This is interesting, though i would expect snape to have a little bit more difficulty keeping his voice calm and soothing. He can still be kind while having a twinge of sharpness to his way of speaking. Please give harry a name soon.
Here is a link to a good example of a careing but still true to character snape if you would like to check it out.
http://archive.skyehawke.com/story.php?no=5036
please keep writing and improving.