When you're playing music through it, you can literally see the bass ports on each side of the speaker moving as air passes through them. For a such small speaker, it's able to output an impressive amount of bass. However, like all of these small speakers, you can only push it so hard, and when maxing out the volume and playing more complicated tracks with lots of instruments, things can get rough around the edges.
The internal DSP (digital signal processor) works to limit or clip certain frequencies ("compress" is another way to describe it) to keep the speaker from distorting too badly, and you can literally hear the bass pulling back at times.
Again, that's par for the course for these types of speakers -- I've made similar statements about such competitors as the, , and .
All these speakers have similar sound profiles, and their sound is subtly different. You can end up judging them differently from track to track; they all distort to some degree.
That said, the JBL is right there with its competitors, and I actually thought it sounded a touch better than the Sony SRS X-33 and maybe even the Bose SoundLink Mini II, which features a metal enclosure. The JBL has a little stronger, tighter bass and slightly smoother sound overall. Of the three, it's probably the most natural sounding.
If you're choosing between this speaker and the UE Boom, I'd say the UE holds the advantage with a little bit better build quality and battery life, but it's a close race in terms of sound. If you're looking to save money, this JBL is a good alternative.
Perhaps we'll get full waterproofing in the Charge 3. While this isn't much of an upgrade over the Charge 2, now that JBL's resolved the sound issues that held back the standard Charge 2 at launch, this is an excellent portable mini Bluetooth speaker.
Over time, it should come down in price by $20 or $30. Until then, the standard Charge 2, which is being discounted as it heads towards retirement, is arguably the better deal. Just make sure to do that firmware upgrade to improve the sound.