but my current limitations are largely based on cost, not available space.
Making the actual isolated studio space smaller is certainly the best way to make it cheaper. The question then becomes: How small? As you make a room smaller, it becomes less good acoustically, and needs more acoustic treatment inside to make it usable. So very small rooms use 100% of the entire wall surfaces for treatment, and can still sound bad. So there's a trade-off there too: making a room smaller saves you money on the walls, but if it gets really small then the treatment becomes more expensive, and more complex.
In helping you to define what the minimum useful size for you, it would be good if you could tell us more about the actual purpose of the room: Is this going to be just a rehearsal space, where you can practice as much as you want, by yourself, at all hours, without disturbing or being disturbed? Or is it a place where others will be joining you to practice together? Or will it also be used as a "tracking room" or "live room", for professional quality recording of the instrument(s)? Or will it also be used as a control room, where you will have a console and/or DAW fully set up with good quality studio monitors, so you can mix the songs? And maybe master them too? Each of those adds a level of complexity (and cost) to the room, so it is important to define it well.
Wow. The building is all brick and concrete, so it can handle serious weight. And I'm allowed to build walls, but probably not ones that heavy. Scratch the brick idea.
Right. Most people don't realize just how much bricks weigh, but basically they are similar to rock in consistency. Pick up one brick, and it doesn't seem so heavy, but try to pick up a dozen all at once, and it becomes more apparent... then add a sack of cement to that, and try to pick it up again...
Thank you for explaining mass law. I've been having trouble trying to understand the math, largely because I haven't been finding any in my forum searches.
Yeah, the information isn't easy to find unless you already know exactly what you are looking for! Unfortunately. Another way of describing "mass law" (which is what governs single leaf walls) is that each time you double the total mass of the wall, then you get about 6 dB increase in isolation. So if you have a wall made of one layer of bricks, then you build another identical wall tight up against it, stuck together, then the total isolation goes up by about 6 dB. Then if you build another TWO walls next to the original two (doubling again, total of 4 brick thickness), the isolation once again increases by 6 db: And adding another FOUR walls (total of 8 brick thickness), you get another 6 dB increase. You can easily see why this is not going to get you were you want to go!
Decoupled construction was recommended in a another forum. After some cursory research, I was able to verify that it's significantly superior. Would you mind explaining what MSM is?
"MSM" stands for "Mass-Spring-Mass", which is the principle of physics on which it is based. Also sometimes called "Mass-Air-Mass". Basically, it means that you build your wall as a pair of "leaves" separated by an air gap. The "leaves" on each side can be made of anything: wood, drywall (plasterboard), metal, glass, brick, concrete, etc, and each leaf can be built up from several layers, as long as there is no air trapped inside, between the layers. A common way of building a leaf is with two or three layers of drywall, nailed to one side of a stud frame. So to get "MSM", you'd have a pair of those with an air gap between them, In other words, two stud frames, where each frame has drywall nailed to only ONE side of it (not both sides). You use two frames to get the "decoupled" thing right.
So now you have two leaves, which is the two "M"'s in MSM. Each leaf is "Mass". And the air gap between them is the "spring". People don't normally think of air as being a "spring", but to sound waves air is very springy. So "MSM" is "Mass-Spring-Mass" which is also "Leaf-Air-Leaf".
The question is "why"?
Well, an "MSM" thing, is a resonant system: it resonates at one specific frequency. Think of a weight bouncing up and down on a spring, or a pendulum in a grandfather clock, or a child on a swing: those are all "mass-spring" systems, and they all resonate at only one frequency. But in addition, they refuse to resonate at any other frequency! That's the key. If you want to make a child swing 10% faster, you can't do it. No matter how hard or soft you push, the child will always go at the same rate. That's why pendulums are so good at keeping clocks on time: they ONLY go at one speed, and you CANNOT make them go at another speed. The same is true of an MSM wall: it only wants to resonate at one specific frequency, and does NOT want to resonate at all others. When it "hears" it's note then it resonates wildly, passes that sound through to the other side, and even amplifies it. But for all other frequencies, it resists, actively.
So if you can tune your wall such that it's resonant frequency is lower than all audible frequencies, then the wall will isolate the entire spectrum. It is sort of like an electronic filter, or a bandpass setting on an equalizer: It only lets that one tone through and no others.
Of course, it isn't perfect: there's a region on each side of the resonant frequency where the isolation isn't very good, so you need to take that into account too. But as long as you tune your wall to one octave lower than the lowest frequency you want to isolate, it will do a good job.
So how do you "tune" your wall to the right frequency? There are equations for calculating that, but basically as you add more mass on each leaf the frequency goes down, and as you increase the size of the air gap the frequency goes down, and as you fill up more of the cavity with insulation the frequency goes down. So if you need good isolation at low frequencies, you just add an extra layer of drywall to each leaf, and/or set the two stud frames further apart.
The best point, though, is that an MSM wall is not subject to mass law, but rather to the laws of resonance. So it doesn't just give you 6 dB increase in isolation each time you double the mass (or the frequency), but rather it gives you 18 dB per doubling of mass (or frequency)! That's a really large difference. OK, it isn't 18dB across the entire spectrum: it drops to 12 dB and even 9 dB in some places (due to other reasons), but even so it is vastly superior to the measly 6dB you get from mass law: so you can get a LOT more isolation with a lot less mass, and/or a lot less space.
There are pros and cons, of course, (and a lot more complexity, too) but overall two-leaf MSM is a much smarter way of building isolation walls.
The one point I didn't mention that is critically important, is that the "spring" must be damped, in the same way that the shock absorbers in your car "damp" the springs: They stop resonance. The way you do that in an MSM wall, is by filling the cavity with fluffy insulation, such as mineral wool or fiberglass. All those millions of fibers act on the sound waves to absorb some of the resonant energy, thus "damping" the resonance in the cavity.
So that's it. Not complicated, much less expensive, much less mass, and very effective.
I've been a musician for 30 years and I'm just now learning this?
That's the thing about acoustics: much of it isn't intuitive at first: We can't see sound moving and bouncing around a room, so our brains have a tough time understanding what is really happening. We tend to assume things that just aren't true. Mostly people coming to acoustics for the first time have to initially "unlearn" what they think they know about it, then re-learn how it actually works.
I need to read more, evidently.
I'd suggest two books: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics), and "Home Recording Studio: Build it Like the Pros", by Rod Gervais.
Room acoustics and that sort of technical stuff is where I'm seriously lacking.
Those two books (plus the forum!) will get you a great basic start. The first one "MHoA" is designed to take people who know nothing about acoustics along an easy path to learn enough that they can design a studio. the second book has a bot of that too, but is more "nuts-and-bolts", or rather "studs and nails": it's about the actual methods and materials of how to build a studio. And the forum is here to fill in the gaps, and help you tie all the loose ends together.
Yeah, I was naively hoping for an effective unorthodox approach to save on cost and time.
So are we all!
All studio builders want that. But unfortunately, it turns out there are no magical materials: despite the wonderful claims made by some manufacturers of snake-oil... sorry I mean acoustic products, the fact of the matter is that all materials must obey the laws of physics: No amount of meditation, incantation, "eye-of-newt-and-tongue-of-bat", or any other strange antics, can change the laws of physics. No magic here: just ordinary building materials that obey the ordinary laws of physics...
I think my main question at this point is whether it would be more cost effective to build one really soundproof studio or a bedroom and a studio that aren't quite as soundproof. The studio isn't just to keep sound out. It's also to keep sound in since I have a live-in girlfriend. I can't be keeping her awake practicing or recording at 3am with my bizarre schedule.
If the goal is ONLY to have a studio where you can go nuts without waking someone in the next room, then the best plan it to isolate ONLY the studio. The bedroom doesn't need any more isolation than a normal bedroom: it's only the studio that needs it. Isolation is mostly bi-directional: If it isolates well "going out", then it also isolates well "going in".
So what you need to define here, is how much isolation you need, and what frequencies you need it at. for example, if you plan to play death-metal acoustic drums at 3AM, then you need major isolation, but if you only need to isolate vocals and an acoustic guitar, then that's an awful lot simpler. So get yourself a sound level meter, and measure how loud you are in a typical session that you'd normally do. That's one end of the story. You also need to measure how quiet you need to be. So set up a sound system in one room of wherever you live now and play the typical type of music that you'd be doing in your new place, loud. Then get your girlfriend to go into the next room with the sound level meter, while you slowly turn down the volume until she says it is quiet enough for her. The level you see on the meter at that point is "how quiet you have to be".
Subtract "B" from "A" and you have the answer to the question "How much isolation do you need".
Simple!
Based on that, you can design your studio isolation system.
And what's a more realistic estimate of what I'd need to spend?
More like US$ 20 to 200 per square foot, depending on many factors. In your case, much closer to "20" than "200"! so if you can get the size of the room down to something that is just big enough for you, say 200 ft2, then you'd be looking in the region of US$ 4000 or so to isolate and treat it decently. If you can borrow tools and perhaps skilled carpenters, you can get the costs down. (maybe exchange their skills for yours? If you know folks who are good at carpentry and also are budding musicians, you could strike a deal here: They help build your place for free, and you then record and mix a few songs for them, for free...). You can also get the price down by shopping for discounted building materials: sometimes demolition sites sell old wood cheap, and so do places like Home Depot when there's damaged goods in stock. I once picked up a pallet of drywall that had been damaged by a careless forklift driver, for about half price, and most of the drywall was just fine! So look around, and you can save money.
- Stuart -
You mentioned "loft": Are you SURE the building structure can handle you piling on seventy TONS of extra weight onto the top floor? Very likely, it cannot handle that. The only person who can tell you for sure, is a qualified structural engineer. Hire one before you do anything.
Then your goals are totally achievable, and at reasonable cost. You can isolate that fairly easily, without needing to go to extremes. I predict success! 
Ummm... well, I guess that's ONE possible solution! But ... ummm... well... probably not really practical at all! 
They seem to have that prettify much covered.. 
