Like its Bose and Jawbone competitors, this model has a built-in rechargeable lithium ion battery. It provides up to six hours of continuous playback, though you can do better than that if you play your music at lower volumes.
The SRS-BTX500 has a 2 x 10W power rating, which adds up to 20W of total power. For a small speaker, it's got some kick to it and can fill a small to medium-size room with sound.
What I liked most about it is that it sounds very clean for a Bluetooth speaker and the punchy bass holds together pretty well at higher volumes. That said, the bass isn't huge, and I did get some distortion when I cranked up the volume on bass-heavy tracks such as Swedish House Mafia's "Greyhound." It sounded fine up till about 75 percent volume (call it 8 out of 10), then got a little crunchy when I pushed it past that point. In other words, the speaker does have its limitations and you're going to get your best results with the volume in the 40-to-60 percent range.
As noted, there's a sound mode button on the side of the speaker with a little LED light next to it. The default setting is for Mega Bass (amber LED), which is supposed to help deliver "high-quality bass." Tap it once and it shifts to a green LED and Mega Bass + Surround, which opens up the sound stage a bit with some digital processing. Tap it again and the sound effects are turned off. After playing around with sound button a bit, I leaned toward the default Mega Bass setting.
I compared the SRS-BTX500 with the Bose SoundLink Bluetooth Mobile Speaker II, which I like a lot and offers similar battery life (6 hours is OK but not great; the Jawbone Big Jambox is the winner there, with up to 15 hours of continuous play). The Bose also plays impressively loud for its size, but I thought the Sony sounded a little bit clearer and was a bit better overall. But it is a larger speaker, so you'd hope it would deliver better sound.
If you're considering the $199.99 SRS-BTX300, that model also is a very good performer for its size, but the BTX500 is a noticeable step up in sound quality. I personally would pay the extra dough for the BTX500.
As for speakerphone performance, it was decent, though not great; the Big Jawbone offers better speakerphone performance. Callers said I sounded slightly muffled, though my voice did get clearer if I moved closer to the speaker, which was about two feet away. I could hear callers fine.
The Sony SRS-BTX500 won't get that kind of support from Sony, but it certainly holds its own against the Bose. It's a slick, excellent-sounding portable Bluetooth speaker that also features speakerphone capabilities (the Bose doesn't offer that), a USB charging option for smartphones, and NFC pairing for NFC-enabled devices. As I said in the beginning of this review, if you're in the market for a premium portable Bluetooth speaker, the SRS-BTX500 should certainly make your short list.