My control room is 5.9 L x 2.84 W x 2.4 - 2.7 H (sloping ceiling) - almost a double cube so I figure cutting 60cm from the length would help both rooms sound better.
And you would be wrong with that assumption!
You are missing the point: I would suggest that you do some research on room modes and room ratios, as well as room volume, to find out why making a room smaller would not make it "sound better". Getting perfect modal response has very little to do with how the room "sounds". Room "sound" is achieve by treating the room accordingly, after it has been isolated, in order to meet the specs (such as ITU BS.1116-3m for example, for a control room). As I said, it is far better to maximize the room VOLUME, rather than go pointlessly chasing after the "room mode ghost" that doesn't even exist. With your current dimensions, you only have 16m2 of floor area: the minimum spec is 20m2. By chopping of another 60cm from the length, you make it ven smaller, bringing down the area to 15m2, and NOT noticeably improving the modal response! It still fails two out of the three critical tests used by the BBC (and others) to reject non-usable ratios.
Here's what your Bonello plot looks like for the smaller room:
PauleBerton-Smaller-Bonello.jpg
And for the larger room:
PauleBerton-Larger-Bonello.jpg
Do you see any
major improvement there? I don't. A slight improvement in the mid range, which isn't even that important. On the other hand, by shrinking your room you shoe up the Schroeder frequency by 4%, from 125 to 130Hz, you reduce the total room volume by 12%, from 42 m3 to 38 m3, and your lowest modal support frequency jumps from 29 Hz to 32 Hz, which of course distorts the entire acoustic signature of the room further than it needs to be. 3 Hz doesn't sound like much, but it's huge down that low. That's two entire notes on the musical spectrum: going from A to C.
I'd like to hear your theory on how all of that would somehow make the room sound "better"!
Having said all that, I'm rather confused regarding which room we are talking about: Are you referring to your control room or your iso booth? IF we are talking about your iso booth, then why are you even concern about modal spread and room ratios?
As far as designing / building my booth I am on a tight budget!
Then why would you waste 750 bucks on stuff you don't need?
The loaded vinyl is $750 for 40 sq m - I have a friend who runs Pony Music one of Australia's largest rehearsal / recording studio complexes - they have built 2 complexes over the years. They have Metal bands rehearsing next to their recording studio so he knows about isolation.
Once again, you missed the point: I never said that MLV does not work! What I DID say is that it is extremely expensive, and you do not need to spend that much to get good isolation! Your pal at Pony Music can perhaps afford to splurge money on expensive, exotic materials: you can't.
Here's the issue, in very, very simple terms. This is the equation that defines how well a single-leaf barrier will stop sound, overall:
TL = 14.5 log (Ms * 0.205) + 23 dB
Where: M = Surface Mass in kg/m2
That's it. That is often referred to as the "Mass Law" equation, because it describes the law of physics that governs the simplest possible barrier to sound. ("TL" means "Transmission Loss", which is what acousticians call the ability of a wall to block sound.)
OK, so please show me in that equation, where I can plug in the price tag....
There is no variable in there that you can adjust to say "Well, my mass is REALLY expensive mass, so it MUST be better than any other mass"!
The ONLY variable in that equation, is "mass". That's it. Price does not come into it.
You see, sound waves can't read, and they are not impressed by price tags. The are not elitist or snobbish at all! The ONLY thing that sound waves react to in a single-leaf barrier, is mass. Pure and simple. They have no way of "feeling" if your mass cost three times more than anybody else's mass. All they feel is the mass: More kilograms per square meter means they are more attenuated. Less mass means they are less attenuated. Price does not come into it. If a sound wave encounters a wall that has a surface mass of 30 kg/m2, it will be attenuated by exactly the same amount regardless of whether that wall is made from mud, sheetrock, OSB, MLV, steel, glass, gold, or titanium. The material itself is irrelevant: what matters is the mass, pure and simple.
Mass is mass. Sound waves don't care about anything else.
So that leads back to the basic question: If you are on a tight budget, then why would you pay MORE for your mass than you need to? Why would you spend mountains of cash on MLV that you don't need?
OK, so you might hear someone argue: "But, but, but... but MLV is not just ORDINARY mass it is LIMP mass, which is much better for attenuating low frequencies!" Sure it is! Exactly correct! ... Provided that you actually
USE it as limp mass! In other words, configured as a membrane trap inside your wall. The way you are proposing to use it, is NOT as limp mass. You re using it as pure mass,not limp mass. In order to work as limp mass, it would have to hang freely in the middle of the wall cavity, sealed to the studs, with air and damping on both sides, and without touching the drywall, to do that. Good luck with achieving that on a low budget!
Plus, if you do want to hang it as a limp mass membrane, you would need to make your walls a hell of a lot thicker to compensate for the three-leaf effect (look it up...), and you'd be getting into much more complicated math to figure out your isolation. Instead of the simple 2-leaf MSM equations, or the even simpler (but less encouraging) singe-leaf mass-law equation.
So once again, we get back to the point: you do NOT need to use exotic, expensive materials such as MLV, especially when you are on a tight budget, and especially when you are not even using it in the manner where it offers an advantage.
MLV does have its uses, but I VERY rarely use it in the studios I design and build. The cost is too high, compared to other materials, and it's a bitch to work with if you try to hang it as limp mass. The sensible thing to do, is to use the cheapest mass that will get the job done. In most places around the world, that is usually plain old drywall/sheetrock/plasterboard/gypsum board, or whatever else it might be called in different places.
He tells me that mass loaded vinyl is excellent bang for buck when the issue is trying to keep my walls thin.
The density of MLV is roughly 1500 kg/m3. The density of drywall is roughly 700 kg/m3. So yes, it's about twice as dense, and therefore you can make the leaf about half as thick. But you cannot use MLV on its own, due to its physical properties; it is fragile. If you lean on a wall made only of 4mm MLV, you will push right through! So you need to have some type of backing, such as drywall. If you use it along with drywall, then the 2:1 mass advantage is no longer there... It's more like 1.5 : 1. And considering that MLV is far more expensive than the same mass of drywall, there's no advantage at all.
On the other hand, aluminium has a density of 2800 kg/m3 (roughly twice as dense as MLV), steel has a density of around 7800 kg/m3 (5 times as dense as MLV), and lead has a density of around 12,500 kg/m3 (8 times as dense). So you could feasibly use lead foil just 0.5mm thick and get the same isolation you would from 4mm MLV (and lead is also limp mass, just like MLV). Or 1mm steel sheet, or 2mm aluminum sheet. Compare the prices of those options, to see how they stack up against drywall and MLV.
Usually when I need higher density to get thinner walls, I use fiber-cement board. It is a bit more dense than MLV, costs less (although still more expensive than drywall), and is easier to work with (as long as you are careful).
Now that you know all of the above, let's test what you have been told and see if it holds water: You were told that "MLV is better for thin walls, since it is higher density". True. But in the real world? You were planning to use 4mm MLV. That has the same mass as 8mm drywall. Do you REALLY want to spend all that extra money to save 4mm?
he also tells me that a variety of different wall materials & thicknesses is also good.
He's right, but also wrong! I get this argument a lot, but it's a myth. A true myth, but still a myth, if that makes sense!
Yes, the impedance mismatch from having materials of different density inside your wall does have a positive effect on improving isolation. This is true. However, by doing that it obviously implies that one of the materials is of considerable LOWER density then the others! Right? So you have one layer of high density material, and one layer of low density material, and the interface between them causes an impedance mismatch that can attenuate SOME frequencies more effectively. True. ... HOWEVER, the frequencies that get the most benefit are high frequencies, which are not a problem anyway in a properly built wall, and here's the kicker: One of the materials is LOWER density than it needs to be, so it has to be THICKER to get back to the right total mass! Therefore, you entirely lost your advantage for thin walls.
Oops! It turns out that it would have been better to just make the wall using two layers of the higher density material, rather one higher and one lower... You would get better isolation like that, down to lower frequencies. So what he said is true, but is also a myth. True because the underlying claim is correct, acoustically, but a myth because there's no real-world advantage to doing that.
Green glue is $1,000 for 40 sq me and my friend says he thinks loaded vinyl performs isolation better.
And he would be totally wrong about that! That's like saying "Steak costs 17 dollars per kilo, but rocks are better for building dams". So what? You are comparing entirely different things, that are used for two entirely different purposes! You don't eat rocks, you don't use steak to build dams! You don't use Green Glue to add mass to a wall, and you don't use MLV as constrained layer damping! The analogy is good, because there is no relationship at all between what MLV does for a wall, and what Green Glue does for a wall. MLV is mass, and it can also be used as limp mass. Period. Green Glue is a visco-elastic polymer that is never used as mass, and instead is intended to be used as constrained layer damping between layers of a wall leaf. Two totally different and unrelated principles. Green glue works by acting to damp certain types of resonance in the wall structure itself, notably the bending waves that run along the surface of the wall. MLV is just mass. Green Glue has some mass too, but that is not its purpose, and the mass is negligible becuase it is applied in a very thin layer, and the increase in surface density is tiny. What Green Glue does CANNOT by duplicated in any other way: not by construction glue, or caulk, or MLV, or carpet, or anything else. It is a very specific principle of acoustics that it uses, and it is very effective at doing that: It is great if you need to isolate low frequencies, and it does that in layer that is far, far thinner than MLV: maybe a mm or so. It is very effective.
Therefore, if you really do want the thinnest wall possible, and high isolation, forget MLV and go for two layers of drywall with Green Glue, or better still one layer of drywall plus one layer of fiber-cement board, with Green Glue. That would be about as thin as you can get, without going to things like steel plate or lead sheet.
It also does not cost one grand for 40m2...
OSB is expensive in Australia - 12mm is approx $35 sq m
22mm Tongue & groove floorboard is approx $20 sq m - almost twice the mass of 12mm OSB
I doubt that, since you are talking about thickness, not density, but even if it is true the T&G is MUCH harder to seal! You do know that you absolutely must seal the entire wall totally air-tight, right? Your pal did explain to you that there cannot be any gaps, cracks, holes or other penetrations where air can get through? Not even a single hairline crack? He did tell you about that? If you want to use T&G then you will need to carefully caulk every single joint between the planks, on both sides... It takes a lot of caulk to do that. Have you priced acoustic caulk yet?
Not only that, but the result looks pretty ugly, where the caulk leaks out of the T&G joints...
Also, I'm not understanding you at all here: On the one hand you want to use an extremely expensive product to save 4mm of thickness on your wall, and on the other hand you want to use a cheap product to save money, but it is 10mm thicker! Huh?
What am I not getting here? Why do you want so spend big money to save 4mm, while at the same time you want to save LESS money by WASTING 10mm? So which is it? Are you trying to save money or are you trying to get a thin wall? Because you are not doing either with your current plan...
This makes no sense. It seems to me that you are not thinking this thing through very well, and are basing your entire design on half-truths, myths, misunderstandings of the laws of physics, hearsay, and lack of understanding of how acoustic isolation works.
That is the thickness of the wall
No it isn't! That's the thickness of
HALF the wall. That's only one leaf. An acoustic isolation wall is
two leaves, decoupled. I think you did not understand what Greg was telling you. He did not tell you to put both leaves on the same stud frame....
Then there is stud & insulation. 90
Ummmm.... what's the purpose of that? So inside your completed room, after you fully build and finish the isolation shell, you then plan to put up yet another 90mm stud frame, with insulation in it, just sort of standing there on the floor, around the sides? Why? What do you think that would do for you? How would it work? In what way will insulation inside a stud frame without any mass or seal, improve the isolation? What equation should I use to calculate the effect that this would have?
Sorry if I'm coming across as harsh, or a bit sarcastic, and "in your face", but that's what we do around here: it gets your attention, and shows you exactly where you are going wrong. It's a not-too-gentle wake-up call. We don't beat around the bush, and we don't believe in PC at all. We just tell it like it is. If you are messing up, not understanding something, or being mislead, then we'll tell you exactly that: You are messing up. It might seem unfriendly, but it's actually the opposite: friends don't hide the truth from friends: they put it out on the table. "Tough love" some call it.
You obviously came to the forum because you trust us to give you solid advice on how to build your place right, and that's what we are doing. You have obviously asked others too, and they gave you some information but you didn't fully understand it, and that's OK! It is not a sin if you don't understand what someone told you, due to not yet having the necessary knowledge and understanding. Acoustics is complex, sound does not behave the way we expect it to, and it's tough to get your head around some of the concepts the first time you come across them. That's why you came here! Acoustics is confusing, and non-intuitive, and that's why the forum exists: to help people who don't get it yet, so they can understand as much as they need to understand, in order to design and build their studios.
So my suggestion would be that you do some more research here on the forum, to better understand the principles behind isolation, so you can build your booth better and get the level of isolation you need. What you should look for, is "fully decoupled two-leaf MSM isolation". Take a close look at that, redesign your wall so it costs half the price and works twice as well, and update your design here, so we can check it for you.
- Stuart -
Smart move!