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We dont have any device to check the actuall noise level but if 23.5 DBA is accepted quiet this fans are not 23.5 as i found them little too loud. i assume only way to use them is 5V . It runs really quiet at 5V.
Other option is changing the fans on bracket with any other fans like YSTech 20 DBa Fans.

There is 2 80 mm fans on the bracket each fan blowing 30 cfm so altogether it is 60 cfm. Also model number of the fans used on the bracket are EC8025M12S . According to evercoiol this fans run at 23.5 DBA. Also if 23.5 DBa does not satisfy; you can reduce the voltage to 7v or 5v . So overkilling is ...

it does not come with thermal sensors it reads the tempreture from bios. It looks nice...

Why dont you try our system bracket fan. Specially designed to cool pci cards by directly blowing air trough them. http://www.quicklyshop.com/shop/images/sys_bracket_fans.gif FAN: 80*80*25mm Movable design, adjust the proper position for best performace. Reduce your add-on cards and mother board ope...

We are working on Panaflo fans also but PANASONIC Europe do not supply Panaflo fans currently europe.
Only option i have is ordering them from US in 1000 pcs quantity from a US reseller. To order direct from Panasonic ASIA minimum requirement is 100,000 pcs

We will be getting YSTECH 80 mm 20 DBA Fans in 1-2 weeks time. So you wont need to go for Panaflo ones