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Bringing multizone digital audio to life

Posted: 31 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:digital audio? music system? LCD? Wi-Fi?

Rallying around an emphasis on ease of use, software upgradability, multi-room capability and wireless connectivity and control, Sonos Inc. developed the Sonos Digital Music System, a multi-zone digital music system with a wireless, full-color LCD screen controller that lets users play all their digital music, anywhere in their home or yard, while controlling it all from the palm of their hand. No server required.

According to Andrew Schulert, VP of product development at Sonos, audio systems historically were all about amps and speakers. But people weren't buying amps or stereos like they used to," he said, thanks to the rise of digital formats such as MP3. "So the question became, 'How would it be done now?'"

First announced in 2004, the system has gone through no less than eight downloadable upgrades that now not only gives users access to their own local music archives!a veritable jukebox for the entire home!but also to Internet radio and music outlets such as Napster, Rhapsody and Sirius.

Figure 1: Sonos system comprises ZP100 (center) with integrated 50W amplifier, ZP80 and wireless controller (left).

While the Sonos Digital Music System now quite admirably answers the question of how digital audio should be handled, the designers had to overcome many problems along the way. Those problems included making the system as simple to use as a legacy audio appliance, enabling system upgrades in a rapidly changing consumer space, multi-room audio synchronization and of course ensuring reliable, latency-free wireless connectivity. On top of that, the design team was thrown some curve balls, such as RF harmonic interference and problems derived from designing the motion-sensitive controller separately from the cradle it goes into.

The base system costs $1,000 and comprises two ZonePlayers!the ZP100 and ZP80!accompanied by a single wireless controller. The ZonePlayers can access and play a wide variety of music formats, including MP3, WMA, AAC (MPEG4) and WAV, stored on a PC, Mac or network-attached storage (NAS), and comes bundled with customizable Internet radio stations. Built-in wired and secure wireless capabilities provide the consumer flexibility of installation at no extra cost.

The ZP100 comes with an integrated amplifier that distributes, plays and amplifies music in any "zone" in the home. The device is designed to deliver 50W/channel into 8? or 120W/channel into 4?, with a total harmonic distortion of 0.02 . (Off the record, it can actually deliver a bit more than that, up to 68 W/channel into 8?). The ZP80 has no amplifier and is instead designed to integrate into an existing audio system or simple off-board amplifier/speaker system. Either device can form the wired connection to the home network, though the ZP100 has a 4-port Ethernet switch compared to the ZP80's 2-port switch. Both have digital (optical and coaxial) and analog RCA inputs and outputs. The wireless controller comes with a rechargeable battery that rests in its own powered cradle when not in use. It has a full-color screen, a powerful touch scroll wheel and it allows the user to access, customize and control any of up to 32 ZonePlayers!anywhere. From the bedroom to the backyard.

The latest addition to the lineup is the ZoneBridge, which simplifies setup of the SonosNet wireless network and extends the range of the network to remote locations, such as a garage or guest house. Its Ethernet jacks also bring Internet connectivity to PVRs, STBs etc. It retails for $99.

Right connections
On unpacking the system I charged the controller in its cradle. The next day, I hooked the ZP100 up to a pair of 'olden but golden' Celestion 3 bookshelf speakers that I still had lying around. I then connected one of the ZP100's Ethernet ports to one of the ports on my wireless router, installed the software on my laptop and powered everything up. Note: Laptop interface software was optional. The system immediately and flawlessly performed a software upgrade and I was able to assign a zone name (basement office) via the computer's desktop controller. On powering on the controller it immediately found the office ZP100 and I had full control of my system's music archives, as well as Rhapsody and Sirius radio and Napster files. The 30-day trial connections worked without a hitch and within seconds I was listening to U2 and Pavarotti singing Miss Sarajevo. Frankly, I was more than pleasantly surprised at not only the simplicity of setup but also the sound quality of the ZP100. It was clear, crisp and powerful and no detectable distortion or latency-induced artifacts.

Figure 2: Rear view of system showing Ethernet, speaker, analog (RCA) and digital connections. (Click to view larger image)

The next step was to hook up the ZP80 to my main audio system upstairs. It seemed to connect OK but then lost the connection. Turns out there was an issue with associating that was likely due to a previous connection to another network. In any case, it resolved itself and I was quickly controlling both the main system and my basement office ZP100 using the Sonos controller. Any combination of audio streaming was flawlessly reproduced: from a single stream to multiple streams from different Internet and local-storage sources. All worked without a hitch.

Design choices
At the heart of the Sonos system is a consistent commitment to simplicity. At the time of its introduction, systems such as Audiotron (Turtle Beach) and SlimDevices were already available, but were wired or were simply gateways and in Sonos' mind didn't adequately resolve the problem of getting audio from a computer to the bedroom. In addition, and more symbolic of the sea-change underway in audio reproduction, "What if I didn't even have a stereo and didn't want a PC on all the time?" The designers focused on the software interface and leveraging software to hide the technical complexity behind the audio distribution mechanism.

To that end, the team made four critical design decisions early on. The first was to go with a software-upgradable approach that gives the controller a 5-year expected lifespan and the ZP100 10 years. "We can innovate on the software," said Schulert. "Since first shipping, we've had eight updates so far!all for new features, not bug fixes. All were done easily!just reflash and reboot."

Figure 3: Rear view of system showing Ethernet, speaker, analog (RCA) and digital connections. (Click to view larger image)

The second critical decision was to use a proprietary mesh network, SonosNet, versus working with existing 802.11-based access points. According to Schulert, the downside to their decision for the mesh is requiring that at least one unit be wired to the home network (something they've since mitigated with the ZoneBridge). "But this is more than outweighed by the ease of setup, the increased range of the mesh and some other more minor changes that increase the robustness of the network." One example of how they could make the network more robust was the ability to use two antennas and thereby choose any of four combinations for devices to talk to each other. More on that later when we look at the difficulties of working with wireless. For now, it's important to note that SonosNet is a secure network that uses 128bit AES encryption and runs on 2.45GHz 802.11b/g-based radios.

Thirdly, the team decided to use file sharing to access music, versus requiring a server process on the PC. "Having a server would let us leverage the processing power of the PC," said Schulert. "However, we didn't like the complexity of setup and requiring that the server always be running. We also wanted to work with NAS devices, where we couldn't run a server."

Finally, the team decided to develop a thick client versus building a web-based interface that could run in a browser on both Windows and MacOS. The thinking was user centric: "The end-user experience was more important than any time we could save," said Schulert. "With thick clients we can have the appropriate look and feel for each platform."

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