Go any poultry farm and buy some cheap egg cartons (without the eggs). Usually the ones that can hold 36 or 48 are the best. Or you can eat alot of eggs for a while.
We used this type of sound proofing for our schools internal radio station. It worked perfectly. Just use wood glue to stick it on the wall.
Need more details! We use self adhesive sound insulation from a small local manufacturer here in the UK. Where are you and what are you sound proofing?
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'The truth is out there' The lies are in your head.
Try to use rockwool. It's a little bit expensive but their results are quite good. We are usyng in ships that we built and it seems the Shipowner can sleep all night long...