Great! That makes things a lot more clear. The dimensions and accurate layout making it a lot easier to understand! For example, form the initial description I did't realize that the room is actually coupled to another room at the rear, through a passage with no doors on it. That is potentially a problem, since your room will now have two distinct decay curves: one for itself, and a different one for the combined space of both rooms.
The room definitely has possibilities, but it's going to be complicated. As I mentioned before, its reasonably large room, and if it were rectangular, that would be fantastic. But the bay window introduces a bunch of issues that complicate things. Good in some senses, not so good in others. Good in the sense that it "smears" modal and SBIR issues to a certain extent, not so good in the sense that it messes up locations for your speakers and front wall treatment, as well as possibly creating unwanted reflections, due to the angles.
As you probably know, curved surfaces tend to focus sound at a specific point (much like a curved mirror focuses light, or a curved lens), and low frequency sound will see your front wall as a curve (even though it is really a series of flat surfaces). So finding a good location for the speakers and mix position is going to be a challenge. For rectangular rooms, here are simple "rules of thumb" and geometric formula for calculating that. But when you throw in a curved wall, none of that is useful any more. There's still a procedure for finding the best layout, but it's a bit more complex... and very boring! It involves making a very large number of acoustics measurements in your room, with the speakers and mix position in slightly different locations for each measurement, moved slightly from the previous in, in a fixed pattern, then analyzing the results to see which layouts are promising. Then repeat on a finer scale, until you get to the optimum layout. Tedious, time-consuming, and frustrating. This method produces mountains of data that will have you scratching your head and banging it against the wall, trying to understand that the hell is going on! It takes a while.... quite a while! But it does get results, and will lead you to the best layout. It is possible to cut some corners by first predicting what they likely layout will be, and starting from there, but even so it's a slow process.
So, I guess the question is this: How good do you want the room to be? If this is just a hobby studio, for fooling around with basic mixes, entertaining yourself and your family/friends, then its probably fine to just do a rough geometric layout based on theory and leave it at that. But if this is a more serious studio, where you will do work for paying clients, or for your own job, then its probably worth your while taking the time to do it right. In other words, if you will be using htis room to produce money, then its in your best interest to invest the money and time to make it as good as it can be. That's your call, of course, but that room is a nice size, and can be good!
OK, on to isolation: Once you have your sound level meter (get one that has both "A" and "C" scales, as well as "Fast" and "Slow" response settings), then do some tests to find out how loud you are and how quiet you need to be. Do a very rough setup of a typical session, a very loud typical session, with whatever instruments you plan to track in there, with a bunch of friendly musicians to make noise on them, and tell them to make a loud noise, as loud as they want, to their heart's content. Then measure that level inside the room, with the meter set to "C" and "Slow". While they are still playing the same song over and over, go out of the room, close the doors and windows, and measure the levels in various locations around the house, and various locations outside in the garden, and several spots right out to your property line (and beyond too, if you can). That will give you a good indication of how loud you are, and how much isolation you are getting at present, just from the existing walls/doors/windows. Then send everyone home (after feeding them pizza and beer, of course!), wait until the dead of night, when it's really silent outside, and measure the background ambient sound levels again at the exact same points as before (make notes on paper!). Compare those numbers to the original "loud" ones, and you now what target you would need to aim for, if you wanted to isolate your place well enough that your noise would only just be audible, faintly, compared to ambient. Finally, you need to check the other way too: Since you do plan to track in there, you need to be sure that exterior sounds won't be picked up by your mics, and trash your recording sessions. There's a huge bunch of possible sounds that could accomplish that: Thunder, rain, hail, wind. Traffic on nearby roads. Aircraft or helicopters flying over. Sirens from ambulances / police / fire engines. Nearby trains. Cars arriving / leaving / driving past. Dogs barking outside. Lawnmowers. Loud radios/TVs. Also things inside the building itself, such as water running in pipes, fans, pumps and other motors, people walking on floors, doors closing, people talking, vacuum cleaners, washing machine,phones ringing, furnace.... So here's what you do; have your trusty SLM (Sound Level Meter) on hand, and wait for those noises to happen, then measure inside the room! Once again, keep notes. Some of those are easy to arrange: getting family members to walk around the house, talking, opening(closing doors, flushing the toilet, running the vacuum cleaner, turning on the radio/TV, getting phones to ring: those are easy to stage. Not so easy is to persuade a helicopter to fly over, or an ambulance to drive past three blocks away with the siren on.... So you'll just have to wait for those.
Doing all that will give you a comprehensive picture of the isolation that you are getting, the levels, and the additional isolation you might need.
The thing with isolation is this: once the room is already treated, if you then discover that you need more isolation you will have to tear down all the treatment, do the isolating, then re-do all the treatment as well. And when I say "re-do", I don't mean just put the same stuff back again, because that won0t work. The simple fact of isolating the room will change the acoustic response of the room, so you'll need to go through the entire process again: find the new best layout for the speakers and mix position, and the new treatment, then re-build all the treatment, and re-tune the room. In other words, its smart to do the isolation first, so that you don't have to design and treat the room twice!
For example: the bay windows will very probably just pass through a lot of bass energy, that will escape and leave the room, never coming back in again, so you won't have to deal with the consequences of having that sound inside the room (your neighbors will have that pleasure instead, since they will get the full force of all the sound that escpaed!:) ). But if you then isolate the windows later, the bass will NOT escape, and you will be stuck with it, bouncing around inside the room..... where you will need extensive treatment to tame it. That changes the entire treatment plan, because bass trapping is large, takes up lots of space, and also tends to "suck out" too much of the mids and highs... so you'll need to compensate for that with LESS absorption in the highs, and maybe also so diffusion, or reflection for that. It's an entirely different situation if your windows are isolated, or not isolated.
Not trying to scare you here: just pointing out factors that you should take into account, and might not have cnsidered.
Upon checking out the SPL chart, I'd say I'd be after 35 - 50 dB. Does that sound reasonable for what info I've provided?
If the level outside in your garden after isolation is 35 dB, then you've done a pretty good job of isolating, and likely your neighbors won't ever even hear you. That would also bode will for those exterior sounds getting into your mics. But if you are getting 50 dB outside, that's not so good. Its not bad, for sure! Just less good that 35 dB. 50 dB outside your walls when you have a 110 dB tracking session going on inside is good isolation, for sure. That would be audible for a few dozen feet around. Probably still fine, since you have no close neighbors.
As you can see, the room also has an opening at the rear (2030mm x 1240mm) which leads into another room. I'm happy to leave this opening unsealed, for now,
As I mentioned above, that's a potential problem, since that other room will be acoustically coupled to yours, in bot directions. Your room will appear to have two different decay rates, which will be different for different frequencies. First, the initial decay at the mix position will be just the decay of the room itself, but when the level decreases enough, the decay of the other room will become noticeable. Or rather, the decay of the combined two rooms. That might or might not be an issue.
I may even hang a velvet curtain over it for aesthetic purposes
Fine for aesthetics, but it won't fool the sound waves! They will still figure out that there's another room back there, and still remain acoustically coupled to it...
I know I haven't provided you with a specific isolation number, but is there anything I could do immediately to help with isolation? I assume that I'd be looking at proofing the windows and doors to reduce ambient noise? what kind of materials would I be looking at to do that?
That depends on how much isolation you need, of course, but some options here are to simply seal the existing windows to be totally air tight (ie, caulk all the edges and gaps), adding a second window over each of the existing ones, completely replacing the windows with ones that have much thicker glass (laminated), and building plywood "plugs" to fit over the existing windows. There are options, but the one you choose will depend on the isolation level you need to achieve.
Apologies in advance if I haven't given you enough information, I'll get more info to you shortly.
Priorities here:
1) Define your isolation needs.
2) Decide how seriously good you need the room to be, acoustically, based on the function: just for fun, or serious business.
Once you define those two, then we can get down to details.
- Stuart -
That's the first approximation: mostly empty room, before much treatment goes in. I normally repeat the process again after most of the treatment is in, since the treatment can drastically change the room response, and also because in an empty room there's so much modal stuff, flutter, reverence, resonance, reflections, and other nasty stuff, that it can hide the details that you need to see in the data. Once the treatment has cleaned up most of that junk, then you can see things more clearly in the graphs, and maybe find a better spot that was hidden before.