Hello again. I’ve finally taken digital photos of my project! I borrowed a friend’s phone. So, I figure I may as well “start over” with my post to include all relevant information (like I should have done in the first place!) So, here it goes.
The now fully constructed (except for any sound-treatment related construction) studio’s main purpose is a mixing room, but also must function as a rehearsal space for a five piece band (drums, two electric guitars, bass and keys); however, this secondary use is very much subordinate to the primary use as a mixing room. It is a “room within a room” construction located in a detached single-car garage on a concrete slab. The walls and ceiling are 2x4 timber framed. Two layers of 5/8 inch gypsum with 30 pound roofing felt sandwiched between make up the walls' and ceiling's surface area. All relevant seams have been caulked with Green Glue acoustic caulk.
I realize roofing felt is a sub-par material to help with decoupling the two pieces of gypsum (thought I have read, perhaps erroneously, that it is a workable substitute for mass loaded vinyl), and that it might have been better to use different thicknesses for the two gypsum layers, but as my budget for the entire studio was about $3500 (which I have already surpassed, of course) and I got a big discount on a pallet of 5/8” drywall, (the roofing felt was free!), that’s what I used. Fortunately, highly effective soundproofing wasn’t a major concern for me, and now that the construction is done, I’m satisfied that it is “soundproof enough” for my purposes (a drum kit being played in the studio is barely audible within 50 feet of the outside structure, which with respect to the distance of my nearest neighbors is ok. I live on the very edge of a residential to industrial area)
On to the studio’s dimensions. Once they are all listed, I’ll do my best to explain the peculiarities. Length: 18’ 2 9/16” Height: 8’ 4 5/8” for a length of 13’ 11 7/16” and then a height of 7’10 1/8” for the remaining 4’3 1/8” of room length. Width: 10’ 4 7/8” at the tall end, to 10 ‘ 7 13/16” at the short end.
And now for those peculiarities — some of which are the focus of questions I’d like to ask the forum. I’ll list these questions, and all others, at the end of the post, for organization’s sake, and for now just continue with information:
Peculiarity #1: The original structure has a pitched roof (9.5 ft on the high end to 8 ft on the low end over a distance of 19.5 ft. These numbers are approximate, as I’ve misplaced where I had the original dimensions of the inside of the existing structure). To make matters worse, the concrete slab is sloped so that it is one inch higher at the short end of the structure than it is at the tall end. During the planning stage, I wrestled with whether or not to attempt to follow the pitch of the roof with my build, but ultimately decided against it. Not only would my limited construction skills (I’ve done the whole thing by myself except the occasional help with heavy lifting, etc.) make that difficult, my research on this forum and elsewhere seemed to add up to “not worth it.” So, I decided to make the ceiling as tall as I could for as long as I could, and then make a “step down” for the last 4’3 1/8” of the length of the room. Here is what this “step-down” looks:
studio picture 13.jpg
Peculiarity # 2: The varying width has a twofold explanation. One: the outside structure, though solidly built and in fine condition, was not built particularly square. Two: I am just not a very good carpenter and I have nearly inadequate tools. I tried to keep things as square as I could, especially given that the external structure wasn’t square, but I was still bound by its realities and wanted to have as big an inner room as possible. I fell short far from perfect. (For anyone following this thread, you’ll notice that my being a bit of a hack is a commonality.)
The other peculiarities, or more accurately — problems — were a result of design flaws, arrived at through my attempts to solve certain other problems through the process. Two of the main four questions I have deal with these “me created” problems and the way in which I handled the ventilation for the studio.
I live on the north coast of California (only about 80 miles south of the Oregon border), a very temperate climate (it very rarely freezes and very rarely reaches 80 degrees F). So, my ventilation needs are probably not as extreme as other folks contend with. I am concerned mostly with just exchanging air within the room. I did some research and it seems that a 10” duct, and a 10” duct boost fan (which I have located outside the external structure in an attached tin shack), will work fine for my needs.
Having read somewhere that ducts should have at least a couple 90 degree turns in them to help with sound isolation, I went about installing flexible insulated ducting in the studio. The places to install the duct collars through the studio wall, and leading to the outside structure, was predestined because there were already vents cut into the existing structure — one at the southeast corner, and one at the northwest corner, both of which are located at the ends of the room lengthwise.
A quick aside: I should mention at this point that I do not own the garage in which the studio is built. I rent the garage (and the house it belongs to) from a good friend of mine who has graciously allowed me to build this studio but has asked that I minimize impact to the original structure. Soo…I didn’t want to cut different vent locations in to the existing structure, and didn’t have the room to spare to run ducts elsewhere to the inside from the outside. So, I installed the ducts where the outside vents were located, installing them into cavities surrounded in gypsum on the inside — two layers of 5/8 with roofing felt sandwiched within, like the rest of the walls. The intake, located in the right corner of the rear wall of the studio (as you face the front wall from the listening position) looks like this on the inside where the rectangular figure represents the wall that is straddling the corner (please excuse the incredibly poor hand drawings —they are pretty terrible — but hopefully, they are sufficient to give you an idea):
The dotted line is supposed to represent a flexible 10” duct curling inside the cavity from each duct opening:
studio picture 15.jpg
Here is a couple of photos of what it looks like on the outside:
studio picture 7.jpg
studio picture 9.jpg
It’s my understanding that symmetry isn’t as important on the rear wall of a mixing room, so I’m hoping I can get away without adding a similar corner straddling wall on the adjacent corner of the rear wall, and instead use that corner for bass treatment, as that seems more important than maintaining symmetry in the rear of the room. I’d welcome any ideas for how to minimize whatever impact that irregular corner may have on the response of the rear wall.
The next problem concerns the location of the outtake duct. It’s a long story as to why the actual duct opening ended up where it is. Aside from what I already explained about where it had to be located based on the existing conditions of the outside structure, its current, and unfortunately practically unchangeable location (the various layers of the soffit wall are glued together) , is, as you will see from the photo below, far from ideal. I had planned on using a different pair of speakers, and there were other considerations that have changed since I built the ventilation in. It doesn’t really matter now how it happened. It happened. And I would like to take the most reasonable action in fixing the problem, or at least minimize its negative impact. Here it is in all its palm-to-forehead-inducing glory:
studio picture 3.jpg
And here is a diagram showing the internal framing of the ventilations soffit and how it interacts with the speaker soffit. They are separate entities:
studio picture 16.jpg
As you can see, the speakers are installed tweeter facing down, as that seemed to place the speakers at a better practical height. The tweeter is 4 feet off the ground. Either orientation of the woofer seemed to be ok for the the ceiling-to-floor distance, but having the woofer higher up seems like it would help to minimize problems interacting with the as yet not installed mixing desk. Having the woofer underneath the tweeter seems like it would be difficult to keep the woofer from being obstructed by the desk and/or gear to the listening position. Unfortunately, this speaker orientation puts the speaker on a more direct vertical plane as the duct and might augment whatever problems the duct would create in the first place. I have a few thoughts on how to deal with the problem—some of which (I hope not all!) might be completely hare-brained. Hopefully, you have some light to shine on the best solution, or perhaps why I should take a sledgehammer to the whole thing.
Solution one: Install variable-depth slat resonators (one on each wall) that would serve as a sort of splayed wall to deal with reflections, as well as cover the duct hole and eliminate whatever, I assume, acoustic nightmare would occur having a giant hole in the soffit on one side of one speaker but not the other speaker. That slat resonator could be about 45 inches on its face (any longer and it would cover up a light switch, plus the door is only a few inches back from that light switch, anyway), creating a 53 degree angle to the speaker. It would be six feet tall. The 2’ 4 5/8” remaining space of room height could be divided between floor and ceiling and used for superchunks. It would look like this, only in real life instead of a 5 year old’s drawing:
studio picture 17.jpg
Solution two: Install splayed walls with an opening at the top and bottom. Behind these walls would be acoustic hangers.
Solution three: Cut an identical hole into the soffit wall on the right side of the right speaker. This doesn’t seem like a great solution, because on the left side the hole is the mouth of a duct that goes through 3 turns to the outside, while on the right it would just lead to a cavity (that though equal in volume to the cavity housing the coiled up duct) is stuffed with insulation. In this scenario, I would forgo splayed walls and just use absorption at the reflection points.
Solution four: The duct hole isn’t as big of a problem as I think and I should just go about installing absorption at both side wall reflection points as I had originally planned.
At this point, I should provide some information about the speaker soffits. They are framed with 2x4s in a very piecemeal, but I hope effective fashion. That is to say, the framing is connected to the studio walls via 2x4 blocks holding it out from, and also connecting it to, the wall. It’s kind of hard to explain. I wish I had taken pictures of the framing as I did it. Now that its done, it’s pretty impossible to get a good picture of what’s going on with it. I’ve tried and I can’t seem to draw it to make it translate at all. Probably because my drawing skills are awful. Sigh. I'm no construction, or acoustic, expert (obviously!) but the soffit framing seems quite sturdy to me. The speakers are strapped down onto the framing of the soffits themselves— like they were sitting on a window frame in a conventionally framed wall of a house (which is pretty much how I treated the speakers -- as the windows -- in the framing of a wall in a house) with blocks of 2x4 attached to the back of the bottom horizontal frame of the “window” and providing a platform for the speaker to sit on. The speakers are strapped down with ratchet tie downs, as I mentioned in my previous post, to the framing and attached blocks. The soffit walls are made of two layers of 5/8” gypsum, except for the middle third which substitutes the outermost layer of gypsum for a 5/8” layer of plywood to provide as nailing for the final layer of 3/4” thick 3 1/2” wide planks of spruce and ceder timbers. In the end, I ended up extending the height of those planks to go further than the nailing beneath, and just screwed into where I knew studs were, which worked fine. All layers are screwed and glued together except the planks, which are just screwed. I wanted to be able to re-use them someday down the line if I ever tear this place down and build another. It's a long story, but the wood has sentimental value to me, and is also, though not of amazing quality, not super cheap to have to buy again someday.
Reading through what I’ve just written regarding the soffits, I realize it’s pretty convoluted. Perhaps embarrassingly so. But, in some ways, it’s a moot point because at this stage I just don’t have the budget (or probably sanity) to redo the soffits. I’m pretty much stuck with what they are. That said, I (wishfully) think I’ve executed the concept pretty well considering my many shortcomings. I think the most important elements of mass and rigidity are present. Also, to my knowledge, the angles are correct, etc. So, hopefully, I’ve done an “okay enough” job!
Here is a close up of the “flush mount” of the speakers. Big surprise, it isn’t perfect! I it recessed maybe 1/8 inch. I guess this is due to the slight imperfections of all the materials used as compared to my measurements (which were also probably not perfect!). I’m thinking I can take a hand sander and feather out those edges so that they smoothly blend into the rest of the wall. It was very difficult to get that sucker seated in there that well. The speaker doesn’t actually touch the soffit wall. There is a tiny gap (it’s really hard to see in the pictures. The only way to see it is to be in the dark and shine a light through one side o the soffit wall) between the speakers and the wall. It’s only about 1 or 2 mm.
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And, here is a front shot of the soffits. The space between, I plan on filling with 703 or whatever material I end up getting.
Soffit front view.jpg
This is a shot of the cavity underneath the soffit to be used for hangers. The piece of plywood with the 4" hole you see on the right of the cavity is just the divider that separates the lower cavity from the speaker cavity. I stuffed the speaker cavity with insulation last night and haven't screwed the divider back into place yet so it is just leaning against the wall.
studio picture 6.jpg
Well, that’s about it for my pictorial. I hope it’s been helpful to have images along with full disclosure of all my mistakes along the way! I will be running REW tests on the room, I hope, later this week. I realize that some of the questions and concerns I have will possibly be better answered once that data is posted, but in the meantime, I’m sure you have some much valued advice based on these pictures and explanations alone. In conclusion, I will just list the main questions and concerns I have:
1. How can I minimize the impact of the ceiling height “stepping down”?
2. How can I minimize the impact of the air intake duct’s gypsum wall straddling the rear right corner of the room, and is it ok to not match it for symmetry in the rear left corner?
3. What is the best way to fix the problem created by the duct hole’s proximity to the speaker on the soffit wall
I have other questions regarding types and locations of treatment, but I realize that most of those questions are dependent upon the REW results, so I’ll save those for my next post. Thanks so much for reading the long saga of my mistake-riddled, humble attempts! This has been, and continues to be, one of the most challenging things I’ve ever done! I’m extremely thankful for any and all help that you so graciously provide . . .