Turntable on suspended floor - shelf or braces?

Don't get Mike Holmes started on that one...
Really though, if FF is so bad it is most likely going to muck up your bass as well.
A decent carpenter should be able to take a lot of the bounce out of the floor without much effort. You could either "toenail" in extra boards to the joists to make the stronger with less flex and/or put cross members between the joists. Either way, you would need a nail gun, a bunch of wood glue and some inexpensive 2x6 or 2x8 boards anywhere from 4 feet to 12 feet long...

it depends on how technical you want to get. Your interior walls that you may want to hang your table could be supported by the bouncy floors you mentioned. An exterior wall would load down to the foaundation in most cases and be the best solution for wall mount. The simple way to take some bounce out of a floor is to add a row or rows of bridging perpendicular to and flush with the floor joists. You are looking to increase your "load bearing" of your floor system and a google search of that would guide you further down the path of obcession.

I put a Vibraplane isolation platform under my suspended table and it solved all of the problems you mention but also isolates the table so well that I hear all sorts of new detail and extension. The sound improved tremendously. Details can be found on my system page.

My effective inexpensive solution for a suspended turntable (B&O) was to place cryogenically treated tempered steel isolation springs (Machina Dynamica Cryo Baby Promethean Mini-isolators) between the maple board the turntable rests upon and the horizontal top furniture shelf beneath.
For further vibration control, a VibraBlock Damper rests on the horizontal top furniture shelf.
As mentioned by Peterayer above, the sound is upgraded to a surprisingly impressive degree with appropriate isolation.
My turntable is protected down to about 3 Hz which is incredible for the low cost of the setup. When Godzilla next stalks the earth my vinyl won't miss a beat.

Hi djm,

My living room has a suspended wood floor with 20' spans for L and W. A closet, enclosed stairwell and fireplace column on one wall prevent the dreaded "square room" for sonics. But the long span meant bouncy motion even when walking light-footed. I had a heavy cabinet placed by a sidewall but the suspended table still bounced the arm/stylus whenever anyone moved around the room.

I too have a crawl space so I installed three 4x4 posts on concrete footers at 5', 10', and 15' along the center axis of the room. My floor joists run perpendicular to the line of the posts so that helped distribute the support. That cured my floor flex and bouncing stylus problem.

An easier solution might be to mount your turntable support on a load bearing wall. But my floor supports also minimized the floor flex to improve bass response (stiffer boundary) so I gained two benefits.

If you have much flex to your floor it would seem to me any sort of suspension under your table would only be a band aid. Why not cure the ailment instead of taking an aspirin?

Good luck.