Staggered studs

Hi folks, I cant work this out….. 13mm drywall ….90mm stud-frame (common studs) with 90mm fibreglass …..... 13mm drywall = 32 STC 13mm drywall ...130mm stud-frame (staggered studs) with 130mm fibreglass ...13mm drywall = 46 STC That’s quite an increase for just a 40mm wider gap, and staggered studwork - so staggered studs offer greater isolation than a shared frame assemly, but why ? Each leaf is in contact with the shared base plate / wall plate, and even though each leaf is fixed to its own set of staggered studs, in turn those studs are still coupled by the same wall plate, so how does such an increase come about ? Thanks Steve

It might simply be the extra weight in the Rockwool.

Steeeve wrote:

That’s quite an increase for just a 40mm wider gap, and staggered studwork - so staggered studs offer greater isolation than a shared frame assemly, but why ?

You said it with the word "shared". Sound is like any thing you may have heard about in that it will take the path of least resistance. If you give it a path, like a shared vertical frame, it (sound) will use it like a bridge to continue until the path outward or inward depending on where it is coming from changes. Breaking the path is what we are always trying to achieve in relation to sound isolation. Even more then just staggered studs, it is common to cut sheetrock just short of hitting any other boundary for this same reason, break that connection or decouple the members. This is also the reason a room-in-a-room design is the most sought after sound related environment. Every connection that can be broken IS broken, in the highest level of isolation, slabs are decoupled that only have frames for walls resting on one slab with the ceiling frame resting on that wall frame that rests on the one slab. Air/distance is another factor after breaking the connection with decoupling via staggered studs but more often, a double framed enclosure with no exterior wall touching the interior wall, ceilings the same, not one touching the other. A lot of weight is already in a concrete slab due to the concrete, add to that the compounding effect of more walls and more mass and you have a boundary that will be difficult to shake, your floor that is. So even with staggered studs making a connection at the floor, this connection has to move a very heavy object usually damped by the earth below it, so if it does it is in the low frequencies.

here's all the combinations http://johnlsayers.com/Recmanual/Pages/STC%20Chart.htm

Hi thanks for the replies. Am correct in thinking the staggered studs are fixed to a common wall-plate, both top and bottom ? Surely, as the Drywall is touching both the top and bottom wall plates (despite being fixed to independent staggered studs), both layers are directly coupled together already so why have staggered studs ? Is it a case of the less direct contact the better - i.e. two assemblies with touching surface areas of 10cm2 will transmit less sound than a 20cm2 area? Thanks greatly! Steve

Less contact surface area for conduction is one component of decoupling. The other is that each side (leaf) can move in and out independent of the other side. A single stud wall with razor thin studs may have reduced contact area, but it's still coupled. Once decoupled, a partition will have a lower low frequency resonance point, as a side note. The correspondingly deeper cavity will also lower that resonance point, as will the addition of absorption and mass.

John- What would you be getting as far as STC for The same as side show? [EDIT] sorry no common base- except slab

lilith_envy wrote:

John- What would you be getting as far as STC for The same as side show?

Not preserved: Wall STC.JPG

[EDIT] sorry no common base- except slab

well you'd place insulation in the 100mm gap but that is basically how Left Bank Works. http://johnlsayers.com/Studio/Mainpage/MP-Leftbank.htm It was a typical American Barn with 6" x 1/2" (150mm x 12mm) hardwood cladding that had warped and opened up in cracks etc. as it was originally put on when the timber was green - we used to call it hippy cladding :) as all the hippies built their houses out of it as it was cheap. We ignored it as a skin and just added a new 16mm inner lining. We then built an inside/out internal structure with a 50mm air gap and 3" x 2" (70mm x 45mm) framing. Amirel has been operating the studio for years now - he has bands at all hours of the day and night and he has had no complaints from neighbours, not even a word. Outside you can just hear the kick drum as a low thud, basically what side show said about his setup. As I keep trying to emphasis - most people overbuild!!