New Construction in a 2 car garage. Need advice desperately!

Is this one of those places that seismic impact would be a factor?

UPDATE So I have been so busy in the new room that this is the first time I have had to update. I plan to post in sections with pics relevant to each section. First, I must say that the isolation is really very good. I haven't done any readings yet but when I am at about 90db inside the room you can hear practically nothing outside. And this is with the 2 doors not even close to being perfectly sealed! I was really surprised at this but all the science seems to actually add up. I expected to hear a lot more outside than I can. The one weak link is the back wall where the mini-split pipes go through the wall but even then I need to be CRANKING in the CR and you can only hear some LF. I plan to do some readings soon. One thing that works in my favor is that ambient noise is quite high where I am. Not far from the infamous 405 freeway in LA! But even at around midnight when things have quietened down I can work at very high levels and you can't hear anything. Our bedroom is just across from the studio door, about 10 feet away and you can't hear anything at all. So...on to the construction. I will attempt to cover it all with explanations but it will happen in parts as I am still trying to finish the interior acoustics while working at the same time. EXISTING STRUCTURE viewtopic.php?f=2&t=16803#p117371 This is what I started with. If you read back in this thread you can get all the other info. There were originally built ins that the landlord wanted to keep. I have no idea why cos they were butt ugly and ancient. After learning that I wanted to construct a room within a room they relented and said I could use the entire space as long as when I left they would have a finished garage. So I couldn't build an RFZ as I had originally planned. A rectangle would have to do. CONTRACTORS The reasons for me using a contractor were numerous. Firstly, I am a composer and as such my time is my most valuable possession. If I'm not writing I'm not earning. I have never done any kind of construction and I come from South Africa originally where we build with bricks and plaster so I have NO idea about wood construction. Secondly, I had roughly a month to design and build. In fact a bit less than a month. There was no way I could take the time to learn how to do construction and actually do it in the amount of time I had while still working and dealing with family stuff ( 2 kids ). So a contractor had to be found. I started by putting an ad up on craigslist asking for a contractor with studio building experience. I got about 50 replies in the first hour! I made about 8 selections based on their experience in studio building and made the calls. When I had it down to 4 I met with each of them at the site so they could get an idea of what I wanted and get me an estimate. I can't stress how important it is to know EXACTLY what you want before requesting an estimate. My designs changed a lot during that time and there were many back and forths with the contractors. This was mainly because of my time crunch and still reading Rod's book and consulting with Stuart ( Soundman2020 - more about his genius later...). If I had had everything all worked out and properly planned and designed it would have gone much smoother. I eventually selected a construction company rather than an individual although there were some very competent guys on my list. The company is licensed and bonded so I felt better about that. I sent them my sketchups and lots of Stuarts posts about my construction. I must say that they were resistant to some of the techniques calling them overkill etc but i was adamant hat they do as I request otherwise they would need to undo what they had done wrong and start again.....which they had t do more than once during construction. CONSTRUCTION My biggest challenge was figuring out the walls. I wanted new framing for all 4 walls in true room within a room construction but the budget just didn't allow for that. I then decided that the Isotrax system was a good idea with Green Glue in between 5/8 drywall. WRONG! Very expensive and could have been problematic. In the end I decided on resilient channel on existing studs with 2 layers of 5/8 and Green Glue between the layers. Cavities stuffed with Owens Corning R-13. The fourth wall would be framed with 2 x 4's 16 OC and have a door that lined up with the exterior door. I had to explain to the contractors that this wall could not be anchored to any other wall and had to be freestanding, framed with acoustical caulk under the base plate. They also removed the roof cross braces and put up 2 x 6 ceiling joists. viewtopic.php?f=2&t=16803&start=30#p118255 The studs did not extend far enough into the room so that the drywall could be extended all the way to the floor over the cement base that runs all the way around the room so they added 2 x 4's horizontally to the existing studs to attach the resilient channel to. You can see this in the pics. Stuart then pointed out that if you install RC this way it will not work at all!! A quick check on the site confirmed this. I had a big argument with the contractor as he assured me it would work. I made them take the 2 x 4 's down and cut them into small blocks to be attached to the studs leaving the correct space in between studs for the drywall screws to go. viewtopic.php?f=2&t=16803&start=45#p118417 At the same time they ran the electrical. I have 4 outlets one on each wall. I decided to add 2x 20amp breakers. One for lights, AC and 3 outlets and one separate breaker just for the audio gear so i would not have clicks and pops every time the AC kicked in. They ran the cables overhead from the electrical box attached to the house. TO BE CONTINUED........

Ok moving on.... The one wall we framed.... 2 x 4's 16 OC. Acoustic caulk under the baseplate and the framing does not attach to anything els in the construction. Then 2 layers of 5/8 drywall with Green Glue. The back is stuffed with Owens R-13. The garage door had the one hinge removed then it was screwed tightly shut with backer rod across the top followed by acoustic caulk all around the inside and outside edges. The garage door itself need a little more sealing as it's pretty old and there are small air gaps on the edges. I must say though that the isolation on this side is truly fantastic. That storage space that acts as the "air" in the MAM system really does the trick. As you can see from the pics the door is nowhere NEAR being sealed yet. Our very slow landlord has to finish the threshold and the door finishings. He will use backer rod and caulk around the frame the I will get some kind of weatherstripping for the bottom of the door. More tomorrow.....