Under the Hood: Sonos brings multi-zone digital audio to life

Design issues
The cradle for the controller raises an interesting design oversight in that it was designed after and separately from the controller itself. As a result, when the controller was placed in the cradle, it put the controller at the exact angle of maximum sensitivity of the motion-control sensor. As a result, the controller would turn on with the slightest vibration. That problem was fixed with a software upgrade that turned the controller off when in the cradle.

However, that was the least of the designers' worries when it came to the system's design. Wireless and EMI issues took centerstage, particularly on the ZP100. That system's memory bus —between the SH-4, the NAND flash and the synchronous DRAM — was initially designed to operate at 60 MHz. However, Wi-Fi interference ensued and it was discovered that the 40th. harmonic of 60 MHz fell smack into the 2.46-GHz region, affecting channel 11 of the Wi-Fi network. As result, the designers had to bump the frequency up to 80 MHz, thereby pushing that harmonic safely out to 2.48 GHz.

But that wasn't all. The ZP80 has far less metal surrounding it than the ZP100, where the casing and support structures within act as a Faraday cage. The ZP80 has only a plastic housing. Consequently, the designers encased both the Wi-Fi and digital processing circuitry in metal enclosures as there were serious EMI issues. That worked. "We found that wireless performance has to be designed from the ground up, both in hardware and software," said Schulert adding, "Wi-Fi is very sensitive to EMI: removing interference in our Wi-Fi was much harder than passing FCC [regulations]."

Future designs
Sonos wouldn't comment on future upgrades, but said it was looking at other ways to move audio throughout the home. Patents surround its core technology and relate to audio performance, audio synchronization, and mesh networking. "We also have many applications around our GUI, addressing the ease of use of our product and setup," said Schulert. "Finally, we have several design applications capturing our unique style."