Multi-zone Audio: the last 15 years

Multi-zone audio has been possible in the home for decades now, but until recently has only been an option for the super-house; the high price of systems and installation meant it was out of reach for the average home.

The first cheap device I know of that opened-up multi-zone audio to the consumer market was the SliMP3 (2001), which quickly matured into the Logitech Squeezebox ecosystem of devices and apps. Unlike the old paradigm, where a multi-zone amplifier had to be connected to a central source which was then controlled from each room – thus requiring direct connection from each room to the central unit (i.e. in-wall wiring) plus speaker cable running from a central location back out to the rooms (i.e. in-ceiling wiring) – the Squeezebox was situated in your living room and bedroom and connected to your speakers directly. It used a wireless connection to talk to the central controller, providing access to a central store of music, sync’d or independent control of audio for each zone, internet music, and other bells and whistles.

Sadly Logitech abandoned the product in 2013, but as of 2015 the ecosystem lives on thanks to software players and a surplus of cheap, high quality second-hand audio players which are still traded online.

Sonos filled the vacuum. Their units are more expensive than Squeezebox devices and many have built-in amplification. They are frankly sexier and more user-friendly, but for the audiophile, advanced music cataloger, classical music listener, DIYer, or home automation expert, Squeezebox still has huge advantages over Sonos.

The Problem / The Dream

The problem with the Squeezebox/Sonos paradigm of multi-zone audio is this: although you can play different music or listen to different radio stations in each room, you are limited by what the system itself can do. For example, Squeezebox and Sonos are internet-enabled music players. They don’t play Bluetooth audio or music playing on your Apple TV, they don’t play CDs, and they can’t pump the music from a YouTube video projected onto your wall around the home. Surely this is “The Dream”?

You still need a multi-zone audio amplifier for this. And they cost bucks. Big bucks.

You want

• expensive hi-fi quality audio in your living room, and some cheap amplifier to power the speakers in your bathroom and hallways?
• 12 zones of control instead of 4 because your hallway speakers are next to the kids room and you would rather have them off and night?

Forget it. Not without quadrupling your budget from £1500 to £6000.

The likes of Niles Audio who produce a network-controlled amplifier, and Russound who make interesting looking wireless-powered receiver amplifiers amongst other things seem like good options. Again these options do appear to total the thousands, not the (very) low hundreds which I’m aiming for.

And sadly even if you spend £6k+ do you think you can have the bells and whistles? What about

• controlling audio volumes in each room from your central automation system (e.g. OpenHAB) as well as some proprietary wall panel?
• fading the music across the whole house when someone calls you on the ‘phone?
• fading the music down when the doorbell goes?
• having your house speak to you?
• speaking to the burglar when he enters to freak him out?
• [insert your own #homeautomation fantasies!]

Possible Solutions

I looked at multiple source, multiple zone systems for a long time before deciding that I needed to home-brew my own. Here was my thought process:

• I have some nice Class A amps sitting around. They cost me hundreds in total, not thousands. Why can’t I use them?
• I can pick up a Class D amp with power supply for £20, for kitchen and non-audiophile zones
• I just need to find a way to do the switching and mixing of multiple audio sources

Reed relay switches. With a view to making my own Arduino-controlled source switcher I looked at using transistors, relays, or dedicated audio ICs. I gravitated towards the idea of a series of reed relays to switch multiple audio sources. A relay is a cheap and very high quality way to switch an audio signal because it introduces no distortion or load to a circuit. Reed relays are great because they would minimise the audio click you’d otherwise get when using a metal relay to switch from one source to another. Reed relays unfortunately don’t come in complex arrangements such as 2P6T which would be nice, as this would allow you to switch the positive signal path for L and R between 6 sources – but this is not a huge problem as they are only a couple of quid each and so you can buy multiple reed relays.

After thinking about this a little more, it becomes apparent that you can’t just connect up a load of relays and hope for the best: your board design must account for minimising cross-talk. Whatsmore, using relays only solves 1/3rd of the problem: the input stage. You still have to route signals to multiple rooms and if you are aiming for the dream option of fading something down when something else happens, you have to design gating and signal detection. Routing audio to multiple rooms isn’t simply a case of connecting one signal path up to multiple rooms’ amplifiers. Adding more than one load will introduce distortion. And although gating and signal detection is possible with cheap ICs, this is starting to grow into a big project!

Wow… this idea got out of hand quickly.

Using dedicated audio ICs. Whilst it’s possible to find audio switching and mixing ICs, it becomes apparent after a little research that such ICs have rather specific applications, furthermore then aren’t very “black box”; a significant investment of understanding about their inner workings is required to design them into an application. When an ICs application notes is a document 45 pages long, this particular home automation DIYer knows it’s time to consider alternative options!

Making the Dream Happen!

Sorry, dear reader, to drag you through this rather pointless process. I’ve banged-on about my take on the development of multi-zone audio over the years, and let you into my raw thoughts about designing my own system, which amounted to nothing.

If you’ve got this far, however, I do have a great solution for the Audio / Home Automation enthusiast looking for the same things as me.

The ClearOne XAP 800

• It’s a 12×12 audio switch / mixer
• No it’s not an amplifier, but it will be the core of your multi-zone automation system
• It’s cheap – very cheap and highly available second hand (£30 ebay)
• It’s very powerful
• It’s rackmount

And here it is:

ClearOne XAP 800 – a 12×12 audio mixer

If the above looks to you like it has worryingly few buttons on the front, then like me you may be thinking… “hmmm, is this thing software controlled?” Yes it is.

And if the above looks to you like it may be far too small to house the numbers of inputs and outputs you would need to power a whole home, then rest assured:

I’ve just bought mine on eBay for £25.

Don’t be put off, it’s called a “microphone mixer” and a “conferencing system”, and whilst I’m sure it’s great for B&Q’s staff announcements, this baby is a dream come true for home automation and multi-zone audio.

Why is it so cool? The product manual will answer that (nicely written too), but here’s my take with a Home Automation hat on:

• Core use: an audio routing matrix. Basically this provides everything that the most expensive Crestron multi-zone system does, and more. Route an audio source to a single room, multiple rooms, or groups of rooms. Route another audio source to another room or set of rooms. Switch the source or zones from anywhere in the home. Keep going until all rooms have the exact audio you want. Rooms could be set up as stereo zones, mono zones (e.g. bathroom), or even 5.1 theatre zones.
• Scenario presets. Because of the possible complexity of a 12×12 routing matrix (i.e. assigning different sets of audio to different rooms) you will want to have presets. The XAP 800 supports 32 whole-system user presets.
• GPIO: interface with your home automation hub via an Arduino. Amazing! Imagine the possibilities:
  • Remotely control the presets, e.g. listening scenarios.
  • Remotely control volume, set EQ Presets, and control audio routing direct from my MQTT wall panels! (Did I mention this thing has digital signal processing?)
  • Page someone from another room, and fade-down the audio if they are listening to something
• Not only does the unit have GPIO, it has GPIO assignment. There’s even a “GPIO builder window” in the software, meaning that you can assign whatever you wish to the input / output pins.
• The device supports gating, gating groups, configurable ramps, and a whole load of other advanced stuff when it comes to stopping one sound when another one happens.
• The device has echo cancellation and some advanced “adaptive ambient level”, which means it can detect noise even when there’s ambient noise in a room. Useful if you want to hook-up some home automation voice commands with boundary mics
• Rest assured, mic/line level can be configured for each input

Looking forward to getting my new XAP 800 hooked up with some pre-amps, amps, audio sources, speakers, and an Arduino to give it all a whirl!

Disclaimer

First up I’d say in any professional environment there’s no way I’d recommend anything but “proper” PoE, that is to say 802.3af or PoE plus.

For DIY home installations, however, we can do things differently. And I don’t mean “substandard” by any means. Rather we can do them in a more tightly-spec’d way, we can design our own system of distributing power that is equally efficient in terms of power loss, and equally reliable… but far cheaper.

(The reason you wouldn’t inflict this on a corporate environment is not because it isn’t as good, but rather the next guy / girl who comes along won’t spec the replacement power supply properly, and blow something up. Also DIY jobs tend to vary in quality, whereas using a PoE switch and device gives a standard of power distribution quality that can be relied upon. We DIY types do things properly, we are masters of our own home, and we know how to do basic maths, so it’s okay, right?)

DIY PoE with a buck converter – dodgy connections fine for prototyping but we can do better

Preliminary

I suppose I would sing the praises of DIY PoE for the home, because when it comes to electronics I love doing things myself.

This isn’t true with computers, I can’t be bothered to faff around swapping RAM out or upgrading motherboards for my own gear any more, although I used to love doing that. Perhaps that’s because in the 90s desktop PCs were the rage and to play better games you had to have the better video card, which required knowing how to change the video card, which meant knowing how to build a computer. I don’t play games any more and I certainly don’t remember the last time I used thermal paste on a CPU. Or maybe it’s because there are no cost gains to be had with DIY computers these days.

Not so with PoE!

Below is a little chat about PoE, and at the bottom of the post I’ll go into what I am using in my wall controller project.

Most computer / network techies already know the basics when it comes to PoE, but this post seeks to shed some light on the choices to be made when considering PoE for Home Automation.

Why PoE? (Skip this if you already get it.)

Most wired network devices also need some way of powering them. Wireless Access Points, network cameras, intercom systems, control panels, they all need power – but if you are already taking a network cable to them, why not use that cable to also deliver power to them as well? Here are two benefits: no need to hire an electrician to extend your ring mains to awkward places, no ugly extra cables on wall-mounted devices to compound the felony.

Certainly in the case of my uber wall control panels, they are being sited inside wall boxes at various points in the house that don’t require power. To bring power to each panel would be a lot of extra cables in walls, and the installation cost would increase hugely. There’s spare capacity in a CAT6 or CAT7 cable, why not use it?

Active vs. Passive PoE

“Passive PoE” is a bit of a misnomer, but that aside – here’s a comparison.

Active PoE is industry standard in business, and involves sending 48V down a network cable to the device. The power usually* comes from the network switch itself, and the device has some special electronics that talks to the switch on the other end of the wire and negotiates power using a series of signals (resistance detections and presentations of loads). It’s pretty complex, and in fact PoE isn’t really one standard at all. (“The thing I like about standards is that there are so many to choose from…”)

The other thing the device must do is step-down the voltage to whatever it requires.

* Many people use mid-span injectors, that’s where the switch doesn’t supply power but you can inject power using a separate device. This gets messy if you have very many devices requiring power, but as a general rule fine for the odd one or two.

Passive PoE is a system that simply splits your ethernet cable at both ends, allowing you to place your own power supply at one end, and then connect your device power to the splitter the other end. No power negotiation – no voltage step-down.

There are shoddy implementations of passive PoE, and there are lovely ones.

A common example is where, instead of hooking up a power supply directly to where your security camera is installed, you can install a splitter at both ends. On the camera end, your splitter has a little power plug that connects to your camera (sinking power), and on the other end your splitter has a socket that connects to the power supply (sourcing power).

Active PoE – pros and cons for home use

Pros:

• Higher 48V transmission over cable means lower voltage drop-off = decreased power loss (saving money on bills).
  • NB Passive PoE allows you to supply whatever voltage you like, but more often than not it’s used with existing 12V or 9V device power supplies
• Power negotiation is great because it means that a device is only allocated the power it requires; where there are more than a few PoE devices, this quickly becomes a sensible idea for all aspects of a system (cooling, conserving energy, etc.)

Cons:

• PoE switches are usually expensive (£350+)
• PoE switches are usually very noisy (bad for the home environment). You can find cheap fanless switches such as the Cisco 2960C-12PC-L or D-Link DGS-1008P/B, but most smaller switches tend to have PoE capability only on half the number of ports (e.g. 8 port switch has PoE on 4 ports).
• PoE requires your Arduino project OR your network device must support it. Network devices supporting PoE are usually far more expensive.

Re the last point, it’s possible to include some electronics that will supply your Arduino project with PoE but they cost £16 on top of the network shield:

From Sparkfun: a network shield with PoE module (the black board that sits vertical on the shield)

£160 for 10 units, not including the network shield!

Or you could get an Arduino with built-in network and PoE, such as the excellent EtherMega. These are wonderful, but this is even more expensive.

Finally you could get your own chip and include this in a project but it’s still about £6 per unit, see Silvertel Ag9800 themal protected 12vDC module.

Passive PoE – pros and cons

Pros

• Reduced complexity for your project. No inherent need for power negotiation electronics, or step-down converters (unless you want to)
• Far cheaper. PoE passive injectors cost £20 for 8 ports. You supply your own power supply. Of course, no extra electronics at the device end, so it will support most things that come with their own power supply. Your Arduino project may need no special electronics, depending on how you implement it. In my case I added step-down voltage at the other end, read on for more info.

Cons

• Most devices want to run at 9, 12, 15, 18v DC. At these lower voltages, the power loss over cables is significantly higher. This requires thought about two things:
  • Electricity bills – are you wasting money?
  • Power tolerances – will your device work reliably if running from a slightly lower voltage?
• An extra hub in your comms cabinet = double the number of patch cables = more mess

Which is best?

So which is better for Home Automation? Looking at the Passive PoE cons, I can live with the extra mess, but really how much power is lost over a CAT6 cable?

Joule’s Law

If we can minimise power loss, perhaps we can justify the cheaper option as our cable runs in the home won’t be so long. Let’s take a closer look.

According to Joule’s Law, if we keep the voltage high then DC electrical transmission power line loss will be low. So the first thing we want to do with passive PoE is get the voltage as high as we can (within reason – we are talking low voltage systems here!)

On the other hand, the higher the voltage on your Arduino, the less efficient the conversion down to 5V will be, this is because your Arduino has a linear voltage regulator which is not wonderfully efficient. Also the harder you drive that voltage reg, the hotter it gets. And don’t forget the acceptable voltage input range that your particular Arduino can handle – check the data sheet!

As you can see it’s a trade-off. The best option is to use a non-linear voltage regulator, aka a switch-mode power supply or buck converter. Obviously this is places at the same end of the CAT5/6/7 as your Arduino, so you can benefit from lower power loss over the cable.

Pros of using a separate buck converter to power your arduino over ethernet:

• Doesn’t get as hot = safer for home installations
• Doesn’t waste as much power in the conversion down to 5V. Buck converters are typically 95% efficient. Linear regs’ efficiencies depend on a number of factors such as how hard you drive them, but they are generally 50-70% efficient. (I’ve pulled these numbers from the air!)
• Means you can put a far higher voltage down the line, e.g. some small buck converters can take 30V down to 5V without getting too hot. This in turn means less wasted power because of Joule’s Law.

Cons of using a separate buck converter

• Introduces another component that takes up space on your circuit board or project board
• Can introduce EMI (electric noise) to your circuit, which means you need to be careful about how you design your circuit, and how you lay out your circuit board.

For an excellent introduction to buck converters, check out the videos of Julian Ilett or Afrotechmods on Youtube.

For the sake of answering my own question above, “how much power is lost over a CAT6 cable”, I measured 12V down a 20m cable sinking 400mA at the end of it, and the power had dropped 0.9V. This is fine, but it will vary for cable runs, so let’s run at a higher voltage and not use the Arduino’s in-built linear regulator.

In the end I found this lovely little device on eBay. You can pick them up for £8.30 for 5 = £1.66 each including shipping. Search for “Ultra Mini DC Buck Converter”.

Cheap as chips. (Actually cheaper.) Ultra mini buck converter.

Strangely the auction says “12V to 5V Power Supply 7-22V to 5V”. I think that means you can get them in various flavours outputting anything from 12V to 5V. Lower down on the auction it says “Output Voltage: DC 5V”, so that’s okay. I tested them before I hooked them up and the voltage was a very reliable 5V… although I didn’t test with different current draws, only about 550mA.

Incidentally if anyone with an oscilloscope has used these before, let me know how clean the output is.

They also come in 1A and 2A flavours, I plumped for the 2A versions of course. I’m sceptical about driving 2A from it and I don’t plan to do that ever!

This “Fulree” branded cheap buck converter seems like the same thing as one you can get from Sparkfun:

Sparkfun Buck Converter – tiny

I’ve no doubt the “Traco Power” branded one, also available from Farnell, is superior in quality, shielding, and design. But it’s £5 and I’m a complete cheapskate. (i.e. I’m making 20 of these things and every little saving will reduce my total project cost from thousands to hundreds.)

You could also buy another type of buck converter, even cheaper but not as compact. It exposes the whole circuit on a board of its own and is based on the LM2596 switching regulator. If you do, make sure to watch Julian Ilett’s warning video on not getting a dodgy version:

The other alternative is to include your own buck converter circuit in your project using components from scratch, but there are some design challenges you must be aware of and the components stack up to be more like £3-4 – not worth it. See this beautiful Youtube vid from Afrotechmods for more info.

What cable to use with DIY PoE?

We don’t normally bother about cable gauge when it comes to CAT6, as performance is more about minimising cross talk, shielding, and data transmission speed – not wire thickness. Well, of course the latter does affect the former, but either way for the pursuit of low cost PoE, we must consider this.

Do get good quality CAT5/6/7 cable – preferably CAT6 minimum for PoE. I measured a single strand of my CAT6 cable. The cable measured 0.6mm diameter on my Vernier scale, which is approximately equal to 23AWG. I’m using LSZH (low smoke zero halogen, aka LS0H) infrastructure cable, that is, rigid non-stranded cable that can bend a few times but is not designed for regular movement. Good for home installation if a little rigid. It cost £100 for 305m reel from a local electrical reseller.

My wall controller project

After a whole load of price checking and electronics research, I decided on this solution for powering my Arduino over ethernet:

• Standard network switch
• Cheap 8 port PoE injector (£20 each)
• Re-use old Dell power supply (free if you have them already)
  • 19.5V = perfect for longer runs
  • High power (90W or 60W), high quality
    • 90W split 8-ways is 11.25W per port
    • Almost certainly enough for your project, unless you are powering motors or lights
    • P = VI. My project uses max. 450mA at 5V, so that’s 2.25W.
    • 2.5W. Don’t forget to do a back-of-fag-packet calculation for power loss and include a lot of headroom. Include line loss, and assume 5-10% loss in the buck converter
  • Chop connector off and replace with 2.1mm connector
• CAT6 LSZH
• Fulree buck converter at Arduino end. Connect both browns to GND and both blues to IN (check wiring standards and verify this yourself!)
• Split ethernet cable at Arduino end and use PCB block connectors. I may develop this to route power through the W5100 board in the future, but right now this works for me.
• Connect output of buck converter to Arduino’s 5V connector.

I do have a PoE switch at home, but given the amazing cost benefits of the above option, and the fact it makes a big noise, I’m not going to use it for my project.

A number of months ago I became obsessed with the idea of controlling my room lighting using knobs in the wall. Crazy, I know 😉

Seriously though, most lighting automation systems do not use rotary controllers (i.e. knobs), but rather you have to keep your finger on a button until the desired light level is reached. Isn’t that so 1990s? Knobs are the way forward. Worse still, many only let you select “scenes” without even controlling individual light level. So I set about making my own digitally controlled lightswitch. The process has been one of research and learning new skills. Soon enough I stumbled upon the ultimate way for things within the home to communicate with other things: MQTT.

Here are my design goals for the ultimate home control panel for each room.

Aesthetics

Use physical buttons and lights NOT touchscreen. I find touchscreens great for web browsing but when I want to control lights and volume I need an accuracy and responsiveness that can only come from;

• tactile switches with visual feedback
• rotary controller knobs
• display screen showing levels as percentage (i.e. numbers) for fine adjustment

Look sexy. DIY metal faceplates with push buttons conjure-up images of 1970s style control panels. Disabled toilets. Hobby aeroplane remotes. I’m going with brushed stainless steel faceplates with no visible screws, smaller LED-integrated tactile buttons, matching brushed steel knob.

Use numbers on the display. In the increased sexification of home automation, things have become too touchy-feely. Having controlled lights and music from my iPad, I get annoyed if you press in slightly the wrong place, or need to make that super-fine adjustment. Also I get annoyed by the ubiquitous slider and the lack of information it provides the user.

Installation

• The faceplate must run at low voltage, requiring no special electrical certification
• Connected with ethernet (CAT5, 6, or 7)
• Powered over the same ethernet cable
• Fit within a back-box readily available in shops: 47mm depth max

Function

• Use “Scene” buttons to quickly select the lighting mood in a room
• Dim individual lights in a room to create your own scene
• Quickly cycle between different lights in a room
• Control music volume and see what’s playing (track title and artist)
• Similar to light scenes, there should be audio “favourites” (i.e. radio channels, playlists, shuffle mode for a given genre, etc.)

Scalability

• The unit is designed for a range of functions, but can be expanded later to incorporate more. e.g. lighting and audio modes have their special uses and displays. As it’s based on Arduino, the sketch can be updated by USB later.
• “Thing” settings (i.e. how many lights in a room, the name of a light in the room, the name of a scene for a given room) should be queried from a server and downloaded to volatile memory at startup. These things are not stored in the unit.
• We should be able to press an “update” button to pick-up the latest settings. Home automation installers and users change their minds all the time!

Interface

• “WAF” is an offensive phrase used in #homeautomation talk. It stands for “wife adoption factor”. Maybe “GAF” – grandparent adoption factor? No – that’s swapping one prejudice for another. “HAF” will do nicely – human adoption factor. The controller must be the perfect balance between powerful and usable. I don’t mean “powerful for the geek, usable for the granny”. I mean “equally powerful and usable for both”.
• This means: consistency of display and immediate access to primary functions. No menus, no prompts! Placement of buttons should be intuitive.
• All light should cease when it hasn’t been touched for a while. No lights in the middle of the night!

The solution I’ve settled for is a “mode cycle” one. Like old digital watches. The mode button is set apart from other buttons and placed near the icon displaying the current mode. All other physical controls depend on the mode in question, and their function is intuitive given the placement.

Consistency comes from the unit defaulting back to a “primary” mode after x seconds of not being touched. The display dims appropriately.

Here’s a brief demo of the progress so far – January 2015: