It is recommended for the caller (muezzin) to raise his voice during the call to prayer (adhan); because the purpose of the adhan is to announce, and this can only be achieved by doing so loudly. Abdullah ibn Zayd (may Allah be pleased with him) said that the Prophet (peace be upon him) told him: "This vision is true, so go with Bilal, for he has a clearer or louder voice than you, and convey to him what you were told so that he can call out with it." This is found in Sahih Ibn Khuzaymah 1: 189, Sahih Ibn Hibban 4: 573, Al-Muntaqa 1: 49, Al-Ahadith Al-Mukhtarah 9: 375, Sunan Al-Tirmidhi 1: 359, and Sunan Al-Darimi 1: 286. Therefore, it is preferable to call the adhan in a place that can be heard by the neighbors, such as the minaret or similar locations. He should not strain himself; as he may fear the occurrence of some ailments, such as hernias and the like. He should also raise his voice during the iqamah (second call to prayer), but not as loudly as during the adhan; because the goal is to announce it, unlike the purpose of the adhan.