Great Bass for such a size. Mp3 goes inside and there's a belt clip on it too.

I bought one of these years ago and it is absolutely AWESOME for the backpacker who likes having music around. The blue one is about 15 x 10 x 4 cm and doesn’t weigh much for its size.  The other one is CD sized.

I recommend the bigger one as the sound is better.  It unzips at the side and is relatively hollow (which boosts the bass).  There’s a space for two AA batteries and a headphone jack on a small wire.  There’s also a small netted area so when your mp3 is inside, it doesn’t move around too much.

I’ve added a link to the Australian company I bought it from and you should be able to order one – I’d get an extra one for a friend too to economise on postage as they’re perfect backpacker gifts.