to combine in free space and double in energy. Usually in normal, real life, this would mean a 6 dB boost. But with actual comb filtering and small differences between the speakers, we have our center point for our pan at 3 dB down for both sides. This is called the stereo pan law. As you turn the pan to one side or to the other, it turns up one side just a little bit and it turns down the other side quite a bit. As you move farther over, now you've turned it up all the way on one side and all the way off on the other.

So if we pan two of our vocals to 30% left and 30% right, now people on the left side are going to get a little bit more level on that left background vocal and a little bit less level on the right background vocal. And if this was just a purely sterile anechoic chamber that people were listening to, you might say, “Now you're changing the balance of those background vocals for one side of the room versus the other side of the room!” And while that's true, we're not in an anechoic chamber and there are reflections going on. So while you're getting less energy directly from that speaker, you're still getting more energy from the far-side speaker. That added energy and warm, reverberant sound adds a certain amount of space. So we didn't just change the balance of one versus the other. We added more space or depth to one background vocal versus another one.

And people on the opposite side are getting the opposite balance, right? The people on the right side of the room are hearing more of one vocal and they're hearing a farther away version of the other vocal. So it's not just that we change the balance. We've added space and depth by using a little bit of panning. And people right in the middle get just a little bit of separation left to right, and that's cool too. So you have to be careful with using your pan and you can't always go to the extremes, but for some things, you can.

Testing Out Panning on Your P.A.

You can test this out with your P.A. if you want. Take a signal and pan it all the way to one side so that it's only coming out of one speaker. Now walk to the other side of the room and you're still hearing sounds coming from that speaker. Even though they're not direct, you’re getting the reverberance and the bounces and the off-axis response of that speaker. So you're still getting that from the other side, but you're also getting a little bit less level on your side when you pan something over. Ten and two doesn't make it too extreme, and that's a good way to balance things out.

Now, the only problem with this is when somebody that was singing a background vocal is now singing the lead part and you have to compensate for that. And maybe those are other changes that you need to make and mix on-the-fly from song to song. Now, you could be a purist and argue that somebody on one side is getting an inferior mix because they're not getting the perfect balance of all of those vocal parts. And to that I say, if that's really important to you, and your band needs really tight harmonies where everybody gets the balance just the same, yeah, in that situation, keep them panned right in the middle. But you can do it for, say, two rhythm guitars or a guitar and a piano as well. And that can be pretty cool. Just don't go crazy, and walk around the room and check the different sides and make sure that it still works for everybody.

Playing with Hard Panning Live

The Nerd Zone - Binaural Hearing & Depth

Welcome back to the Nerd Zone! For today's lesson, let's jump into the subject of binaural hearing. Your ears perceive sounds that come from 360 degrees around your head, and up and down. This is called binaural hearing. It's really cool.

We're a lot better at localizing sounds on the horizontal plane than we are on the vertical plane, but we can still hear up and down pretty well. We localize sounds in two different ways (Or maybe three if you categorize them a different way. But basically, there are two). The first one is the level difference between our ears. If something's louder on the left side than it is on the right side, our brain says “That's coming from over there!” The other way is with timing. Lower frequencies will bend around your head, so it's hard to tell what the level difference is. You mostly hear a timing difference between left and right. So if a sound arrives at one ear before the other ear, our brain is like a big phase computer and it says, “Huh, the sound is coming from that direction!”

We also use sound cues to tell how close or far away something is. High frequencies dissipate over distance, so something that's farther away is going to sound darker, or there will be a lower proportion of high frequencies compared to the low frequencies. The other way we tell distance is by the proportion of direct sound to reflected sound. If you're standing in a gymnasium and somebody is really close to you and talking, you hear more of their direct sound from their voice than you do the reverberant sound. But if they move very far away, you're hearing more of the reverberant sound compared to the direct sound. But if we move outside to someplace where there are not a lot of reflections, we're not going to hear as many of the reflected sounds, but the sound will be darker the farther away they are. High frequencies dissipate over distance in the form of friction. So if something sounds really dark, it probably means that it's far away.

Now in live sound reinforcement, we’re trying to take two speakers to emulate what it's like for a lot of different sound sources and put them all so that they can cover a large area, so lots of people can enjoy the sound we make. With a mono system and our mixer, we can approximate depth by pulling something quieter or making it darker like it's farther away or adding artificial reverberation, which makes it feel like it's in a room or someplace else. When we add two speakers, we can place the same signal to both speakers at the same time, and if we're the same distance from both of those speakers, our brain will say, “Hey, I think that's coming from straight in front of me.” This is called the phantom center channel.

One problem that can get created when we have two different speakers with the same thing coming out of both of them is that not everybody is the exact same distance from both speakers. This causes the same sound to arrive at your ear at two different times, and that creates a phenomenon called comb filtering. Comb filtering cancels out certain frequencies so that they go away. And if that time difference changes as we walk around from one side of the room to the other, then we get different frequencies that cancel out. 

Lessons from Sound Expert Dave Rat

Next, we're going to talk about a method from a guy named Dave Rat. Now, Dave Rat is the founder of Rat Sound. He's done front-of-house for Red Hot Chili Peppers, Weezer, a bunch of other really huge acts. He's been really innovative in the audio sphere, and he's recently come out with a method of stereo mixing that's trying to reduce this comb filtering that's happening between the left and the right speakers for your live sound system. So this would be another reason why you would want to go stereo for your live sound P.A. (If this is a little bit heady and nerdy for you, you can go ahead and skip down to the next section where I give you my final thoughts. This is going to get a little bit deep if you're just kind of like, “Eh, I just want to know the surface stuff.” There's your disclaimer.)

So Dave Rat, on his channel, has been talking about a stereo method that's supposed to reduce comb filtering by having two inputs from the same source that are decoupled. So they're not interacting and exactly the same as one another, but they sound similar and those are panned hard left and hard right. This way, those two signals don't interact in the same way that a signal that's mono or the exact same signal coming from both speakers at the same time, but arriving to each listener at a different time. It's going to interact in a different way and produce less comb filtering. The theory behind this is that yes, each input might have a little bit of comb filtering from the left and the right side, but all of those inputs are going to have a little bit different comb filtering from the left and the right side. So whereas your electric guitar might be comb filtering out a certain way, your acoustic guitar is comb filtering in a different way. And so the combination of both of those ends up overlapping and creating a more pleasing sonic landscape.

A mono source that you might try to decouple and kind of make a stereo source is an electric guitar amp. So you put a microphone on the center of the cone, and you put a microphone on the outside of the cone. There are different distances from that guitar amp, so they're going to have a little bit of a different arrival time to those microphones, and then you EQ each microphone to sound similar. So the mic that's closer to the outside of the cone, maybe you try to make that brighter, or you use a brighter microphone in the first place so that the tones somewhat match and your painting with a similar color on both sides, though these inputs are now decoupled. They won't completely cancel out when you flip the polarity of one of them. Some of this is better heard than talked about. So let's head over to the computer and I'll show you some stuff about it.

Listening Examples for Decorrelation & Comb Filtering

So the benefit of this is that your band inputs that are now in stereo sound bigger because not all of them are comb filtering in the same way in every seat.

Now the thing that I don't quite 100% understand with this, and haven't tested out, is that the lead vocal is going to be pinned right to the middle. So no matter what that's going to comb filter in a different way, no matter what seat you're in. The potential problem that I see with this is that certain frequencies of the vocal are going to cancel out, and maybe that decreases intelligibility in a way that you can't perceive from front-of-house unless you're in that one spot. Or the mix is doing something on the left in the right that kind of clutters up and makes it so that it's harder to keep that lead vocal out in front and uncovered. At least when everything is comb filtering the same way, you're getting all the same cuts across your entire mix. I've done a little bit of testing on this and I would love to dive into this subject a bit more. If you're interested and want to go deep down the rabbit hole, I'm game. I’ve just got to find some P.A.s to test it out on. I mean, it could be really cool or it could be overkill if your band isn't the Red Hot Chili Peppers. So maybe we'll find out.

Testing for Comb Filtering On Your Own Sound System

If you want to explore this a little bit and kind of see if your sound system is creating a lot of comb filtering, turn on some pink noise or any other test signal and walk left or right through your room, making sure that you're going a different distance from both of the speakers. You might hear something that sounds a lot like a phaser pedal, if you're a guitar player, or there's a “shoooo” thing that's happening as you change distances from each of the speakers. Sometimes you can hear it on music, but it's really apparent when you put on pink noise. (But don't put the pink noise too loud, that’s just obnoxious.)

In Conclusion - Should You Go With Mono or Stereo?

To sum things up, with all the deep nerd stuff set aside, would I recommend a stereo P.A. over a mono P.A.? In most situations, the answer is yes. When would I recommend mono? Well, if you've got a really odd-shaped room with many different zones and tangents coming off the main listening area, that might be a lot easier just to make it mono and call it a day. Sometimes budget constraints mean that you can't hang stereo hangs under your balcony, things like that. It's going to make a bigger difference to make sure that your sources are sounding good and that your mono mix sounds good in that situation.

Setting up your room in stereo gives you a lot more options for creating depth and space in your mix, and I think it's actually worth it. You're going to have to cover every single area anyway, you might as well run a different signal to each of those channels. And it's more than ear candy, and it's more than things that just the sound tech can appreciate. So it really does make a difference for what you can do and how you can open up space for the vocals by having stereo inputs panned hard left and right. Even if your average listener can't tell that they're listening in stereo, they still will appreciate having that extra space and depth.

Hey, if you enjoyed this article, go ahead and check out my other blog posts HERE and share it with a friend that might be interested in setting up their P.A. the right way. If you want to actually practice mixing and take your mixing skills to the next level, go ahead and sign up for my FREE Virtual Sound Check Challenge.

Remember: it's all about the low end, avoid the sound tech solo, and nobody leaves humming the kick drum. We'll see you back here next time on Attaway Audio. 

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