[Stevensonart]

How are you going to go about asking him about his voice? Might want to really put some thought into that. Don't get me wrong, I would love to know myself but he may turn a little cold after the first question unless it's phrased right and maybe it kind of tricks him into giving us something. For example, you maybe could ask him,

Are you using any different singing techniques than you did in the past?

Is it true you have an allergy condition that effects your singing?

I notice that your voice will be great one concert and then you may have some trouble the next,
Do you have a condition that effects your singing?

As apposed to, what the hell is wrong with your voice?