Most phones regardless of cost with such a small speaker will unfortunately lose a lot of sound when they are covered on a flat surface. The surface type is also important to gauge roughly how much sound is lost. As for quality of speaker, they are all a bit hit or mess. My 2006 Samsung Monte has a far better, louder and bassier speaker than the recent LG G3, as an example.
According to trustedreviews (click here), it fares better than the Samsung Galaxy s5, if that's any help. If you can't find anything from google, youtube is usually the best place, although for this particular phone, there seems to be more non-english reviews