Hi there Tim, and welcome to the forum!
This is my first post so I'm a little nervous about getting it right and following all the rules. Forgive me if I mess up
IT looks like you ticked all the boxes perfectly!
I'm looking at a 14mx9m foundation and a wall height of 2.8m
I want to fit a Control Room, Live Room and 2 ISO booths into this space.
My priorities will be:
a) a Live room that can help me achieve beautiful BIG drum sounds (most of what I will be recording will be of the Heavy Rock variety)
The height is fine for the control room and iso booths, but if you could go higher for the live room, that would help with your goal of "beautiful BIG drum sounds". Drums sound better in fairly large spaces, especially if you plan to have overhead mics on them, so the rule here is "the higher, the better". If you could figure out how to get more headroom there, that would be great. For example, how about digging a bit deeper where the LR will go, and having a step (or two) down? That would keep your roof line the same while still giving you more headroom.
If not, then 2.8m is OK, but more would be better.
The CR dimensions I came up with are these:
H: 2.80m; W: 4.58m; L: 5.50m
That's a nice large CR, so it bodes well for meeting your goals. However, a couple of comments on that:
1) You say the wall height will be 2.8 m, so it's hard to see how the finished ceiling height can also be 2.8m, while also attaining high isolation!
You will lose a fair chunk off of that 2.8m for the isolation system of your ceiling, probably around 15 to 20 cm, maybe more. Even if you went with "interleaved" joists, or with an "inside-out" ceiling, you'd still be losing at least 5 cm, so I can't see how you would end up with 2.8 m for your finished inner-leaf ceiling height.
2) the ratio isn't that good. if you look part way down the page on Bob's calculator, on the right, you'll see a section of text under the heading "Computed Information:" Part of that is a set of three BBC critical tests. You are failing one of those tests, because "ratio3 = ratio1 * 2". In other words, your length is almost exactly twice your height, or within 5% of each other. If you check the list of modal resonance frequencies, you'll see this:
61.5 hz 20.4% 5.6 : 2.8 : 1.4 (0,0,1 Axial)
62.6 hz 1.7% 5.5 : 2.75 : 1.38 (2,0,0 Axial)
And also this:
123.0 hz 2.1% 2.8 : 1.4 : 0.7 (0,0,2 Axial)
125.2 hz 1.7% 2.75 : 1.38 : 0.69 (4,0,0 Axial)
In other words, those two modes, and all of their harmonics, will line up nearly perfectly, so basically when an instrument plays those notes (or close to them), BOTH modes will potentially be triggered, doubling your problem. One mode could also easily decay in to the other, causing strange things to happen. If you follow Wes Lachot's philosophy, then you should also aim for musical relationships between fundamental modal frequencies, which also implies that you should try to get the modes aligned with actual notes. That just makes sense, actually: if not, then as the instrument note itself dies away, the related mode can die away at a slightly different frequency, thus creating strange BFO effects.
So you would need to change your dimensions a bit. For example, making them 5.55 long, 4.16 wide and 2.62 high improves things considerably, as that hits B's, E's, G#'s, D's and C's with your first few modes, and also improves the modal spread. Plus, it passes all three "BBC Critical" tests, and also brings your inner-leaf ceiling height down to a feasible level. But you could probably find other good ratios by playing around a bit. Here's another calculator that you might find useful, as it displays things in a slightly different way, and also "auralizes" the modes, so you can actually hear what they sound like:
http://amroc.andymel.eu/
I'll looking at needing to take a 115+dB drummer inside my LR down to somewhere around 40dB at my fence line (roughly 3m from the studio wall).
That's a pretty tall order! 75 dB of isolation ain't easy to accomplish. OK, so let's allow for that 3m distance to help you a little, and say that you need 70 dB of isolation at the standard 1m distance from the wall (theoretically, that would decay to 72dB at 2m and 69dB at 4m). So, 70 dB.... Hmmmm and a lot of that in the low end (drums). Hmmm.... You sure do have your work cut out for you! It is do-able, but not easy. What you need: mass (huge amount of it!) damping (oodles) and air space (truck loads).
On the plus side, you are starting out with Besser brick, which is reasonable mass, and good down to reasonably low frequencies. But nowhere near what you are aiming for. You did mention filling them with concrete, but I would also suggest filling them with sand: Sand will help with damping, to a certain extent, and also has plenty of mass: around 1800 kg/m3, which is pretty close to concrete. So assuming standard besser blocks (190mm thick), you'd be looking at a surface density of around 380 kg/m2, which implies around 48 dB of isolation overall, maybe 50 if you are lucky. Still far short of the 70 you need. That would fall to about 30 dB of isolation at 30 Hz, which is not bad, but still not as good as you need.
Clearly mass law alone is not going to provide what you need (it never does!). But you already knew that, and added an inner-leaf of 2x16mm drywall over a 150mm air gap, for a true MSM system. Theory says that the combination will give you an MSM resonant frequency of about 22 Hz, and your wall will isolate well above 43 Hz, with total isolation estimated at about 67 dB (I'm developing an "isolation estimator" spreadsheet right now, but it isn't ready for public consumption yet as it makes a lot of questionable assumptions. But FWIW, that's what it predicts for your wall). Adding one more layer of drywall and increasing your air gap to 180mm would get you to 69 dB (according to my spreadsheet), but in reality probably a bit more. I would also stucco (plaster) the outside surface of that wall, and seal the inside surface with masonry sealer (or even just paint), to improve the isolation that extra bit. Or even plaster the inner surface as well: extra mass plus good seal: that would get you a touch over 70 dB, I reckon.
So from that point of view, you'd be good to go. Theoretically...
However, at high levels of isolation such as that, you are getting close to the flanking limit for your concrete floor, especially considering that drums are involved (impact noise as well as airborne noise), so you might want to consider pouring the floor of the control room as a separate isolated slab. Since you are building from the ground up, that does not increase cost or complexity much at all: it just involves a bit more concrete for the monolithic footer for that slab, and a bit more work in keeping it separate, but no big deal. You would then build your inner-leaf walls on top of that slab, totally isolating the inner-leaf from the outer leaf.
That would take care of things down below (the slab) and to the sides (the walls) ... but what about up above? Isolation is an "all or nothing" proposition, requiring that you maintain the same surface density of each leaf around the complete building shell. Since your outer-leaf walls and floor are basically thick concrete, you'd have to do the same to the roof to complete the outer shell. So that implies that the roof over your studio will be flat concrete slab. That's the only way to get the level of isolation you are talking about, at reasonable cost.
Isolation is only as good as the weakest link. If you build your walls and floor to 70 dB, but your roof is only good for 40 db, then your total isolation is 40 dB. Period. And of course, whatever gets out through the roof will be just as audible for your neighbors as it if went out through the walls: Especially low frequencies, which are not directional.
So your roof is going to need to have the same surface density as your wall and floor, if you want 70 dB of isolation.
OK, so assuming you already have that resolved, and your entire MSM system will be done to the same 70 dB level all around (walls, floor and roof), the next issue is doors / windows. Getting 70 dB for walls is relatively easy, compared with getting 70 dB for doors, since doors have to open! Your doors will need to be extremely massive, and extremely well sealed. I would suggest triple rabbeted seals on all doors, all around all the perimeters, and I would also suggest using a pair of Rod Gervais style "superdoors" back to back. You will need to heavily beef up the framing for those doors too, of course, to support the huge weight. Hanging a couple of hundred kg on ordinary frames is going to bend them substantially, and perhaps break them, considering the moment arm. Heavy duty hinges are also needed, of course. With a couple of those doors and a sufficiently large air gap between them, you should be able to get in the general ball-park of 70 dB, but it will require careful work and good precision with the seals.
Then come windows: Thick laminated glass is your only option, but you probably already knew that.
And finally, the least-considered but most important aspect of studio isolation: HVAC. After you have built your two perfectly sealed, perfectly decoupled, extremely massive leaves, you then have to chop huge holes in them to get your HVAC ducts through! So you are going to need silencer boxes ("baffle boxes") on all penetrations where a duct goes through a leaf, and they will also have to be massively built, in order to retain the level of isolation you are talking about.
So overall what you propose to do can be achieved, but it does require careful design, careful planning, and careful construction. It also requires a pretty big budget. You didn't mention how much you plan to spend here, but at a rough estimate, from what I understand of Australian building costs, I would estimate somewhere north of $100,000.
I am thinking of large sliding glass doors (3 standard door widths) on both the north (leading to LR) and south side (leading outside).
Sliding glass doors are really nice in studios, and for the path from LR to CR that's certainly a good option.
However, from the CR to outside? I don't think that is on. There's no way you'll get 70 dB from a pair of sliding glass doors. 50 dB maybe, with luck, but 70 dB is a hundred times harder (100 times the sound intensity). I would suggest no doors at all on that wall: Maybe a window, of you want natural light, but no doors.
In terms of isolation I guess I will need 2 lots of doors on each side and some thick glass. I suppose the question is how thick is thick?
Right. Thick glass. How thick? Thick enough to maintain the same surface density as the rest of the wall. So for your inner leaf: Drywall weighs about 12kg/m2, three layers will be about 36 kg/m2, glass is about 2500 kg/m3, so to get 36 kg/m2 you would need a thickness of about 15mm thick, so probably a 7+8 laminate would work fine for that, or 8+8 to be safe.
For your outer leaf: your besser brick wall is coming in at about 380 kg/m2, so to maintain that you'd need about 15 cm thick. Yes, that does say 15 centimeters, not 15 millimeters. So your best bet for that if you want natural light and high levels of isolation, would be glass bricks. Solid ones. If you wanted to go with normal glass, then you might have to go to a three-leaf system with two leaves on the besser brick wall, using say 12+12 mm laminate on the middle leaf and 10+10 on the outer leaf, then maybe 9+9 0n the inner leaf (drywall). I didn't do the calculations on that, and I might be over-estimating a bit, but it's probably not far off from what you would actually need.
From the above, you can see why I said that sliding glass doors are out of the question, for 70 dB of isolation to the outside world.
As for speaker placement. I have drawn in guidelines using an equilateral triangle from the listening point.
Right, but you have the triangle apex incorrect, in what is actually a very common misconception: Your ears are on the SIDE of your head, not the FRONT, so if you want the acoustic axes of the speakers aimed at your ears, then the apex of the triangle actually has to be located a distance
behind your head, not
inside your head. The normal recommendation is that the axes intercept about 20 to 60 cm behind your head. That means you have to move your speakers further apart, or reduce the toe-in angle a bit, or both.
Any suggestions about soffit vs stands for this room. I like the idea of soffit but I am struggling to see how it would work in this room.
Do I have to set them back in the existing wall?
OR
Bring the wall out further to accommodate them?
Soffits provide major advantages in practically any room, and IMHO soffiting your speakers is about the single most useful thing you can do to eliminate many of the artifacts associate with having speakers inside a room. In your case, you would build the soffits within the inner-leaf, extending into the room diagonally across the front corners of the room.
If either of the later is the case would that mean I'd need to recalculate my room dimension for Room Modes?
Correct: modal response refers to the massive, rigid, hard, solid reflective inner-leaf boundary of the room, which is the front face of the soffits.
Lastly (for now haha!) I am wondering about placing small windows in the back wall of the control room so as to have a line of sight into the 2 ISO booths. Do you see this posing a problem acoustically?
How about turning your CR around so it faces those booths? That way you have direct sight lines into them... Even better; turn the room to face the LR, with a window into that too, then put the booths on either side of the angled front walls of the CR, also with windows. Best case, all around...
Hope I've been clear enough with my questions. Be gentle
Very good first post! I wish all first-posts were as clear, concise, and well thought out as yours. Good job!
- Stuart -
Try ray tracing both options (no-tilt and tilt), and you'll see what I mean. The best way to minimize reflections off the console surface is to have the speakers as far away from the desk as you can get, so the sound hits at a more glancing angle, and therefore bounces off into your stomach and chest, not your head. That's another good thing about soffit mounting: it does indeed put the speakers as far away as is physically possible. You should be fine, from that point of view. There's a couple of other tricks you can use to minimize desk reflections...