Proper method when rack is not on cement floor


I'm moving my 2 channel system into another room. Right now it's in a room that has a wood floor over cement (with area rug), so I have the rack spiked to the floor and everything seems okay. The new location is still on the first floor of the house, but the floor is over a 2-1/2' crawlspace, so it's pretty much a hollow cavity under the rack. Again it's a wooden floor, but with a rug. Is spiking under the rack still advisable for this sort of arrangement? If not, what is the preferred method?

The rack will be in a corner location in this other room, if that helps.
tonyptony
Rushton, that link takes me to a sort of general page on HD. I see no jack posts there. I did a search and found a Tiger Brand selection in HD. Are these the ones you were referring to?
Sorry about the bad link. Yes, the Tiger Brand posts are the ones I used and was trying to show you.
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No problem. Is the idea to "push up" a bit on the jack once it has been put into place? That is, to put some counterpressure on what is probably a sagging floor? If so, how is that done with these jacks?
Yes, that is the idea. The jacks are very heavy steal, with plates at top and bottom, and a threaded rod at one end. They telescope to several interim lengths, you choose the length that is just short of your overall height from floor-to-joist. Then you turn the threaded rod until tight between floor and joist, and turn a bit more to either add just a touch of support or a bit more beyond that to lift out a sag. By using a number of these, you can end up with a very rigid, very strong, floor.
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Okay. Just have to find someone willing to get into that crawlspace! I'm too big a guy to squeeze into something like that. I took another look at it, and it's more along the lines of two feet or so.