Two ceiling insulation/isolation questions

I have 2 questions about ceiling isolation: 1) In Rod's book, and in several threads around here, it is recommended to beef up the ceiling of a lower floor like a basement when there is a heavily trafficked floor above. Additional layers of sheet rock attached to the bottom of the subfloor seems to be the most common recommendation. It is also pretty clear that a structural engineer needs to be consulted with regard to load-bearing issues. I got all of that... My question(s) here is more in the actual implementation of the process. I have a lot of "junk" between the floor joists above me. Things like HVAC ducts, cross braces, etc. How do you go about sticking a layer or two of sheet rock into an area like this? Also, how does one go about affixing it? I have seen the use of battens and caulk, but how the heck do you get in there with all the junk in the way? 2) I have *another* area of the studio that is being utilized from a previous construction. This means that the ceiling is already drywalled. I do not plan on taking this layer down due to all of the work involved and the huge mess that it will create! I will most likely add a second layer of drywall to the ceiling sometime in the not-to-distant future. At this point, I still have access to the ability to blow in some of the loose fluffy insulation between the joists (there is currently no insulation there at all). Is this worth the effort/expense? Once I finish the current construction phase, I will not have easy access to this space, so this is my best opportunity to blow some stuff in there if I am going to do it. Thanks!

Friendly bump... anyone?

DH, ually - if i were to do that - leave the lower mass in place I would probably try to do some sort of a foam insulatin in the cavity - that (at least) would act to make the floor a masss assembly as a whole - as it would damp both faces simultaneously - making them one member for all intent and purpose. The you wouldn't have a 3 leaf system - it wouldn't add a lot from an islation point of view ( not a lot of mass - but at least you wouldn't have the TL los that you get with a short spring triple leaf system. Rod

Rod, DH Just a question. I should like to see a better description of this floor. You must be careful to make the solution we once used for Paul Woodlock's garage door (gluing with foam) for a lightweight door on a heavy brick wall, as some general approach. We aimed there at a very high MSM, which didn't had much influence anymore in combination with that total wall. If you have something as a wooden floor and gypsum beneath the joists this same method will create a very unhealthy combination. But maybe I misunderstand here.

Just 2 copyrighted pictures of one of my Dutch acoustics courses: What you see is the influence of putting wool in the cavity. The dotted lines relate to prognoses theory. Wall buildup 1) Hardboard 3 mm 2) Cavity 16 cm 3) Hardboard 6 mm No Contact bridges Curve 1: Empty cavity Curve 2: 5 cm mineral wool Curve 3: 10 cm mineral wool Without wool the rise is limited in a large part to 6 dB/oct (equals +/- mass wall total mass) A double leaf system without wool filling is often a bad thing. Only when the MSM should be too high, and therefore damaging in the overall TL one has to look for other solutions, otherwise empty cavities are generally a bad thing. Resilient skin glued on pseudo heavy base wall of gypsum blocks 10 cm thick density 1200 kg/m3 (120 kg/m2). Curve a: Sandwich Gypsum board 10 mm on elastic open cell polyether foam (hence acoustic foam = bonded foam often used for this purpose) density 60 kg/m3. Glued directly to wall. Hence the whole combination becomes a glued sandwich panel (thickness foam 3 or 4 cm, not sure anymore). Curve b: Sandwich Gypsum board 10 mm (as above) on polystyrene (PS), hence comparable with thermal expanding spray polyurethane. Glued directly to wall. Hence the whole combination becomes a glued sandwich panel (thickness PS 4 cm). In the Paul Woodlock case, we decided to ga that route based on a small cavity (wall specially build as close as possible to door) and a lightweight door. As curve b shows even with stiff material there is a clear MSM which hold that curve down to a certain frequency after which it starts rising as a traditional double leaf system. Hence also spray polyurethane and PS has a dynamic stiffness, behaving as a spring in a double leaf system. The smaller the filled cavity the higher the damping. When using this system as in Paul's case, one must guestimate that one shifts the problem to an area it doesn't matter anymore, which was the base on which that advise was founded. One can not generalize this that a double leaf system becomes an harmless single leaf system when filling it with spray foam. This latter graph are Delta isolations. With higher spring thickness this dip will become larger and shift towards the lower frequencies. Filling the space between the joists as such doesn't feel right. But the question is: Can DH work on the top of the floor rather than working from below trying to to increase mass of the top floor between the joists? Such solution is only advisable is working on the top is not possible. For the rest, I believe it's good that DH gives a more detailed description of his circumstances.

Eric_Desart wrote:

The smaller the filled cavity the higher the damping. . . One can not generalize this that a double leaf system becomes an harmless single leaf system when filling it with spray foam. . . . With higher spring thickness this dip will become larger and shift towards the lower frequencies.

Very interesting, Eric! 8) I had always assumed that the reason we'd try to "fuse" (join) two leaves together with closed cell foam in order to prevent a third leaf situation was to not waste space, but now I see that there are advantages beyond that. It also leads us to be cautious when recommending fusing two leaves that are pre-existing and are not especially close together. I hope I'm interpreting your information correctly. 8) --Keith :mrgreen:

Keith, Your conclusion is correct. AFAIK this is one of the first times this solution was discussed: http://forum.studiotips.com/viewtopic.p ... ight=#3655 Look few posts before and mainly the following. I even made a joke about it in these posts telling:

Eric wrote:

Edited: You can check that afterwards: If you knock on the garage door and the generated pitch is 4 to 500 Hz or higher, you may kiss me. Correction: Woman may kiss me. (that's how Paul standard referred to his wife/girlfriend) If it should be in the neighborhoud of 200 Hz or somewhere you may kill me. Condition: you give me advanced warning so I can start running beforehand.

Here you can find the tables I once made: http://www.johnlsayers.com/phpBB2/viewt ... ght=#48870 The idea of gluing/fusing them together is to get rid of this higher generated MSM resonance caused by a triple leaf system. Just roughly say that the overall insulation (weighted single number rating) for studio music sound is mainly defined by the below 250 Hz region. When we bring that fused panel's problem high enough (and/or damped enough), say 500 Hz (just a number) then it won't harm the overall insulation (a bit comparable with a coïncidence in thin panels which is a physical problem but rarely, if ever, defining in the overall picture). If however we fuse a double leaf system in a manner that this MSM comes, say << 250/300 Hz, and isn't very much damped, then we tried to solve a triple leaf problem by creating ourselves another one, which can be as bad. (or worse? depends ...). On the net sometimes, solutions (carefully formulated with uncertainties and little experience to build upon) within a set of boundary conditions can get their own life, often outside these boundary conditions. Stuff like PU, PS and comparable are still springs. Making them thicker lowers MSM in the same manner as increasing an air cavity (a less stiff spring, but the principles of dynamic stiffness versus masses remain for both)

Wow guys! Thanks for the detailed responses Eric! I have been out of town on a short holiday for the last 4 days, and I return to all of this! It is a bit over my head however! I understand the basic gist of what you are saying however. Here are some more details: The current state of the room in question is a 31 X 14 foot basement room with 2X10 floor joists. The top floor has pretty standard particle board sub-flooring, topped with a thin luan (sp?) board, then a wooden floor. The gap between the floor joists is empty air (other than a few HVAC ducts and water pipes). The ceiling in the basement room is just a single layer of 1/2" gypsum that has been textured. Thanks!

I apologize for taking so long to reply here - I have been unable to log in for some days now. Eric, Thanks for the wake up on this one - when I referred to "some sort of a foam insulation" I was actually picturing a rather high density - not foam in a can like you in your local harware store......... Seeing as this stuff is available in higher densities - I was picturing something in the 5 to 10 pcf range in a slow rise product as having the qualities needed to create the one leaf effect - As i am mistaken in this I wil have to revisit the concept. Sincerely, Rod