Hello! how can I set my iMac's(late 2015 retina) volume, or sound, setting at its default? and by default I mean the state of when I first booted it. I posted a thread regarding reduced bass sound of the computer but no one has answered yet. I suspected an injection of few drops of windex into the speakers to be the cause of the problem but I don't think it is anymore. I think my mac's general level of volume is lowered since sometime past I didn't notice. Any suggestion for such issue? I would really really appreciate your help.