I updated my profile to add my location
Yup! That was the biggie!
11.6'x9.6' room ... height is 8' inside
Great! That gives us the basics for figuring out your modal response. Your ratio is 1 : 1.2 : 1.45, which is close to Louden's 5th best ratio, at 1 : 1.2 : 1.5. That's number 9 on a list of 25 generally accepted good ratios. It's not fantastic, but certainly not terrible.
However, the floor area is only 111 ft^2, which is only about half of the "minimum recommended" area for critical listening rooms, which is 215 ft^2. That's not so good. Your room is going to need a LOT of treatment to make it usable. The smaller a room is, then more treatment it needs.
It's a simple 2"x4" framed room 24'' spaced beams for the two interior walls which have drywall and basic insulation between the beams.
Studs. Not beams, but studs. Beams run horizontally, spanning over empty space, and support large loads. Studs are the vertical members inside walls that support the actual sheathing (drywall). Terminology is important!
So you have 2x4 stud framed walls, 24" OC, and you need better isolation and great acoustics.
There's just thin (1/8") wood paneling all around (against the drywall of the two interior walls and against the other two concrete walls. I plan on removing all the 1/8" paneling. Adding soundboards all around for panels on a light steel frame.
... which would actually
decrease your isolation in the low end!
Yup. Surprising as that may be, it is true nonetheless. You would be creating a 3-leaf system like that, and even worse, two of the leaves would be coupled.
Here's the issue:
All objects have a natural resonant frequency. If you bang any particular object with something hard, that's the "note" that it will produce. A wall is obviously made up of "objects" (such as studs and drywall), each of which has its own natural resonant frequency. But when you put objects together to create an air cavity in between, you also create another resonant frequency, which is not related at all to the resonant frequency of each object. Rather, it is related to only two things: the mass (surface density) of the "objects" that define the cavity (in your case: the drywall on either side of the studs), and the depth of the air cavity between them. In effect, you have a Mass-Spring-Mass system (MSM) where the air trapped in the middle is the "spring". All MSM systems resonate.
So your entire wall system will resonate at this new MSM frequency. The problem is, if the wall is resonating, then obviously it is not isolating! In fact, not only is it not isolating, it is actively
amplifying that particular note. So if your music happens to contain the note that makes your wall resonate, then that note (and the ones around it) will be clearly heard outside, very loudly, since the wall itself transmits and amplifies them. Not good! So walls are designed to have a MSM resonant frequency that is lower than the notes that it has to isolate. Ordinary house walls typically have resonant frequencies in the lower mid-range portion of the musical scale, or the upper part of the low frequency portion of the scale. Which is why they are reasonably good at stopping voices, but not so good at stopping music, and lousy at stopping bass guitars and drums.
That's the situation you have now, and what you propose sounds logical and good at first glance, but is in fact a very common error.
By adding another thin frame and another layer of drywall, you change the system from being a 2-leaf MSM system, into a 3-leaf MSMSM system. You need a very different equation to calculates the resonant frequency, because there are now TWO air gaps (two springs) and THREE masses (leaves of drywall). It turns out that the resonant frequency for such a system will
always be higher than for the equivalent 2-leaf system, all other factors being equal. So although the wall will isolate voices even better, it will isolate bass guitars and kick drums even WORSE than before (which it wasn't doing very well anyway!).
Resonance is a bitch: Excuse my French. Resonance will always get you when you least expect it, and this is one of those cases that gets a lot of people, because it just isn't intuitive at all! Who would expect that adding an extra layer to a wall would make it worse? Not obvious... until you understand resonance. Many people make the mistake you were about to make, and end up with walls that don't work, after they spend a lot of time and money on them.
Here's what you really need to do: You need to keep your wall as a 2-leaf system. It turns out that this is the best of all possible wall configurations for studio isolation, and is the reason why practically all pro studios are built as 2-leaf systems these days. So that's your first priority: Do whatever it takes to make your final wall into a 2-leaf system. Not 3-leaf, not 4-leaf, not one-leaf. 2-leaf only.
But you also need to "de-couple" the leaves: right now, the studs are transmitting the sound directly from the drywall on one side to the drywall on the other side, bypassing the air gap, and the drywall then acts like an enormous loudspeaker. You need to cut that path, such that the drywall on side "A" is totally independent from the drywall on side "B".
You also need more mass on your wall.
And you need a bigger air gap.
So, here's the plan: take off the paneling, and also the drywall, and also the insulation, so that you have bare studs facing the room. While you have it like that, seal that framing and drywall absolutely air-tight, all around the edges, any cracks, gaps, slits, etc. Fill any holes, too (like where nails are badly placed, leaving tiny air holes). If there are electrical boxes on the other side for switches or outlets, remove those completely and cover over the holes with drywall, carefully sealed in place. Seal the hell out of it! Then seal it all over again. Did I mention that air-tight seals are important?
Now add more mass to that "leaf" of your wall. The easiest way to do this is to put strips of drywall in between the studs, pressed up against the drywall on the far side. This is often called "beefing up the wall from the inside". Cut the strips if drywall to shape, push them in carefully, seal up the edges with caulk (did I mention that sealing is important?), and put in small cleats nailed sideways into the studs, to hold the drywall "beef" in place.
Now put insulation in there. But not just any insulation: It can be either mineral wool with a density of 50 kg/m3, or fiberglass with a density of 30 kg/m3.
Now build your new frame about an inch away from that existing wall, put more insulation in that frame, put a layer of ordinary 5/8" fire rated drywall on the frame, seal up the edges very well (I think I forget to mention that sealing is critical...), then put another layer of drywall directly on top of the first layer with Green Glue in between.
And you are done! It's that easy. That is now a fully-decoupled 2-leaf MSM isolation wall, and it will give you pretty darn good isolation across practically all of the spectrum, except for the very low lows (canon fire, earthquakes, planets colliding, etc.).
You were planning to do most of this anyway (new frame, new drywall), so it's not such a big deal. You'd' just be adding "strip old sheathing / seal / beef up outer leaf". (Oh, I nearly forget: it's important to seal everything air-tight.)
The ceiling I'm going to completely redo as right now there's just a drop ceiling and some flimsy 1"x6" joists running across. I plan on making an air tight ceiling.
Right! Pull all of that out, then take a close look at what is above that: the existing ceiling. That's the key. Your new ceiling is only half the equation: Remember MSM? Your ceiling is just one of those "M's". You need to take a look at the other "M", the existing ceiling above you, and figure out what to do about it.
Top layer drywall or soundboard, MLV layer, frame, sound insulation between beams, outer MLV layer, soundboard, green glue, second layer of soundboard.
That's one hell of a sandwich! But not a lot of use for good isolation. And rather expensive. And rather complex to build.
Once again, you would be making a two-leaf ceiling, and you would be combining it with the existing ceiling above it, thus making it into a 3-leaf system or maybe even a [GASP!] 4-leaf system! Not good at all.
What you need to do here is this:
After fixing whatever needs fixing in the existing ceiling above you, in whatever way is necessary, put new joists across your new inner-leaf walls, taking care that they don't extend too far and touch the old outer leaf. (You must avoid all connections between inner-leaf and outer-leaf.) Your new joists should be sized correctly to take the live load and dead load of the new ceiling. Stuff the same type of insulation as for the walls up there, as thick as you can get it without compressing it too much, then put one layer of 5/8" drywall, seal, and a second layer of 5/8" drywall directly on the first layer, once again with Green Glue in between. (Damn! I keep forgetting to tell you about the importance of sealing! It's important.)
And you are done!
OK, so how come I'm not suggesting exotic things like "soundboard" and "MLV", considering that they are so highly recommended? One simple reason: cost. I'm assuming you want to do this at the lowest cost possible? So here's the thing. The equations for MSM resonance consider only two main factors, and neither of those is "price". Here's the actual equation:
F=c[(m1 + m2)]^.5 / [(m1 x m2 x d)]^.5
Where:
C=43 for imperial, 1897 for metric
m1, m2 = surface density of leaf #1 and leaf #2 (pounds per square foot, or kg/m2)
d=depth of air gap
Did you notice something interesting there? There's no place to plug in the price tag! It would seem that the price you pay for the materials is irrelevant! Darn! This is bad news for the manufacturers of those expensive products. Sound waves just don't care! They can't read the price tag, and they aren't elitist at all, so they really don't care how much you paid for your mass. All they see is mass, and they react to the
quantity of mass, not the
cost of the mass. So it seems logical that you should use the mass that costs the least, pound for pound (or kg for kg).
It turns out that in most places on Planet Earth, the cheapest mass you can get in common building materials is found in plain old drywall. Best is fire-rated drywall, which is usually a bit heavier for not much increase in price. Yes "soundboard" is heavier still... but compare the prices! Ask yourself: "For the same money or less, could I put on another layer of ordinary drywall, or use thicker drywall?" If the answer is "yes", then your path is clear: ordinary drywall.
"But what about MLV"? you say. "That's even better," you say, "because it is limp mass. And limp mas is wonderful stuff!". Yes it is, but if you restrain it with layers of drywall, then it isn't "limp" any more: it is now just "mass"... and you are paying an awful lot for that "limp mass that isn't limp"! I know of a much cheaper option for "mass that isn't limp". Its called "drywall"...
MLV has some uses in acoustics, but adding mass to a wall isn't a good one. (Despite what the manufacturers say). It works, of course, because it
IS mass, after all. But the cost... sound waves... reading skills--- price tags.... Hmmmmmm....
Also using acoustic sealant to seal up all seams etc.
Yes! Very much so! (Not sure if I already mentioned that sealing is very, very important...?)
Also putting in a proper window to look into warehouse as there is already one there just not good with plexi.
Right. You will need two panes of laminated glass for that window. One pane goes in each leaf: You calculate the thickness of the glass such that it has the same surface density as the leaf itself. So fore example, two layers of 5/8 drywall has a density of about 24 kg/m2, so you'd need each pane of glass to have at least the same density, and preferably a bit higher. The density of glass is roughly three times higher than the density of drywall, so you need about one third the thickness. Two layers of 5/8" drywall is 1-1/4" thick, so you need laminated glass that is about 7/16" thick. call it 1/2", to be safe. So you would need to order '
1/4"+1/4" laminated glass with acoustic PVB interlayer '. It might also be listed as "6mm+6mm with acoustic PVB". You would need two of those for each window, one in the inner leaf and one in the outer leaf.
The rest of the warehouse (outside this room) is carpeted and has acoustic foam on like 85% of it (from previous band).
It must sound like crap in there! (Excuse my French again...) Let me guess: a bit "boomy", somewhat "honky", very "muddy", mostly "mushy" in the mid range, harsh in the high mids, and teeth-achingly tinder-dry in the high end. Am I close?
I imagine that after you get the CR in shape, your next project will be to fix the "other" room and make it into a usable live room / tracking room?
Anyway, that's the outline of what I'd suggest for getting the control room isolation in order. The only other things is doors: you need two doors in each doorway, not just one. They go back-to-back, one door in each leaf. And each door needs at least two full-perimeter seals (both sides, top and threshold). Because you need the doors to seal completely air tight when they are closed. I should mention that sealing things air-tight is critical to getting good isolation. I forgot to mention that before, I think...
- Stuart -
(Edited to correct some schpelink mizteaks, to clarify some not-so-clear things, and to add a bit more detail)
