Booth Build Blunder

As construction was wrapping up on the building of my home recording studio, it became clear we are having trouble blocking out air and street traffic noise. Also, you can hear foot traffic when someone walks across the kitchen floor. Mistakes were made. The studio is built in an attached garage, in the corner of the garage attached to the house, using the existing studs for the wall attached to the house. Double drywall was used, but green glue was not. Studio is 4 x 5 1/2 x 9 (ft) Moving fwd my contractor has come up with an option he thinks will work. He's suggesting, add another layer of drywall on top of the carpet, and a layer of quietrock with greenglue sealant and compound in between. As for the foot traffic noise, he is going to insulate under the house where the kitchen floor. The studio in the garage is right next to the kitchen and sits about a foot lower, as you can see by where the door to the house is in the before picture. An mp3 is attached with sound samples, the foot traffic noise is amplified at the end. My question, does this seem like a good idea and will it work to block out street and air traffic noise?

Hi Darren, and welcome to the forum! I hate to be the bearer or bad tidings, but based on the sound of that plane flying over, there's a much more serious underlying issue here that is not going to be fixed by simply adding another layer of drywall or stuffing some insulation under the floor.

My question, does this seem like a good idea and will it work to block out street and air traffic noise?

In a word? No. There's a whole spectrum of things that could be causing this rather serious lack of isolation, so I'd suggest taking a logical approach, and looking at them one by one, from most likely to least likely, and from easiest to fix through to hardest to fix. But first, it would help if you could post some more detailed, higher resolution photos of the framing, to see how that was done, and a more detailed description of the existing structure (what was there before you even started), and what you did over that, to actually build the booth. Especially important is photos of how you sealed the sole plates to the floor. OK, so starting with the most likely: Number 1 is door seals. They aren't visible at all in your photos, so please provide some close-ups of the seals all the way around the door, and describe how you did them. You'd be amazed at how much isolation can be lost from poor door seals. Also some photos of the handles and hinges. The door might be part of your problem, but the sound of that plane makes me think that it isn't the only problem by any means. You should be getting around close to 40 dB of isolation with what you have (mid to high 30's, at least), but clearly you aren't getting much more than 20-something, so there's a serious issue in there someplace. Something major is wrong, beyond just door seals. Number 2: Windows. You have some type of window in there, but it looks like just a thin pane of ordinary window glass in the photos. How thick is the glass? What type of glass? How was that put in? How were the seals done around the edges? Once again, close up photos would be good. Next: electrical system. Explain what you did to get the lights, plugs and switches into your booth, and post some ion photos of that. Also how the power actually gets in to the booth (photos / description / diagram). One very basic suspect would be your light fitting above the desk. I'm just guessing here, but did you by any chance cut a hole in the ceiling drywall and install some type of fitting up through that hole? Please post a photo of the ceiling that shows the light fitting, and also photos of your plugs and switches. Next: Ceiling. What is above the ceiling? How is it built? From outside (where the plane was) to inside, write down each layer, mentioning the material and the dimensions, and the size of the gap (if any) between that layer and the next layer. eg: "Tin roof, 2x3 roof joists, 1" air gap, 2" fiberglass insulation, 2x4 ceiling joists, 2 layers 5/8" fire-rated drywall". or whatever it is in your case. Next: HVAC. Given the tiny size of that booth, you must have some type of ventilation in there. Please provide photos of how that was done, and also descriptions. Next: Walls. You mention that you put up a stud frame, then put 2 layers of drywall on it, but how did you do that? Is that 2 layers on the outside of the studs, then another two layers on the inside? Did you put insulation in the cavity? If so, what type and how thick? Did you decouple the inner layer from the studs somehow (eg. resilient channel / clips plus hat channel, etc.)? What thickness drywall did you use? Did you stagger the joints? Did you caulk / mud and tape the first layer before putting on the second layer? Next: Floor. What is it? It's a garage, so I'm guessing your floor is a concrete slab on grade? How thick is the concrete? Is it the same slab the rest of the house is on, or is it separate? Let's start with those, and see what we can figure out. Hopefully it's one or two of the simple ones that is causing your problem! - Stuart -

First off, thank you for such a detailed response, I greatly appreciate your help. Unfortunately, I was away from home during the build so I have very limited photos of the construction. Another mistake, I know. I don't have better photos of the framing, but I here is a larger photo of the one posted. And here is a photo of the space before the build. And a photo of the door seals. So the booth, or room, was built using the two existing walls, one of which is a wall to the exterior, the other connects to the interior of the house. Then framing was put in to build the rest. The booth has two rooms, the first is the room for equipment, and the 2nd is the recording room. Separated by a 2 ft x 3 ft half in glass window and door. I recommended to my contractor to use green glue to seal the walls prior to insulting and adding drywall. He used something he calls "PL", I have no idea what it is and Im pretty sure its not an acoustic sealant. He added 2 layers of drywall, but without the green glue it seems like it was a waste of drywall. He insulated the walls, but Im not sure what he used. At this point, I think the only option may be to open up the walls and start over with the interior booth. Decouple the walls with offset studs, properly seal everything with green glue, make sure the insulation is right, add a layer of MLV, and then double drywall with green glue. Sound good? ...Overkill? ...or not enough? answering your # 2 - the window is 1/2 inch temper glass. There is room to add another layer of glass if needed, but there doesn't seem to be any sound coming through the glass when I tested between the rooms. Not sure how is was put in, or sealed.. Lights were (hopefully) built with backer boxes. The ceiling actually seems pretty tight, no noise seems to be coming from above, as of now it all seems to be leaking in through the wall connected to the exterior. There are no outlets in the recording room, only the equipment room. They were also supposed to be acoustically sealed, but Im not sure what he used. They is a vent connected to our HVAC system. I had him run a 25 or 30 ft insulated tube zig zagged around my attic. that also seems to be done right. We have a pretty loud HVAC system and you can hear it at all coming through the vent. And there is a nice stream of heat/AC coming in. There is a vent system between to two rooms. Also using about 20 ft of insulted tubing. Using silent computer fans. Also seems to be down well. No sounds leaking through them. Drywall is single layer outside the booth in the garage. Not sure what type of insulation. As for the inside, it is double layer in the recording room. It was caulk/mud and tapped before 2nd layer was applied. Floor, the floor is also clearly an issue. It seems like I am directly on the concrete floor in the recording room. Separated only by minimal padding and carpet. Not sure if it is the same slab as the house, or the size. There is also an issue of an old laundry dryer vent on the exterior wall of the house. And an exterior outlet on that wall. I dont think these were properly sealed. Photo attached (outside wall). Again, thank you. I greatly appreciate your help and advice.

So the booth, or room, was built using the two existing walls, one of which is a wall to the exterior, the other connects to the interior of the house.

OK, that sounds like a big part of your problem: You only have a typical fully coupled two-leaf house wall for isolation which is pretty worthless for a studio. What should have been done there is to take off the drywall facing the studio, beef up the drywall on the other side of that wall from inside it (between the studs), then put RSIC clips and hat channel on those studs, then put two layers of 5/8" drywall on them, with Green Glue in between, and insualtion in the cavity. That would have provided the mass and isolation that you needed.

Then framing was put in to build the rest.

The same plan should have been followed for that new framing too: two layers of drywall directly on the studs facing outwards (away from the room), RSIC clips plus hat channel on the inside (facing the room), and insulation in the cavity. The same for the ceiling.

I recommended to my contractor to use green glue to seal the walls prior to insulting and adding drywall. He used something he calls "PL",

I've never heard of "PL", and you are dead right: there is no substitute for Green Glue. People think it is adhesive (due to the name), but it is NOT actually glue at all! It is a visco-elastic polymer that never hardens, and creates what is called constrained layer damping between the two layers of drywall. Contractors who don't have a clue about acoustics and don't want to learn (and don't even read the instructions) think that it is glue, but then don't like the price and think that they can substitute any old glue: That does not work, and in fact if he used ordinary construction glue or something similar, he made things drastically worse than not putting anything in there at all. Sorry to tell you that, but it is true: Two layers of 5/8" drywall on top of each other with nothing in between make for pretty decent isolation, but glue them together and that screws up the acoustic properties. Green Glue does NOT glue them together, and there is no substitute.

He added 2 layers of drywall, but without the green glue it seems like it was a waste of drywall. He insulated the walls, but Im not sure what he used.

The right type of insulation is also important. Mineral wool or fiberglass is good (provided the density is in the acceptable range), but things like sprayed foam, Styrofoam, and such like are useless: They are cheap, but acoustically worthless.

At this point, I think the only option may be to open up the walls and start over with the interior booth.

Agreed. It's heart braking to have to do that, but it really is the only way to fix it.

Decouple the walls with offset studs,

You might need to go that far. RSIC clips are pretty good at decoupling. You attach them directly to the existing studs, then put hat channel on them, then attach your drywall to the hat channel ONLY, taking great care to ensure that no drywall screw touches a stud. You can get pretty good isolation like that, very similar to staggered-studs.

properly seal everything with green glue,

Green Glue Company makes several products. Their flagship product, is the damping compound, which you spread over the second layer of drywall before you lift it in place and nail it. That's not really a sealant: it serves a very specific acoustic purpose inside the wall, which improves the overall isolation, especially for low frequencies. But Green Glue Company also makes acoustic sealant, which is a different product, meant for a different purpose. You can use their sealant, or you can use other sealants. They aren't the only ones that make sealant. But they are the only ones that make the damping compound. So be careful what you order from them, and make sure you are using the right product in the right place for the right purpose!

make sure the insulation is right, add a layer of MLV,

Forget the MLV: you do not need it. It is just mass, but it is very expensive mass. Sound waves don't care how much you paid for your mass: they only react to how much mass is in the wall, regardless of the price tag... :) Two layers of drywall with GG in between is going to give you much better isolation than you have right now. I doubt that you will need more, but if you do then a third layer of drywall is a hell of a lot cheaper than a layer of MLV, more massive, much easier to install, and more effective.

The ceiling actually seems pretty tight, no noise seems to be coming from above,

That's good, but if you are going to go to all the trouble of taking apart the walls, you might as well take apart the ceiling too and do that the same as the walls, to ensure that the entire shell is consistent all around. Sound will take the weakest path in or out, and if you do the walls fantastic but leave the ceiling mediocre, then guess where the sound will go... :)

They is a vent connected to our HVAC system. I had him run a 25 or 30 ft insulated tube zig zagged around my attic. that also seems to be done right.

That's probably a big part of the problem too: you need something called a "silencer box" where the supply duct comes into the room, and another one on the return duct, where it leaves the room. Here are some examples of how people have built their own silencers. It's easy: viewtopic.php?f=2&t=15430&start=45 viewtopic.php?f=2&t=1929&start=74 viewtopic.php?t=8425&start=2 viewtopic.php?f=1&t=11542&start=5 viewtopic.php?f=2&t=9761&start=0 viewtopic.php?f=2&t=11485&start=98 viewtopic.php?f=2&t=11508&start=157 viewtopic.php?f=2&t=13821 viewtopic.php?f=1&t=15378&start=44 viewtopic.php?f=2&t=18202&start=16 Yours don't need to be as big as some of those, but you do need to do the math to calculate how big they need to be.

We have a pretty loud HVAC system and you can hear it at all coming through the vent.

That's a clear sign that the HVAC was done wrong. You should NOT be able to hear the HVAC system noise coming through the vent.

And there is a nice stream of heat/AC coming in.

Another clear sign it was done wrong: the vents are too small and so are the ducts. For a studio, the most basic HVAC concept is very slow moving air, but large volume. So you can't really feel it very much, and you cannot hear it at all. The speed of the air at the vent should be no more than 300 FPM, and preferably only about 100 FPM, and the volume of air in CFM) should be sufficient to ensure about 8 or 10 air changes per hour. You have to do the math to figure these things out: you can't just slap in a couple of ducts and registers and hope for the best. It sounds like that is what your contractor did!

There is a vent system between to two rooms. Also using about 20 ft of insulted tubing. Using silent computer fans.

That is also wrong, and I'm surprised it passed inspection. Most building codes do not allow one habitable room to exhaust into another habitable room. There should be separate supply ducts for each room, and also separate return ducts. Once again, your contractor should have been aware of that, and not have done it that way.

Drywall is single layer outside the booth in the garage. Not sure what type of insulation. As for the inside, it is double layer in the recording room. It was caulk/mud and tapped before 2nd layer was applied.

Once again, there's no decoupling there: any vibration in the drywall on one side of the wall is direclty transferred across the studs to the drywall on the other side, which then acts as a huge speaker... Here too there should have been RSIC clips and hat channel, or something similar, to decouple the dryrwall on the inside.

Floor, the floor is also clearly an issue. It seems like I am directly on the concrete floor in the recording room. Separated only by minimal padding and carpet. Not sure if it is the same slab as the house, or the size.

That's probably the least of your worries. If the floor is concrete "slab on grade", then there shouldn't be much of an issue there, except perhaps for impact noise (footsteps, and similar things). And carpet has no place as treatment inside studios. Leave the floor hard, such as laminate flooring on acoustic underlay.

There is also an issue of an old laundry dryer vent on the exterior wall of the house. And an exterior outlet on that wall. I dont think these were properly sealed. Photo attached (outside wall).

You are dead right again! They are both still THERE, so clearly they have not been sealed. They have to be physically removed and the holes properly patched with drywall, compound, mud, tape and finish.

Again, thank you. I greatly appreciate your help and advice.

That's what we are here for! So I would suggest that your best bet is to get the drywall off the inside of that room so you can see the studs all around, and post photos here of what you find. Based on that we can suggest ways of proceeding, but if it is the way I suspect it is, then the methods I outline above will be your best course. - Stuart -