Rosh Hashana 3:6

If a shofar cracked and was mended with glue, it is unfit for the mitzvah. If one glued pieces of shofars, it is unfit. If a shofar is pierced and the hole is sealed, then if the hole impeded the blowing, the shofar is unfit; otherwise, it is fit.

Rosh Hashana 3:7

If a person blows shofar into a pit, a cellar or a barrel, if he heard the sound of the shofar, he has fulfilled his obligation but if he heard the echo, he has not fulfilled his obligation. Similarly, if one was passing behind a shul, or if his home was near a shul, and he heard the sound of a shofar or of someone reading the Megillah, then if he had the intention to perform the mitzvah, he has fulfilled his obligation; otherwise, he has not. Even if two people heard the same thing, it makes a difference if one had intention to perform the mitzvah and the other one didn’t.