QuickFix wrote:

ways of *cheaply* reducing the volume of the sounds passing through our
shared wall without actually turning the volume of my music down. Some
people have recommended egg cartons, carpet tiles and even hanging a duvet
from the wall, but what I'd like to know is; do any of these methods
actually work? And if not, can anybody recommend some similarly cheap
alternatives?

Build a room within the room, solid, airtight and
suspended on springs from the roof.
If that doesn't attenuate sufficiently,
build a room....

--
Roger.