EDNE December 2012 - (Page 34)

AdvAnces in wireless speAker performAnce And technology B y JA MES LEWIS • CEO HI WAv E T ECHNO LO G I ES AdvAnces in the efficiency of Amplifier ics hAve enAbled bAttery-powered wireless hifi speAkers for consumer ApplicAtions to become A reAlity. the following Article compAres And contrAsts the mAjor wireless stAndArds AvAilAble to the wireless speAker designer. T o adapt and update a classical piece of phraseology by 19th century British author Jane Austen: “It is a truth universally acknowledged, that a single man in possession of a smartphone must be in want of better speaker.” However, it is apparent that poor audio quality hasn’t deterred users from making the switch from CDs to digitally stored audio. According to a September 2011 report by Gartner, the adoption of web-connected devices, both PCs and portable devices, is driving a shift in the way audio is consumed. The analyst predicts premium internet radio services, such as Pandora and Last FM, and subscription based on-demand streaming sites, such as Spotify, will see a five-fold increase by 2015 and account for nearly one third (29%) of the $7.7 billion online music spend. At the same time consumer spending on physical media such as CDs will fall by over 33% to approximately $10 billion. Online streaming adds to an already growing shift towards digital formats; For example the 10 billionth iTunes download (Johnny Cash’s Guess Things Happen That Way) sold on the 24th February 2010, Steve Jobs’ 55th birthday. This joins music from other major corporations, such as Amazon, Play – and, of course, illegal downloads. Neither is the sale of devices slackening: analyst reports for 2011 alone state that over 1.5 billion phones (source; IDC), 350 million PCs (Gartner) and 60 million tablets (IDC) were shipped. In short, the consumer’s consumption of music is shifting from the CD player to the computer or phone. And this brings us back to the poor audio quality: the housing of portable devices prevents good sound and connecting them via a 3.5mm-jack to a stereo removes the portability. The answer is of course, go wireless. EFFICIENT AMPLIFIER DESIGN levels (around 73dBC at 1 metre) they often have single digit efficiency figures. However, an amplifier is not like a light bulb; the audio signal waveform has a very high peak-to-average ratio and the amplifier will only need to output at full power for a fraction of the time. The latest class of amplifier topologies are being created to be efficient at typical listening levels and exploit this facet of audio; cutting quiescent power to a minimum, implementing intelligent rail switching to accurately reproduce peaks and employing digital signal processing to prevent any audible artefact of the switching from reaching the listener. Such topologies are between 10 and 20 times more efficient than comparable Class D chips. Putting this in context, one of the most popular wireless speakers today is the Jawbone Jambox Class D / Bluetooth speaker. Its marketing literature cites “about 10 hours of continuous play (varies by volume level and audio content).” Tests performed last year in HiWave’s labs, using a 2200mAh Li-ion battery, Bluetooth silicon from CSR and our stereo amplifier IC, gave 30 hours of continuous playback – the Spotify list used can be found here. And his could be increased to 40 hours if using an AA battery, which can hold 3000mAh. Tests were also run using SMSC’s low power wireless chips and WiFi (see below) and the wireless standard used can significantly affect the efficiency of a system. STANDARDS FOR WIRELESS SPEAKERS Until recently, the key power drain in a wireless speaker was the amplifier, meaning that wireless systems needed to be attached to a power cable, which detracts from claims to be wireless. Whilst Class D amplifiers cite better-than-90% efficiency, this is only achieved at output levels many times greater than anyone would normally listen to – for fans of the film This is Spinal Tap, when you turn it “up to 11”. At typical listening 34 EDN EUROPE | december 2012 Selecting the most efficient wireless standard is only a starting point. Data throughput, range, interference, usability and battery life all need to be balanced in the design of wireless amplified speakers. In an ideal world a single standard would optimise all of these factors, but this isn’t an ideal world and compromises are inevitable. The most ubiquitous standards are Bluetooth, with its variants, and WiFi. Both operate at 2.4 GHz and are found almost universally in both laptops and phones. The main codecs for Bluetooth are SBC and lossless aptX, which has reportedly been part of the Apple iOS operating system since 2010. WiFi is notably part of Apple’s AirPlay wireless networking system. www.edn-europe.com http://www.mobithinking.com/mobile-marketing-tools/latest-mobile-stats#phone-shipments http://www.spoti.fi/lHMLVR http://www.mobithinking.com/mobile-marketing-tools/latest-mobile-stats#phone-shipments http://www.guardian.co.uk/technology/2011/sep/08/gartner-pc-sales-forecast-slashed-2011 http://www.mobithinking.com/mobile-marketing-tools/latest-mobile-stats#phone-shipments http://www.digitalsmarthomes.com/vancouver_canada/files/APTX_Bluetooth.html http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE December 2012

Cover
Contents
Texas Instruments Europe
Microchip
Digi-Key
Masthead
EDN comment
Pulse
Digi-Key
Baker’s Best
Embedded World 2013
Test & Measurement World
Rohde & Schwarz
Digi-Key
Squeezing the most from battery cells with a switched-mode pump
Signal integrity
Processor architectures : one to rule them all ?
Digi-Key
Mechatronics in Design
Advances in wireless speaker performance and technology
Design Ideas
Teardown; the ultimate Consumer Product ?
Product roundup
Tales from the Cube

EDNE December 2012