Feasibility of Isolating Studio Above Attached Garage

#46

the blue wall side - deeper batts space once you slide over the green wall towards the ERV, then open it like a closet. simply leaving it as a closed space won't really do much once you're past 12" of air anyways without a bunch of other things happening.

#47

Ok let me see if I got this right. So you are suggestion moving the inner baffle box to inside the airspace between the blue and green walls like this, yes?

Then build a new soffit here where the flexible ducts enter the isolated space here, yes?

Then fill the space around the duct, in the soffit, with FG Batts for bass trapping, yes?

In addition to that, build out a "closet" space which is inside the isolated space, inside the blue wall like this, yes?

Then this closet space would be filled with fluffy pink FG, for more LF trapping?

#48

maybe i mis-understood - i thought the blue and green were the top plate of the walls, not the soffits. it looks like you have the green top plate for the wall and another for the soffit :-)

if you're actually only talking about a given soffit space separating the two silencers units, then i'd just leave it as-is for the isolated room silencer and put the green soffit segment back over the soffit wall. technically you don't need the ERV room silencer since that room will be noisy from the ERV and with proper vertical straight walls, easier to add more mass.

#49

Let me start over and try to clarify my questions with better drawings. This is a top view of my initial plan:

My first question was if I enlarged the space between the green and blue walls where the white line is in the above drawing, would the larger air gap act as a bass trap? This modification to that wall would only be done above the mezzanine, by moving the green wall out towards the ERV. Here are more detailed drawings of how I'd build that:

So by moving the green wall (above the mezzanine) out towards the ERV, all I've done is create a larger air gap between the blue inner wall and green outer wall. I have not really created a soffit here, unless my understanding of the term soffit is wrong ?...

The mass of the outer leaf (which now includes the ceiling of the existing construction below the mezzanine) would be consistent, in this case new 2x 5/8 DW over existing 1/2 DW for the wall below the mezzanine and the existing ceiling below the mezz, and new 2x 5/8 DW over new 3/4 PW where the wall has been moved outwards above the mezzanine.

So in this scenario I now have locations A, B and C in which I can place my inner and outer baffles:

My first thought was to leave the baffles in A and C and completely fill B with pink FG for bass trapping, but I think you suggested that filling B with FG would not give me that benefit, and could cause other unspecified problems, do I understand that right?

I think you also suggested moving the inner baffle to location B, and then constructing a new soffit in location A, then fill this new soffit with FG and that would be the best way to add bass trapping:

Is the soffit in position A what you were refering to as the "closet space"?

#50

the last drawing will work.

#51

gullfo wrote:the last drawing will work.

Ok, and would I get more LF absorption if I completely fill location B with pink fluffy FG?

#52

#53

Been a while since I posted an update.

Long story. Unfortunately the engineer that I had hired to help evaluate my structure has lost her licence and is being sued for negligence related to concrete works in a bunch of commercial buildings. I've decided to hire another engineering firm to redo the evaluation. Fortunately the new report shows only a few minor modifications to the structure will be needed to allow me to build as per my plans including the concrete topper. I had been waiting since September for this report, and now that I know I can proceed. I'd like to clarify a few questions about how to add additional bass trapping above the mezzanine above the walk in closet. Post incoming below.

#54

TLDR: How to best create additional bass trapping using the space above the existing mezzanine. Five questions, A though E in the text below. Here are some annotated drawings and some videos that should clarify my questions.

[ Play Quicktime file ] Mezz V1.mp4 [ 5.02 MiB | Viewed 675 times ]

[ Play Quicktime file ] Mezz V2.mp4 [ 7.54 MiB | Viewed 675 times ]

[ Play Quicktime file ] Mezz V3.mp4 [ 5.63 MiB | Viewed 675 times ]

[ Play Quicktime file ] Mezz V4.mp4 [ 8.66 MiB | Viewed 675 times ]

The first 2 images show the original plan for the double wall construction (Inner wall blue, outer wall green). It also shows the mezzanine space above the existing walk in closet. This is where the air exchanger will be. My question is how can I best use some of that space to increase LF absorption.

The next 2 images show Option 1: Increasing the air gap between the inner and outer walls above the mezzanine. This would create an air space above the mezzanine of approx. 82"x82"x46" or 179 cubic feet. At minimum, all 2x4 stud bays and 2x6 mezzanine floor joist bays would be filled with pink FG batts. I was wonder if A) having this added air volume in the double wall would result in more low frequency absorption or if B) completely filling the 179 ft3 space with pink FG would add yet LF absorption.

With Option 1 the outer leaf density (DW layers between stud and joist bays shown in dark pink) would be maintained through the vertical walls and the horizontal mezzanine floor joists.

The last 4 images show Option 2: Above the mezzanine; move both inner AND outer walls outward, AND build a new "floor" platform above the existing mezzanine floor. This new "floor" platform would be built in such a way that the double wall system and air gap would be extended from the subfloor, up the walls, through the horizontal floor platform and up the walls to the ceiling trusses. Flanking would be avoided between existing and new mezzanine platforms and would be concentrated at the ceiling such as the rest of the perimeter walls (not shown).

Given the added cost and complexity of option 2; I'd like to know if C) this would be the best way to use the mezzanine space to create additional LF absorption in the room (inside the blue framed walls). D) If this is the best use of the mezzanine, which strategy LF absorption strategy would be best given the added volume of space approx 102 cubic feet? E) Might this space be suitable for tuned options versus a super chunk? I know measurements will be key to help me determine this, but I want to start thinking about it.

#55

Elusive Sounds wrote: the engineer that I had hired to help evaluate my structure has lost her licence and is being sued for negligence related to concrete works in a bunch of commercial buildings. I've decided to hire another engineering firm

Wow! Sounds like a really smart move to get a new engineer! Glad to hear that the design was basically OK, and you can move forward now.

Regarding your question about using the space above the closet, which will be part of your MSM air gap, for bass trapping: Not really. The MSM gap isn't part of the room, so it can't really be used for bass trapping. Making it deeper would certainly increase your isolation... but only in that area. It won't really do much for attenuating modes... at least, not directly.

That said, if your inner leaf is thin and low mass, it might do something for bass, but at the expense of isolation. In general, acoustic treatment has to be exposed to the air inside the room. If vibrations in the room air cannot get to the treatment device, then it can't be effective.

If you really do want to use that space for bass trapping (it is attractive!), then you'd need to build that "kink" in both the outer and inner leaf, leaving an empty "nook" which you could fill with absorption, or maybe use for a panel trap, membrane trap, or other tuned resonator. This seems to be what you are proposing with your Option #2. That's a lot of work, though. Not sure if the cost/benefit is worthwhile. You could get some really deep trapping up there, in an area where it would be effective, so from that point of view, it makes sense. But that's a lot of finicky work in a tight area, so it might be more trouble than it's worth.

- Stuart -

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