can i quieten a fan?

[templeball]

Can anyone help pls - Is there a way of making two cable suspended 'airforce' fans (one 4 inch the other 6inch) quieter, safely - and does the duct tubing make more noise if it has bends in it when the fans are working does anyone know, might that be a contributory factor to the bloody racket it all makes. BTW apparently the fans are operating fine normally, thats not the problem

[Trad]

You mention that they are hung from cables, perhaps the cables are vibrating and tranferring that to the rafters. My friend has his hung from rubber straps and no problems...so far. I have also noticed that the vibration is amplified by the flexiduct.

[Drugsbunny]

Hi, yes the more bends you have the louder the throuput of air will be . Try to keep the ducting as straight as possibe and make sure ducting is tightly attached to the fans. Use insulated/ accoustic ducting

[templeball]

thanks everyone so far
first of all straightening has helped now it doesnt rattle so much so thank you, but discovered the main cause of the loudness was the shitty new SMSCOMS speed contollers which ive read up on are commonly said to give a hum with the airforce fans, so it looks like the proper air force speed controllers must be got to eliminate that bit of the racket..also I was feeding the 6 '' outduct into a 4'' hole, that has been altered and that has made it quieter also
live and learn