John Sayers' Recording Studio Design Forum Archive

Hi all. Long post warning. I tried my utmost to give as much information as possible and go by all of the posting guidelines. I also put subtitle categories in if you want to skip ahead. Here we go...

Background:
I am a musician, electronics tech, technical director and freelance sound engineer. I have been researching this and other forums for years. I have read Built It Like The Pros by Rod Gervais as well as other books. I have a working understanding of the principals involved in MSM assemblies to achieve isolation; therefore, I know my goal below will be difficult and expensive.

Overview:
I have small music room on the second floor of an attached garage with a cathedral ceiling. It is adjacent to the master bedroom and adjacent to a partially finished workshop at the rear. The music room faces a busy street 39' in front, and faces two large apartment complexes 108' in front, across the street. The house is under a flight path, and has a railroad track approx. 600' behind the back yard. The approximate Dimensions: of the room are: Floor area 270.5"x182.5", knee wall height is 31.5", and the subfloor to bottom of central support beam 117.5"

Use of the space:
1. The space is used primarily for writing, tracking and mixing, all in the same room. I play and record acoustic drums, electric guitar and bass as well as keys and synth. I will sometimes put amps in the rear workshop when tracking guitar and bass.
2. I use the space for mixing music recorded in other larger, better sounding rooms.
3. The room has been used to record voice over successfully but with some difficulty.
4. The room had also been used as a rehearsal space for rock bands, but due to the proximity to neighbours, has caused issues and I now rehearse elsewhere.

My goal:
To achieve the best possible isolation from external noise, and to have the noise that I make blend in with the outdoor ambiance to not bother neighbours. Isolation between the music room and other parts of the house is not the goal; however, I know I will need to address all partitions above, around and below the music room to get any meaningful results.

Specific to my uses: For use 1, 2, 3 the most offending is traffic noise from large trucks, Harley motorcycles, and vehicles with loud exhausts. Only the occasional yet extremely loud Fedex Freighter airplanes, require pausing or retakes of louder sources like drums and amps. For use 3, quiet voice over and vocal recording, sometime even a neighbour's dog barking can affect a take.

For use 4: The biggest issue with full bands of course is the low frequency content from drums and electric bass being much louder then the outside ambience. If it is determined that enough broadband isolation can be achieved within budget and structural limitations to allow me to resume rehearsal in my room, that is a bonus. If not, I can continue rehearsals elsewhere. If the level of isolation for full band practice can not be achieved, it is still worth it for me to address the problem for uses 1, 2 and 3, as it is difficult to work exclusively during low traffic hours, noise bylaws taking effect in the evening.

Budget:
My budget is $15k-$20k cad including HVAC. This does not include studio equipment nor acoustic treatment.

Consultation: I am now consulting with an architect who specializes in acoustics, and am reaching out to structural engineerings to determine my existing live, dead, and point load capacities, and determine options for beefing up the structure to support the extra mass that will be needed. I intend on doing most of the work myself to keep labour costs at a minimum.

Noise Measurements:
Measurements were done with a Galaxie Audio CM130 SPL meter on C weight and slow. This first series of tests (A) represent use 1 where I would be tracking drums:

Test A1 - Drums: Outside, night, no traffic. Lowest outdoor ambiance was 47dbc. Loudest measured drums 73dbc.
Test A2 - Drums: Garage, daytime, low traffic. Lowest garage ambiance was 40dbc. Loudest measured drums 80dbc.
Test A3 - Drums: Studio, daytime, low traffic. Lowest studio ambiance was 39.5dbc. Loudest measured drums 111dbc.

I think this shows the absolute minimum amount of transmission loss I need, but there are two more tests I want to do now that I have a baseline of quiet ambiences in three locations: (B) Same test as (A) with a full rock band, and (C) measure the worst case scenario outside noise during peak traffic hours (motorcycles, train, flights, etc.) With the COVID-19 lockdown measures I will need to wait a while before I can do tests (B) and (C).

Existing Construction Details
Please find a download link to a comprehensive, as built, to scale Sketchup file detailing the existing structure with the different structural elements in separate layers:

Sketchup File: https://drive.google.com/open?id=1ALMR0 ... Diy4rPVke6

To summarize the existing construction:

-1st and 2nd floor walls are 2x4 wood frame, with R12 fibre glass batts, outside wall sheathing is 1/2" OSB, cladding is vinyl siding.
-The 2nd floor rests on wooden webbed trusses, 16" OC with a 16" high truss depth, and a span of approx. 270-1/2".
-The 2nd floor deck is OSB, appears to be 5/8", I could not confirm thickness at the time of writing this post.
-The under side of the 2nd floor deck is spray foamed. I'm not sure what kind of spray foam, density, open or closed cell, etc.
-The music room currently has 3/4" hardwood floor atop the OSB subfloor.
-Roof sheathing is 3/4" OSB and rests on wooden trusses with metal webbing, they are 24" OC with a 16" high truss depth.
-The roof is vented at the soffits and at the ridge, and the spaces between trusses are filled with approx. 14" thick fibre glass batts.
-The only heat source in the music room is a vented natural gas fireplace insert which vents through the roof.
-A Skylight is installed in the workshop and a stair case may eventually be installed descending into the garage from the workshop.

Here are some 2d renders from the Sketchup file: Outdoor Pictures: Indoor Pictures: Working towards a design
In addition to professional consultation, I am seeking advice and criticism here to help me come up with a design. My approach will be to primarily use the techniques outlined in Rod Gervais' book, prepare some drafts, get some feedback, start costing things out, and hopefully, many revisions later, end up with a workable design. Below are some of the elements that would go into the first draft. None of this is set in stone... If I say some silly things and present uninformed assumptions, please point it out.

The specifics
1. Walls: I will add mass to the outer wall between the existing 2x4 studs with at least two layers of 5/8" drywall and Green Glue such as: OSB > GG > DW > GG > DW > R12 FG. I have looked at airspace and stud depths for the inner wall using Gregwor & Audiomutt's MSM TL Calculator, but I haven't decided if a 2x6 24"o/c inner wall will be worth the extra materials cost and loss of footprint. The inner wall would be: FG batts > vapour barrier > structural OSB sheathing > GG > DW > GG > DW

2. Windows: The two front facing windows already need to be replaced as the seals are completely shot, and my wife says the windows must remain. I don't need egress so I will opt for a units that don't open. A local supplier is able to build exterior windows according to the specs in this pdf: https://www.viracon.com/pdf/ViraconAcou ... Tables.pdf.
So I am thinking that a double glazed insulated unit with two laminated panes of different thickness, with the largest possible air cavity between the panes is the way to go for the outer leaf.

For the interior leaf, I'm considering a single massive laminated pane in a custom frame, with desiccant in the air space, like the one described here: https://www.gearslutz.com/board/studio- ... indow.html

3. Doors: I will be using the Super Door design in Fig. 5.6 in Rod Gervais' book for the entrance to the studio and for the adjacent workshop.

4. Ceiling: The approach for the ceiling is what is described in Fig. 10.23 and 10.22 in Rod's book, but with the addition of Green Glue (2 or 3 tubes worth per 4'x8') in between all layers of DW and sheathing. I will also add a layer of structural sheathing to the underside of the existing roof trusses to add mass and to have a continuous substrate to screw the DW sheets into. To increase the height of a new inner ceiling, the existing 2x6 joists on the sides of the central beam would be removed. I may be left with space at the apex that can be used for bass traps. 5. Floor: The approach for the floor would include techniques described in Fig. 10.16 and 10.19 in Rod's book. I can only add mass form above due to spray foam on the underside of the OSB. I have read the thread describing why floating a floor is probably a bad idea. If I can avoid doing that and still get "some" amount of TL the project could still be worth doing. The math needs to be done to determine how much "some TL" actually is. I understand what is involved in calculating TL for MSM assemblies, but I'm not sure how to approach it for an undamped floor (that is not sitting on a concrete slab) beyond what Mass Law says about +6db of TL each time the mass doubles.

If I don't completely float a new floor assembly and go for a decoupled solution as in figures 10.16 and 10.19, my thinking is to add as much Gypcrete mass as possible, replace the two layers of 1/2" plywood with two layers of 3/4" MDF, and apply 2-3 tubes worth of Green Glue (per 4'x8' area) between all solid faces. The entire studio floor would essentially resemble the Glenn Drum Riser design sitting on top of Gypcrete. Its still not 100% clear to me how effective these decoupling methods are for airborne versus impact sound...

It also is worth noting that the previous owner had a woodworking shop and machinery above the garage before it was renovated as it is now. He tells me the floor was rated for 90psf, but did not specify if this was live or dead load, so I'm taking this with a grain of salt. In any case my engineer will investigate this.

6. HVAC - This is the next area I need to research. For budget reasons I'd like to keep the fireplace, but the roof vent needs addressing. I will talk to natural gas installers to see what code allows for moving the vent away from the street. If it can't be done, I'll likely need to go with a mini split. Ventilation, HRV/ERV, and silencer boxes also need to be researched. I'm hoping this stuff can be installed in the storage mezzanines in the workshop, above the walk in closet.

7. Electrical. I do not plan any changes to the existing electrical at this time.

8. Acoustic Treatment The only thing I am considering adding at this time is bass traps at the knee walls and ceiling apex The geometry of these spaces make them hard to utilize for anything else. Maybe integrate nice wooden shelf top into the design of the knee wall bass traps...


Questions

1. Wall Questions:
1.1 - How do I calculate the thermal properties of an MSM wall assembly? Is it as simple as adding the R values of inner + outer wall batts?
1. 2 - It has been shown that fluffy batt insulation has a better cost-benefit ratio than mineral wool in MSM assemblies. Since I am not on a concrete substrate, would I get more benefit form denser mineral fibre in my walls and ceilings? Would this increase the overall damping effect?
1.3 - If I go with 2x4 inner wall framing, would 24" o/c spacing for the knee walls and front and rear walls further lower the MSM resonant frequency?

2. Windows Questions:
2.1 - Are there any other considerations for my exterior windows that could further increase TL given the obligatory 3 glass leaves?
2.2 - Would it be best to go with a vinyl frame or aluminum frame given the choice?
2.3 - Is it best to compensate for the limited surface density of the outer two pane window by increasing the density of the inner single pane window?
2.4 - Would it be best to insulate between the window frame and jamb with mineral wool versus expanding spray foam?

3. Ceiling Questions:
3.1 - Would it be a good idea to try to seal the metal the webbing of the roof trusses in to try to keep the airflow from the soffit above the FG batts?
3.2 - Regarding the use of resilient clips: On P.274 of Built it Like The Pros Rod writes "There are things however that you can do to maximize isolation in these cases (Attics and Other Rooms Inside Your Home), even if you can't build a room within a room. To begin, this would be a case where I would strongly advocate the use of isolation clips." Is Rod advocating the use of isolation clips in addition to MSM construction or only in cases where you can not build a room in a room?

4. Floor Questions
4.1 What is the best mathematical approach for my type of "drum head" floor? I assume its resonant frequency first needs to be calculated, then find the right amount of mass that will lower the resonant frequency below the audible range?
4.2 Are the decoupled floors in figures 10.19 and 10.16 effective against airborne sound? Are they only effective for impact sound?
4.3 In those decoupled systems, is the space occupied by the OC703 considered an airspace in an MSM assembly where the outer leaf would is the underlayment and the inner leaf is the plywood (or MDF) above it? I know there is technically no air gap, but the OC703 is porous to air. If it can be seen as an airspace, would two layers of OC703 increase damping?


Ouff, that was a lot...


Huge thanks to everyone who read parts or all of this post.

Stay safe and Happy Easter.

The quest continues.

1.1 - How do I calculate the thermal properties of an MSM wall assembly? Is it as simple as adding the R values of inner + outer wall batts?

I'm not certain, but I believe you would add them.

1. 2 - It has been shown that fluffy batt insulation has a better cost-benefit ratio than mineral wool in MSM assemblies. Since I am not on a concrete substrate, would I get more benefit form denser mineral fibre in my walls and ceilings? Would this increase the overall damping effect?

It makes sense to me to use insulation that would target the resonant frequency of the room, however this chart proves that you should probably just use the cheapest fluffy you can get.

1.3 - If I go with 2x4 inner wall framing, would 24" o/c spacing for the knee walls and front and rear walls further lower the MSM resonant frequency?

I saw earlier in your post that you considered using 2x6 for your inner leaf framing. The only time you need 2x6 would be for walls taller than 10'. If you noticed a performance difference on the calculator between 2x4 and 2x6, it's because the calculator automatically adds the extra 2" gained by using a 2x6 into the equations. You can achieve the same results by using a 2x4 and then adding 2" to your gap. 24" o/c will give you better results both acoustically and thermally.

2.1 - Are there any other considerations for my exterior windows that could further increase TL given the obligatory 3 glass leaves?

Acoustic isolation of glass and drywall require the same properties. Air gap + density. Therefore, in my opinion, you should use 1 leaf of glass in each wall assembly. 3 glass leaves suffer the same issues as 3 wall leaves. Why do you think you need 2 leaves of glass for your exterior wall assembly? The link you posted clearly shows that 2 thick pieces of glass have the best acoustic isolation.

2.2 - Would it be best to go with a vinyl frame or aluminum frame given the choice?

Aluminum has more surface density, so I'd choose that.

2.3 - Is it best to compensate for the limited surface density of the outer two pane window by increasing the density of the inner single pane window?

See my answer to question 2.1.

2.4 - Would it be best to insulate between the window frame and jamb with mineral wool versus expanding spray foam?

Mineral wool and enough caulk to match your sheathing density.

3.1 - Would it be a good idea to try to seal the metal the webbing of the roof trusses in to try to keep the airflow from the soffit above the FG batts?

I can't picture what you mean exactly. I'm sorry.

3.2 - Regarding the use of resilient clips: On P.274 of Built it Like The Pros Rod writes "There are things however that you can do to maximize isolation in these cases (Attics and Other Rooms Inside Your Home), even if you can't build a room within a room. To begin, this would be a case where I would strongly advocate the use of isolation clips." Is Rod advocating the use of isolation clips in addition to MSM construction or only in cases where you can not build a room in a room?

Do not use isolation clips in an MSM construction.

4.1 What is the best mathematical approach for my type of "drum head" floor? I assume its resonant frequency first needs to be calculated, then find the right amount of mass that will lower the resonant frequency below the audible range?

I believe you would just use the MSM equations for this. However, you should realize that there are some factors skewing the results. For example, the extra weight on your sheathing due to people and equipment resting on it. Also, there isn't a true decoupling achieved with this floor design. Lastly, your inner leaf walls/ceiling will be directly coupled to the floor. In this case, I'd recommend using some rubber under the sole plate. I question these though because in order to actually decouple via a device like this, you need a certain deflection. Also, you have to ensure that your screw/bolt/anchor is fully isolated from your inner leaf frame as well.

4.2 Are the decoupled floors in figures 10.19 and 10.16 effective against airborne sound? Are they only effective for impact sound?

I answered this for you already in one of your other posts, but again, I believe it should work well for airborne sound as well due to it's MSM style design.

4.3 In those decoupled systems, is the space occupied by the OC703 considered an airspace in an MSM assembly where the outer leaf would is the underlayment and the inner leaf is the plywood (or MDF) above it?

No different than an actual MSM wall or ceiling cavity, the "air gap" is actually fully filled with insulation.

I know there is technically no air gap, but the OC703 is porous to air. If it can be seen as an airspace, would two layers of OC703 increase damping?

In theory, yes. I question how stable the floor would be with thicker insulation though.

Greg

1.2 It makes sense to me to use insulation that would target the resonant frequency of the room, however this chart proves that you should probably just use the cheapest fluffy you can get.

Thanks for posting that diagram, it is the first airflow resistivity chart I come across. Only a couple db variance across the frequency range.

1.3 You can achieve the same results by using a 2x4 and then adding 2" to your gap. 24" o/c will give you better results both acoustically and thermally.

2.1 Why do you think you need 2 leaves of glass for your exterior wall assembly? The link you posted clearly shows that 2 thick pieces of glass have the best acoustic isolation.

From what a local window supplier tells me it is my understanding that I could not do this due to the condensation that will inevitably form on the inside of the single exterior pane. I'm not sure what code requires on this. I'm going through the NRC website to try to find code documents to check this and other things. I'm under the impression it is one of those things I will have to live with.

3.1 I can't picture what you mean exactly.

This is more about improving the thermal performance of the existing FG batts in between the roof trusses. The original builders installed loosely fitted 1" rigid foam insulation on both sides of each roof truss from starting from the soffits up to the vented attic space. The rigid foam creates a void inside the metal webbing where air is allowed to flow from the soffit to above, below and through the FG batts. I'm wondering if I should try to address this so that the air from the soffit is forced to remain above the FG batts, right below the roof deck. This to reduce the air flow through the batts. In the partially finished workshop, the vapour barrier below the roof truss is exposed. On windy days you can actually see the vapour barrier "breath" with the wind gusts.

3.2 Do not use isolation clips in an MSM construction.

Copy that.

4.1I believe you would just use the MSM equations for this. However, you should realize that there are some factors skewing the results. For example, the extra weight on your sheathing due to people and equipment resting on it. Also, there isn't a true decoupling achieved with this floor design. Lastly, your inner leaf walls/ceiling will be directly coupled to the floor. In this case, I'd recommend using some rubber under the sole plate. I question these though because in order to actually decouple via a device like this, you need a certain deflection. Also, you have to ensure that your screw/bolt/anchor is fully isolated from your inner leaf frame as well.

Gotcha.

4.2I answered this for you already in one of your other posts, but again, I believe it should work well for airborne sound as well due to it's MSM style design.

Thanks for re-iterating here. I wanted to keep all my questions in the same thread. Also for others to offer their thoughts.

4.3 In theory, yes. I question how stable the floor would be with thicker insulation though.

Very good point.

Thanks again for taking the time to answer.

The rigid foam creates a void inside the metal webbing where air is allowed to flow from the soffit to above, below and through the FG batts. I'm wondering if I should try to address this so that the air from the soffit is forced to remain above the FG batts, right below the roof deck. This to reduce the air flow through the batts. In the partially finished workshop, the vapour barrier below the roof truss is exposed. On windy days you can actually see the vapour barrier "breath" with the wind gusts.

Gotcha. I'm not really sure what to suggest because you don't have much space there and as far as I know, you need a good gap under the sheathing. The thermal situation is a concern of course as well. I would maybe research your local code to see what is required in your area.

Greg

Hi everyone. This is still a work in progress, oh how life happens!

Where should the mix position be given my vaulted ceilings? I know for small rectangle rooms the default is to fire along the long walls (position A), but would I benefit from the added ceiling height at mix position B? Would the first reflection points on the vaulted walls be less problematic to treat as reflections would be reflected downwards?

Its approx. 115" from floor to existing ceiling. Other dimensions noted previously.

Thanks,

either position would work given you're probably going to want to use the peak to create a large absorber and with some hard surfaces can provide the desired symmetry either direction. the disadvantage of the long approach is that door on your right (when facing the speakers) because if you like to have instruments and gear on either side, the door can be a hinderance.

Thank you for addressing the mix position question. I will come back to this in a later post. Onto the flooring assembly.

According to my structural engineer: "these existing floor joists would be able to withstand an additionnal unfactored deadload of 1.45 kPa (30 psf) if the load is applied all on the top chord." Based on the 30 psf limit this is what I have come up with.

0.75" maple hardwood finish over 2" Plywood (3/4" + 1/2" + 3/4" with Green glue in between.) over 2" OC703 over 1.75" Gypcrete over existing 1" OSB subfloor. This will also give me 6.5" of rise to match the rise of the floor on the other side of the sunken landing adjacent to the studio. I have never worked with Gypsum Concrete so if anyone can offer insight on prepping the subfloor and pouring Gypcrete that would help. Any other thoughts on this would be greatly appreciated as always.

I have sent my plans to Green Glue to see if they can offer more insight and I'm calling suppliers today regarding the gypsum concrete and OC703.

Gypsum concrete is lightweight and fire-resistant. A 1.5-inch slab of gypsum concrete weighs 13 pounds per square foot versus 18 pounds per square foot for regular concrete. it's also poured very running so a good seal on the subfloor is important. the 703 in-between might not be the best decoupling approach for stopping impact noise transferring below. you may be better served with a layer of OSB or plywood, then something like Kinetics Noise RIM (rubber blocks and semi-rigid), another layers of osb/ply, the gypsum concrete or similar mass, a thicker layer of plywood and then the finished floor. this is closer to a "floating floor" and at least some of the required loading on the isolators would be there. you can have a call with KN engineer/sales to discuss and get the right product.

note: there are two loads - dead load - the structure itself and some infrastructure. and live load - people equipment etc. so make sure to factor in both. you might have to "sister" the existing joists with stronger joists to ensure proper load handling.

gullfo wrote:You may be better served with a layer of OSB or plywood, then something like Kinetics Noise RIM (rubber blocks and semi-rigid), another layers of osb/ply, the gypsum concrete or similar mass, a thicker layer of plywood and then the finished floor. this is closer to a "floating floor" and at least some of the required loading on the isolators would be there. you can have a call with KN engineer/sales to discuss and get the right product.

The Kinetics Noise Rim products are interesting. Will look at this closely. Have you ever used these in your projects with success?

yes, several projects using RIM. the most visible is the Red Bull Music Studio in NYC - we used these with about 15 tons of aerated cement to float the live, control, and booth rooms. my preference would be in most situation to use spring loaded adjustable units like Mason Industry has, depends on the projects and if they're not feasible due to structural layouts.

Now onto a new ceiling assembly. What is shown in the pictures here is only approximate to help me visualize what may be involved. The plan is to get my engineer to draft proper plans and fully evaluate the loads involved. My starting point for this assembly is the notion that in a 3 leaf system M2 = M1 + M3 where:

M3 = Existing outer leaf
M2 = Middle leaf on bottom chord of existing roof truss.
M1 = New inner leaf
My engineers has determined ""possible to add an unfactored deadload of 0.85kPa (18 psf) on the bottom chord." for M2. It will be impossible for me to add mass to M3. Assuming there is nothing to be gained by making M1 > M2 in a 3 leaf system, and that most of the mass needs to go in the middle leaf, these are the numbers I have worked out for M2 and M1:

M3 = 3/4" OSB (2.5 PSF) + Asphalt Shingles (2.7 PSF) + Tar paper? (? PSF) = 5.2 PSF
M2 = 1/2" OSB (1.7 PSF) + 1/2" DW (2.1 PSF) + 5/8" DW (2.3 PSF) = 6.1 PSF
M1 = 2 layers of 3/4" OSB (5 PSF) + 3 layers 5/8" DW (6.9 PSF) = 11.9 PSF

Before I propose this to my engineer I would like clarification a few things:

Questions:
1. Mass in 3 leaf systems: I have read most of the Wyle report to gain insight on 3 leaf systems but its not fully clear to me. Is my assumption correct that there is little to be gained in making M1 (inner leave) greater than M3 (outer leave)?

2. Apex Flanking In the sketch I have included 2x12 blocking in the voids of the existing ridge beam (in yellow) to avoid creating a flanking path between it and the new inner ceiling rafters. The rafters would not touch the ridge beam and the only flanking path would be though the new knee walls (in white). This would add a lot of complexity when it comes to creating an air tight seal, especially if new collar ties (red) will be needed. But, it still could be part of the design criteria. Would there be much to gain in isolation by avoiding this flanking path?

3. Green Glue I intend to use GG between all sheet layers. Does GG in a 3 leaf system offer benefits in all three leaves? Are the benefits of GG only effective in the middle leaf since this is where most of the mass goes?

so, not option to add gwb to the m3 layer between rafters? ok, then on m2 - 3/4" osb + 2x 5/8" gwb - your new "exterior mass" layer. then m1 - 3/4" osb + 2x 5/8" gwb w/ GG - your new "interior mass" layer. why 2x12 rafters? that seems to be too much - why not 2x8?

There was an error in my previous question on mass which I have fixed.

gullfo wrote: why 2x12 rafters? that seems to be too much - why not 2x8?

Sizes and spacing in those sketches are approximate as I will let the engineer determine them. I sketched 2x12 for a couple reason: 1. I went with what Rod had in fig 10.23. 2. I'm hoping for 24" O.C. spacing. 3. I want the same amount of batt insulation on both sides of the middle leave. 4. I wanted to see what a worst case rafter size would look like because if I keep the distance between the Inside-middle leaves and the distance between middle-outside leaves equal, the new ceiling assembly will intrude on the geometry of the existing window opening as seen here:
As for load bearing capacity of new rafters, I will refer to my previous question about where the mass is most valuable in a 3 leaf system. The masses I laid out in the previous post were worked out so that the inner leave (M1) was (approximately) only equal to the outside leave (M3). However if having M3 greater than M1 would yield better results than M3 = M1, I could definitely increase M1 while still respecting the dead load limit on M2 of 18 PSF.

m1 and m2 formed the boundaries. m3 if no additional mass is happening there, should be relatively inconsequential. so i would beef up on m1 and m2.

gullfo wrote:m1 and m2 formed the boundaries.

Can you please explain what you mean by that?

gullfo wrote: m3 if no additional mass is happening there, should be relatively inconsequential. so i would beef up on m1 and m2.

Ok. Is there a ratio between M1 and M2 that is optimal?

Any thoughts on the question of eliminating a flanking path at the apex of the cathedral ceiling? Worth doing?

What about GG in the layers of M1 and M2?