[TenTec] Noise from Fans

[Rick - DJ0IP / NJ0IP]

The noise of all fans is highly dependent on their speed and the
relationship of speed to noise is not linear.
It may be log rhythmic - I can't recall the exact relationship.  But the
racket goes up much faster than the speed of the fan does.

Reducing the voltage to a fan and slowing it down just a little, greatly
reduces the noise it makes.  In many applications, the fan is overkill for
the job and its speed can be reduced in favor of a quieter application.

In one of my ex-lives, I owned a small company producing PCs.
At the time, most small PC towers had small case fans that ran on 12v,
turned fast and made a lot of racket.
I found a case actually designed for a small server, which had provision for
a large boxer fan.
Running on 12v, the larger fan would have been total overkill for the medium
speed PC.
I ran it off of the 5v line.  It ran slow but did the job just fine, and you
could not even hear it.
All you could hear from the PC was the faint noise from the disk drive or CD
drive movement.

It is always better to use an oversized fan and run it on lower voltage, if
you have the space to do it.

A good example of where "we" can implement this is with the external cooling
fan option for TT transceivers.  
The fan bolts to the heat sink on the back of the rig and plugs to the 13.8v
Acc jack.  If you insert a few diodes in the line in series with the d.c.,
you drop the voltage a few volts, slow the fan down to the point it is
inaudible, yet it still works well enough to keep the heat sink cool.
Voila!

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

----- Original Message -----
From: "Bob McGraw - K4TAX" <RMcGraw at Blomand.net>

>From an earlier commercial product which I was associated,  we learned that
"tip speed" of the fan creates noise.  So less RPM larger and more blades
mean lower tip speed for a given amount of air.