Re: Low noise fans

["S. Hieber" <shieber at yahoo_com>]

Giancarlo Podio gave a useful tip, saying, in part:

> . . .I have found the easiest and
> most cost effective
> method is to use regular brushless fans (from electronics
> supply) and reduce
> the speed using either a fixed resistor or variable
> resistor to tune the
> speed down to your desired noise level. . . Most of the 
> noise is actually air
> turbulance unless the
> bearings are bad or the fan is out of balance, there are
> special blade
> designs to reduce noise at high speed but they do get
> expensive. You'd be
> surprised how well the cheap fans run if the speed is
> turned down somewhat,
> also reduces any balancing problems the fan may have and
> lasts much longer.

Or you can just buy slower fans to start with -- you can
find fans in all price ranges.  If you use AC fans and put
a dropping resistor in series, you can muck them up
sometimes.  Dropping resistors are a great way to slow down
a DC fan.  And remember, a slightly larger fan turning at
the same speed as a slightly smaller one will move much
more air, and more quietly, other things being equal.

Cheaper fans tend to get noisier with age faster than well
made, well-balanced fans.

Consider, also, allowing for lots of ventilation of the
hood with openings instead of using a fan.  This can be
very effective, is totally silent, and never wears out ;-)

Most of my experience with fans comes from dealing with
audiophile sound equipment, where noise is anathema. 
Sleeve bearing fans are generally shunned in favor of high
quality ball bearing fans.  As a rule ball-bearing fans
stay quiet longer but the quality of fans within either
type varies more than the difference between types.  In
other words, you can get a good sleeve bearing fan that
performs better and longer than a not so good ball-bearing
fan but generally ball-bearing fans can be made to last
longer and remain quieter.  They often cost more too.

Sometimes a room fan will suffice.

Good luck,
Scott H.

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