Ceiling Exhaust Fan -How loud is .5 sones?

Thanks Aby,
Since I wanted to avoid ANY unwanted sound in my HT room, the design that you mentioned (relocate the fan futher away) was first on my drawing board. But if .5 sones is an exeptional number, then I can live with it. Problem is, what is .5 sones equivalent to realife example?
This is what you are talking: http://www.youtube.com/watch?v=B-qWg60xFtY

Forget Sones those are all WAY to loud - sound like jet engines. You need something with DbA of around 10 at one meter (a big very slow moving fan if you want to move a lot of air). You can hear about 15 to 30 db below the noise floor and this means you will hear any and I mean any bathroom type evacuation fan.

You will need to go custom, IMHO.

Here is a Calculator

Here's some info....

http://www.sengpielaudio.com/calculatorSonephon.htm

I run a whisper fan that is rated at about 30db,too lound. So I have reduced the fan speed in half and sitting 4ft away i can barely hear it.

If I read the graphs right .5 sone = 30 phons which in db level would be about 30db. I think you need to put a potentionmeter on this fan and reduce the speed in half.

Does it have to run while listening/watching, or can it be turned on and then back off, or during some other times?

Noise then wouldn't be as integral an issue.

Insulating the housing the fan would reside in would attenuate the sound... like a whisper box for a projector or what ever they call that added box surrounding the PJ.

Speaking of which, with the lamp turned up to full brightness I can hear the PJ runing... until I turn up the sound of the whatever... Flick, CD, etc. Then of course, the noise is not a consideration.

Adding to the insulation of the fan housing, or even setting it into a duct work which turns by 90 degrees should also diminish the noted or audible sound of the motor itself. Further lengthening the ducting, and thereby removing the fan still farther away will surely decrease the noise it makes.

Go with a large register as you can too. that will help.

Good luck.

BJ,
Yes,the exhaust fan must run when the system is on to get the heat up on attic. Reason I'm looking for maximum quiteness is because I listen to soft music on low volume normally at 2 to 4am. So basically, at these hours, I will hear everything else as well.
I just read an DIY article about an exhaust fan with .5 sones and the author gave a real life example: In his bedroom, the fan ran very quite that he was 10' away and he couldn't tell if it was On or not. That's a very good info for me.