Designing a recodring studio in an underground garage

Geez, Stuart, when you get fired up, nothin' stops ya!

You bet!!!! Nobody ever accused me of being wishy-washy in my opinions, or doing things half-heartedly!!!! :) But seriously, I'm hoping to give you enough food for thought that you'll either drop the idea of floating your floor, or hire a qualified professional studio designer to do it for you. From what I've read, there are a huge number of things that we untrained DIY folks can do to build our studios, but floating a floor successfully isn't one of them.

... is a civil engineer with experience on anti-earthquake solutions, and when someone designs and builds structures to contain such a low frequency bourne noise as an earthquake, you pay attentiion to him! The principles envolved should be similar, only on a different scale.

I'm not so sure about that. I don't think you can stop an earthquake with a good MSM wall, or a floated floor.... :) But seriously, although earthquakes and sound waves have a lot in common, I'm not sure that all of the same principles apply. Maybe they do: I really don't know. I do know that your issue is going to be mainly impact noise from the machinery, I think, not the building falling down due to the earth shaking! But I'm way out of my league on that, so maybe one of the experts can comment. Personally, I think I'd hire an experienced acoustician to do those calculations. But that's probably just my "fired-up-and-nothing-stops-him" belt-and-braces character kicking in!

Come on Stuart, I know and you know that we can't get such a low frequency without an isolated or floated concrete slab...

My point exactly! BINGO! Yup, that is the issue here. In order to get down to the frequency you need, it requires lots of mass and some unusual construction techniques. Rod mentions shooting for a floor resonance of 10 Hz or lower. His books shows you how to do that, in principle, and it needs lots of mass in a floated concrete slab. If you don't do that, then you can't get the frequency low enough. The equations don't lie! From what I understand of those equations, your break-even point occurs at the square root of twice your resonant frequency. That's the point where your floor just passes the sound through directly as though it was not even there (neither amplifying nor attenuating it). A sound at that frequency passes right through as though your floor was just air, basically. As if you had no floor at all. That point occurs at rough 1.414 times your resonant frequency. BELOW that point, the floor actually AMPLIFIES the sound. And only ABOVE that point do you start to get a little attenuation. You start getting some isolation at one octave above your resonant frequency, and decent isolation at two octaves above. So, if you do NOT want that delicious Harley Davidson thumping-rumble in your room, then you DO need a resonant frequency that is at least half of the lowest frequency noise that you will have close by. I'd suggest that you need to do some real measurements of the noise spectrum in that parking area, to see what kind of frequencies are going to be an issue, and design your floor to have a resonant frequency of less than half of the lowest noise problem. Anything else is just a waste of money. It would be really sad to invest all that money in a 20Hz floor, then find out that the floor "disappears" every time a car comes past, and the noise gets through, as though the car were right there, inside your studio. Or even worse, that your floor actually amplifies the sounds of some engines, which it will do if you cannot drive the resonance down low enough. You mentioned mass law in some of your posts a while back, but the transmission loss of your floor design is not governed by mass law at those low frequencies. It is governed by stiffness. However, your design is for a timber-frame and plywood floor, resting on neoprene pucks. That isn't very stiff! So you can't even rely on doubling the mass to get greater isolation: it wont work very well, since you are on the part of the curve where mass law doesn't apply. You have to increase the stiffness to improve isolation down that low. I'm not sure how you can make wood stiffer... Look at the curves on the graphs for transmission loss around the resonant frequency of an MSM structure. The slope on those curves is scary. And the graphs don't lie. My $ 0.02. :blah: - Stuart -

Just to give Stuart a moment to catch his breath, I'll change the subject of the "floating floor" discussion and I'll present to you my one only... :shot: slot resonator design! :yahoo: You'll find a picture and a sketchup file of the design attached below. It contains:

a 5cmx10cm (2"x4") rectangular frame ,which by the way, can be converted easily to an angled one (5cmx10cm (2"x4") frame on one end, 5cmx30cm (2"x12") on the other for example). pieces of 10cmx80cm (4"x32") rigid fiberglass insulation hinges screwed on the frame to support the frames carrying the slats fabric wraped and stabled around the frame to cover the frames and the insulation hinges screwed on wooden finished frames and placed inside the hinges of the construction's frame rails placed on the wooden finished frames to allow horizontal movement of the slats wooden finish slats placed vertically on the rails and adjusted according to our needs of acoustic treatment (do not duplicate the placement of the slats as it is on the design, I just placed them like that for the needs of the picture snapshot)

You can adjust the slats manually, you can open the slat frames and you can remove them completely. It gives so many choices as far as acoustic treatment is conserned and it definetely looks awesome! Next stop, bass traps for the ceiling... :mrgreen: John

Soundman2020 wrote:

Rod mentions shooting for a floor resonance of 10 Hz or lower. His books shows you how to do that, in principle, and it needs lots of mass in a floated concrete slab.

Stuart, I've read Rod's book, I've quoted him before, he knows what he's talking about, I'm gonna give his book to my contructor for reference. In the end, it's all about choises: 1. expensive but great isolation 2. less expensive but medium isolation 3. no isolation at all Now, let us assume that we can succesfully build 1, 2 and 3. If we figure out the ratio of the difference in isolation between 1, 2 and 3 and of the difference in cost between 1, 2 and 3, we could decide which choise is the best-applicable. Simple as that. I just used 2 as an example in my design because it's the "average" solution. I'll update my design, including an isolated/floated concrete slab under the studio for future reference. Always gratefull for your comments, John

Oh, and a quick question on the "inside-out" wall layout. My understanding about its use is that it saves coverage area because you don't have to build another frame for acoustic treatment, you use the existing wall frames for that. Is there a difference in transmission loss between a normal wall frame and a "inside-out" wall frame, provided that we keep the air gap between the double frame walls the same? Stuart, I think you are the one that favours this design the most, so if you care to clarify this for me, it would be great! John

Things are going pretty slow on the forum lately... Anyway, I've managed to get hold of my brother (my contractor, remember?) and we discussed the garage studio project. My first priority was to tell him about floating the floor. After I laid my choices on the table, he rejected the isolated/floating concrete slab choice on the spot due to the building's stabilty issues. On the other hand, he is confident that the elavated frames on neoprane pads will be sufficient enough to isolate the floor from vehicle and machinery vibrations and the cost of construction should be reasonable. We'll see about that when the right time comes... :? Next he pointed out that if I move the kitchen/wc to the right end of the building and use a corridor to access it from the hallway, we would gain an extra parking space. The cost just went up and one more car to park near my studio walls... :roll: It's all about the money these days... :( I made the necessary adjustments to my sketchup file including some more details. Due to its size, I can't attach it, but you can find a compressed version HERE. Any opinions? John

Another updated version of my design with sand filled floor frames on rubber sheets is available for downloading HERE. Another scenario would be to have only perimeter floor frames and the rubber, drywall, plywood, wood finish lay on the vapour barrier. But I think it would be best for the stability and bonding of the construction to have crossed frames on the floor just like a wall's. The mass goes on top and we have a cavity that needs to be filled. Sand or Rigid Fiberglass? Any opinions? John

Almost forgot! My design for a corner bass trap! It's nothing fancy, it consists of: A frame of a equilateral rectangular triangle, 1m (3f) width for the front side. Rigid insulation fills the frames. Fluffy insulation stacks from the bottom to the top in the middle of the frame Fabric stapled to the frame to cover the whole thing. *Wood finish screwed on the perimeter of the front side, just for the looks or if you like, you can build the wood finish frame like I did on the slot resonator design and have it on and off as you see fit. *optional Image and sketchup file attached below. Just for future reference... :thu: John

Wow! Talking about slow in the forums lately... Come on people, wake up! Where's all the expert heads? Busy, I guess... Anyway, sometimes I don't sleep, sometimes I don't eat, sometimes I don't DO many things because of this project cause I get so involved with it that time flies by so fast! And I love it! One of those times, I got the idea that I would like to present you with (even if I don't get any feedback from you guys to feel that I'm on the right track). There's a picture and a sketchup file attached below, describing what I call a "double frame portal connection suprise"! You see, I had some thoughts about the area between two frames at the point of the door openings. Inner frame and Outer frame are not supposed to be touching! Anywhere! As little as it can be! It ruins the whole consept of the "room-inside-a-room" philosophy. Rod, in his book, page 93, says and I quote: "...this is one place I don't worry about maintaining the separation of wall assemblies with frames, even when using totally separated assemblies...". I respectfully disagree. I think, if you put a mass between the separation of two other masses, you create a link for sound to pass through. That's a fact. The real question is: what frequencies and in what quantity? It depends on how dense is the mass and what absorbtion properties has. My quess, for extending the drywall walls to connect to each other, is that we are gonna have definate leakage problems, as much as cutting holes on those drywall walls. Someone mentioned something of a rigid fiberglass panel wrapped on cloth and stuffed in between the drywall walls, creating a piece of pseudo-wall. That, in my little world of knowledge, would work. But! That solution doesn't take into account the clamsiness factor! My band consists of great guys, great friends but very clamsy. It's a fact that at some point, someone will trip and smash into that piece of insulation. Oops! So, what do we do? This is where the "double frame portal connection suprise" comes to save the day! It consists of a frame of wood finish panels, 5mm thick, screwed together, with 5mm thick glass in between, screwed alltogether on the separated frames, between those drywall layers. I think it will work as far as isolation is conserned, it's gonna be sturdy enough in case of an "accident" and the best thing is that it looks great! With a couple of spotlights, you will be able to actually see in between your walls! I bet clients and friends will be attracted to it like moths on a candle... 8) Until next time, John PS: This design is not applicable in constructions envolving frames separated by an air gap smaller than 5cm (2"). The glass area would be very small to carry the effect we want to get.

zzzzzzz.... hibernating..... Yeah, but then again, every thing's been said and done. This forum becomes a treasure in the form of an archive for studio construction. Wow! [/sleep] mkay, nuff said. :twisted:

Ro wrote:

zzzzzzz.... hibernating.....

Look alive Ro! :P

Ro wrote:

Yeah, but then again, every thing's been said and done. This forum becomes a treasure in the form of an archive for studio construction. Wow!

A little encouragement now and then didn't hurt anybody I know of... :thu: John

Well, you know. That's how Forums work, sadly enough. ppl come and go. Haven't seen Keith, Steve, Andre, Eric, Gullfo and many others for a while now... Even Stuart's typing less than before... well, no wonder with the speed he produced words. dang! He prolly takes up all bandwidth and leaves no room for others! :finger:

Thanks for the "kind" words, Ro!!! :) I'm just tied up finishing off an album for a client. But as soon as I'm done with that, I'll just HAVE to release all these words that have been accumulating in the mean time!!!! :) - Stuart -

Oh, and a quick question on the "inside-out" wall layout. My understanding about its use is that it saves coverage area because you don't have to build another frame for acoustic treatment, you use the existing wall frames for that. Is there a difference in transmission loss between a normal wall frame and a "inside-out" wall frame, provided that we keep the air gap between the double frame walls the same? Stuart, I think you are the one that favours this design the most, so if you care to clarify this for me, it would be great!

Hey John! I didn't invent the "inside out" approach. As far as I know, I think that is John Sayers smart idea. And the reason I've been promoting it so much lately, is because I see the space-saving benefits for small studios, and I'm going to use it in my own studio, for the exact same reasons. Regarding your question: As far as I can see, there should be no difference at all in transmission loss if you keep all other factors the same (mass of each leaf, and separation between the actual drywall on the leaves). As long as the mass is there, and the gap is there, and the insulation is there, and everything is sealed airtight, then I can't see how it matters if the studs are on the "inside" (between the leaves) or on the "outside" (facing away from the leaves). One minor detail: If you build your wall inside out, then yes, you can use the stud space for treatment inside your room, but you now don't have those studs inside the wall any more, so hanging your insulation INSIDE the wall becomes an issue! You need to plan for that. There are some solutions for that. One of them is called something like "bat hangers", IIRC, and is basically like a small metal plate with a long metal spike sticking out. Attach several across the top of your wall, and just press the insulation over the spikes. - Stuart -

Soundman2020 wrote:

As long as the mass is there, and the gap is there, and the insulation is there, and everything is sealed airtight, then I can't see how it matters if the studs are on the "inside" (between the leaves) or on the "outside" (facing away from the leaves).

Hey Stuart, thanks for confirming this. :thu: I'm in the process of modifying my design in order to illustrate the "inside-out" approach, as soon as I finish this I'll post it for comments. Cheers, John