I just setup a new entertainment center in my home. The home is from the 50's and has wood floors. The ent center is big and heavy. When I walk through the entrance way, that is about 4 feet from the ent center, stepping on a certain area, about 2 square feet in size, causes the entertainment center to shake. The unit is not off blanace, I cannot shake it by hand myself, but if I was to hop in this one area, the unit shakes a lot. Even when my 35 lb dog walks thorugh this area, the system vibrates a lot.
Any suggestion as to what is going on here and how I can possilby fix it?
It's tough to eliminate all of the rattling caused by floor flexing. The stiffer the floor, the less rattling, but there's almost always some deflection and some rattling. If you have access from below, you could investigate nailing and gluing another joist to the sides of the existing joists in the affected areas - called sistering or sistered joists. The new piece doesn't have to extend the full length, but the closer the ends of the sistered joists are to the joist supports, the better.
Another way would be to glue and screw a sheet of 3/4" plywood to the underside of the existing joists. That will force the neighboring joists to assist in sharing the load, stiffen the floor and dampen some of the vibrations. This method would probably be my first choice. You could test it with screws on 6" centers before committing to the installation by gluing it.
It is clear that the floor is transmitting this shaking. I could be that the flooring in this area is not securely fastened to the joists in that area. It could also be that the floor joists are undersized or that the floor framing was poorly designed. You need to determine the location of the floor joists. Maybe you can go in the basement to take a look. Measure the size and spacing of the joists and let us know what it is. You can have a helper stand down there to see what happens when you walk across it. The joists can be re-fastened to the floor in the problem area and may help. It is also possible that you can upgrade the framing in this area to make it more rigid. You could beef up each joist by sistering another board along side. You might also be able to add additional joist in between the existing ones. It is also possible to add a vertical support like a steel column in order to support the floor in that area.
Living in an old house requires learning the art of shimming. I'd say there is space between the floor and the floor joist. If you have a basement, no problem, if you have a crawl space and are slim and athletic, no problem. Get a package of wood shims and a hammer and flashlight, get an assistant to tap on the spot, fill the gap. If, however you are on slab, disregard this post.
This is a classic problem with larger heavier modern furniture.
Long winded answer..........
Your floor system is not infinitely stiff (no residnetial one is)
when one walks on the floor each foot fall is like a large deadhammer blow, the floor deflects from this force, changing shape slightly
So you have a large tall piece of furniture mounted on the same floor system, when floor deflects it also deflects under the front of the unit. I assume the back of the unit is against the wall. Since the unit is tall (about 3+ times taller than its shortest base dimension?) it "amplifies" the motion that it gets at its base by this ratio.
Depending which way the joists run that can make the problem worse.....I'm guessing that the joists run in the same direction as the long dimension of the unit?
Making the floor system stiffer will reduce the problem.
Other have suggested shims, screws, "sistered" joists, blocking to share load, etc.
BTDT......these all can work but they can be a lot of effort
If it was my house & the chances of reloacting the unit were small I would:
"survey" floor....that is jump in various location to find ALL the points that give you the undesired behavior.....hopefully only one or two.
I'd install a jack post at each location.....very high added stifness, quck & easy if slightly inelegant (but better than the rock idea)
II have four adjustable jack posts sitting in my garage but I cannot find a link for them
If the thing is up against a wall, and after trying whatever you can conveniently do to stiffen/support the floor, you can put down a pad of high-density foam (like a camping pad) under a sheet if plywood under the entertainment center, and then screw the furniture to the wall. If the exposed edge of the plywood and foam offends you, staple a cloth skirt around it, or attach moulding to the floor, but not the plywood.
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