Any chance of definitions for the various orientations?

Vertical, Shaft Center Line Parallel, Perpendicular are mentioned

Basically, ball bearing fans can be used in any mounting angle -- blowing up, down, sideways. Traditional sleeve bearing fans should only be mounted vertically. In a typical tower case, this means the sleeve bearing would be fine as an exhaust or intake fan, but not as a blow hole fan on top of the case, blowing up. It would be fine as a blow down or up fan on a conventional heatsink, and also pointing towards the back panel on a tower heatsink -- but not blowing up toward the PSU on a tower heatsink.

What a brilliant article. It's safe to say this is the most exhaustive free resource dealing with the design of acoustically benign small axial fans on the web. The exhaustive section on bearings and the causes of noise (ie vortex shedding etc) were particularly rewarding.

Indeed, this is a great resource. Thanks for all the time adding this very important aspect of silencing.

In response to some critics, I've...

1) added a conclusion.... missing originally
2) increased the resolution of Neil's fan comparison images on the 3rd page.

Thanks for the precise praise, jaganath.

As you might have guessed, most of it was simply presenting the information I compiled in a last minute scramble to ensure the article was ready in time to support Devon's roundup piece.

One more thing, just added: A Postscript on page 4, in which Dorothy Bradbury answers a Russ Kinder question, What makes one fan spin at 2000 rpm's and another at 4000 when the same voltage is applied?

God bless Dorothy, she has probably forgotten more about fan design and manufacture than any of us will ever know. Please pass on copious thanks from me and I'm sure all at SPCR.

Brilliant! Especially the post-script, which answered some questions I had been thinking of for some time.

I had assumed that fan speed was controlled by different winding designs for a given speed, which led me to believe that a higher speed fan would require more voltage to start, due to more resistance from more windings. Apparently this is not the case? Instead, all fans start at roughly the same voltage, but the speed they spin at a given voltage is dependent on the default switching speed?

Excellent, some very interesting points.

MikeC - if you don't have one already, you could seriously consider writing all your work up as a PhD thesis, there's certainly enough research there. Whether you'd want to or not is an entirely different matter though

:

Not in this article alone, I'm afraid. Maybe everything I've done w/SPCR -- Qty is probably adequate, and maybe even quality.... but which department / discipline would ever consider SPCR relevant enough for them?

no. not just this article, but all of the others... I guess you'd just have to find some supervisor broadminded and interdisciplinary enough, probably in electrical or mechanical engineering, systems technology, even social sciences (for the impact of of computer noise on operators aspect). It's about as far from my field as you can get (molecular parasitology), but I'm sure there are people out there that are interested, it's just a case of finding them.

Then all you'd need to do is sign:

"I, Mike Chin, hereby sign away half of my sense of humour, with the balance payable on completion of my thesis"

and you'll be done!

Sheesh... I dunno if trading away all of my SoH (and probably $50k for the title) is worth a PhD in SPC even if I'm the first and only ever....