Reference: Sharh ‘Umdatil-Fiqh – Tape No.8, Question No.7
Question: If we are outdoors, such as a farm or a recreational villa, and we hear the sounds of the various callers to prayer from afar, are we required to respond to their call to prayer [by going to the masjid for prayer]?
Response: If you could hear [the call to prayer] without [the caller to prayer having used] a microphone, then you are required to respond [to the call to prayer]. If, however, you did not hear [the call to prayer] other than by way of a microphone [and speakers], then you are not required [to respond to that call to prayer], because it is far away.