Hello Sammy, welcome to the board. Well straight up, it looks like you've got a tough one. Sam, theres some things you need to understand from the gitgo.
First, unless you build a bunker with 10' concrete walls, there is no such thing as "sound proof"
It's all relative to frequency and db profiles. Soundproof for an
acoustic guitar might as well not exist for a set of drums.
Here is the deal. Without writing a book thats already been written many times here before, what you are really dealing with is "sound transmission loss" through assemblies. My best advice to you is to understand ALL this stuff has been tested and tested and tested. Do not experiment. Bite the bullet and make decisions based on TESTED ASSEMBLIES.
What this boils down to is very simple. The best bang for the buck isolation is TWO LEAF - MASS AIR MASS assembly, period. This means floor, ceiling, and walls. In your case, you have NO mass other than the concrete floor. To
consider a metal building as an EXTERIOR leaf is useless, and almost detremental to the assembly. This exterior shell can almost be considered NON EXISTANT. However, since it does exist, then it has to be delt with in the context of a VENTED SHELL. This is why.
Think of these assemblies as a HERMETICALLY SEALED MASS AIR MASS box.
There is no way to hermetically seal a metal shell. And you wouldn't want it anyway, because there is no mass. To prevent the possibility of creating a THREE leaf system, the skin of the building must "leak" air. Which metal buildings do, because of the formed stiffining channels or corrugated shapes.
Because a MASS AIR MASS assembly creates a RESONANT system, the point is to lower this RESONACE frequency, via airgap DEPTH and mass stiffness. This is the distance from MASS to MASS within the airgap. The mass itself also has a bearing on this LF TL.
So what you are left with is actually having to build a complete M-A-M system within the exterior shell. This can be accomplished in a variety of ways, depending on budget, existing conditions, target low frequency TL(transmission loss), available materials and hardware, construction skills etc. The fact that there is an existing metal building shell makes for considrable difficulty for some choices of methods. But here are your options.
Note that the existing framing material and construction will have a direct bearing on option choices in relationship to what may or not be appropriate or not. Wood vs metal, trusses vs timber or metal roof framing etc will determine various options for fastening, decoupling, sealing etc.
Exterior Leaf
Option #1A Use existing fremework for supporting exterior mass leaf.
Beefing up exterior wall and roof leaf by removal of existing metal skin and
application of SEALED mass.(probably not an option)
Option #1B Leave metal skin as is for weather protection.(
Beef up exterior leaf mass from the interior. This means adding layers of
mass to the INTERIOR side of the metal skin, between studs by means of
adhesive. However, this layer must be hermetically sealed from the inside,
which with metal studs, because of all the flanges, makes for great
difficulty, although not impossible. If this framing is wood, all the better
for this option as well as the interior leaf option 2B.
Option #1C Use exterior shell as THIRD LEAF
This may be detrimental in some way to LF TL, however, adding more
mass to interior leaves to overcome it, has been suggested by other
parties, but we need to confirm this. This would intail adding insulation
between existing studs, and adding sealed mass directly to stud face.
This seems the easiest, and may be the most logical option but still
must be balanced with interior leaf options as this is an intermediate
leaf.
In reality, this option is probably the ONLY option for adding mass to
the exterior shell for the ROOF. And actually is accomplished by adding
the mass to the underside of existing ceiling "joists", which may or may
not actually exist in your case. Usually in a metal building, there are a
few "tie joists, or there may be roof trusses, or there may be timber
framing. These all have a bearing on your choice of method to beef up
this leaf. AND it will determine the choice of option for the INTERIOR
ceiling leaf. No matter the choice, filling of the attic space with as
much insulation as you can afford is a matter of fact.
INTERIOR WALL Leaf. Note that Exterior leaf option choices will determine Interior leaf choices also, or vice versa, as the each must allow for the other.
Option #2A Walls only(exterior 2nd ceiling leaf would become Interior Leaf)
Adding mass directly to existing metal studs. This could be done if mass
is added to exterior leaf between the studs as in Option 1B. Not a
good choice as the airgap would be small(depending on stud width),
and the interior leaf would NOT be decoupled from the exterior shell.
Option #2B Filling stud cavities with insulation and fastening Resiliant
Channel to existing studs for walls, but ceiling must be determined by
exterior leaf mass options. The interior ceiling leaf options are listed
below. Fasten one or more layers of mass to RC. Difficult and precise
fastening are the downside of this option. So is door and window jamb
construction and sealing.
Option #2C. Build seperate WALL framing directly on existing slab. Fill both
existing and new wall cavities with insulation. Fasten one or more
layers of mass to interior face of new framing. Note that ceiling
option choices MUST be considered prior as dimensional factors,
decoupling and practical fastening options become critical should one
loose track of attention to detail and sequence of construction.
This actually applies to ALL option choices. However, the following
options become even more critical.
Option #2D Build complete floating inner shell.
Right from the gitgo,
this is EXPENSIVE, difficult, demanding to attention to detail and
creates MANY MANY other problems that are beyond the scope of this
reply to address. Should you choose this option, prepare for lengthly
PLANNING, PERMIT, CONSTUCTION and INSPECTION periods. This is
NOT a fly by the seat of your pants option.
Ceiling options. These will be determined by all other option choices.
Since gravity is the overall determining force in this area of
construction, there are many things that will determine decoupling
methods, airgap filling, support, and fastening. Here are the
determining factors. Working backwards.
3A Room within a room. Since your existing ROOF is useless as an exterior leaf, a leaf mass must be added between this existing roof and the interior leaf. This is the most difficult area of option choices. In the case of a Room within a Room, this leaf can be either fastened from below to existing or added ceiling joists or trusses, suspended by ISOLATED HANGERS and HAT CHANNEL. This last option would also dictate how the interior ceiling leaf framing would be supported also. In the case of a ROOM within a ROOM, regardless if it is floated on a seperate floor. The INTERIOR ceiling leaf framing could be done in two or three different ways also, depending on the previous leaf option choice. It could be supported on the new walls, or it too could be suspended between the new walls. As you can see, MANY options are available, and all are determined by other factors.
#3B Regardless whether or not a room within a room option is chosen, the intermediate leaf must be added in leu of the roofs lack of mass. This new leaf is in between the roof and the interior ceiling leaf. That is why choices for this leaf and the interior leaf construction type are interwoven. In the case of wall options such as adding RC to the existing wall framing, the same may be done to decouple the interior ceiling leaf, again depending on existing ceiling or roof framing. OR a complete new interior ceiling leaf framing may suspended by the Isolated hanger/hat channel concept, between the new wall leafs(RC decoupled or not).
For each solution there are many caveats and details to consider too. Caulking, door and window jambs, weight(especially for ceiling framing), spans, flanking paths between partition walls and ceiling connections, sway devices, actual fastening methods, metal skin dampening and many others. All fall under the heading of PLANNING PLANNING PLANNING.
In addition to these concepts, there are other considerations that must be factored in. Exterior Doors, Partition walls between adjacent rooms, HVAC ducting and connection, electrical, and even more important, is structural weight on an existing slab, as a floating room is EXTREMELY heavy, to the point of possibly cracking slabs at the footing connection. All these must be taken into account.
Well, it looks like my verbosity struck again
Hope this helps illustrate some of the options available, which actually are not complete. Others may have more, and there are tons of materials to choose from. However, the choice of mass for interior leafs is usually multiple drywall layers.
MDF is expensive, hard to detail at connections and edge sealing and also needs precision cuts to align correctly. Not only that, but if a floating ROOM WITHIN A ROOM option is chosen, the actual decoupling via isolation pads becomes a matter of weight calculation and distribution, step up and floor height alignment becomes difficult for door jamb/threshold/ decoupling scenarios, and various other mind boggleing details become very obvious once planning proceeds.
One of the best things that you can do for us to help you further is to describe in DETAIL what exists. Only then can we offer direct advice. There are many other sites that are directly involved in design, construction, and treatment of studios. Here are a couple of links to give you access to this information.
http://www.johnlsayers.com/phpBB2/viewforum.php?f=2&sid=f8f186822f24bb012e5d73978154c7ca
http://www.saecollege.de/reference_material/index.html
http://forum.studiotips.com/index.php
fitZ
