what do you mean? you mean you have a 8cm blowhole below and you want to suck air from the hole using a 12 cm fan? well. funnel adaptors are great to retain the casing design while ultilizing a bigger fan. but do take note that there might not be improvement in noise reduction. instead it'll interfere with the flow of air and causes turbulance. this will generate more noise. so my advise is to mod the hole for a bigger blowhole