I made a construction mistake--worth redoing?

Hello, Summary: I built what seems to be a best-practice (within my budget--about $1,000) wall in my project studio, but I now believe I did one feature of it poorly--the insulation--and I'm trying to determine, in practical terms, the value of redoing it. Goals: I am a drummer and teacher building a home project studio with the goal of being able to teach, practice, jam, and do some semi-pro recording. I live in a house with about 75' between the exterior wall of my studio and my nearest neighbor, the only one I'm concerned about. I am on the third floor with only roof above me. Detail: To create a separate control room and tracking room (and put the control room between the tracking room and that neighbor), I have subdivided a long (35') thin (14'9") room with a MSM wall: two decoupled metal frames allowing 7" of air space, standard R-13 fiberglass insulation between the 16" o.c. framing, and two layers of 5/8" sheetrock per side with Green Glue between the layers. I have two solid core doors with an equivalent to the GM type K gasketing. I have a 2' x 4' window with 1/4" laminated glass each side (I wanted to do thicker and two different thicknesses, but cost got in the way, for now). A few cables (ethernet, coax, and an audio snake) run through the wall via staggered holes (7' apart). Everything is caulked and sealed as far as I can tell. I don't know about the relevance to my question, but just to be thorough: The wall is basically 14'9" wide x 7'10" tall. The roof slopes perpendicular to this, cutting into that dimension so that the flat part of the top is 8'5", sloping down to 19" off the floor. Due to incomplete research, I chose standard fiberglass instead of something designed for transmission loss, and I also left little room for air. My question: Are the gains from using a different type of insulation and installing it differently significant, or are we only talking a couple of DB? Bottom line, for 6 db, I'm not going to open up the wall (I just don't have the cash to justify small gains for a home studio). But if we're talking potential gains in the 15 db or more area, it may be worth it. I understand that I have other issues with the rest of the room and flanking paths, but my only concern at the moment is that one wall. I also realize STC differences here may not be quantifiable without actually measuring my wall both ways, but I'm hoping in the cumulative years of experience of forum participants that a recommendation can be made. Thank you in advance for any guidance. I respect and appreciate the presence of this forum and all the time and work it takes to run it and help each other. I hope to be able to assist other participants as I gain experience. Cheers.

w1111e wrote:

My question: Are the gains from using a different type of insulation and installing it differently significant

No sir, there would be no gain worth tearing the wall apart and re-installing different insulation. Considering your flanking issues from being elevated on a wooden structure (assuming wooden) even if there was a 6dB gain it would be reduced from the flanking. Typical residential, pink fluffy insulation is highly recommended here and any other place with serious concern towards isolation. Brien

Thank you, Brien. This is a relief... You are correct: I'm on the third floor of a wood frame house--lots of flanking transmission audible within the house. I seem to find conflicting information on the web, or at least I don't understand the distinctions between when to use the pink stuff and when something else is best in wall cavities, and when to use just a little and leave lots of air vs. when to fill the cavity. I certainly want to avoid, as the reference thread points out, creating a "third leaf" out of insulation, and destroying the gains from having air. Thanks again, Scott

Scott, as Brien said, the issue isn't the fiberglass at all: fiberglass is just fine in that application, and it sounds like you did that wall perfectly right. Filling the entire cavity increases isolation, leaving it empty decreases isolation, and ordinary pink fluffy fiberglass insulation won't ever form a third leaf. So you did it right, and there is nothing much more you can do that wall to improve it, and that wall actually isn't the problem at all. And this is the part you are not going to want to hear: the issue is that you only did one sixth of what you need to to in order to isolate your room.... Analogy: if you want to build an aquarium to keep fish in, then you could buy an aquarium frame and put glass in it yourself. That would work fine: just put glass in all four sides of the frame, plus the bottom, put a lid on the top, seal everything tight, fill it with water, and you have an aquarium that doesn't leak! Your room is like the aquarium, except that with your one single wall, you have done the equivalent of putting glass on only one side of the aquarium. The other three sides, and the top and bottom, are basically made of tissue paper.... An aquarium built like that will not hold water. Your room doesn't "hold sound" for the same reason that an aquarium will not "hold water" if you only put one piece of glass in it. In other words, in order to isolate your room fully, you have to do the other three walls, and the floor, and the ceiling, in the same way that you did the first wall. And here's the other part that you are going to like even less: Since you are on the third floor of a residential building, doing the other five sides of the room is not going to be easy, nor cheap. The existing structure of the building most likely cannot take the weight that you'd need to add in order to do it right. Now for the good news: what MIGHT help a bit is if you were to take off the drywall on the other three sides of the room and the ceiling, install resilient channel across the studs, fill the cavity with the same pink fluffy fiberglass, then put on new 5/8 drywall making sure that it is mounted ONLY to the resilient channel. That would leave the floor, but there just isn't much you can do about that unless you want to get into modifying the structure of the entire building ( :shock: ), so maybe your best bet there would be to build a drum riser, to at least decouple the drum kit from the floor, as far as direct impact is concerned. The last issues would be doors and windows: I'd suggest building plugs for the windows, and beefing up / sealing the doors as much as you can That might, theoretically, get you the extra 15 dB you are after. Perhaps a bit more, with luck. All together the above is not going to silence your drum kit, so don't get any high hopes about it. But it might just make enough difference to be worthwhile, such that the neighbor isn't calling the cops on you every half hour... I'm sure you didn't want to hear that, but folks here will give you the truth without any sugar coating. - Stuart -

w1111e wrote:

I seem to find conflicting information on the web, or at least I don't understand the distinctions between when to use the pink stuff and when something else is best in wall cavities, and when to use just a little and leave lots of air vs. when to fill the cavity. I certainly want to avoid, as the reference thread points out, creating a "third leaf" out of insulation, and destroying the gains from having air. Thanks again, Scott

In wall cavities, in general when speaking of wood frames and sheetrock panels, pink fluffy insulation is always the recommended product by those that do this type of thing, always. The only time it might change would be if someone has, already, a different insulation product that is comparable then it would be reckoned to use what is on hand rather then spend extra monies for something of this sort. The insulation is always considered as part of the "air" of an assembly so no matter how much air is available the insulation in the cavity is integrated into the air and the two become one, so to speak. Some of the data that we all here have seen suggest filling the cavity complete with insulation will yield higher transmission loss capable walls. But to do that requires a lot of effort on the installers part to have the often unavailable overhead room to fill this cavity and the actual gains received from this effort which do not seem to be much, from what I have read, to make this common practice. Actually you would not create a third leaf from the over stuffing of insulation but would effectively bridge the two decoupled barriers back together again creating a two leaf, coupled wall, which like you stated would still be a reduction in isolation ability, but would not produce a third leaf, for the record. Brien

Thanks, Stuart, for that detailed and instructive response. Much appreciated. And I certainly appreciate the truth and straight info! As you noted, between my budget and the nature of the space, there's only so much I can do. This wall was a big first step, and now I'm turning my attention to what I can do with the rest of the space. The good news is that I own the home, and noise within the house is fine as my wife (also a musician, so she gets it) hangs out two floors down and doesn't mind what little she can hear (unless, of course, it's 2 a.m.). For the neighbors, they are far enough away for a lot of sound to drop off (or at least end up somewhat blended with the environmental noise floor--traffic, wind, birds, air conditioners) and they are also quite nice, though I want to be respectful. For the neighbors who are closest, even without doing the rest, this wall (because of it's position now putting the control room between them and the drums) has dropped the drum transients deep into the noise floor so it's hard to detect unless listening closely for it. For now, this was my goal. Fortunately, I'm in the position of doing this work preventatively--before I have any complaints--and probably mainly symbolically: to show good faith to my neighbors that I'm doing everything I can to respect their right to quiet enjoyment of their property (short of not playing drums, which ain't gonna happen anytime soon). If they hear a little bit after I've done all I can, that's okay. Your recommendations for what to do with the remaining walls and ceiling are what I intend to do as my budget allows going forward, though for now I'm tapped. And I expect that decoupled risers will suffice for bass pedal impact noise and under amps (I was hoping to do something like Gypcrete at one point, but I am sure you are right, that structurally this place couldn't handle it, and certainly couldn't handle any kind of floating approach). Thanks again for your guidance, Scott

Thanks, Brien, for the clarification and good info on how the airspace works in terms of insulation, and how insulation relates to coupling and leaves. This addressed some confusion I had. The fiberglass is what I have on hand, so I'm happy to hear it's a viable option and certainly that I don't need to tear out this wall. And when I move to the other walls, I will use that but be careful not to overstuff the cavity and bridge the two walls (which I think I did with this first one, at least here and there). Cheers, Scott

I will use that but be careful not to overstuff the cavity and bridge the two walls (which I think I did with this first one, at least here and there)

You would have to stuff it in fairly tightly to cause it to bridge. If it is just touching both leaves then it won't bridge. Do you have any pictures of the construction in progress? - Stuart -

Soundman2020 wrote:

You would have to stuff it in fairly tightly to cause it to bridge. If it is just touching both leaves then it won't bridge. Do you have any pictures of the construction in progress?

This is good news: While each wall's insulation is touching the other, I didn't cram it in there, so I think I'm in good shape. I positioned it snugly between the studs of each wall, and due to its thickness and some buckling, the opposite sides "fell against each other" a bit. The cavity is 7" wide (wall to wall), and the two thicknesses of insulation add up to that when not compressed in any way, but there are still many spots where they don't touch at all. I have pictures of other phases, but not this part of it. Thanks again, Scott