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.
