I am using "15.0". I don't know how realistic that is yet because I haven't fully tested, but I am probably going to lower that amount. Mainly because you don't want someone hearing some from FAR away. Like across the street unless they are "shouting" or "talking loud". But my /me's and stuff go a little bit more than "15.0".
For an accurate amount that you want, you're going to have to have someone help you test out distances that you're comfortable with.