One researcher I know is pretty sure they don't actually "Wood knock" so much as they just slam their hands together or something, I have gotten knocks back immediately and also sometimes had to wait a good 5-10 seconds before they happened so I really don't know. I have heard some that were more reasonably loud but louder than i could do that were pretty dang close to me(But behind cover, which I followed and found what may well be a pretty big heel print), and some that were like a shotgun or a explosion going off into the air in a way.
Off the top of my head I am thinking they may have to use the knocks more often at those times due to lower visibility! They seem to use stuff like that to ping each others location!
The Giants in my area almost solely use knocking as a means of communication it seems and definitely use it to get my attention, you hear animal imitations sometimes, but the knocks are real common in some parts and getting a response is pretty easy. My experience with these big guys may not apply to all of them, but it seems to me that they just really aren't that serious or mean at all but rather get a kick out of messing with me, and I do too. I personally think the problem with most people who go into the field for research is that they are just to friggin defensive when out in the field...people gotta loosen the heck up and pull the stick out of their butts!
Thanks for the advice all! I am gonna look into all suggestions. One thing I would like to say is that when you are out in the field and hear a gunshot off in the distance or whatever, look into whether or not it is even possible for a hunter to be back in the area....so far where I am at it is absolutely not.