Disregarding whether the role play setting is fantasy or supernatural or whichever that requires or allows a superhuman trait on a character, I have a habit of making my characters' powers be a seemingly effortless alteration of reality that can possibly be 'explained' with science [hopefully that makes sense]. Sometimes... well, almost all the time actually, I have trouble grasping whether what I assumed is actually feasible or not but I didn't really had a place to ask. That was when I figured I'll try asking here. 

So for the time being, these are the thoughts I have at the moment.

[u]Maintaining a constant temperature[/u]: The idea behind this would be a power that is able to keep the same temperature on an object, person or thing. An example will be ice cubes that seemingly never melts [because the ice cubes will be under this power and stay below freezing temperature even in a hot place].
The problem is what would happen if an object, person or thing that is under this power:
-is bathed in something like fire? I understand that the object, person or thing will not be affected by the scorching heat from the fire but does that mean it will also prevent burning and if so would it be classified as a complete immunity to fire? Or better yet what would be the entire effects of coming in contact with it.
-came in contact with something of a vastly different temperature the moment the power is dispelled? So if an object is cooled down to, idk, minus a hundred degrees celsius [disregarding the fact whether that's possible or not] and then placed in something that is at least a thousand degrees celsius at which point the power is lifted.
-considering thermal radiation? from what I know heat radiates off anything above absolute zero. Would it make sense to say this power will prevent thermal radiation to enter or escape the object that is being powered? If this is the case, that means this can effectively prevent heat sensors, doesn't it?

[u]Acoustic Levitation[/u]: Basically this is sound waves bouncing off or reflecting to and fro an object which in turn makes the object levitate. At least that is what I know of it from reading about it. An example of this would be from that. X-men episode I happened to see; I think it was the movie 'beginnings' or something where a hyper voice guy flew using his voice. From what I know, acoustic levitation achieved with sound waves not in hearing range to an average person can only lift small objects and not people. I suppose what I really want to know is what would be the requirements for sound waves not in hearing range to be able to lift a person or heavier?

EDIT: well, this post is longer than I expected. Sorry about that.