Treating Floor in New Construction - Reducing Footfall and Vibration

Stickman:  Sounds like you're all in on this music room.  I'm envious for sure.  And you're getting some great recommendations.  I did a music room in 1994 and used 10 inch fabricated beams on twelve inch center.  Then plywood and wonderboard, and finally a thin layer of concrete to level the locally quarried field stone.  The floor is incredibly solid and the floor joists met the engineering requirements at sixteen inch centers.  Stone is incredibly durable, permanent, and maintenance free.  And when it's sealed it's dust-free and requires only  a mop to clean periodically.  If you have access to local stone you might want to give it a look.  Best of luck.  Tarheeltraveler

 As for walls you can use a concrete board like they use in bathrooms behind tile and then half-inch sheet rock on top of that which will  achieve a dense-rigid system 

 Whatever you do it is very important that any  sub flooring be adhered as tightly as possible and that any additional flooring layers be adhered just as strongly as the first subfloor so that you don't end up with a system that allows vibration to be absorbed. Unless of course you're trying to absorb sound. But if not the more rigid the system obviously the more lively the sound 

Oh and cross brace you're floor joists beyond code requirements. Cross bracing is there to distribute live and dead loads to adjacent joists.  Plywood on the underside of the joist is a good helper as well.  Also at very little added cost ask them to double up or even triple up the floor joists under where the speakers will be - or even better use a glue-Lam member in liue of a open web joists as this will be substantially stronger and more rigid  then anything other than steel. 

Use tongue and groove structural plywood glued and secured to floor joists with deck screws. Then use a self leveling floor system like gypcrete to a 3/4" tickness. This has about a 900 psi strength. For reference typical concrete has about 3000 psi strength. So this means the gypcrete will need to be covered. Cork is good for absorbing but it is soft. If you go wood flooring for a more lively room try to go glue down for the most rigid system. 

For decorating reasons I would go with all parallel walls. 10 foot or higher ceilings provide more flexibility for multiple levels,middle area treatment and massive crown mouldings. As a listening room I assume some sound treatments will be used for standing waves,etc. I live in the Vancouver area in Canada where it is not uncommon to install hot water radiant heating in concrete on all floors in better homes."Double" 5/8 plywood subfloor is minimum where a tile floor will be over the concrete in-floor heating of minimum 4 inches of concrete. Now the floor is stiff! and massive!! Enjoy 

Also,forgot to mention. Re the floor; 3/8 plywood glued and screwed to the underside of the joists gives 'tremendous' boost to rigidity and is how I would go if building new or renovating today. Between floors I like a second layer of press fit insulation resting on the plywood base.
I'm with needlefree re the benefits of QuietRock drywall. They claim 1 sheet of their 5/8 is equal 7 sheets of normal drywall if I remember correctly. 

Instead of 2 x 5/8 drywall I experimented with 1 x 5/8 MDF under 1 x 5/8 drywall and was amazed at the improvement overall.  I used adhesive on the studs, probably PL400,can't remember. That's how I would go now,all around.  Seemed to put the sound on steroids for clarity,dynamics,nuance and overall sense of aliveness.The room was incredibly "quiet". What about your ceiling?

If I was use I would consider using quiet rock for all your drywall applications. Best of Luck

All the walls will be double layers 5/8" sheetrock with green glue between the sheets.

Ceiling is 11' high and will be subdivided into six partitions; the partitions or soffit that forms them will hold the HVAC and lighting.

Do you have questions re your wall and ceiling construction? Vital as well. Don't skimp. Big room,big sound,big problems : )  Pete

I suggest you check the 'Acoustiguard' website. I envy your opportunity to create a glorious sound room of about the size I would appreciate.

I would glue wherever plywood touches wood ; okay a bit o/c, but results are impeccable. Cheers. Peter

Interesting question where my experience  may help.
You mentioned footfall and vibration.(Flex is also important)
Mass and rigidity are the factors.
Your decision must consider the "plywood" thickness used
throughout the adjoining areas;and the depth of finish flooring in
those areas.(There's nothing worse than irregular flooring-and I've seen it in luxury penthouses : ( ...
--The heaviest thickest plywood is best;glued and screwed (don't consider even 'ring' nails)  " carefully"  installed (i.e. supervised,we do not want a any rushing on this)
--I prefer 3/4 inch "Marine Grade" -you're research (check out Homestead Marine) will tell you why--  'T&G (tongue and groove) plywood with high quality adhesive on every inch of every stud -- that retains some flexibility.
Check out PL400,PL Premium, Titebond,Sika & 3M products with your builder/carpenter. I like bldr to be involved in the choice in any excellent product they like to use;they're pro's and 'pro's have preferences'.
I like your carpet (over heavy rubber underlay) with wood floor at the speaker area;it would be my choice (my speakers weigh >450+ lbs each).
--Regarding the framing or joist spacing I would be comfortable with 16 inch spacing - with carefully installed "blocking" between the joists. I will be using  'tight' fitting insulation batts of either used cotton or Roxul  Rock wool soundproofing type - carefully installed  right up to the floor above (I would go to the extreme of using spray glue for permanent adherence to the floor). 
Your carpenter should fasten (screw) at 4" along the joints and perimeter and 8 inches elsewhere.
I would have all joints glued as well to eliminate 'voids'.
Note re joists.  2x thickness gives double strength and rigidity
                            "depth"       "       "          " &  4 x rigidity.....
Gotta go but welcome your questions.
Pete

Not a bad idea from rja....
Best to jack up the joists to 'level' (or even slightly higher....'pre-camber') prior to to the gluing and screwing so that you allow the box-beams to neutralise stresses before 'loading'.
Key word here is 'glue'...
Screws alone will not allow the 'skins' to stress....

My room is over the garage. Fortunately the garage is quite high so I was able to strengthen the music room floor by running two 10in deep joists under and perpendicular to the existing joists. 
I laid a very dense sound deadening material
http://www.customaudiodesigns.co.uk/tecsound-acoustic-membrane.htm
 plus a thin insulating layer over the existing chipboard floor with an  engineered wood floor on top. Works really well no movement in the floor and no bass emphasis from the floor even with 2 big subs.

Dweller with a 30x30 room the listening position might have been located in a "NULL zone" - was the poor bass performance the same all over the room.

Without any acoustic treatments you should get hotspots and cold spots for bass

Also - I have found the distance between the speakers and the amount of toe-in can either impact or augment bass performance considerably.

Regards...

Glue and screw 5/8 plywood on the bottom of every other pair of floor joists. Turns them into box beams.

Joists 16" on center is the industry standard.  Usually you will get 5/8 plywood on top.  1 inch tongue and groove plywood all glued and screwed will be as Williewonka said "concrete".  You shouldn't need more joists.  The plywood is a cheaper and easier option.

I followed a recomendation to create a floating sub-floor with a layer of roofing felt over the normal plywood floor, then with a layer of 3/4 plywood screwed into the flooring  (not the joists). I then used a quality pad with Berber carpet..

I am thinking floor joists on 12" centers are a idefinite requirement.   I am not sure what the building code requires but since the room is fairly large at 22' x 29', 12" centers would seem reasonable.

I don't care for the OSB subflooring myself, so I will discuss with my builder the possibillity of using good quality 3/4 plywood.  Gluing the subfloor sounds reasonable also.  

Stickman - One thing that I know for sure will stiffen a floor is to use good quality ply wood, glued directly to the joists.

The houses in our development were built with that cheapo board made from large flakes of wood. 

When I upgraded my kitchen I put reinforcing beams in the basement because we were putting ceramic floors down and I wanted to prevent bouncing.cracking - it worked somewhat.

Then I helped my neighbour replace a high traffic section of his kitchen floor - we ripped up the old floor and replaced it with quality plywood glued directly to the joists

The difference was amazing - his floor is like concrete (i.e. by comparison)

Both houses have joists at 12" centres

Hope that helps

Making floor joists deeper than necessary for the span, and/or shorter, will do more to increase stiffness than adding more joists, although 12 inches oc will not hurt in your listening room since there would be less opportunity for speakers and heavy equipment to not be fully positioned over joists.  Proper lateral bracing is also important.

let us know what your engineer says.

Actually I am considering putting hardwood on the front (speaker end) ten feet of the room and carpet on the remaining 19 ft.

I have considered taking a hard look at cork; what brand/type did you use?  I have read that cork has good sound characteristics but that it is very soft and hence easy to damage.

Carpet? Carpet pad? Your're thinking wall to wall carpet right?
I did cork flooring in my basement listening room @ $3.29 PSF from Lumber Liquidators + installation (you can do it yourself in about a day).
I laid a black moisture barrier over the cement floor & then the cork flooring.
1,000 SF cost me around $5K with tax, delivery & moisture pad- Wall to wall carpeting would have cost me around $3K & I would probably be replacing it now.
It's soft, quiet, very durable (25 year warrantee) & wont have to be replaced every 5-7 years.
It's also a "green" product.
BTW - It looks fantastic!