[redjr]

Just buy two solid doors (recommend insulated exterior fiberglass oak grained doors that can be painted/stained) and a removable mullion (if you have big items to move in/out).  Add rubber weather stripping/door sweep as sound seals.  If you don't need an extra wide door opening, recommend just buying a pre-hung insulated exterior fiberglass door.  If sound transmission is a really big deal, provide two such doors (can be on the same wall with one swinging into the room and the other swinging out of the room, if the wall is thick enough the door handles won't hit or else hinge them on opposite sides of the opening).

Unfortunately, both doors will need to open in, due to a structural beam bulkhead on the outside.    But you've given me something to think about, by fabricating my own custom solution.  I'd much rather just buy a set of pre-hung double french doors, that are solid as possible and start with that solution. - Rick

[gschotland]

I'm in residential & commercial construction and have experience over the last ten years on numerous projects requiring cost effective solutions to limit sound transmission including luxury apartments and mixed use buildings (commercial w/residential above). 

We've gotten great results with single layer QuietRock (http://www.quietrock.com/) with Green Glue on the seams and in and around all penetrations.  One of the other major drywall producers (USG?) has a similar copycat product.  This product is a little pricey, but single layer saves a lot of time and labor.  This is far more effective than double layer standard drywall.  You can create a similar effect by using Green Glue between two layers of standard sheetrock, but we never saw the point.  Once you figure in the time, labor and cost of all the glue and 2nd layer of rock, there really isn't any cost savings vs QuietRock. 

You can see a wide range of sample wall assemblies on their website detailing things you can do to improve performance such as staggered stud walls, double stud walls, 24" on center stud spacing vs 16", resilient channel, batt insulation, etc.  It really depends on how far you want to go - and how much you want to spend.

[Scottdazzle]

Hi Scottdazzle - Appreciate your comments.  I recognized your avatar so I must have read some of your previous posts.

The room dimensions are already set, as are the decisions to have a drop-ceiling and french doors.  I'm also aware that these two items are not at all helping my isolation efforts.  But since this is a multi-purpose room that is the path I'm on.  However, I have taken some measures to help minimize sound coming in and going out.  Not total measures mind you, but things I trust will help after doing a bit of research.  Such as; double 5/8" DW, insulation in all walls, between overhead floor joists and offset studs on my primary forward TV wall.  The room size is not a rectangle, but is 10' wide at the screen end and 14' at opposite end with and angled wall on one side where the french doors will be.  It will be on the small..ish side, but my man-cave nonetheless. 

My basic question remains... If I haven't taken measures A and B, will C even matter?  If I've got 2 big holes in my fishtank (using that analogy) - my drop-ceiling and french doors, does double DW even matter, much less what I put between them?  Or, am I simply going after a < 5% additional improvement in isolation, mass, and absorption qualities for which there will be little difference noticed?  If I can save $400-600 on GG and use something else because of the minimal % improvement factor, I'd rather spend that same amount on, say, nicer speakers - for instance.  Are there other compounds in the marketplace that are similar to GG, cheaper and still work as a damping agent between DW sheets?

Rick

The un-parallel wall should be good for sound. Rectangles aren't great and squares are awful.  If you're not going to use green glue, my suggestion would be to just go with single drywall and spend the savings on some strategic room treatments after the room is finished.  After the room is done and you've set up your system, you'll be able to tell where to make improvements.  It's amazing how much improvement a few bass traps and/or a diffusor can make.  Much better results than you'd probably get from a slight speaker upgrade. 

[Big Red Machine]

Edit:  I know GG won't hurt, but will it's benefit be out-weighed, not necessarily negated, by the lack of other isolation measures?

I think that risk exists.  I see double drywall onto the structure as a thicker transmitter of vibrations through the wall. So while the added thickness changes the resonant frequency of the wall itself from that of one layer, it is still attached to the structure and you don't get the isolation that truly keeps sound in and out.  The GG keeps the  walls from vibrating and eats up the transmission through side to side movement of the sheets of drywall (heat, if you will).  I never forgot the explanation Bryan P. gave me about what you should shoot for:  a large mass that is hard to move isolated from that which would want to move it.  So suspending the drywall from the structure is step 1 and adding the mass of 2 layers is step 2, and having any movement of the heavy drywall waste its energy in side to side movement that is rather benign to the intended room quiet is step 3.

Your room will still be quieter than normal but you will have missed some opportunities if it is hard attached and is not internally damped.  Could be a major moot point if it is large enough that the natural room modes really don't bite you in the end.

[redjr]

I think that risk exists.  I see double drywall onto the structure as a thicker transmitter of vibrations through the wall. So while the added thickness changes the resonant frequency of the wall itself from that of one layer, it is still attached to the structure and you don't get the isolation that truly keeps sound in and out.  The GG keeps the  walls from vibrating and eats up the transmission through side to side movement of the sheets of drywall (heat, if you will).  I never forgot the explanation Bryan P. gave me about what you should shoot for:  a large mass that is hard to move isolated from that which would want to move it.  So suspending the drywall from the structure is step 1 and adding the mass of 2 layers is step 2, and having any movement of the heavy drywall waste its energy in side to side movement that is rather benign to the intended room quiet is step 3.

Your room will still be quieter than normal but you will have missed some opportunities if it is hard attached and is not internally damped.  Could be a major moot point if it is large enough that the natural room modes really don't bite you in the end.

That risk does indeed exist...However, I don't think - from all I've read - anyone can conclusively - quantify the risk because all rooms are not structured alike.  Nor (do they) have precisely the same characteristics, hence it is difficult to create a lab example to scientifically prove or not of various degrees of further isolation properties/efforts.

My understanding, or at least partial understanding is the added mass helps the absorption characteristics of the room, stealing some of the energy of the sound as it decays and allows less (sound) to get transmitted onto the superstructure of the wall and be flanked off to other parts sans the use of clips or floating the wall.  If that assumption is correct, then more would 'seem' to be better as the first barrier against the sound traveling. Maybe BPape could chime in here and correct me.  Maybe full-length heavy drapes hung in front of bare studded walls do the same thing too. Somehow the density has to come into play here. 

Just as an aside... The primary (front) wall in question will have my electronic shop on the other side of it.  After I got the first layer of DW up between the offset studs, packed with SafeNSound insulation, I placed 23/32" plywood on the shop side of the same wall.  My son was in the shop side doing some wire labeling and I was trying to test the same wires on the TV side.  We could barely hear each other through that wall.  It was very interesting how much the insulation and 5/8" DW and 3/4" plywood added to the absorption and isolation of the sound.  We had to walk around outside to hear each other!  I was impressed. - Rick

[redjr]

...If you're not going to use green glue, my suggestion would be to just go with single drywall and spend the savings on some strategic room treatments after the room is finished.  After the room is done and you've set up your system, you'll be able to tell where to make improvements.  It's amazing how much improvement a few bass traps and/or a diffusor can make.  Much better results than you'd probably get from a slight speaker upgrade.

Only one problem with that... That was my original plan last Fall and I purchased the extra DW.   What to do with ~14 extra sheets of 5/8" DW?     I can tell you one thing.  I'm not carrying them back out of my basement!  Plus, I made a few screw-ups with the first layer (nothing major) that I was hoping to cover over with the second and a little professional help with the mudding and taping.    I guess it's time to Pony up for some GG or QG.