1) All Shofars are valid for blowing, whether they are straight or curved. However, ideally one blows with a curved shofar, to allude to a person that he should bend his heart before Hashem. It is correct to try to find a shofar from a ram, as a reminder of the Akeidah. (Shulchan Aruch and Mishne Beruah 586)
2) Any sound which comes out from a shofar is valid, be it thin or thick, lush or dry. (ibid)