Sound of Silence
Part 23— Designing and building a DIY home recording studio
The whole story — part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, part 10, part 11, part 12, part 13, part 14, part 15, part 16, part 17, part 18, part 19, part 20, part 21, part 22, part 23, part 24, part 25
Soundproofing the air ducts in the ceiling
As I have begun to mass-load the ceiling with double layers of 5/8" sheetrock, it has been interesting to observe what sounds I can still hear and where in the ceiling I can hear them from.
For instance. When a radio has been playing upstairs, I have mostly been hearing it (loud and clear), through the huge air return hole where I could actually see right into the living room upstairs. Now that the air return joist cavity is completely wrapped and sealed with layers of sheetrock and Green Glue, I can’t hear sound coming from there anymore. I can still hear the radio, but it is softer and it’s coming from other areas.
I wanted to figure out where it was coming from, so I climbed up and down the ladder — sticking my ear in the ceiling in at least 20 different places. Finally I discovered that it was coming through the loudest from the two long, round metal air ducts that runs from the HVAC trunk at the back of the studio, all the way across the studio ceiling joist and eventually up into the bedroom floor above. One feed the bathroom (the one on the left of the picture that you can’t see) and the other feeds the bedroom. (the arrow pointing to the duct on the right).
I’ll seal these both up and then go from there. I’ll still put a double layer lid on the bottom of them, but I’m not really sure how to attach the lids because both sides of the joist cavities aren’t accessible anymore now because I’ve already sealed the adjacent joist cavities with lids. So, instead of screwing the lid in from the sides- like I did with the others, I’m going to have to attach small blocks of wood that I can screw the lids up against.
The wood I screw the lid to has to be really strong wood — so the screws don’t strip out or pull out. I think I have the perfect wood. I recently inherited the family dinner table I grew up eating at. There are 10 children in my family plus mom and dad, so a large sturdy table was a must and it has been an amazing table with lots of memories. I’ve taken apart many radios and various mechanical things throughout my childhood. I completed homework assignments (not as many as I should have) and comically watched one of my sisters take mushrooms off her plate and hide them on the floor under her chair. I even fixed a bike and a small engine or two on that thing (sorry mom if you’re just finding this out now).
It is really nice white oak but after a couple decades almost of being in a very humid area in Washington state near the ocean, the glue joints are all drying out and splitting now that it’s here in Utah. The table has basically fallen apart, but was just being held together with a few screws.
My parents were very kind to allow me to repurpose it once they discovered it wouldn’t make sense to try to restore it. The top slab had already split into its various strips. I have set those aside for the time being. For now though, the side supports that aren’t big enough to really use for anything, will actually be perfect for what I’m needing.
In fact, after sticking my head up into the joists some more, I’ve discovered that I’m going to have to seal up another supply duct joist as well. So, I’m going to trim the side supports into strips that I can then cut into 3"-4" blocks that I can attach to the bottom strip of the joists. Lot’s of cutting, so here I go. Like an Eskimo, I’m going to attempt to use every single part and piece of this amazing solid wood.
What’s really cool, is I will forever benefit now from my childhood table in I way I never could have imagined. Thanks again mom and dad!
Wow, this wood is quite hard. It does cut, but the saw has to work a lot harder than it did with the douglas fir framing studs.
The blocks are going to work great. Pre-drilling the holes went ok, but wow, that wood is really dense. The wood is so hard that it made the sharp drill bit seem dull.
Using the same idea as the joist muffler I built for the fresh air ventilation, I’m nesting the supply ducts in insulation to help absorb sound pressure that leaves the duct. Also, to help prevent studio sound from entering the ducts which would push sound into the bedroom.
Just a little more nesting with R-19 ceiling insulation and I can attach the lid.
The bathroom supply lid is on and worked great. Now the bedroom supply lid.
There is something highly satisfying about this process.
The oak blocks are working great!
I’m Installing a lining of insulation along the bottom of the duct and then I’ll seal it with a double layer lid.
This all actually went pretty smoothly. I realized I don’t have a final picture of all the lids on, but I will a little later. The air return and supply ducts are sealed and isolated and I don’t hear sound coming from them anymore and they don’t hear sound through anymore them from me. Mission accomplished!
