This is what I am trying to determine.
The best way of doing that (in fact, the only accurate way) is with a sound level meter. You can buy a good one for around US$ 100 on eBay or Amazon (just don't buy the cheap Chinese garbage! They are little more than toys...) Look for an Extech or Galaxy in that range, and make sure it has both "A" and "C" weighting, and both "Fast" and "Slow" response. Additional features are good to, but it must have at least those.
Once you have your meter, a good way of determining how much isolation you have at present is by simply making a noise and measuring it!
Set up some good full-range speakers inside each of the rooms in turn, and play loud music through the system. Use the type of music that you'll normally be recording / mixing in your studio. Play it at around 100 dB as measured inside the room at least three feet away from the speaker(s) (use "C" weighting, "slow" response on the meter). And wear ear protection while you do that. You might also want to warn your neighbors in advance that you'll be doing an isolation test for a few minutes with loud music. Then Walk around the rest of the house taking careful measurements in the other parts of the studio, and the other rooms in the house: Make notes about where you take each reading, and what the reading was. Do the same outside: walk around all sides of your house, measuring about three feet away from the walls, and also at your property line, in several different locations. This part of the test will give you a god indication of how good the isolation is right now.
The second part of the test is to then go back to the place where you recorded the LOWEST level outside your house (quietest) and get someone else to slowly turn down the volume on the speakers until you can't hear it any more when standing in that location and keep it at that level. Now walk around to all the other points where you took measurements before, and note down the new lower level for each location.
The final part of the test is to then go back to the place where you recorded the HIGHEST level outside your house originally in the first test, and once again get someone to slowly turn down the volume on the speakers until you can't hear it any more when standing in that location, or at least until you think it is at a reasonable and acceptable level for that location. Now with the system still playing at that new lower level, go back inside and measure 3 feet from the speakers once again, to see how loud they are playing.
You now have enough data to figure out how much isolation you have, and how much more you need.
All of those tests should be done with the windows and doors tightly closed, or course.
The whole of these two rooms, while they are very nice living spaces, are built over a 6 ft crawl space with CB foundation and the joist floor has a sub floor and real wood hardwood slats installed (no air gap).
That's sort of what I was expecting you'd say... Not the best situation, since basically both rooms are sitting on top of the same "drum head". So any sound or resonance in either room will get through the crawl space to the other room, either via airborne transmission or by structure-borne flanking. If you plan on recording drums, bass guitar, piano, or anything else that has potential impact noise, I'd suggest that are going to need a "drum riser" type of platform to improve the impact isolation.
Also, is you have access to the crawl space, you might want to consider getting in there to "beef up" the floor from below, with extra mass and damping. (Assuming you need good isolation).
When they attached the ductwork for the HVAC (which I might add is very quiet since it is new and physically exists in another portion of the house) they screwed them to the joists and this causes creaking.
So they did it the "quick and cheap" way, not the right way! You seriously should consider re-hanging those ducts on isolation hangers, to help prevent sound form your studio from flanking into the rest of the HVAC system, and hence the rest of the house. You'll also need to install silencer boxes between the main ducts and the branches that go to/from your studio rooms: HVAC is a
major source of sound transfer between rooms. You can have the best isolated walls, doors, windows, ceilings and floors, but if you have ordinary HVAC installation with no silencers, then you don't have any isolation at all. Even normal speaking voices in one room will be audible in the other room.
When you take those photos around your place, see if you can get a few inside the crawl space, showing how those ducts are mounted, and how they connect to the registers.
The french doors swing independently into a tiled 8 ft. breezeway attached to the house. They are two separate doors with 16 panes each, but isolating them is not critical due to the fact that I do not plan to be using the other side for recording unless for a vocal booth possibly. This is my entrance into the control room. There is a lot of glass there and it may become useful for an highly reflective echo type of sound if this entire space is salvageable at all.
Ahhhh! OK, I thought you were talking about sliding glass doors. It might be possible to seal up those a bit better, to improve isolation.
I'm sure your rooms can be "salvaged" for a studio!
They are decently sized, and one of the good things is that they have very high ceilings: 10 feet is unusual in typical houses these days. That allows for a lot of options, for both isolation and for treatment.
Anyway, if you can provide photos and more details, and also do those tests to determine how much isolation you need (in decibels) then we'll be able to help you figure it all out!
- Stuart -
Sorry about that. Here it is: