Here’s a little scientist type stuff I found that you could throw at you downstairs neighbor…
“Deflection
Deflection of sound is achieved by adding mass and density to any structure such as a wall, floor or ceiling.
All solid materials which have a thick consistency and are dense or somewhat heavy, can help to block sound.
By adding mass and dense materials between the source of the sound and the receiving point will offer additional bulk that the sound wave will have to pass through and in doing so will reduce its energy.
Increased mass and density of a wall ‘s construction can be achieved with concrete for example, or dense finishing boards such as ply, OSB, drywall or plasterboard.
Deflection with mass and density proves more effective with airborne sounds such as voices or music, and not so effective with impact noise such as foot fall, which is usually associated with stronger power, pressure and therefore vibration.
As sound waves strike the mass and dense materials, vibration will occur and in doing so will pass the energy from one side to the other through the materials’ own rigidity.
This is the principle of flanking transmission noise – a common problem with all structural scenarios.”
There’s a lot more to read if you’re interested…
https://www.acoustiblok.co.uk/sound...is cleverly converted to a trace heat energy.