John Sayers' Recording Studio Design Forum

Greetings!

I did a little searching around on the forum and could not find a lot of info on it, so forgive me if this topic has already been covered already.

This is my first post here, but I've been lurking for a while now picking up a lot of useful info. Basically I'm curious about a particular element in my ceiling construction. Right now I am building an Iso booth that's about 9.5 feet by 7.5 feet with an 8 foot high ceiling. Now, the actual ceiling of the booth will be on joists attached to the new studio walls that are double wall room within a room design on top of a floated floor, so they will not be in contact with the floor joists for the floor above in my basement space. So far I've done double drywall with green glue between on both sides of the double wall structure, and the floor under the floated part is concrete. Contained in the floor joists that are above the booth area is a lot of duct work, and on top of the joists is just osb plywood with red oak hardwood floors. If I want to add mass to this leaf, should I Insulate and cover the floor joists with 2 layers of 5/8 drywall with green glue between before I do my dropped ceiling for the booth, or am I just creating a 3rd leaf that won't help me reach my goal of keeping guitar amp isolation good? Thanks for any advice I can get!

~ Kiger

Hi Kiger, and welcome.

Why would the booth need a double-wall, if it is sitting inside your basement? You only need two leaves for isolation, not three. The walls of the basement are the outer leaf, so your booth only needs ONE wall to complete the system. with a double wall around your booth, you now have a 3-leaf system.

How did you manage to float the floor of an iso both? Whatever did you put in there to get enough mass to make it float? At 9.5 x 7.5 feet, there's nowhere near enough mass to float it, unless you used something extremely massive in the floor layers. Concrete? Steel? Lead? What did you use for the floor?

Also, if I understand correctly what you wrote, it seems that you put the walls on top of the floated floor? So the floor is not floated within the walls, separate from them, but rather you tried to float the entire booth? Sorry, but I don't understand the point of doing that in an iso booth...

So why did you need to float anything at all then? With a concrete slab on grade in a basement, there's no need to float at all, unless you have extreme isolation requirements from impact noise or something similar. Even then, a simple riser platform would have done the trick much cheaper, and with a lot less mass.

From what you say, that would create a 4th leaf, it seems (assuming you did your booth ceiling the same way you did the walls).

I'd say there are a lot of issues with what you have built, and it is not at all clear that it is going to do the job you hope it will. So let's start from the beginning: How much isolation do you need, in terms of decibels? You say that your goal is "keeping guitar amp isolation good", so this is basically an iso booth for a guitar cab, not for vocals, drums, or bass guitar. Heavy electric guitar can have energy across pretty much the entire spectrum, but at least it isn't as serious in the very low as bass or drums. However, it would still be good to know how loud your amp is when you normally play, in decibels, and how quiet you need that to be outside the booth, also in terms of decibels. That's the basis for determining how to build the booth.

There's one other point you didn't mention: HVAC. The booth is only for equipment, not people, so your HVAC requirements aren't as complicated, but you probably still need some cooling in there: What are your plans for that?


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks for the reply!

Nah, the walls are only double leaf, let me take you on a bit of a tour of what I'm working with with a few pictures.







Right now, if you look up when you're standing in the booth, you see the floor joists for the floor above me because they are exposed, as well as a great deal of duct work that feeds the rest of the house and insulation. One of those ducts will be for the iso booth as well as an air return line I will be running back out, so it'll be suitable for humans to be inside there for long periods of time. What I need to know though is, since none of the duct work is hanging below these floor joists, should I cover everything with 5/8's drywall before I build my dropped ceiling in the booth, resting atop the inner leaf? I cant imagine that the flooring and osb on the 2nd level above me are going to provide good insulation or nearly enough mass, and that also allows me to use acoustic calk to seal everything to the outer leaf and prevent some of the flanking.

I'm sure you don't want to hear this, but that floor is NOT floating, will not isolate like you are hoping, and is most likely illegal anyway, since it is not anchored to the slab/foundations.

You might want to read this:
viewtopic.php?f=2&t=8173

What is the load on each of those pucks, what type of rubber is it made from, how much is it deflecting, and what is the optimal deflection?

MSM isolation is a tuned system: the mass on one leaf does not provide the isolation directly, and neither does the mass on the other leaf, and nor is it the air gap or insulation that provides the isolation. It is the combination of all of them working together as a tuned system that creates the isolation. That's why you get so much more isolation from an MSM wall than you could ever get from a mass-law wall.

In other words, the floor above you by itself will not isolate much, and neither will your new ceiling. But together they will, if done correctly. The system needs to be tuned to a low enough frequency (1.414 times lower than the lowest tone you need to isolate), and they way you tune it is by having the right amount of mass on each leaf, and the right amount of air gap between them. So why you do your MSM calculations, you'll need to know the mass of the floor. You can calculate that from the type of materials and thickness of each one. So for example if you have 3/4" OSB as the subfloor, then that would be about about 11 kg/m2 surface density, plus that of whatever the actual flooring is.

If you add all that up and find that you don't have enough mass to get down to your target MSM frequency, then you need to add mass up there.

But anyway, to answer your question: If those HVAC ducts are hard-mounted to the joists or subfloor (ie, not hanging on acoustic isolation hangers), and if they don't have acoustic silencer boxes on each penetration of the outer leaf, then yes, you should seal them off inside their stud bays with plenty of mass. However, that does mean that you will then have sections of your booth ceiling that are three-leaf, instead of two leaf, and with reduced air gaps on both sides, so that will reduce your low frequency isolation. You will need to compensate for that.

You can only prevent flanking by decoupling. Sealing alone does not prevent flanking. It just closes off air gaps, to prevent sound penetration, but it does nothing at all to stop flanking.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Okay, that seems like what I needed to know then. Thanks for all the detailed info Stuart! It's my first time ever building a structure like this so i'm really glad that I have this forum as a resource.

The pucks are made of a EPDM rubber and i used them in the manner they were intended for according to the manufacturers instructions, and that was simply to place them 16" on center. However they are just like the uboats from auralex in that they have no lab testing to back them up, they are just a generic version of the auralex product. I understand that without running numbers floating the floor seems to be a crap shoot, but in this case I figured I would go for it because I cannot drill any anchor holes into the concrete below anyways per the requirements of my landlord who is allowing me to do this and the floor is not entirely flat and smooth either. I also want to do nailed down oak wood floors in my booth too, so I would be building up a platform no matter what to attach the wood flooring down since that stuff cant go straight on concrete. I might look at gluing that down if i can find a good adhesive for it.

Then you have a major problem! You cannot legally build ANYTHING in there, if I'm not wrong.

Brien can probably confirm this, but as far as I know, in the USA all walls must be firmly anchored to the floor, or suitably attached with proper approved resilient mounts. Yours aren't. It seems to me that your plans are not code compliant: the structure will be dangerous if not anchored. Where I live, there's no way that a structure like that will pass inspection, and even if it did, you would not catch me inside it, due to the danger.

Have you had your framing inspected yet? Did the inspector sign off n that, and clear you to proceed to the next stage?

Think of it this way: every time you open or close a door, you are creating major pressure changes around the rooms, as well as swinging large masses on long moment-arms, and also putting vibration into the structure. Bottom line: your entire room will move, each time you open and close doors... And if there is ever an earthquake where you live, even a small one, there's a major risk of disaster: If the are not bolted down, your room will move independently of the rest of the building, slamming into the walls and ceiling... It doesn't need much of an earthquake to accomplish that.

You really, really should get your building contractor or qualified structural engineer to take a look at your plans and tell you if it is even possible to do anything at all without anchoring. If you build an illegal structure ans something goes wring, your homeowner's insurance will NOT pay a single cent. And neither will the insurance of your landlord. You would be responsible for all damages, both to your own place, as well as to the rest of the building, and also to third parties. That's not a situation I would like to be in! Does your landlord know that he is exposing himself to huge liability by NOT allowing you to comply with code?

I would strongly suggest that you should stop what you are doing right now, and get qualified professionals to come, analyze what you have done, and give you a signed, written report stating if it is correct and legal. Maybe you are OK, but you need to have the proper documentation to prove it. And like I say, where I live, that would not be legal. The inspector would order you to tear it down and re-do it according to code.

Then U-boats with 2x4s is not the way to go either! You are putting much more load on some of those and much less on others, depending on the unevenness in the floor. Perhaps there is no load at all on many of those pucks, where there happens to be a dip right under them that leaves them barely touching the ground. And much greater loads on the ones next to them...

What you should do is to just put thick, soft rubber strips under your walls to create proper seals. Run them the full width and length of the sole plates, but not with the intention of floating them: you still need to anchor the walls through the rubber. The rubber is just there to improve the seal due to the uneven floor. The bolts compress the rubber and the sole plate correctly, to create the seal.

I'm trying to understand this: so you are saying that aesthetics takes priority over acoustics here, no matter what? If you have a thin, light-weight floor suspended over an air gap, then you have created a resonant cavity. Basically, you have a drum head: a membrane over a resonant cavity. It WILL vibrate and resonate in various different ways, at various different frequencies. And yes, what you are proposing does constitute "thin, lightweight floor", form the point of view of acoustics. There is nowhere near enough mass in that to get it to float.

So basically you have built your booth as a large resonant kick-drum, and you will be standing on top of that, or placing instruments on top of it, and expecting to record them cleanly, uncolored, and also expecting good isolation: sorry, but it simply is not going to work out that way.

I hate to be the bearer of bad tidings, but there are so many red flags waving with your build that it would be irresponsible not to point them out.

Seriously, get a qualified structural engineer in to look at what you have done, and either confirm in writing that you are OK to proceed, or tell you what you have to do to fix it. The few hundred dollars that you spend on his fee is a drop in the ocean compared to the liability you would be exposing yourself to if your build is not compliant.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

There's no engineer or inspector on this project, just me and my research. I'm pretty sure you can build a structure like I have in the US as long as the walls that are on the platform are not load bearing (as in not holding up another floor above it or the roof). As I was starting my build, I read a lot from the auralex acoustics 101 guide, and that's where I got a lot of my ideas from on how I am building things. Auralex is a US company, so I don't think they would be publishing a guide on how to build a structure illegally, and I dont think they would be making a product like uboats if they were essentially illegal to use for their intended purpose. Check out the article on their page here http://www.acoustics101.com/floors.asp. I built everything using a very similar approach with some exceptions, most of those being things like using green glue products instead, using 1/2" mdf instead of 3/4" because my oak flooring is 1" thick and I feel that will make up for most of the loss in mass, using 5/8" firecode drywall, and not using resilient channels because that seems redundant in a double wall scenario. I also have a lot of friends who are carpenters, framers, and even an architect (who works in earthquake riddled southern California) that I've talked to about building things this way, and shown some of them my build, and they didn't mention any code issues, and had a lot nice things to say about how sturdy and well built it is. So, though I don't have an engineer, I have had a guide written by one that I am following, and I dont have an inspector, but I have enough input from people who deal with them every day to keep me sleeping at night about it.

The outer leaf walls, and i should have been more specific about this, are anchored to existing framing in the house, and all of that framing is anchored to the concrete. So though I am not bolting it straight to the floor like I would like too, the walls are well attached to everything around it on at least 3 sides.

As I was considering the floor, I tried to think of it as another wall, except instead of using drywall, I'm using 3/4" plywood, a layer of green glue, MDF, and 1" oak flooring. Right now I'm up to the mdf part, and when you step on that floor, it's dead and doesn't ring at all, much like my walls that i've double layered with drywall and green glue. Though I know a layer of 3/4" plywood does not have the same amount of mass as a sheet of drywall, I would say that the mdf is close if not a bit more, and anyone who has dealt with hardwood red oak flooring knows that's not light weight stuff like the pergo crap thats in style right now. So, the way I look at it, in my system, my floor should at least be as strong as my walls as far as creating isolation, isn't that really the goal here?

And don't worry about being the bearer of bad news Stuart, I was looking to find out what you all thought and you're telling me so I appreciate it man!

What Stuart is saying is that your build is going to disappoint you. You will not know that since you will not be able to compare it to a proper isolated construction method.

While I admit the lightweight floor is going to thump like a drum head and that I am not convinced that there is a mass/spring/mass system in place as of yet, I have other concerns.

Nevermind that you could have just as easily used fluted hard nails to attache the wall assembly bottom plate to the concrete with no fear of breaching the barrier and could have applied caulking to the underside of the bottom plate and /or to the interior exterior side and achieved the same sealing.

Two things come to mind, the deflection of the overhead floor (the downward movement when weight is placed on it) and the upward movement of the concrete slab. You run the risk of several things in that if the floor deflects and there is not enough room below the bottom side of the upper joists these same joists will bind against the structure you are currently building. This will essentially short circuit the double wall assembly and make the upper floor very rigid meaning that it will telescope sound even more so due to this short circuit and added rigidity.

You should never build a wall assembly tightly against an upper floor/truss since the upper floor/truss has to have room to move up and down, mostly down

Depending on the seasons, you can get water in the ground that will create "hydraulic pressure" that can actually lift the slab. This is not uncommon in your neck of the woods, or any neck of anyone's woods to be quite honest.

So you take the potential binding from deflection and couple that with an upward movement of the slab...I'm talking small numbers like eights of an inch and you can actually push that upstairs structure off of the upper foundation.

This is a dangerous thing...dangerous. And people can get hurt and properties can be ruined possessions lost and Insurance will not help you in a non-sanctioned construction procedure.

You really, really need to back this thing down a notch, map out a re-build, for your health and your families well being and you get a better isolated environment.

You can take free advice for what it cost you, but you have to know that you are doing many things that are not acoustically sanctioned from anyone here and your build methods are going to cost you.

Maybe not to day, but it will happen so while time might seem like a warm blanket in bliss, the second these two things come into play (and they will) you will know within a few days what the cost is to have had the bliss.

And the cost is high my friend.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

I would really suggest that you need to get a structural engineer involved. You might see that as an unnecessary expense, but in reality it is more like buying an insurance policy. Right now, you have no idea at all if your structure is safe, or if it meets code. Especially after what Brien was saying.

And I'm not sure how you can be building without an inspector: I was under the impression that all building modifications or additions in the USA need some sort of permit, and occasional inspections. Maybe I'm wrong on that, but I though you weren't allowed to do major work like this without permits and inspections. You really should check on that point. Here, too, if you have built something that legally requires inspection and/or permits, and you didn't get them, then I'm pretty certain you'll find that your homeowner's insurance policy is now void, and does not cover you for anything that might go wrong. You should check on that too: you are most likely legally liable for everything that might ever happen to the building, regardless of whether or not it is related to the studio: For example if the place burns down, even if the fire was totally unrelated to what you built, I'm betting the insurance company would still use that as a valid reason to not pay out, leaving you liable. I'm no lawyer, I'm just repeating what I have read and heard, so once again I may be wrong here, but you really, really should check into that.

"Pretty sure" won't hold up in court! I strongly suggest you should double-check that! While you might well be allowed to do it, you might also be required to get permits in advance, and inspections along the way.

Well, I imagine that their advice is well meant, and probably legal, but that doesn't relieve YOU of the legal responsibility of making sure you are doing things correctly in YOUR state, county, city and municipality. Just because you read something on the internet does not mean that it is 100% correct, or 100% legal.

You might be making up for lost mass, but you are not making up for the undesirable characteristics of the thinner and more flexible 1/2" MDF. Since it is thinner than it should be, it is also more flexible (less rigid). Meaning that it does not isolate well in very low frequencies, below the MSM resonance of the floor.

There are five regions on the audio spectrum that are governed by four different physical characteristics of the materials. At very low frequency, what matters is not mass but stiffness (rigidity). It is the most important single factor for very low frequencies. Flexible, non-rigid materials do not isolate well in this part of the spectrum. Next comes the resonance region, where MSM rules, and that is based mostly on the total mass on each side of the barrier, and the resilience of the spring between them. In your floor, you have two springs: one is the rubber (assuming that it is loaded correctly) and the other is the air. They are both springs, and both have their separate, independent resonant characteristics. So even though the rubber might be isolating at some frequency, the air might not be. Next comes the mass-law governed part of the spectrum, where the predominant factor is just the total mass in the wall. Next comes the coincidence dip, which is large drop-off in isolation due to another type of resonance, where the wavelength of the sound waves in air matches that of bending waves in the wall materials, and since it depends on angle of incidence, it is a broad region of the spectrum, with a deep dip. Thin materials, once again, do not stand up well at coincidence. Finally, above coincidence, stiffness becomes the major component again. And once again, thin flexible materials don't cut it well.

And even though you might think that the flexibility doesn't matter since the thin MDF will be "held in place" by other things, in reality it does matter. It still acts alone, as well as acting together with the rest of the materials.

That's correct. If you have separate stud frames, then you do not need resilient channel as well.

... which wont mean a thing if you are sued because something went wrong! You can't claim that what you read in a book or on a web site, or what someone told you, overrides what the law actually says. The only thing that WOULD stand up in court is a report signed by a qualified structural engineer stating that your structure is safe and complies with all applicable code.

Well, you might sleep comfortably right up to the moment the inspector comes knocking on your door, and then tells you to tear it all down...

Inspectors are not an optional part of building: they are a legal requirement. At least, where I live they are, and since our earthquake code is even tougher than yours (since we get hit more frequently and a lot harder by earthquakes than you do), I'm assuming that your code requires the same.

But regardless of how well you sleep, it would simply be wise and prudent to find out for sure what your code says, and if you are complying with it.

Great! That's the outer leaf. But we are talking about the inner-leaf here. By the time you are finished building, you will have thousands of pounds of construction materials around you and above you: I don't know about you, but I would certainly be very interested in hearing the opinion of a QUALIFIED expert on that! I kind of value my head, and I don't think it would work too well after 500 kg of drywall come crashing down on it because I forgot to bolt down the walls...

Have you also tried setting your subwoofer on it, and playing bass-heavy music at typical studio levels? Walking on the floor is not the issue: isolation of low frequency music is the issue.

Actually, no. The goal is not strength. The goal is isolation. The various parts of the floor work together as a system to isolate sound, and as I explained above, different characteristics have different effects at different frequencies. Overall, the all work together to isolate across the entire spectrum: If they are chosen correctly, and assembled correctly...

Well, I do hope you take it to heart, and spend a little time down at your municipality finding out about building code, as well as spending a few hundred dollars on getting a qualified structural engineer in to take a look and write up a report!

At the end of the day, what matters is that your studio not only works in the manner you desire as a a studio, but also that you and your customers are safe inside it.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.