Another Floated Floor / Drum Riser, with questions

[vanilladuck]

I'm building a basic drum riser based loosely on this layout:

Studio SOS: Ingestre Hall Residential Arts Centre

Just ordered Roxul 3" Safe'n'Sound from the local Lowes. While density is a bit low @ 2.5 pcf (40 kg/m3), my requirements are slim for total load:
- one drummer
- two drum kits (one acoustic, one electronic/vdrum)
- 8' x 10' top dimensions
- placement in a finished attic
- reduce/decouple structural-borne vibrations from the floor

Layers:
1) 3" Roxul rockwool
2) 0.451" finishing plywood (interlaced with next layer)
3) 0.451" finishing plywood (nailed/screwed together)
4) 0.5" or 1.0" side skirting wood, making sure NOT to contact existing carpet/flooring

This is one of probably many iterative changes I'll be making to the space to try and create a balance between sound absorption and recording/practice space for the band. Typical troubleshooting process: make a small change, measure results.

Questions:
a) Would adding MLV (mass-loaded vinyl) at 1/8" and 1lb/sf between the plywood layers help reduce vibrations or help absorb either structural or airborne sound?
b) Is there a large difference between screws vs. nails for the plywood?
c) Other than listening in lower floors and in the room, what methods can I use to measure the differences? (note: I'm on a budget but have access to recording microphones, some gear, etc)

Any suggestions/comments welcome! Thanks,
- Bryan

[gullfo]

using a layer of plywood on top which you can remove over time as the screws rip it up is a good option. adding the MLV won't really do much if anything. if need be go to 3/4" ply. remember to stagger the seams on the plywood layers (consider 90 degrees on the panels) as this helps ensure a nice flat rigid surface. you can also make smaller ones for speaker cabinets so you reduce the sound transfers from guitars, bass, and keyboards. use the heavier plywood or MDF for those and 4" insulation for bigger amps as the compression is higher.

[vanilladuck]

Thanks, Glenn

Access to the attic is cramped, so I had to cut the plywood into 2'x8' sections. I was planning on overlapping seams as you suggest, like Drum Riser diagram

Do you think stacking leftover 3" rockwool to create wall panels/traps and amp risers would be appropriate? (trying to conserve $$ a bit) The panels I would wrap in budget burlap cloth.

[gullfo]

try to overlap on 90 degrees instead of parallel offsets. also, you can cut the insulation to get it the right thickness and wrap it in cloth then set the panels on it. definitely try to use/re-use as much as possible.