what quantity of a material is enough to convert 95 decibel to 65 decibel?

Question

This question is about soundproofing generator.

Answer 1

The "quantity" or thickness depends on the insulating material itself. You will want a material that can be attached to an enclosure, or which can support itself. A search on sound insulation will lead you to some good information.

Don't forget about providing a means of removing heat from the enclosure. Otherwise the generator will overheat.