Dealing with an unstable, vibrating wood floor...

Hi everyone, as some of you know, I've been substantially upgrading my hi-fi lately. Currently a CJ amp, just got a Michell Gyro SE, and a JJ 243 pre on the way. I'm admittedly a newbie to audiophilia. Now I need to worry about stablizing the equipment rack. Here's the deal.

I have my rig on a four-shelf rack, a welded steel Sanus on spikes with 3/4" MDF shelves. I live in a 130 year old bulding on the third floor. The hardwood floors have seen better days--some loose slats, and the floor is VERY loose and prone to vibration. I can't even walk across the floor without making the turntable bobble on its suspension a little--the floor flexes slightly under my feet and takes the rack with it. I really, really need to work on stabilizing the rack! I've found that vibration is a significant cause of poor sound from my vinyl rig--pops and ticks, lack of clarity and detail, etc. and forget using a subwoofer, the low frequency waves render my vinyl rig far, far worse than my ho-hum Marantz CD5000!

Some problems--I know I'd be better off with a wall shelf for the Gyro, but you'd be right to guess that my walls about as good as my floor. They can't hold a spice rack much less a shelf with a turntable sitting on it. So I'm stuck with the 'table on top of the rack. I also can't afford to get a Neuance shelf or some such.

I'm wondering if sheer mass would do the trick. Could I put the whole rack on top of, say, a couple inches thick cement flat, then level the rack on it? Or could I have a cement or sand-filled shelf in place of the standard 3/4" MDF shelf my Gyro currently sits on? My main problem is the whole rack is unstable, so that's another reason why I hesitate on a massive shelf for my 'table. Would it pay to put the whole rack on something solid, of great mass?

I don't have a ton of money to work with, but my current situation is unacceptable! If anyone could steer me in the right direction or give me some DIY tips, this newb would be very greatful!

P.S. I have scoured archives, and found some interesting points, but I haven't found a discussion of isolating the rack from a loose floor.
It doesn't fit your budget, but perhaps you can look down the road some. I recommend you take a look at the Promethean Base from Machina Dynamica. It will blow you away and should solve your stated difficulty.
Your walls will definitely hold a shelf. If it really can't then I'd be looking for a safe place to live tomorrow. It just needs to be anchored properly. If the wall stud layout doesn't meet your needs for location then drywall anchors will work fine. Slamming doors might become problematic. Hopefully you can make use of an outside wall or a load bearing wall. A shelf doesn't need to cost much and can be home made. The question I have is do you know someone with carpentry skills that will help you on this? This is by far the cheapest and best solution to your problem.
You won't find ANY type of isolation device that can counteract the magnitude of movement that loose, flexing floorboards can generate. As you have surmised, adding mass to lessen the movement might help, but if your floors are really that poor, your rack may wind up with your downstairs neighbors. I do agree with Lugnut in that a wall shelf attached to a load bearing wall would be the next best thing to moving to a more structurally sound building.
My suggestion is going to sound a little bizarre, but many years ago, when I was an undergrad student, I lived in a place similar to the one you describe. There weren't any good, cost-effective solutions to the wobbly floor, so I devised an equipment rack system that was suspended at three points from the floor joists in the ceiling above, and secured to three points on the equipment rack. This triangular setup, while not terribly attractive, is quite stable, and you could use rope or chain to suspend the equipment rack.

The wall shelf will probably work best for the turntable, but the wall mount will need some reinforcing. You could try nailing some 2X6 boards to the wall studs, and then mount the turntable shelf to the 2x6's.
Very good answers above. My house is century-old wood box (3-inch thick planks all over) on shallow stone foundation, and every piece is connected to every other piece so that an upstairs door slams and the whole house trembles for a second. But wall shelf on outside wall, in my experience, works perfectly. Problem is siting the rest of the equipment!

Mass under rack may not tame seismic vibration from footfalls and door slams. I worked in a store with a low brick wall as a TT demo shelf. The whole wall oscillated at maybe 2 Hz if we danced, and sprung suspensions hated that.
Wall mounting your deck to a load bearing structural wall would be your best option.
Think of your upper story floor to be a diaphragm attached at the edges of the load bearing walls.When the floor is disturbed, there will be more vertical movement at the unsupported center of the floor and less at the supported edges near the wall.
Footfalls,etc will thus cause a floor mounted stand to sway/rock(lateral) as well as bounce (vertical).The taller the stand,the more exaggerated the swaying/rocking motion will be.
Any turntable (and particularly suspended designs like your Gyrodeck) will react quite negatively to any lateral movement.Tho obviously having no motion at all is better, your Michell's long travel suspension is designed to deal with vertically oriented movement/vibrations fairly effectively.
Increasing the mass will only change the rate of the floor's motion but will not do anything to stabilize the flooring & stand.In addition,the increased mass will store more energy in the floor, resulting in a longer duration for the energy to dissipate.
A wall mounted support should provide you with the least vertical and lateral movement as well as storing the smallest amount of vibrational energies as you'd only be supporting the mass of the turntable and shelf.
If wall mounting is unacceptable or a monetary concern, you could move your present rack very close to a load bearing wall and improvise a bracket to solidly affix the stand to the wall(attach it near the top of the rack), thus mimicking a majority of a wall support's benefits.
You could alternately place the turntable on a low stand as close as possible to the wall to minimise the swaying effect. The inexpensive IKEA Lack sidetable(~$15) makes a very good performing low mass, cost effective dedicated low stand option.

Good luck.

Dirtyragamuffin, I didn't factor in the suspension of your TT. It probably would not be a good match with the Promethean Base.
If your walls aren't strong enough to hold a spice rack then you need to move.
Your situation is difficult indeed. Don't think you might be able to fix completely but you can "improve".
1-Do you have any place where the floor doesnt bobble that much? If you can find the betterplace you can decrease the ammount of problem to begin with. Move your rack there
2-You need to provide degrees of freedom i.e. movement to your rack as a whole shooting for horizontal movement (easy to implement via ballbearing etc) and in the vertical plane (more difficult via innertubes ) the idea is to have the larger mass the rack supported by means of a damping mechanism that will "lessen" the vibration effect.

3- If possible try to "link" loose slats by means of adhesive between adjacent moving seams.

Some thoughts to share. Your comments
Thanks for all the very informative advice! I will try to move the rack towards the outside wall where there is indeed less movement; my main problem is, the wall is lined with huge windows with radiators between them :(

It's really a bizzarre apartment building--I'm impressed the place is still standing. It's heavy brick on the outside, but my neighbor and I have done some exploring. The interior is very shoddy...electrical,, which must have been added after the place was built, is, shall we say, an absolute wonder... ;)

Probably my best bet would be to try the 2x6 idea if I could find a large enough section of open wall and hope I can get them anchored, however, my landord might well frown upon big holes in the wall--I picture large chunks of drywall coming out ;( I'd need much longer ICs as well...

I really just need to buy a house! Maybe then I'd have an excuse to get some AvantGarde Duos, hee hee ;)

Thanks again for the tips. I'm going to play around and see if the rack and the floor can reach some kind of compromise...

You'll be the best to judge your compromises considering improvements doing the play around.... but I'd say that the windows and the radiators can be dealt with on a for listening time basis kind of treatments (carpets, curtains,etc) that if cosmetic is a restraint you can take off for not listening time.
You can even make metal or wooden "L" brackets to be screwed to the wall (proper size) and even put your rack spikes there instead of thinking just for a shelf you could fix the whole thing to the external wall. it's not easy but i believe doable. Your motivation to improve your sound will tell if you would go this radical or if simpler tricks could be an improvement "good enough" for a time.
Keep us posted
Actually I got to thinking, ideally what I'd like to do is put the rack up against the wall with the rear spikes removed, and put up at the top rear of the rack--this way the rack would be coupled to the wall by two spikes and to the floor by the other two. The problem again is I have no wall space to do this, though I might be able to free something by literally moving everything in the room around. My main problem with the windows and radiators was that they take up literally almost the entire length of the wall--about 25'! This is why I'd been asking about massive additions to the rack. My apartment really is a dumpy college kid pad (and I, a dumpy college kid (with a nice hi-fi, hee hee)), pseudo-studio style--basically, one room ~25' long by about 12' wide with 10' ceilings, then the bedroom/closets/john in other rooms. The "kitchen" is at one end of the room; the rest is the living room, with a tapestry hanging to divide the area.

Since it sounds like a massive block under the rack won't help much, I'm starting to think that I might just have to live with this situation until I move, however, I will try a couple things when I have time and post the results :)

Thanks again everyone for helping me out. I'd gladly take more advice, if there is any!
Sounds like it's time for a trip to IKEA.
Tell them Ingmar sent you.
A Sony Biotracer (servo controlled arm) might handle your vibration problem. Several hundred dollars. Check E-Bay.

For several thousand dollars there are active vibration isolation tables (used in industrial labs) that would solve your problem.

The only cost-effective solution is to forego LP's, and use digital discs. They work in autos on pot-holed roads.

I have a thorens TD-125 on top of a five shelf rack, and it used to be very susceptible to footsteps. Just adding mass did not help. Adding sand to the rack did not help at all. I had a wall mount stand for awhile and it worked great, but I didn't like the way it looked. What I use now is a DIY sandbox on the top rack of the stand, and then wedge foam rubber between the wall and the top of the rack so that it is a tight fit with a good amount amount of pressure going against the wall. The extra weight from the sandbox helps put more weight on the wall. This coupling to the wall simulates a wall mount, and really helps reduce impact of footsteps.

Instead of a sand box, you could try a 18" square concrete patio block. You could try this out for under $10.