An introduction to EAS

Last updated 

27. Aug 2020

When you’re trying to understand a large topic, it can be tempting to start reading about the details, since there might be a resource teaching you to do that one specific thing. This article, however, will try to approach the EAS system on broader terms. If you want to understand what you’re doing when building an EAS system, this is a good place to start.

The water hose

To understand anything about EAS, you have to understand how the bus behaves. Let’s distance ourselves from the technical side of the system for a moment and think of the bus as a water hose. You’re not building a sound system for a building, but a watering system in your garden. Where you want the water to go, the hose must go – right?

So, we’ve got some outlets from our hose at the tress, the tulips, roses, and lawn, but there’s no water yet. The hose is there to transfer and distribute water to all outlets along the way and doesn’t really care how or where the water gets in, so let’s just hook it up to a water tap somewhere.

The tap is in place, and no matter where we connect it, the water will flow to all outlets.

Back to reality

Now let’s convert this concept to a building that needs sound in four locations. Let’s make it a mid-size restaurant with an entrance, a dining room, a bar, and a kitchen.

As you can see, the curly water hose is still there, providing an outlet to all four areas of the building. It’s time to switch out the imaginary water hose with a signal path flowing through cables in our EAS bus.

Let’s say there’s a technical room at the end of the hallway. Since it doesn’t matter where the bus get’s its sound from, we’ll put an input module and a Spotify music streamer there.

Remember, the music audio signal flows through our bus like water in a hose. If the music streamer was located in the kitchen or behind the bar, you would get the same result.

Three components

To keep it simple we have pictured the bus as a single water hose with a single flow of water inside, but in fact, there are three separate components inside the bus. They all flow in the same manner but contain very different things: audio, power, and data.

The EAS system uses off-the-shelf shielded CAT-6 cables to carry the bus, both since they are so available, and because we can use the eight separate wires inside this type of cable to carry the three different components. Let’s look at each one in greater detail:

Audio

Two channels of audio get distributed using balanced analog transmissions. Since it flows through the bus like water in a hose, there’s no need for addressing. Just add on to the bus as many output modules as you need – they all simply get the same signal.

There can however be only one input module playing over the bus at any given time, so if you want more than one sound source, you’ll have to mix them down to two channels before entering the bus, or you’ll switch between sources using a system controller audio matrix like the EAS-SYSCON-12. More on that later.

Power

To power DSPs and other electronics on-board the modules, 15 volts of power also flows like water inside a separate part of the bus. One power supply per bus. You just need to make it’s got enough power to go around for all the modules connected to the bus, and that’s taken care of.

Depending on the modules you’re using, though, there might be some options and things to consider. For instance, some modules have the option to serve as a power supply for the rest of the bus (or not). A few will need a separate power supply to serve extended 24-volt amplifiers. Others just live off the 15 volts flowing along the bus.

So both be aware of the power requirements of each module you use and how many watts you need for the entire bus to be powered off that one single power supply. You’ll find figures on power consumption on each module’s product page or datasheet.

Data

Lastly, you should be aware of the digtal data communications flowing along the bus. The water hose analogy is true here as well, but you won’t have to supply it like you would audio and power. This is simply the modules themselves talking to each other to change volumes and other parameters. You can also communicate with modules using the EAS Admin software to change DSP settings, make volume groups, configure a SYSCON, make presets, etc.

One bus

When we put the three components together again, the bus flowing through our building looks a bit more like this:

  • Audio (in orange) enters the bus from the music streamer in the technical room, then flows like water in a hose to whoever wants to listen in. An amplifier module with a few speakers in each room, and you’re done. They all get the same signal.
  • For the sake of this example, power (in blue) gets supplied from the kitchen. There you’ll find an EAS-AMP-250D amplifier. It has a built-in power supply that can both power the module itself, and an option to serve 15 volts to the rest of the bus at the same time, so we chose to power this small system that way.
  • And again, data (in green) just flows along the bus without you needing to think about it.

What about multiple inputs?

Sure, in larger systems that might be required. Maybe there are microphones here and there, a DJ input in the lounge, or multiple music players lined up with different types of music.

In larger systems, it’s also fair to assume you’ve got more than one bus going to more than one physical area as well, right? And you’ve just learned that you can only have one two-channel audio source going to each bus at the time, right? So how do we do that?

In any modern house, you’ll have water pipes going to different rooms like the toilet, bathroom, the kitchen, the tap to water your garden outside, etc. All these pipes gather somewhere central, usually behind a closed door in your basement. Down there you can adjust the water pressure and even shut off the water flow to parts of your house.

In simple terms, this is essentially what a system controller does. Here’s a picture of the EAS-SYSCON-12:

Our water analogy ends here though since this module not only could route water to the bathroom but send milk to the toilet, juice to the kitchen, and water your garden with coffee – all at the same time. Multiple inputs going to multiple outputs. It’s a central device that handles many buses, instantly mixing and matching inputs and outputs and volumes and mutes depending on the situation.

Let’s talk a bit about how it works without going too far down the rabbit hole. You can see RCA inputs and outputs up top, and a row of twelve RJ-45 ports for CAT-6 cables down below. These ports connect to your buses and act in one of two ways:

  1. As an audio source and starting point of a normal bus, like the one we set up in our restaurant example above.
  2. Or as an audio input and endpoint of a bus connected to input modules, like microphone inputs, XLR/RCA receivers, etc.

That means you both have local RCA inputs on the module itself and can get audio from far away by using one or more ports for receiving audio from an EAS bus. It might be obvious by now but a port/bus only goes one way.

Expanding a bit

Let’s up the game in our restaurant example by adding the following:

  • We want each of the four areas to have its own bus (some call these “zones”), allowing for different audio sources in each zone.
  • We want an RCA input and a microphone available for DJs playing in the bar on weekends.
  • We also want two Spotify streamers in the technical room playing two different styles of music. Business in the morning, party in the evening.

Yes, it definitely got a bit more cluttered, but hang in there.

Focus first on the input side in blue. You’ve got your two Spotify streamers in the technical room going into the system controller locally. You’ve also got a bus connected to one of the ports coming from the bar, carrying a mix of microphone and DJ deck audio.

On the output side in orange, there are four buses going to each area of the building. To keep it simple we just have one amplifier in each area connected to some in-ceiling and wall-mounted speakers.

The system controller would also take care of the 15-volt power we discussed earlier, distributing current from one power supply in the technical room down the lines just like it does with audio.

Expanding a lot

But what about huge spaces, long distances, and large amounts of speakers? While this is just an introduction, there are a few concepts you should know about:

Delay

In huge spaces, or really any space where the speed of sound has a distracting and destructive effect on sound quality, we make an equally huge effort on compensating with delay capabilities in all amplifiers and even some distributing modules.

Since the human ear starts to notice time differences from multiple sound sources down to 6 ms, it’s no wonder that sound feels smudged, mushy, and even like an echo when speakers here and there starts at the same time in a large room.

What the EAS system does is make it easy to delay the sound going to speakers further away from a zero delay location. Together with smart speaker placement, you remove the timing difference between the speakers, and all of a sudden you create an in-sync sound space. It’s a night-and-day difference.

Long distances

While long distances in the same physical space are handled by delay, long distances of pure transmission/distribution is another concern. But we have never, in any project, experienced any significant loss over the EAS-bus, even when pushing it to upwards of 200 meters.

If you wanted to go further on a single bus, your main concern would be a drop in voltage, but then using an EAS-PI-3 power inserter module would make sure it gets back up to 15 volts.

Many speakers

In most projects, our modules operate well within their comfort zone, simply because of practical concerns and how most buildings are laid out. For instance, it often makes sense to have an EAS-24-NODE-4D only utilize a couple of its 24-volt amp outputs, feeding four or five EAS-AMP-30D amps in one location. They some times power two speakers each, so even in this example you’ve got ten speakers running off this one NODE.

The EAS-24-NODE-4D

But as you can tell by looking on the right side of the picture above, it has four of those 24-volt outputs. If they all fed three three amps with two speakers each, this small node would distribute audio to 24 speakers. What then, if we used a larger node? Multiply that number by three.

The EAS-24-NODE-12D

And if you still need more in one location, simply daisy chain to a second node. Or a third. We hardly ever see this happening, but in those rare cases, it’s good to know you certainly could.

Another take if the physical space allows for a more centralized amp location, would be to serial/parallel wire many speakers connected to a powerful EAS-AMP-250D or even the 500 watts EAS-AMP-500D. One of those alone would be able to power a bunch of speakers depending on volume requirements. And again, if you need more, simply daisy chain another amp to keep going.