More weaknesses to my soundproofing objective identified and fixed this past weekend:
1. HVAC return duct
On the upper floor, there is a hallway where there's a return vent at the bottom of a wall. Return air enters that vent, goes down through a hole in the floor, across a joist cavity, and into the return trunk ducting. This joist cavity is in the media room. My first naive attempt to address this months ago now was to
-remove the metal sheeting that was nailed to the joists that boxed in the joist cavity to create the return,
-recreate a shallower return duct with Thermopan (foil faced cardboard meant for HVAC return duct construction) to allow space for a batt of Roxul Safe and sound insulation to go in between the return duct and the ceiling.
No real mass and only a little absorption= WEAK!
I pulled the Roxul down and boxed in the return duct with 5/8 drywall, and then sealed up all the joints with LePage PL Acousti-Seal.
PL Acousti-Seal is the nastiest substance on the planet. It strings up and falls onto everything within a 4' radius and is a nightmare to clean up. I've only ever used this to seal vapor barrier to studs previously and had a few tubes left over from that job, but never again for SP purposes. I hope the GG SilenSeal isn't as nasty.
While I was there, I also removed another return going up a wall cavity into the same return trunk above. I closed off the opening with some more Thermopan and tuck tape, and now will add some drywall and acoustic sealant within the stud wall cavity.
2. Another interior wall received a dose of DD&GG medicine.
The south wall of the bar has a washroom on the other side that I don't want to receive sound/noise from. So, again following Soundproofingcompany.com's 'how to insulate a ceiling page', specifically, SPC Ceiling Solution 4, I added green glue and scrap 5/8 drywall within the stud cavities of the wall to dampen and add mass to the recipient wall. It was tough getting in all in there around plumbing, etc, but I've added mass and damping to that recipient wall.
I also 'painted' the plumbing pipe with the AntiVibe DL, as well as the back of the shower stall. While it might not dampen these noise emitting items much, the Antivibe itself is heavy, and it's mass makes them vibrate less. I've got leftovers of it, and hate wasting materials, so spending it wherever I can.
When I first used this DD&GG within stud wall cavity technique on my staircase wall, I also applied acoustic sealant across the drywall seams and around the perimeter of the studs, and top and bottom plates.
Should I also acoustic seal up all these joints (albeit with a friendlier acoustic sealant) or would that be a waste of time? I've added mass and damping already so am I done and just OCD?
While I was there, someone hit the shower while I was working so I loaded up 3 lbs of Duct Seal over the water valve and copper piping leading up to the shower head that was whining from the water flow. I could hear it getting quieter as I applied it so that was interesting. It didn't eliminate it altogether, but the pipe is mounted to framing, so hands-on lesson in flanking learned!
Next is to isolate the back of the shower from the source side. My plan is to insulate, then slap up a sheet of drywall inside the stud wall cavity.
I've read about the triple leaf effect... does that apply here with the fibreglass shower wall acting as the third leaf? I'm thinking not because it's light and flimsy and thus has a different resonance than drywall. The source side of this wall will be clipped and DD&GG, so from source to recipient side in order will be: DD&GG, clips, studs, insulation and an in-stud drywall sheet, insulation, shower wall. Advice?