Float floor or not?

[woliver]

The common wisdom seems to be that when building, say, a small studio outbuilding on piers or other raised platform, floating the floor is necessary to achieve maximum isolation. However, I just read a post by (I think) Ethan Winer about NOT floating floors in basements or buildings with concrete floors. What I got out of it was that when building in a basement, there is too much mass for even loud, bassey sound to move. I can't help but feel that while this is true, a big part of the reason is the fact that a basement is probably at least partially underground, with a buch of earth packed around it, and so transmission through the floor is not such a huge deal. I, however, am building an above-ground recording 'shed', and building it on a foundation. It will be about 20x30, so it has a larger slab of concrete than some (maybe most) basements, but then again, it will be mostly above ground with almost no dirt holding it in place and a very thin layer of dirt to pass through in order for sound to get up the the surface around the foundation. I would like the best isolation possible (not necessarily from OUTSIDE noises getting IN, but from INSIDE noises getting OUT), so... float the floor? Or not necessary?

I don't need the floor isolation to surpass the rest of the building. I am basically building a standard room within a room shed, but with a 3 foot airspace between the rooms, and triple drywall (1/2 inch) as my mass layers.

If I was to NOT float the floor, I would just use the foundation as the floor in my airspace, and use some OSB or MDF or something as the interior floor with carpet over it. But how would I seal the gaps between the drywall and the foundation on the outer layer? I don't know how well caulk would work for that, is there something better?

Thanks

[Sen]

Hi,
Don't worry about floating them.I built a much bigger studio recently and didn't end up floating floors.CR and LR share a 4.5" concrete slab and isolation is just fine.Walls are massive though and well isnulated.

[rufus13]

I think that floated floors depends on if you are building next to a concrete plant with 80 ton cement trucks accelerating up a ramp only 40 feet away. If so, and another site is impossible, then floated floors may gain a few dB of additional low frequency isolation.

In most urban sites, using good shock mounts on well-weighted stands is enough that hp filtering isn't needed.

The kind of money needed to float a floor can be saved for fixing later found faults or reducing overall debt load.

Cheers.