Hi there "CMP", and welcome to the forum!
Wow, quite a learning curve!
Very true. And the good news, it gets steeper as you progress along it, until it's practically vertical and unassailable ...
Naah, it ain't that bad, but it does seem like it at times! And it does level out a bit, eventually, to the point where any 4x4 can handle it... with a winch, chains, and a military armored troop carrier to help it along!
I’ve seen and worked in a lot of control rooms and live rooms, some great, some terrible and perhaps this is where my measured suspicion of the art of acoustics takes root. I have worked in some fantastic sounding control rooms that have not cost the earth (large and very small) and also some very bad ones that have cost an absolute fortune and I have sometimes struggled to find much of a correlation between budget and result.
If it is of any comfort, I've been hired on a couple of occasions to fix big-money rooms such as the ones you describe, and I know John has too. I'm talking about rooms that were designed by big-name studio designers, and had large price tags attached, but where the owners were far from happy with the outcome. I won't be mentioning names, but it's surprising that designs where lots of dollars were spent could turn out so bad, when they clearly and obviously defy the laws of physics, or the brief of the owner. I know John has also fixed rooms like this, since we have discussed it off-line on a couple of occasions, sort of sharing "horror stories" about big-name, big-money studios that fell flat, acoustically. I'm not exactly in that league of designers (although John certainly is!), but I do know enough to see some really silly things done in those "big" studios, and I'm left wondering.... Why on earth would they do that? And it's also somewhat of an ego boost as well as simultaneously humbling, when a customer who just fell out with a big-name designer comes to me and asks me to fix it. Case in point: I'm just putting the final touches to a mastering studio design for a customer "somewhere in the USA", who was in this situation: originally he paid big money to have a well-known designer draw up detailed plans for his place... but it would never have worked! I tried to re-work his plans, but we ended up re-designing the whole thing from scratch.
I'm not sure which "high end" studios you have been in that didn't impress you, but I'm not surprised: it happens!
On the other hand, there sure are a lot of not-so-high-end studios, done on a tight budget, that turn out really well. You'll find quite a few of those, right here on the forum! And a whole bunch more on John's own web site. Many, many, many. I'm sure that's why you are here! Because you see results, not hype.
OK, so what's the difference? How is it that some "pro" studios end up pretty bad, while many "amateur" studios end up darn great? The only answer that makes sense to me, and that jibes with my own experience, is that the folks who succeed are the ones who take the science of acoustics seriously, and build rooms that logically follow the laws and limitations of how sound actually behaves. Rather than aiming for some bold architectural statement, or going after amazing look, artistic-decoration, or personal biases in some sense. In other words, knowledge beats ignorance. Every time. When you follow the laws of physics and design using them, the result just works. When you try to cut corners, re-invent the wheel, or go with esoteric weirdness, it doesn't work.
There's two approaches here to getting a great studio, that work. One is John's approach: empirical experience. John has been around so many studios for so many decades, in so many places, that he just innately "gets it", and understands exactly what a given space needs to make it work. I do not have his vast experience, so I spend a lot more time working through the math and the the theory, as well as studying what he did and figuring out WHY it works, so I can apply it in other places. You'll notice that a lot of my designs are inspired by John's designs, because I see how and why they work, and how I can adapt them to other rooms. I don't try to copy John, but I sure do try to learn from him, and follow him! Don't get me wrong: I'm not saying that John does not use math and science in designing his rooms: he certainly does! And I'm not saying that I don't use personal empirical experience in designing: I certainly do! It's more along the lines that John already walked the path of science, math and acoustics, years ago, and now understands sound and acoustics so well that he doesn't need to rely on calculating every last thin, like I still do.
Both approaches work: knowledge, and science.
But the approach that does NOT work, is "winging it on a whim", thinking that it if looks good it will sound good, attempting to do things that are acoustically silly. I have no idea why some big-name studios were designed like that, but you've seen it yourself. The look nice but sound ugly.... It's not that the science of acoustics is flawed; it's that some people just don't use it!
Anyway, I'll stop waffling now, and get down to YOUR studio! The point of the waffle was to encourage you that your place really can be one of the "great acoustics on a low budget", provided that you follow one of the two paths above: And since you already admitted that you haven't paid a lot of attention to the empirical side of acoustics (figuring out why some rooms are good and others are bad, despite the budget), to get to your goal you'll probably need to take the other track: theory, math, science, research, study...
The walls are constructed with concrete blocks and rough-cast rendered on the outside and painted on the inside – a total thickness of 237mm.
That's an excellent start! Really good. One of the first things about isolation (which you probably already know) is that it requires mass. Lots of it. The more mass you have, the better your isolation will be. Concrete has mass. Render has mass. And 237mm of concrete+render is a nice sized chunk of mass.
You have probably also learned that isolation requires that the "mass" must be sealed air-tight, for the very simple reason that "if air can get through, then so can sound", which in turn is based on the even simpler concept that, at it's most basic definition, "sound" is just "vibrations moving through air". So no air gaps in your wall. Most types of render are pretty good at sealing air gaps, and your wall is rendered on both sides, which bodes well. If you really want to go for high isolation at low cost, then you could paint that wall with something that will even seal the pores in the render, before you move on to building your inner-leaf wall. The pores can play havoc with the isolation, as they do allow the air (and thus the "vibration of the air") to penetrate into the wall surface. Sealing prevents that. Masonry sealer would be good, or even a cheap wall primer. It doesn't have to look pretty, since it will never be seen, so just slap on a good layer of anything that will seal the surface. If you look around the forum, there's a couple of cases where members have followed this advice, and immediately commented on how different the room sounds from just having the porous surface sealed.
The downstairs (garage part) is one open space 5.97m x 5.97m x 2.25m (I’m guessing that’s where the problems start, right?)
Yep!
For two reasons:
1)
It is square. which is about the worst possible shape, acoustically, as all the modal resonances in the "length" direction will occur at the exact same frequencies as the modal resonances in the "width" direction, so you'll have some very large modal issues at just a few very specific frequencies, with very large gaps in the low-end spectrum in between them... Not a good situation, so you'll need to look into the theory of room ratios, modal spread, room, modes, ratio calculators, etc. You will have to make sure that your inner-leaf room fixes this problem, by NOT having the same dimensions, nor dimensions that come with about 5% of being the same, or being a direct multiple of each other. Use one of these Room Ratio calculators to figure out the best dimensions for your room:
http://www.bobgolds.com/Mode/RoomModes.htm
http://amroc.andymel.eu/
Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions.
2)
Low ceiling.Sound likes space, and it likes space in all directions. You do have nice space horizontally, but sound also likes space vertically. Sound is 3D, not 2D, and sometimes people tend to forget that in their room designs. And you have precious little space in the vertical direction, so you will have to take very special, extra-great care to lose as little of that as possible when you put up your inner-leaf ceiling. I would suggest giving vary careful consideration to using John's famous "inside out" concept for your inner-leaf ceiling. It has man advantages, one of which is allowing you to keep as much
acoustic height as is physically possible. Another is that it automatically provides lots of diffusion at low frequencies, and also provides space where you can have plenty of treatment, that helps to "raise" the ceiling, acoustically, so that it seems higher than it is, psycho-acoustically.
and I am currently seeing that as a reasonable sized control room, for mixing, editing, programming, keyboards, where I spend most of my life.
Yes, but it's not really because you "
see" that! It's because it really
is like that...
There's a document from the ITU called BS.1116-3 that lays out the specifications for "critical listening rooms", which obviously is exactly what a control room really is! It's a place where you can listen critically to your mixes, and make judgement that turn out to work really well, because it is an acoustically neutral space. That's the key goal for a control room: it must be absolutely neutral, acoustically. It must not add any "coloration" to the sound coming from the speakers, and it must not subtract anything from that sound. The room must simply transmit that faithfully and truthfully and cleanly from the speakers to your ears, as you are seated at the mix position. It seems like it is simple, but it's a LOT harder to achieve than it sounds. Here's what it looks like when it is properly done:
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 The acoustic response in that room is truly "neutral". What you hear at the mix position is exactly what came out the speakers, not a single dB more or less, in any sense. That's your goal.
Now, achieving that depends on a number of parameters, commencing with the size of the room. BS.1116-3 is based on years of research by leading acousticians, and the conclusion is simple: You need a floor area of at least 20m2 in order to be able to hit the goal of "acoustic neutrality" easily. You can go a bit smaller, yes, but then it becomes harder to hit the goal, and the room will need more treatment, making it more complex and more expensive. You might be able to get by at 18m2, and right now I'm working on treatment design for a room that is just 16m2, purely for the challenge of seeing just how far I can push it, but I would certainly not want to go smaller than that. The smaller the room is, the more complex it gets acoustically, since the modal issues just become so severe, as does the acoustic loading of the speakers (the way the room itself changes the way the speaker cones can move), and that affects the entire response of the room. Small rooms are really, really tough, and need tons of treatment.
Your room looks good, but close to the edge. You have a bit more than 35m2 to play with, but that's your OUTER-leaf dimensions: you still need to build the INNER-leaf, and that's what those dimensions are about: The hard, rigid, massive internal surfaces of the inner-leaf room. The walls and air gap take up quite a bit of space.
So your next priority is to lose as little floor area as possible, ideally keeping it well above 20m2, but also taking into account that you WILL lose at lot of area due to the need to isolate, and you WILL need to reduce the room width to fix the modal issues.... so this is where you need to learn how to juggle! You have to keep a lot of balls in the air as you fiddle and twiddle and tweak, to maximize both space and modal response and isolation and building materials and budget and internal acoustics...
The floor is a proper concrete slab which has been tiled.
Excellent! Your floor is done already! Nothing more to do there.
The ceiling downstairs is currently 12mm plasterboard screwed onto 8x2 joists.
The drywall (plasterboard) will come off, of course, but seeing as you are on a tight budget, take it off carefully and save it: you can re-use it later, for adding mass to places where it will be needed.
Two annoying windows - at least one will be removed and the void filled with concrete blocks.
It is possible to keep windows, if you like them, and if they are in places that won't interfere with treatment. But if you don't want them, then by all means get rid of them! And bricking up the gap is a great solution. Use the same materials and techniques as for the rest of the wall, if possible, such that your surface density remains consistent across the entire wall. Isolation is only as good as the weakest part, so keeping mass consistent and constant around the entire "leaf" is important.
Double wooden garage doors, which will be fixed in place and a new concrete block wall built inside.
Yup!
Smart move
The upstairs is an eaves room 5.97m x 3.68m x 2.24m (highest), with a dormer window, which I am considering as vocal booth/acoustic guitar/amp room (and I’m guessing that’s where the problems continue!).
Yup! For sure! Big-time...
The floor is 18mm chip-board, with underlay and carpet
The underlay and carpet can go: no use to anyone. The 18mm chipboard is a pretty lousy base for your upper rooms, and you will DEFINITELY need to beef that up with substantial extra mass. However, you are going to need to hire a structural engineer for this part, since you need to know how much extra mass you can add to those skinny 2x8 joists that are going to be supporting your upper-rooms. Those joists are not very big, and they are spanning at nearly 6m, so there's not a lot of live load or dead load available here. Those things need to support not just the floor, people, gear, and equipment, but also your entire inner-leaf rooms! That's a lot of mass to shove on top of a few 2x8s. I have a feeling you'll need to beef those up as well: maybe sistering each one with a second 2x8 right next to it, screwed and glued, or bolted, would likely do the trick. But you'll need a structural engineer to tell you if that is acceptable under your local building code, and how to do it, and what the final load-carrying capacity will be.
The walls and ceiling are all 12mm plasterboard, insulated, but with what, I have no clue.
You'll find out when you take off the drywall, which you WILL need to do, in order to create the isolation system that will give you the isolation you need for the use you are planning...
Without testing, it looks like it might just need some careful extending into the inner room. I have an electrician coming to look at that.
Unfortunately, that isn't really an option. The reason, once again, is simple: You cannot allow multiple large holes in your isolation system. Each hole is a major weak point. Yeah, you COULD try to build massive boxes around each hole, and seal them all air tight, and hope for the best... but that's a lot of complication, expense, and potential points of failure in the future. The general rule in studios is that you can allow just one very small penetration through the wall, to bring in your electrical power feed, and then distribute it internally, inside the room, using surface-mount electrical systems. A lot simpler, a lot more flexible, and only one single weak point. That single penetration needs to be handled in a specific manner too, in order to minimize the potential loss of isolation.
I am very fortunate to have a good friend that is a carpenter who has extensive experience over 15 years of building studios and mastering rooms, who is going to do the build with me.
Excellent! Then you have a major positive on your side. Finding someone with studio experience is indeed very good news. He's already aware of all the unusual techniques and tricks that he needs to know, in order to do this right. I'm just hoping that he's the guy that worked on the GOOD studios you mentioned, not the BAD ones!
I have 2 other quite major issues that will make you laugh – budget and timing.
Welcome! You finally made it! You are now a confirmed member of the Insane Studio Builders Guild! And this forum is the international convention center, where all of your fellow Guild Members meet...
You have passed the final test for admission... not enough money, and not time. (secret decoder ring and handshake instructions coming soon...)
Seriously, those are very, very common issues with home studio building. There's a solution for one of them, but not for the other....
There will be more budget available in the future to make adjustments and improvements, but for now, I need to get something up and running for around £10-15k.
That's the one that DOES have a solution! 15k will get you started, and likely advanced enough that you can use the space to do some initial mixing, while you save up more budget and carry on working on the rest of the place. It's the best solution. So you build in stages, as funds become available. That's the solution. However, it still does require that you design the complete studio in advance, in full detail, before you start building anything. You can't design bits and pieces as you go: take that as first-hand truth from a studio designer. This does not work. When I'm designing a studio for one of my customers, I very often get to a point where I need to go back and change a whole bunch of things because of something that just came up that I hadn't seen before. And you can't do that if the studio is already built! Tearing down parts of your newly completed studio to make modifications that you didn't foresee, is a rather sad situation. Changing stuff on paper or in the computer model is relatively easy, and costs you nothing in materials or contractors... so it's far better to work through the entire design for the complete studio, both upstairs and downstairs, double checking every aspect. before you ever by a single 2x4 or raise your hammer for the first time.
And, just to add a bit of extra stress, I need to try my absolute hardest to get it done in the next 2 months or so.
This is the one that "has no solution". Sorry. It just doesn't. There is no way, at all, zero, zilch, none, that you would even be ready to
start building in two months from now! Even if you were already an experienced studio designer, and already knew exactly what you wanted, it would take you longer than 2 months to just design the place. I'm sure you don't want to hear this, but it's the full, ugly truth. The very fastest I have ever managed to design a complete studio in detail, is about 6 weeks. And that was a simpler studio than yours: just one single room. There's a huge amount of effort that goes into a studio design. Yes, an experienced studio designer could possibly take an existing design and adapt it to fit your building inside a couple of weeks, but it would not be optimized, and it would not be YOUR studio, specifically designed for YOUR needs, on YOUR budget.
So I'd urge you to rethink this, and allow yourself about a year to have the place finished. That's realistic. That's from personal experience.
Let's look at this objectively: You have doubts about how to approach the basic build, in terms of isolation, construction materials, acoustics, and layout. You did not even mention HVAC; which is a large part of studio design. Yes you absolutely do need it: remember that I mentioned "hermetic seals"? Well, with your double air-tight full perimeter hermetic seals, guess what cannot get in and out? Yup: air. In a typical house, office, school, shop, church, etc. there are numerous tiny air leaks all over the place, and air has no problem getting in and out (hence the poor isolation). But in a studio, there are no such air leaks. Thus, no air. And since I'm sure that you are rather partial to breathing, and would really not like to stop doing that, then it's clear that you need HVAC. It's not a luxury in a studio: it's basic life-support. Yet, you didn't mention it much. But HVAC design for studios is a huge thing. I often spend more time designing the HVAC system for a studio, than I do on designing the studio itself.
So you need to know all about acoustic isolation, acoustic treatment, HVAC, structures, materials, techniques, design, etc. You recognize that you don't know a lot about those, so you'll need to learn. You already have Rod's book, which is great, but you will also need another book: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics). You'll need to study that until you understand all of the principles, then you'll need to study Rod's book again, carefully, to see how the theory you learned in MHoA is actually applied in real studio design. That alone will take you about two or three months, just to learn the stuff well enough that you can apply it. Then you need to learn the software that you'll use to design your place: SketchUp is what most people on the forum use, and I saw you already made a start with that. It's really powerful, but it takes a bit of learning. Call that another month or so until you really get the hang of it, practicing a few hours every day. Then at least two months to actually design your studio, probably more like three or four, as you work through the issues, try out different approaches, scrap things, start over, and gradually put the bits and pieces together in the way that makes the most sense.
... including the HVAC system! ... which means you'll need to learn all about latent heat loads and sensible heat loads and climate in your area, and static pressure, and silencer boxes, and insertion loss, and flow rates, and flow volumes, and noise levels, and many other things. Once you have mastered those, then you can design your HVAC system: it will need to move the correct amount of air (volume per unit time, or flow rate) at the correct speed (distance per unit time, or flow velocity) for your room, while removing the correct amount of heat and humidity (they go together) in the form of latent heat and sensible heat, while also bringing in the correct amount of oxygen (fresh air) from the outside world, and simultaneous dumping the correct amount of CO2 and other stale gasses that you don't want (exhaust air), and doing all of that for varying conditions of occupancy (number of people, amount of gear, instruments, etc.) and for various climate conditions. It has to be able to handle a full load of frantically jamming musicians on the hottest, most humid day in mid-summer, with mountains of gear and lights turned on, steaming pizza, hot coffee, etc, and it also has to be able to handle the the minimal load, of just you sitting quietly, alone in the dim dark in mid winter as you contemplate your next move. And it has to do all THAT while not letting any sound escape from your thumping, booming, screaming sessions... That's NOT an easy task! So you'll be doing quite a bit of research on HVAC...
So you have about four to eight months just learning and designing. Realistically. Objectively. That's what it takes. Then another four to eight of actually building, and likely more if it will just be the two of you doing all the work. Some of my customers do build their studios themselves or with a helper, and it seems to take them about a year, on average, from the moment they pick up the first stud and nail, until they sit down to actually do the first session in the finished studio, for studios such as yours.
Only then, once your design is completely finished in every detail, and double-checked, only then will you be able to go out and buy materials and tools, and start actually building the place.
Sorry to rain on your parade and enthusiasm, but rushing to build a studio is
always doomed to failure. It does not work. If you look over the forum, you'll find a few threads where people tried that. Not a single one of them succeeded. Not even one.
In terms of what sort of level I mix at, I have no idea - I have ordered a meter and that information will follow on, but as a quick rule of thumb, I use Genelec 1031As and have always considered that their “overload” light is there to tell you when it sounds just about loud enough
Well, according to the manual, a pair of those can put out 120 dB peak for short periods without frying themselves, but more like 110 dB each in typical half-space applications, or 101 dB when limited by driver protection circuitry. So two of those driven to limiting would be putting out around 105 dB RMS, and maybe 120 dB peak. However, you'll need to get your meter out (set it to "C" and "Slow") to actually check real levels on YOUR system playing YOUR music.
But let's call it 110 dB inside the control room, to be safe. (That's actually illegal and unsafe for a workplace, but getting deaf is your own choice if this is a hobby studio, so I'll leave it at that.) Now, to determine how much isolation you need, you'll have to check your local municipal noise regulations. They will specify what the maximum level can be OUTSIDE your studio, and they will also specify where that level must be measured, and how to measure it. Let's assume it's a typical residential regulation, and specifies 40 dB at night (I'm assuming you want to use your place at night). The math is simple: you need to create isolation that will reduce 110 dB inside to 40 dB outside. So you need 70 dB of isolation. You might also have the benefit of distance: sound attenuates over long distances, so you might have a few dB advantage if your garage is quite a way form your property line. Or you might not.
So that's the figure you are aiming for: 70 dB of isolation. That's HUGE! That's a MAJOR task. Not impossible, but that's pretty much the limit that you can expect for any home studio build, even with a large budget. It is possible to go higher, but you'd need to add a couple of zeros to the budget.
Here's some perspective: A typical house wall provides around 30 dB of isolation. The decibel scale is logarithmic, not linear, meaning that it gets harder and harder to get one extra dB, the further you go up. So going from 30 dB to 31 dB is a piece of cake, but going from 100 dB to 101 dB of isolation is hundreds of thousand of dollars, and huge amounts of mass.
In fact, every time you go up by 10 dB, you need to block ten times more energy. So a wall designed to provide 40 dB of transmission loss (isolation) needs to block ten times more energy than the standard house wall that only does 30. And a wall that blocks 50 dB needs to block one hundred times more energy than the house wall (10x10). And the wall that has to provide 60 dB of isolation must block 10x10x10 = one thousand times more energy than the house wall. And your wall that needs to produce 70 dB of isolation, must block 10x10x10x10 = TEN THOUSAND times more acoustic energy than the standard house wall....
Perspective.
Your isolation system has to be impeccably well designed, and impeccably well built and you need a large budget to do that. Not impossible... just not very easy, and not very cheap.
So, your solution here is to either turn the volume down, or go with less isolation and hope the neighbors don't call the cops on you too often. As a point of reference, most engineers mix at around 85 dBC, since they consider that to be comfortable, good for producing mixes that translate well, and good for long sessions without causing ear fatigue. And that also turns out to be level that studios and cinemas are calibrated for... and is also the maximum permitted legal level for workplace exposure, for normal 8-hour shifts.
Just sayin'!
People always tell me its very loud!
Those people are right! Very right.
I am probably going to incorporate some sort of switchable sub into the room as well, to run with the Genelecs for a bit of extra BS factor during overdubs.
Ummmm.... OK.... so adding a sub to the situation makes it even more complex: low frequencies are the hardest to isolate, and travel long distances in open air very well... So you will need even more isolation....
I realize the dimensions I have are by no means ideal, but they are what they are, so I have to somehow deal with it –
But you CAN change the actual dimensions of your final inner-leaf room! It IS a choice you can make, to optimize the acoustics. Room modes... room ratios... Even just designing your side walls conventionally and your front and back walls inside-out would make a difference in the ratio, moving it off-square. Maybe not enough (I didn't do the math), but at least something. Or you could like into the theory of control room design, and come up with a set of dimensions that absolute optimizes and maximizes your acoustic response, to get it as close to neutral as physically possible...
especially the lack of ceiling height.
I already mentioned this, but I'll repeat it: do your ceiling inside-out. You get to maximize acoustic height (which is what really matters), improve low frequency diffusion, eliminate flutter echo in the vertical plane, and get several other advantages.
For simplicity and budget's sake, I am just considering the downstairs room for the moment.
As I mentioned above, you can start the CONSTRUCTION of the control room downstairs first, but the DESIGN needs to be complete for the entire studio before you can do that.
a) Wall Construction – from outside to in, what is the best possible combination for me to use?
That would be the one that provides the amount of isolation that you need (dB TL, or decibels of transmission loss), for the cost that you can afford, using the materials to which you have access, and the techniques and tools that are available to you. Since we don't know that "amount of isolation that you need" is, it's also hard to say what the best way to build your wall is.
Existing Concrete Block
Gap - what size?
50mm insulation
2 layers 16mm plasterboard -
Yes. So far so good, except that the entire air gap needs to be completely filled with insulation to maximize absorption of cavity resonances, thus improving your isolation greatly at low cost.
would a 3rd layer of 12mm or 18mm mdf sandwiched in the middle improve this much?
Depends on what you mean by "in the middle": if you mean "in the middle of the air gap", then no, it would not help, but if you mean "between the two layers of 16mm drywall", then yes, that would help. Not because it is MDF, but simply because it is mass. Sound waves can't read price tags, so they have no interest in how much you pay for your mass. You can use really expensive mass, or really cheap mass, but all they care about is the actual mass itself. The only advantage to you is the
thickness of the mass: high density (expensive) materials take up less space. If you use low-density material (cheaper) you need to make it much thicker to get to the same amount of mass. So instead of 32mm of drywall (two layers of 16mm) you could use just 2mm of lead sheeting, for example, and still have the same mass, or you could use 500 mm thickness of solid cardboard, or 60 mm of balsa wood, or 4mm steel plate. But apart from the cost, there's the practicability of making your walls from lead sheet, cardboard, or steel plate....
So the point is not the material itself: it's the mass that matters. Or rather the surface density. The higher the surface density, the lower your MSM resonant frequency, and therefore the better your isolation in the low end of the spectrum, which automatically implies better isolation across the rest of the spectrum. So your objective is to find the material that gives you the most mass for the least cost.
However, you do need to do the math here: you need to calculate the amount of mass you'll need on your inner leaf, and the size of the air gap, by using the equations for MSM resonance, coincidence, mass law, etc.
Stud (suggested size was 75mm x 35mm, but if I use 100mm, is that a problem?)
75mm x 35mm is pretty close to standard 2x4 lumber (89x38), which is commonly used for studio design, and commply spaced 400mm OC or 600 mm OC in some cases. You can go up to a larger size if you need to, but why? It's more expensive, takes up more space, harder to work with, and doesn't provide any real benefit.
Insulation between studs 100mm
Treatment and finish.
You seem to be missing the point of John's inside-out wall design: the insulation in the stud bays
IS the treatment. Or rather, it's the basis of the treatment. It might remain just like that, with nothing else (except for a fabric finish), or it might have wood slats over it, to form a slot wall (if sealed and tuned) or a partially reflective, partially absorptive surface (not not sealed and therefore not tuned), or it might have even more insulation over it (bass trap), or it might have something else. Each part of each wall will be designed to deal with the specific acoustic situation that affects that specific location in the room. John's inside-out walls are not just a general "one size fits all" solution. They are merely the basis if the entire acoustic treatment plan for the room, as a whole.
Does that work? Or am I throwing more materials at the problem than is necessary, for not much real gain?
The basic approach is fine, except that I'd swap your 100mm studs for standard 2x4's (whatever they happen to measure where you live), and then add treatment as needed for each part of each wall. And I'd also do all the math to make sure the isolation is sufficient for what I want, at the frequencies where I want it.
The other option is a staggered double stud with 3 sheets on the outside of each stud and insulation between.
Does this constitute a triple leaf wall with the concrete block?
Yes, most definitely. It also constitutes higher cost, more materials, slower progress, and less isolation.
Or does the concrete block not count as a leaf if it is standing on its own? I have searched, but I could not quite untangle that information.
Yes. The concrete block leaf counts as a leaf, due to the definition of a leaf: A leaf is just a massive, hard, solid surface that happens to be located close to (and roughly parallel to) another such massive, hard, sold surface, with a gap in between them that happens to be filled with air. What REALLY defines a leaf is that there's air next to it, followed by another leaf. It's the air that creates the resonant system between them. The air is the spring. It's the "S" in the MSM equations. It does not matter how the leaf (the "M") on either side of the spring is supported: that's irrelevant (mostly). The leaf could be self-standing, or supported on studs, or hung from sky-hooks, or held in place by magical incantations! The only thing that matters is that there's an air gap, then another leaf. That makes an MSM system. If there is yet another air gap beyond that, followed by yet another leaf, then it's an MSMSM system (3-leaf system), which means that you need different equations to figure it out, but the leaf is still a leaf simply because it has an air gap, then another leaf.
b) My builder is suggesting that instead of building a concrete block wall across the garage doors, we fix sheets of 18mm ply to both sides of a 4x2 stud frame and fill it with kiln dried sand.
You COULD do that, yes, but how would you ensure that the enormous weight of the sand will not pop the nails eventually, and allow the sand to leak out? And why would you do that, when concrete block construction is relatively simple and inexpensive? And what lab would you test that construction in, to make sure it does work the way you hope it will work? Or do you already have lab test reports that show how such a system performs when tested under controlled conditions in a reputable acoustic test laboratory, and you are certain that you can build yours the exact same way they did?
I am in the process of working out the mass figures, but there might be something in the theory that the additional mass might be a good starting point for the back of the room. Any thoughts on this?
Where did you figure the additional mass would come from? A concrete block wall 237 mm thick, rendered both sides, will have a surface density of around 350 kg/m2 (assuming the normal densities for such materials). But let's assume that your materials are not quite like that and only work out to 250 kg/m2, just to be safe. The density of your sand-filled wall would be about 143 + 8.2 + 8.2 = 160 kg/m2 aprox. . That seems to be about 36% LESS mass, not more mass. Or am I missing something?
I'm also not sure what you mean by "the theory that the additional mass might be a good starting point for the back of the room". Do you have a link to that theory? Where does it come from? I have not heard of it before. Do you mean "good starting point" for isolation? or "good starting point" for treatment? Those are two different things.
2 sheets of 16mm plasterboard and probably another layer of 15mm ply on the floor above.
Have you done the math? Did you have a structural engineer check that? You would be putting an additional dead load of 35 kg/m2 on those joists. That's over one thousand two hundred kilograms of extra weight, in addition to what is already there, and we have not even looked at your inner-leaf walls for that room, nor the live load (people, gear, instruments, furniture, etc) That seems like a hell of a load for 2x8 joists. My span tables are showing that you'd need at least 2x10s for that load at that span, and likely 2x12's... and that's not even considering the weight of the inner leaf.
It would be far, far better to support your new inner-leaf ceiling on your new inner-leaf walls, and to do it "inside-out", for the reasons I outlined above.
Especially considering that you will need to add considerable mass to that floor above you anyway, just to get the 70 dB isolation that you need for the control room.
Is this going to provide enough isolation?
No.
it feels a little like the weak point of the build
That's because it is!
but I am hamstrung by the ceiling height.
Only if you do it wrong. If you do it right, there are options open to you. It can be done, just not in the way you were imagining.
d) Floor.
It's already finished. Nothing more to do here.
do I actually need to build a stud floor on top?
No. Here's why:
http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173 . That's the plain truth. Trying to add a floor over your slab would be silly, as it would make matters worse in every sense, cost you a lot of money, and produce no benefit, in addition to eating up precious room height.
Or can I use some sort of dpm, acoustic underlay and go straight to a layer of ply and a combination of laminate and carpet tiles or similar?
The floor is already finished. You can't beat a solid concrete floor for a studio. There's nothing better under the sun. Just what the doctor ordered. The tiles are fine too. If you wanted to gain a few extra mm of height, you could take those off (lots of work), or you could just leave them where they are. No problem, acoustically.
If they are in a bad state, or ugly, or you just don't like them, them lay laminate flooring over them (on ordinary underlay), and that's it. However, anything you do to your floor is going to cost money, and you are on a very tight budget, so I'd recommend doing nothing, and save that money for the rest of the build.
Oh yeah, I forgot the HVAC haha… It’s England, it’s always cold and raining right? I guess I need to look into this…
Ahh! I missed that on the first read! So you DID mention HVAC!
The answer is "yes"... you will need to look into it... in fact, quite a bit more than just "look into it"!
Design will follow in a week or so.
I'm looking forward to seeing that, but I have a feeling you are being just a tad optimistic in estimating that you can have a complete studio design done in a week...
- Stuart -
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