In certain applications silencers can reduce noise by up to 50% like an Exhaust Muffler on a Car.
This is where a fan silencer comes in. Placing a fan silencer in the airstream will help to absorb some of these sound waves.
When the sound waves enter the silencer, they expand into the acoustic media. The acoustic media is made up of millions of air pockets. When the sound waves impinge on the air pockets it causes the molecules to move and collide with each other dissipating energy in the form of heat. This is what gives you your noise reduction.