but later realized that my isolation requirements are modest - that is, I can allow some bass to escape -
OK, but did you put a NUMBER to that?
The key to designing the isolation system for a studio is to first know how much isolation you need, in decibels of Transmission Loss (TL), then also to define what frequencies you need it to work down to. With those two in hand, you can then look over the piles of lab tested wall systems, and find one that will give you that isolation, and also meets your budget, and also involves materials you can get where you live. You can plug in numbers like "50 dB TL" and "lowest isolation frequency 48 Hz" to the equations, but you can't plug in "modest" and "let some bass escape"....
Acoustic design is mostly science, some art, and the science part is based on numbers, equations, and suchlike.
Here's a great document about a huge number of possible wall types, and how each of them works in reality (laboratory conditions), with full details about constriction, isolation, TL curves, STC, frequency response, etc:
http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir761.pdf
Well worth looking over. Very useful, and not at all complicated to understand, since you can easily compare the graphs for each type of wall. (They also have similar studies on floors and other things, if you are interested).
recommends a massive, reflective front wall, but later in the book, while discussing surround control rooms, he adds that those front walls should be made diffusive
Yup. Like I said: somewhat of a contradiction! Walls like that, with only small variations in surface irregularity, will only be diffusive at high frequencies, and specular across the rest of the spectrum, down to whatever the MSM resonant frequency of the wall is, at which point they become transparent to sound. It's muddled concepts like this that sort of turn me off to the way he writes.
That type of wall is basically a 2D Schroeder diffuser, but totally random, with no actual numeric sequence (which makes it better in some aspects). However, it is still governed by the same basic laws of physics, so it is a tuned diffuser whose lowest cutoff frequency is defined by the maximum depth of the "wells" (low points in the wall), and the highest frequency is defined by the width of the smallest wells. According to QRD theory, the lowest cutoff wavelength is given by deepest well / 1.5, and the highest cutoff wavelength is given by smallest well width / 0.137 (according to Schroeder). However, since it is truly random, that will only give an approximation of the range, and the coverage will not be as even as for a true QRD. But that's something that you don't see explained in the book! It might help if you look at the works of D'Antonio and Cox. They have done large amounts of research on diffusers, and their papers are very well regarded. The BBC also has a very useful paper on this, which is RC-1990/15 if you are interested.
But getting back to the basic concept of covering entire walls with diffusion, here is what Cox has to say about it in one of his papers: "So why not just cover the whole auditoria with diffusing surfaces? Ignoring what the architect might think of the concept and cost, all one can currently conclude is that there is very little data to say what the effect of including large scale diffusion on the acoustic generated is. There is a fear among some that this would remove spatial cues that are present in early reflections, leading to an imprecise sound, but no one has measured such effects." He then goes on to cite papers by researchers such as Hann and Fricke; Chiles, Torres and others to support his statement.
But then it gets more interesting: he points out that Schroeder diffusers, by nature, are also absorbers! And then adds that the absorption if such diffusers actually turns out to be greater than predicted by theory (then he proposes solutions to that).
In other words, a stone wall like that is a tuned diffuser, with a mathematically defined range of diffusion that is hard to predict, and it is also an absorber at some frequencies, that are also hard to predict. And he ends his paper with a fascinating comment: "Over the last century, the design of rooms has moved from mostly following precedence, to a system by which scientific and engineering principles can be used to maximise the chance of building acoustically-successful spaces." How true! It would be nice if all architects and acousticians were to recognize that...
Anyway, sorry for the rant!
Now, from what little I know of diffusors, the ridge depth on those walls isn't going to affect low or mid frequencies, but I followed this on faith (and, admittedly, because it looks freakin' great).
Sure it looks great! But actually, it will affect frequencies in the mid range: higher frequencies will be diffused, mids will be scattered with lobing, and lows affected very little. Scattering takes place down to at least one octave below the lower cutoff frequency. And diffusion stops at the higher cutoff frequency: beyond that, it is just a an absorber...
And all of the above leads to the question: Is that diffuser wall tuned to the correct frequency range for YOUR room? Does it diffuse the ones that NEED diffusion? Or does it miss those and instead diffuse the ones that DON'T need it? Every room is different. There's no such thing as a "one size fits all" solution in acoustics...
Fortunately, my stone guy set me straight and put me onto stone veneers.
Yes, but that's only part of the story. Stone veneer is still stone, and still darn heavy. Pick up an armload of those stone pieces, and see how heavy. Then project that weight to the entire wall.... But apart from that is the weight of the entire room: There's a huge amount of framing, multiple layers of thick drywall, mountains of insulation, etc. Your stone guy has the right idea, and is warning you for a reason, but you still need a structural engineer! Your floor joists in you house were designed for the typical live and dead loads of a normal house. That does NOT include the many tons of mass that you need to pile on top in order to make it into a studio. And your inspector will NOT sign off on the build unless you have the documents from a qualified structural engineer, saying that the structure is safe and meets code. So you still need one, and you need him now! You might be fine, but you might not. And apart from being legal, there's the even bigger issue of being safe: it would be rather sad to have a beautiful stone wall at the front of the room, and incredible acoustics inside, if it all collapses into the basement the first time you sit down to use it....
Depth varies from 1/2" to 1 1/2":
Great! Then you can calculate the lowest frequency
Newell's drawings show cotton waste felt applied this way. Rod Gervais' book shows walls being built on top of rubber "ND isolators." Jeff Cooper's book (ca. 1984) shows 1/2" inch "sponge rubber" applied this way. ... "
Yup, but NONE of those are MLV! MLV is limp mass, not resilient. It is also not very strong, and falls apart quite easily if you bend it, stretch it, or load it ... It is not meant to be a structural element, and has no useful structural properties. It might look like rubber, but there's nothing at all rubber about it! As Rod (and others) correctly state, you can isolate or float a wall or floor in resilient mounts, provided that you use the correct materials to do so, and that you also do all the calculations to ensure that the structure really is floating. In order to float, the resilient mount must be deflected (compressed) to the correct degree to ensure maximum resilience. For the types of rubber used in acoustics, that is generally somewhere in the range 15% to 25% (depending on the type of rubber). If you do not compress it to this range, then it doesn't float and you wasted a lot of time and money. If you overload it beyond the correct deflection, then it "bottoms out" and does not float. If you don't lead it enough to get deflection, then it "tops out" and does not float. Only at the point where it is loaded within the manufacture specified range for resilience, only then does it float.
Here's a thread that explains all about floating floor and walls:
http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173
And here's one of the best research papers on how it works:
http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir802.pdf
I was confused by this when it came time to nail the walls down. Surely, if there's any benefit to MLV under your wall (or floating, in general), it's pretty much shot when you drive nails through it
Exactly!
Nailing down a floating structure immediately causes it to not float! The correct way to do that is with isolated bolts, where the bolts have rubber collars and rubber washers, and you torque them correctly to get the right mount of deflection...
Like this:
Isosil-anchor-bolt-decoupling-isolation-collar-and-pad.jpg
In general, the types of rubber you need for studios are Neoprene, EPDM and Sorbothane. Each has its uses, and there are different types of each as well, with different characteristics, so you have to be careful to select the right one for each job, then do the calculations to ensure that you are loading it correctly.
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"screw it - the MLV might do no good, but it's there now and can't hurt."
I'm not so sure that it can't hurt: I would check that with your inspector, or even better with your structural engineer. You are using materials for a purpose for which they were never designed. Whether or not that is safe can only be determined by an expert. I have no idea if there has ever been any research done on how MLV reacts to heavy compressive loads over time.
I suppose the alternative would be to not nail, truly floating the walls, and yes, I can't imagine that being acceptable, even for a non-structural inner wall. And we're in earthquake territory, so I'm not messin' with it.
Exactly! You got that right. Some people do, in fact, try to "float" their walls without attaching them to the building structure at all!
They don't like it when we tell them how bad that is. But you get, fortunately. Structures can only be floated in the correct manner, with properly designed and calculated isolation mounts, and also with sway braces, seismic snubbers, and other safeguards to keep things happy.
Check my profile to see where I live, and you'll see why I share your great concern about earthquakes. Of the "top ten" biggest ever earthquakes in recorded history, three hit my country. One of them just a few years back. I can tell you, 8.8 Richter is not a fun place to be.... but luckily, everything that I built stayed up and suffered no damage. However, I wouldn't want to go through that again!
there's nothing under the deck but 12" joists (and braces). Thankfully, the room below is a vacant (usually) guest room. The ceiling isn't isolated at all. I suppose I could've introduced resilient channels - I did have most of the ceiling down at one point - but it seemed unnecessary.
OK; but isolating a studio is like building a fish tank. I often use this analogy to explain how isolation works, since sound is like water in some aspects. If you want to build an aquarium, you get a metal frame and put glass in it, right? But what if you were to decide: "Well, I'll only be looking at the fish from the front, so I'll save money and use cardboard on the back and sides, since they don't matter". How well do you think that tank will hold water?
Obviously, the water will get out through the weaker sides, and the "strong" side (the glass) is basically pointless. Even if you put glass on all four sides, and even a glass lid, if you make the bottom of the tank out of carpet, then it still won't hold water. Water just takes the simple way out, following the easiest path. And once it is out, the it is out, splashing around all over. The same with your room: sound takes the easiest path out. It doesn't matter how great your front wall is, if sound can get out through the other walls and the floor and the ceiling, then you have no isolation. You cannot isolate a room in only one or some directions, since sound does not move in straight lines: it expands outwards as a sphere from every source, so if it gets out through our floor, it expands outwards as a sphere from there, and encompasses the rest of the house, just like water pouring out the bottom of the fish tank.
In other words, isolation is an "all or nothing" proposition. If you don't do all of the room, then you might as well do nothing, because the final outcome is similar, especially for low frequencies.
I was thinking I might get away with a removable plug, alone.
I think you missed the point: you already have two leaves, with two doors. Why would you add a THIRD leaf (the plug), when that will REDUCE your low frequency isolation?
I wanted permanent-install, flush-mounted speakers, but the best I could afford didn't offer this. I see what you mean. I'll have to come up with a way to secure them rigidly. Hammer some shims in there?
Actually, the "totally rigid" method is the most expensive, and the hardest, since it requires a lot of very heavy, massive, rigid materials, and careful workmanship. Resilient mount makes it a bit easier, and is cheaper: only the front baffle needs to be rigid and massive in this case.
I thought it would help prevent the speakers from vibrating the wall.
No, because MLV is not resilient. It isn't rubber. It is limp mass (and very expensive mass, at that!), but it isn't particularly resilient, and I'm not aware of any studies that have been done on its resilient characteristics, nor how one would go about loading it to produce the correct deflection.
Ugh. This is a problem.
Yep. It can be done, and in fact I just completed a design for a customer where his only possible rack space and storage space was in the center section between the soffits. But there is a pair of massive, heavy doors over that, a silencer box built into the bottom section, under the "closet", which draws cooling air in from the side soffits, and another silencer box at the top, over the closet, with silent fans in it (speed controlled), that exhausts air out through the top, behind the front upper bass traps, just below the HVAC return vents. So it can be done, but it's a challenge, both to design and to build. And of course the fans have to be chosen correctly to produce the right amount of air flow at the right speed to keep the equipment cool, and the silencer boxes have to be dimensioned correctly for that specific air flow and for the correct insertion loss and static pressure... Possible to do, but complex.
I love that idea. Unfortunately, the walls are already up....
Which walls are up, and which aren't? It might still be possible to do something, with treatment, or with minor mods to the walls. And especially of your inspector tells you to take out the MLV...
Once I drywall the inner wall, I have to run tests and consider construction and placement of absorbers in the control room. For a clean look, I had hoped to have floor-to-ceiling absorbers, as you described with your inside-out-walls. I'm not sure how that will be done. Will they be attached to the inner wall? Hung from the ceiling? Etc.
There are several ways of doing that. Once common method here is to build the inner-leaf wall "inside out", meaning that the drywall faces the cavity inside the wall, and the studs face the room. That leaves the stud bays available for treatment, which is commonly just to fill them with 703, and also add tuned slot resonators on some surfaces, as needed. The places where there are no slots can simply be covered with acoustic fabric stretched out neatly. If you want a really professional looking finish, there are commercial systems you can buy that clamp the fabric invisibly from behind, or you can use the more common method of stapling or tacking it in place then covering the staples with wood trim. Or stretch the wood over thin framing, stapled on the back, and held in place with velcro, magnets, hidden clips, or just simply pressure fit. This inside-out system is great for many reasons, including space savings, since most of the treatment goes in the stud bays.
However, if your inner leaf studs are already up, then the "inside out" method is not really an option, as you don't have access to be able to nail the drywall to them from the cavity side. So unless you decide to take the framing down and re-do it, you have no choice: you can't do inside out. In that case, the normal method is to make a series of treatment panels and hang them on French cleats attached to the walls. Most of those panels will be absorptive, but some might be diffusive (if the room is large enough to allow that, and if the room needs it), and some might even be resonant devices, in which case they have to be located at the correct points in the room where they can act on the wave peaks.
But your basic approach is correct: after the inner-leaf is up, and before doing any treatment at all, test the room with REW and use that as the baseline firstly for deciding on how to go about treating it, then for comparison with later tests to check that each round of treatment is doing what it is supposed to do, before deciding on the next round.
To create a proper listening triangle in this sized room, I sorta had to squeeze things this way. I experimented with wider separation but the clarity wasn't as good. FWIW, these speakers are highly directional. The sweet spot is very narrow. Of course, those experiments were free-standing. I'm scared things may go bad when the walls are finished.
As with many things in studio design, there are theoretical optimums, and then there's reality. Reality normally dictates that you need to make compromises, and move away from the theoretical best of one "thing" in order to get out of the theoretical worst that it is causing for another "thing". That's where you are: If your head is in the worst possible modal location within the room, then you really should compromise something else that is "perfect" in order to solve that. It's no use having a perfect triangle if your entire perception of frequency response and time domain response is severely distorted! It is far better to have a "less than perfect" triangle in order to get your ears to a position where they can at least hear what the speakers are saying, without that being badly muddied by the room!
Most people have heard that the speakers and your head "must" be set up at the three vertices of a perfect equilateral triangle, but in reality there's a broad range of triangles that work darn well, even though they are not perfect equilaterals. That theoretical perfect triangles has angles of 60°, meaning that the two main speakers are "toed-in" 30° from the room center line, and therefore the acoustic axes meet at a perfect 60° angle just behind your head. But if you change that to get a 61° intercept, or a 62° intercept, then I absolutely guarantee that you will not hear the slightest difference. Nobody can. And if you think about it, even leaning back in your chair just a fraction already puts your ears at the 62° point. In fact, it turns out that you can vary the angles over a very large range, up to a massive 90° intercept angle, without causing too much harm to the psycho-acoustic perception that your brain has of the sound field. So you can angle your soffit faces much more if you need to, to solve two of the bog problems with your current design. You can get your head out of the dreaded "mid room modal null", and you can get your speakers more towards the center of the soffit front baffles, where they belong. Actually, they belong about about 2/5 the width of the baffle, roughly, not right in the center.
You can also go the other way, in rooms that need it: you can go to an intercept angle of less than 60°, down to maybe 45° before you start having sweet spot issues.
So don't be afraid to compromise something that you have perfect at present in order to fix something that is terrible!
The theoretical best point in a room (from the modal distortion point of view) is at 38% of the room depth (distance from front wall to back wall, inner-leaf face), but of course there's no point trying to hit that spot on either! Just get away from 50%, where you are now, to something more like 40%, give or take, and adjust the soffit face angles as necessary to aim them correctly, while also correcting the position of the speakers on the soffit faces.
That should belay your fears about "I'm scared things may go bad when the walls are finished." If you don't fix the room geometry by making the necessary compromises, then those fears may well be realized!
Yeah, I hear that a lot. Again, this is where it sounded best in early tests and, supposedly, a non-environment room sorta addresses this if the walls are 100% absorptive.
Well, not really, and your walls are certainly not 100% absorptive: Last time I checked, stone doesn't absorb sound very well...
But jokes aside, modes are a function of room, geometry, period. Modes exist at certain frequencies simply because the room has the dimensions that it does. You cannot make them "go away", and you cannot change them unless you change the dimensions of the room boundary. Treatment can damp the modes to a certain extent, yes, but it cannot eliminate them. You can still see their effect clearly on an acoustic plot of the room, and there is noting you can do to change that, not with any amount of treatment. They are there, and the highest peaks and lowest nulls always occur in the geometric center of the room, simply because of the laws of physics: that's the way standing waves behave in a room: all modes terminate in corners, and reach their maximum values in the middle. It's just a fact of life, due the way the universe works. There's nothing you can do about it. At best, treatment can damp the modes, that's all. Good room design cannot eliminate modes. The point of modal analysis in room design is to ensure that you have an even, smooth spread of modes in the low end, with none of them too close to its neighbor, and also none to far away. The math is easy to do, actually, and there are several know good ratios for rooms. I'm not sure which one yours is based on. But even so, even if you are using Sepmeyer 1, the modes are still there! They are simply arranged in the least offensive distribution across the
spectrum, but they still terminate in corners and peak in the middle. It's just the way sound works in rooms. That's what you never see the console set up in the middle of a room at live events: sound engineers know this, and always aim to have their location some place where they can hear the sound of the speakers in the room, not the sound of the modes.
So if that's the place where the room sounded best, then there's something seriously wrong with the rest of the room! And don't forget that all that will change once the speakers are properly mounted in their soffits, and the first round of treatment is in place.
I would seriously consider doing a proper predictive analysis of your room, and adjusting your listening position to the best theoretical location, while also compromising for the other factors involved.
That's what studio design is all about: finding the best compromise for all the myriad parameters. It is physically impossible to get them all perfect, since getting one perfect automatically means that others will be bad. So it's a matter of finding the best fit, where each of them as its least objectionable.
The short answer: isolation isn't as critical in my environment.
OK, but then why go to all the trouble of Newell isolation design? Why put all that mass in place if you don't need it?
The only thing separating my room from the attic space is indeed drywall (and fiberglass insulation). The roof employs a scissor-truss architecture, so what you see of the ceiling/roof in the drawings is all existing construction. I haven't designed or considered any ceiling treatments yet. Hanging ceiling? Floating cloud? Is my room-in-room design completely undermined without a de-coupled, hanging ceiling too?
Not totally, but you are missing the point of how true "room-in-a-room" design works: You have two shells, and each of them is a complete air-tight, hermetically sealed envelope. Your attic space is NOT hermetically sealed. It cannot be. It must be ventilated, so there are eave vents and ridge vents or gable vents, and therefore your outer-leaf is not sealed. Therefore sound escapes. That's the issue. You cannot use the attic as the cavity between your inner and outer leaf, simply because it is illegal and unsafe to seal it air-tight. That's the issue.
The bamboo TNG flooring rests on an MLV product that combines noise-absorption and a moisture barrier. The bamboo is not fastened to the floor, but glued together. As such, it "floats," in flooring parlance.
I know the parlance, but it leads to confusion in studio construction since that type of floor does not float at all, in the acoustic sense, or the seismic sense, or even the aesthetic sense! It's just marketing hype, "borrowed" by some creative guy in marketing at some point, and still used, even though it is highly misleading!
I have never seen any manufacturer that recommended that MLV should be used as the underlay for his floor! That's a first. Do you have a link to that? I'd like to add it to my list of "construction curiosities". And once again, I'm surprised to see anyone recommend MLV for a load-bearing application. It doesn't take well to loads. That's not what normal MLV is for. What brand and model of MLV do they recommend? I'd love to see the characteristics.
Uh, I separated the ceiling from the inner wall with more - wait for it - MLV. And then nailed through it.
Yup. Same issue as above. Basically, the MLV is not doing anything useful up there. It's not doing any harm either in that location, I would expect, since that isn't a load-bearing wall, but it's not helping either.
And you also confirmed my other suspicion: the inner-leaf wall is nailed to the lower joist of the ceiling trusses, which in turn rest on the outer-leaf wall, so you have a directly flanking path there, and compromised isolation.
Frankly, I'm sorta crushed right now. Your advice is awesome, but I've spent almost a year pulling my hair out on this, researching books, websites, etc., and though I know remodeling, this whole subject of acoustics has kicked my ass. It's the closest thing to a no-win scenario I've ever experienced. Every question leads to no answers, but three more questions.
Welcome to the world of studio design!
That's what it is all about. Compromise. You can NEVER get everything perfect, since the laws of physics (and most of all Murhpy's law) are against you. So don't get upset about that: you cannot achieve the impossible! No human can, not even with the biggest budget and best materials. But you can get a darn good compromise in most cases. And it seems that you are not too far advanced, so things can still be fixed, or at least improved. Yes, acoustics is a brain-mangling subject, since it doesn't actually work they way we intuitively imagine that it works. We can't see sound waves, and we can't see what they do when they interact with walls, floors, doors, ceilings, objects, treatment, people, and even air itself, so we tend to "invent", and build a mental picture of how we think they SHOULD act, based on how other things act. But it turns out that the mental picture is not correct: sound waves don't really work like that. It takes a while to "unlearn" those pre-conceived notions about sound, then another while to learn about how it actually works. But after a while, it gets to the point where is starts making sense again, and it turns out that intuition can be used again, to a certain extent, provided it us based on the correct underlying premises.
That said, I have to be honest too: the more I learn, the more I realize that there's a huge amount more to still be learned, and even the best researchers are still chasing after the illusive details. As Cox said n that same paper: "More research is needed" to understand diffusers fully.
So don't feel too crushed! It's a huge subject, overwhelming in some aspects, and your room is not that bad! And not so far advanced that it can't be fixed. If you look over some other threads on the forum, you'll find that you are certainly not alone. If it will make you feel any better, here is one such thread from a guy who was in a worse state than you, but ended up with a great room:
http://www.johnlsayers.com/phpBB2/viewt ... =drum+room
It's painful reading in some places, but the results speak for themselves. Please take a few minutes to read over that one, so you don't feel so bad in the end!
Also, please do post pictures of where you are right now, so we can see better what you are facing, and help you figure out what is worth fixing, and what isn't. Some things you might just have to live with, but I'm certain that other things can be changed and improved, so don't get depressed! The entire thing is about compromise anyway, so fixing things is just another compromise in the long chain. And the good things is that you found this forum, with its huge wealth of solid acoustic information, with research and references to back it all up, so you are in the right place now!
- Stuart -
Not sure what you mean by that: you just said that you have already built the inner-leaf, but now you say that you are not sure where it is going to go? How can that be?
Fixing in 3, 2, 1....
This is what I've priced, from Norstone, in southern CA. Depth varies from 1/2" to 1 1/2":
