Gaps or no Gaps where the floor/walls/cieling meet?

I have learned so very much here. Thank you mods/Rod/John for this wonderful resource. I think this is my last construction question before I get started. Hooray!!!! I'm only asking because I want to be absolutely certain of what I'm doing before I begin, and I haven't seen this detail in my searches. Please feel free to direct me to the appropriate thread if it exists. So: I believe I can reach my goal of reducing the dB levels at my property line by beefing up the existing inner leaf of my current room. At present, the dB level decreases from about 112 at the guitar speaker cabinet to about 64 at the property line. Any more reduction will be helpful. My question is: Should I let the new layers of mass butt up against each other at the edges, or should I leave a slight gap between them and fill it with acoustic caulk? Examples: Should where the floor meets the walls look like this: Or like this: Should where the wall meets the cieling look like this: Or like this: I hope I am on the right track with this. Perhaps it should look like something else, please let me know. Thanks!

If you've got a "floating" floor, then it should indeed not tough your walls preferably. Caulk it. You need caulking (around the perimeters) anyway, so a mixture of both ceilingplans will do. It can "tough" the wall since walls and ceiling are one construction (no decoupling, as per your drawings)

Thank you! Unfortunately the room is all pre-existing traditional house construction; nothing floating. Nothing decoupled. The floor touches the walls which touch the cieling. I'm just adding mass to the inner leaves of this existing situation, and making it as airtight as possible. Cieling: so I will let the added sheetrock on walls and ceiling touch; then caulk the seams as usual. Floor: would it make sense to have a gap around the newly added plywood floor and caulk it? It's not floating but would there be an advantage to doing that? There will be loud/vibrating guitar amps on the floor so maybe there is an upside to doing that. Or maybe because the floor is not floating it won't make a difference if the floor and the walls meet without a gap: Basically the structure is still all coupled but just more massive.

If it's already connect, then there's no extra gain. However, a finishing floor usually needs some space around the perimeter to let it expend. Caulking that can do no harm (as long as it's flexible). What's the neoprene for then?

Ro wrote:

What's the neoprene for then?

I'd rather not use it if it doesn't help. Do you think I need it?