Basement Home Theatre Noise Proofing
Boarding done, with little left of the the 20 odd sheets this area soaked up.
I've been doing quick sound tests to see how effective (or not) the sound "proofing" treatments are as we close things up. The measure rig is just my iPhone 6s plus, using the SigScopePro app. The reference pink noise (equal energy across all frequencies) is provided by my computer, which I measure at 94.5 db, about 3 ft away. The computer sits in the basement, just adjacent to the theater area. The three measure points are in the living area on the 1st floor. The loudest point is at a cold air return on 1st floor, almost directly above computer. Our first floor living room is directly above the theatre.
The most important is the last measure point (on floor by couch) as this is in the middle of our living room above the theater. That's where we're looking for max noise attenuation. Here's my ad hoc data table so far

If you're planning on doing a renovation with noise control, this stuff might help.
BASELINE TESTS
iPhone SigScopePro pro meter, Level-Lp, Weighting-A, Response-Slow.
Reference Pink noise from computer sub/spkrs in basement office nook, below 1st floor test areas. HVAC room (completely open) right beside computer. 94.5 db. Pink noise (20 Hz to 20 kHz)
1. Just after demolition, furnace room open, ceiling open, zero sound treatment, both cold air registers open from below (drywall removed):
At cold air return register by front door 65 db.
On cold air return register by south wall 64 db
At floor (on floor) by couch 51 db.
2. Computer in front of basement air return, air returns treated and closed in, floor insulation (R22 Roxul) only, no drywall:
At cold air return register by front door 60 db.
On cold air return register by south wall 57 db
At floor (on floor) by couch 48 db.
3. After two layers 1/2" ceiling dryall + Green Glue, not taped or sealed, furnace room and basement walls open/bare.
At cold air return register by front door 58 db.
On cold air return register by south wall 53 db
At floor (on floor) by couch 44 db
4. Drywall done, no mud. Open equipment rack covered by loose sheet of drywall.
At cold air return register by front door 55 db.
On cold air return register by south wall 46 db
At floor (on floor) by couch 42 db
Essentially a loud 94 db pink noise in the basement is now dropped to 42 db (a library is in the 40db area) in the living room...and there's still more noise work to do. The media rack needs to sound treated and sealed from the HVAC room, and plenty of door work (add mass, weatherstrip) will happen on the HVAC and electrical room. The biggest drop is the air return on 1st floor, in living room which started at 64 db, and has dropped to 46 db. That's 18 db, or about
4 times quieter than when we started. Pink noise includes equal energy from 20 Hz to 20 kHz so the computer sub is rumbling pretty good in this test. We'll likely never listen in the theatre at 94 db as those levels are rather offensive, and after 4-6 hrs likely would damage your hearing.
You could summarize the steps I took as follows:
1. Build duct mufflers on supply air ducts, and air return in basement theatre area. This keeps noise from propagating throughout home via metal ducts.
2. Acoustically line 1st floor air returns in theatre ceiling.
3. Insulate ceiling with R22 Roxul.
4. "Strap" ceiling with 25 gauge steel studs.
5. Apply two layers of drywall and Green glue.
6. (not done) air seal/add mass/Green Glue to basement HVAC and electrical room doors.
The basement walls are spray foamed with R24 or so, and somewhat decoupled from the floor joists, however resilient channel on those walls would have helped. I chose not to do that as floor space is scarce..so every inch matters. Closed cell foam is not a good sound block, although it's hard to beat for air sealing. If you hammer on a stud surrounded by rigid closed cell spray foam it's surprisingly loud as the foam acts a bit like a speaker.
If I had more room, no question I would have further isolated walls and ceiling using sound isolation clips and "hat" channel. However, because the basement is open, ALL of it would need to be done..not just the theatre section. One must pick their battles when it comes to noise control
