ducting

i just thought i would share some observations of the different types of ducting i have used since starting this hobby.

tumble dryer vent duct is fine but a little too flexible for my liking.
stiff aluminium foil duct is good but will develop pinholes in it eventually.
acoustic ducting is a nightmare to work with or at least the piece i bought was as the fibreglass filler between the pipes was awful stuff.
combi ducting is the best stuff i have used so far, silver on the inside and black on the outside not sure it dampens the sound much but the double skin of the pipe gives me a little extra piece of mind that its not going to leak.

as the filling is fiberglass its more difficult to get and keep straight and taut which can be a nightmare. the noise comes from turbulence as the air passes over the spiral winding inside the duct. the smoother the inside of your duct is the less resistance there will be leaving you a little quieter running. i have a filter/fan/silencer/ducting set up which brings me down to super quiet and with my fan controller turned down at lights off its down to nearly a whisper. 

the layer of fibreglass between the inner and outer pipes is very thin and flexible or at least it was with the stuff i had so sanding is not an option. if you were to put it in some box trunking, that would help absorb some the sound as its reflected back in to the fibreglass off the trunking. when i do my next refit i will be using a mixture of solid and combi ducting to try and get the best out of my fans, filters and silencers.