The sound is excellent not crackly, it's clear and definitely more than efficiant for the size and quality. Has quite a deep base which is really great.
The fact that I can charge it outside without a wire etc is what really won this speaker over in my opinion. If it rains - no problem. bump it - no problem!
On occasions I have taken to the bathroom to listen to music whilst having a long soak in the bath.There is a solar panel on one side so fantastic to take outside wherever you go knowing that if it runs out of battery you can charge it with the sunlight.Would be fantastic for trekking.As I said it is waterproof but cannot be put in water.The battery can last up to 30 hours playing time with 1 single charge. It comes with an audio cable and charging cable.The speakers are really well made and you can feel that in the weight and quality of it.
Well worth purchasing you won't be disappointed.
By far the best Bluetooth speaker I have purchased as to date.