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Re: Cooling fans

>to replace the AC fan I am using in my current fan because it produces a
>relatively loud ?whirring/whining? sound that can be very annoying at times.

That's a characteristic sound of a dieing bearing.

>I have been doing some research on AC fans and have found several I am
>considering.  I?ve read up on their CFM and dBa ratings, but don?t really
>understand what they mean.  To be more precise, I KNOW what they mean, but I
>cannot correlate the ratings to anything that means anything to me.  I know

CFM = Cubic Feet per Minute, the volume of air the fan moves. dBa is a
measure of sound pressure (decibels), a weighting uses a response curve
that approximates human hearing and thus results in a measure of loudness
to people. Some rough ideas of sound levels:

whisper = 30 - 40 dB
conversation = 60 - 70 dB
Loud buzzers = 90 - 100 dB
Pain threshold = 130 dB

It is a logarithmic scale, with a 3 dB increase representing a doubling of
noise level, and 10 dB representing a 10x increase. 30 dB is a 1000x

>any information on the noise level of my fan.  I was hoping someone here
>could give me a hand (***Applause*** Ha! Very funny!).  I am currently using
>a Radio Shack 3? 120VAC cooling fan catalog #273-242.  Does anyone know the
>dBa noise level of this fan?  If so, it would really help me in choosing a
>quieter fan for my new hood.  TIA!

The radio shack fans, while overpriced, are typically of reasonable to good
quality. I would guess that your fan is probably in the reasonably quiet
range, maybe 35-45 dB or so. That would be a NEW unit though, and remember
that mounting a fan in a resonant enclosure or on a board can act to
amplify the sound. It is common practice for things that need to be quiet
to mount the fan on a foam-rubber pad using rubber washers around the
screws. The isolation this provides results in a surprisingly quieter fan.

You can find a good selection of quality fans from DigiKey
(http://www.digikey.com). I like the Comair Rotron units myself as I use
them commercially and have found them to be reliable over long periods. I
recommend you try some surplus places first though
(http://www.allelectronics.com and http://www.meci.com notably), since fans
often show up surplus brand new for around $5 or so which is a lot less
than the usual $15-40 that you'll spend on a new fan.


Waveform Technology
UNIX Systems Administrator