3 leaf consiquences or too high expectations?

During the planning of my new studio I had the opportunity to go jam in a friend of mine's jam space in which he had gone through considerable effort and expense in order to "soundproof". Unfortunately he had not come across John's site when researching his soundproofing methods. His space is in a single car detached garage on a fairly narrow suburban lot. From what I understand this is what he did. He stripped the existing structure down to the studs on the inside, removed the insulation and sealed any gaps or cracks with expanding foam (not acoustic cauk) then replaced the insulation. Thus his outer leaf consisted of vinyl siding, one layer of OSB, studs and R12 insulation (not the best outer leaf but it is what it is). He then built an entire freestanding structure inside the garage complete with its own ceiling supported by the interior set of walls maintaining a 4" air gap all the way around. On this structure he attached 2 layers of 5/8" drywall onto the outside of the studs and mudded and taped both layers. (he must have built them on the ground then raised them up I assume). He then put a layer of 5/8" drywall onto the inside of the studs (forming a 3rd leaf!) and filled the cavity between the studs with blown in insulation (kind of pointless in this configuration). He then built a airlock entrance way with 3 heavy doors with 2 layers of drywall glued to the sides. He mud and taped the interior of the room and sealed it pretty well. The results are much less than what he was hoping for. He is a bass player likes to play a loud & fast somewhat obnoxious style, the bass and drums can be heard quite clearly in the yard (equivalent to a loud stereo outside) , and can even be heard in the neighboring house. His neighbors hate him and call in noise complaints often. I know that he has some problems with his design (specifically the 3rd leaf) however this left me wondering two things: A. If he had built a proper two leaf double stud setup and maybe beefed up his outer layer between the studs with the drywall from the inner 3rd leaf, what kind of isolation would you guys expect to result? (ie. could you knock down bass and drums to a point where the neighbors couldn't hear it in their house 10ft away?) I know about STC ratings for double stud walls and such, however since they do not factor in the bass frequencies I am not sure how it would really translate in the real world. (eg. 115dB inside - 60dB STC from double wall = 55dB outside = volume of average conversation?) B. If he were to take off his innermost layer of drywall and cut it to fit between the studs up against the other two, would one expect the isolation to improve significantly? Basically what I am looking for is someone that can tell me from experience a situation where they did everything right and what kind of results they achieved. Were you able to build a room where a drummer could play and you can't even hear it outside? or in the next room (control room?)

Because he used expanding foam to seal his outer leaf it's not really a leaf as it's not airtight and therefore can't create a spring. You also don't mention what he did with his ceiling which is just as important as the walls. So he's basically ended up with a single stud wall with 2 x layers on the outside and a single layer on the inside. He'll be lucky if he gets STC 43.

As far as I know his ceiling is the same construction as his walls (2 layers on outside of joists, one layer on the inside). The question I really should have asked is: If one were to build a two leaf setup following all the rules in order to achieve a STC of around 60, how would that translate to a real life situation with a live 110dB band with bass and drums?

it would mean that outside the building the sound would be at 50db - a car at 10m is 60 - 80db, conversation at 1m is 40 -60db.

I understand this logic, however STC does not take into account low frequencies such as bass guitar, if the actual transmission loss at say 40hz is only 20dB then you'd have 90dB outside at 40hz which would be quite a nuisance to your neighbors... Basically what I am wondering, if I go to all the trouble and expense to do it "right" as per the recommendations on this forum, what should I expect for results? For example, It is worth the effort and the 20 grand it will probably cost me in materials if it will allow me to practice drums anytime of day or night... BTW, Thanks for humoring me... -jER

Death By Darwin wrote:

....removed the insulation and sealed any gaps or cracks with expanding foam (not acoustic cauk) then replaced the insulation. -jER

That is a good idea and works. The issue, as you guys are hearing, is a direct result of the three different mass layers specifically the coupled interior wall. Mr Sayers may have misinterpreted what you guys have attempted with the spray foam which is, I am imagining, only used to fill whatever holes existed in the exterior of the building. Personally, that would have been a red flag for me...what kind of holes exist from the interior side of an OSB/Vinyl covered wall...? There shouldn't be any right? In any event, the interior coupled wall (sheetrock on both sides of the frame) allows frequencies full access into or out of the room by the bridge that exists from the framing that holds the sheetrock up. Then you guys have a thin exterior boundary which is almost always massed up so that it is equivalent to or greater than the interior of the room. So it isn't a three leaf in the sense of how folks may react to it on these forums. It is one exterior leaf and an interior coupled wall, essentially, a two leaf overall. The ceiling may be were you guys are getting hit the hardest due to the actual three leaf that may exist if the interior sheetrock on the building ceiling was never removed plus the cavity and then the roof. Doing the job right is always worth the effort. There are way too many people on this forum that have done it and never looked back ;) Hope that helps and no one gets their feelings hurt....

Apart from the wall sealing and 3-leaf issues mentioned by John and Brien, I'm also wondering about those doors: How are they built and sealed? If he just used ordinary thin jambs, hinges and hardware and only single seals, then I can well imagine that they are not doing a good job of sealing at all. In his book Rod recommends at least two separate seals on door like that, and specific heavy duty hinges to mount them, plus no through-holes for mounting handles. If the seal around those doors is not good, then that would be yet another path for sound to get out. Even a slight gap can make a big difference. Also, what about electrical? I mean, how are his electrical boxes installed: surface mount on top of the drywall, or holes through the drywall? If they are holes, then how well are the sealed? And lights? Are the fixtures surface mounted on the ceiling, or are they stuck in hole in the drywall? What about HVAC? He must have some kind of air venting going in/out of that room. If he didn't do that right, then he has yet another path for sound to get through. Also, I'm assuming that his floor is a concrete slab on grade? In any event, to answer your underlying question: can you silence a bass guitar with good MSM construction? The answer is yes. Do it all correctly, and you can indeed get the levels down low enough that you won't bother the neighbors. But do it wrong (as your friend did) and it just wont work. (But you already figured that out! :) ). - Stuart -

Stuart, Thanks for the response, I guess I should have kept this post to a simple question in the first place. I am prepared to spend the required time and money to "do it right" and I believe I have done enough research to to know what "right" is. I was was just concerned that my isolation expectations were a little high even for a proper MSM system. Anyway I am going ahead with the build, I have the building permits pending ( I need to get some truss profiles to the city but the truss company keeps screwing up the design) and hope to be pouring concrete for the conttrol room addition next weekend! Regards, -jER