19
Apr 15

Multi-zone audio: a discussion of the options

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:

xap800

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:

xap800-rear

 

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!