How far apart do you typically space your calling intervals? 10 mins? 15 mins? Do you prefer soft or loud? What do you use to determine if its time to go on the move?

If I'm calling blind, I call softly first. You don't want to blow out his eardrums if he's close and you didn't know it. If I don't get a response I pick up the volume and give another series or two, maybe a little cutting. When calling blind I give series or two like that and wait anywhere from 10-20 minutes before calling again.

If the gobbler is responding, I judge based on how he responds. If he is hot and cutting me off with his gobbling and double gobbling, I keep it going agressive.
If he's lukewarm in his response I play hard to get (softer, less often).
Just judge based on how the gobbler responds. If he hangs up within 100 yards, try some soft clucks and scratching leaves around you. Or just shut up, he will eventually come looking.

less is most always better..... softer,too.....

I agree with tail feathers. You have to give em what they want. Try and think like a women, tell him what he wants to hear,then take him down and break his heart

I agree with TF as well. When blind calling, I'll tone it down, and usually wait approx. 15-20 minutes between series. It's after the second series of calls is when I usually get a answer.