[time-nuts] Replacement fan in SR620

Charles Steinmetz csteinmetz at yandex.com
Sun Feb 2 15:58:40 EST 2014

Magnus wrote:

>Also, the fan-noise did not change a lot by drying to damp the top 
>lid, so it seems the fan emits it mostly as a direct mode.
>The older unit has a high hiss to its fan

That is what I have observed, as well.  The noise is mostly fan blade 
noise and some bearing noise coming directly out the back of the 
unit.  I did not find that the inlet vents were a significant source 
of noise, or that increasing the inlet area caused the fan itself to 
run quieter.

You probably wouldn't notice a substantial noise reduction until you 
got down to a fan with a 15-18 dBA noise rating, and that would move 
so little air that you'd probably fry the counter.  The Papst fan has 
about the same noise rating as the original Delta, so I wouldn't 
expect changing the fan to have a big effect on the amount of noise 
(but, as you say, the noise spectrum may be different).

Best regards,


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