Why are daytime prayers offered silently and the night time prayers offered audibly?
At the outset, it needs to be appreciated that the Shari'ah is silent on this issue. Thus we can only present our understanding of the matter. It is obvious that the basic purpose of loud recitation during some of the prayers is that the worshippers can listen to the part of the Qur'an recited. Now if we consider the timings in which the Qur'an is not recited loudly we would know that, during these timings, human activities are often at their peak. This leaves little possibility for the worshippers to listen to the recitation very carefully. Therefore, in these hours the Holy Qur'an is not recited loudly.