The Good: For a relatively compact wireless speaker, the simple but classy-looking Sony SRS-X5 offers excellent sound with strong bass. It has built-in speakerphone functionality, a USB charging port (to charge your smartphone), NFC tap-to-pair technology, and eight hours of battery life. The Bad: Sounds better when plugged in with AC power; its design is more suited for indoor use (speaker isn't ruggedized). The Bottom Line: While it doesn't play as loud when it's on battery power, the Sony SRS-X5 holds its own against the top Bluetooth speakers in its size and price class. After reviewing Sony's good-but-not-great SRS-X7 ($250 USD) portable wireless speaker, which includes Wi-Fi streaming on top of Bluetooth, I wasn't expecting that much from its more affordable little brother, the SRS-X5 ($200 USD, \u00a3170, AU$279). But as soon as I turned it on, I was impressed by the amount of bass it delivers for its small size and its clean, relatively natural sound, particularly at more modest volume levels.From a design standpoint, this sports the same simple, minimalist design as its larger siblings -- yes, there's also a SRS-X9 ($700 USD) -- with the same glossy finish and a choice of black, red, or white for the speaker grille cover. It measures 8.8 inches x 4.8 inches x 2.0 inches or 221mm x 118mm x 51mm (w\/h\/d).On top of the unit you'll find a few different buttons, some of which, including the volume and preset sound modes, are touch-sensitive. And yes, that glossy finish will attract some fingerprints, so be prepared to wipe the speaker down from time to time.As far as extras go, there's speakerphone functionality (it worked fine as long as I stood close to the speaker) along with NFC tap-to-pair technology for smartphones that support it. You'll also find AptX support ( AptX is supposed to make Bluetooth streaming sound better, but it's difficult to notice a difference with a speaker this small), an audio input for non-Bluetooth devices, and more importantly, a USB charging port on the back that will charge your smartphone. It can charge tablets, too, but it's rated at only 1.5 amps, so expect slow "trickle charging" for larger tablets (such as the full-size iPad) that generally require 2.1 amps of power.In many ways the SRS-X5 competes directly with Bose's $200 SoundLink Mini and perhaps even Bose's SoundLink Wireless III . It's a portable speaker, but due to its design, it's more of an indoor speaker that, at 2.6 pounds (1.2kg), can be easily moved from room to room. An optional protective cover is available for $30. \tPerformanceBattery life is rated at eight hours, which is slightly better than the Bose SoundLink Mini's 7 hours of battery life. The SRS-X5 right there with the Mini in terms of sound quality and depending on how your tastes run, it may even be a slight notch up, with slightly more refined sound and better bass.As with all these compact Bluetooth speakers, it does have its limitations. But like the Bose's Bluetooth speakers, it manages to eke out a lot of sound from its small frame without distorting. I also found that it didn't move around at higher volumes like its larger sibling, the X7, does (the speaker still vibrates, but it manages to stay in place).On a more critical note, what I did notice it that when you crank the speaker up, you can hear the DSP (digital signal processor) kick in and restrain the speaker, rolling off certain frequencies. In other words, while the speaker can play pretty loud, it performs best at about 50 to 70 percent volume.What I also discovered is that the speaker sounds better when it's powered by its AC adapter. You can get about 20 to 25 percent more volume, and the speaker sounds fuller overall and can better handle bass-heavy material.