What is the decibel value that the sound insulation cover of air conditioning equipment can reduce noise?

Ayffre acoustic noise reduction and sound insulation cover effect: noise reduction is generally above 18-25 DB. Generally, 0.5-2mm galvanized sheet, aluminum plate and other metal materials are used, and sometimes 3-5mm damping coating material is needed for the inner wall to reduce the vibration or standing wave phenomenon of these metal outer walls; However, the inner layer of the wall of the sound insulation cover is mostly the structure of perforated plate and sound absorption material, or some polyester sound absorption materials are directly pasted.