[Test-Equipment] Choosing a quiet replacement fan

[Dave C]

I read occasionally that owners of T&M equipment tire of the noise a cooling fan makes and asks for help to determine if/how a quieter replacement can be found. There are many factors at play in such a decision, none as simple as "it's quieter". 

This web site addresses choosing a fan for PC enclosures, and many of the criteria are the same (heat being the most important one for us):

<http://www.silentpcreview.com/Fan_Test_System_2010>

A quote:

"Over the years, we have observed one clear phenomenon about fans and cooling: The relationship between airflow and temperature invariably becomes exponential at some point. Increase airflow from nothing to something, and the drop in temperature can be dramatic. Keep increasing airflow, and the cooling improvement becomes less and less significant, until at some point, the temperature hardly drops at all. The trick, for the PC builder who seeks both good cooling and low noise, is to find the point where any decrease in airflow (or fan speed) effects a significant increase in temperature, while only a very large airflow increase effects a significant temperature drop. In other words, once you have enough airflow, additional airflow has very little cooling effect, so all you're doing is increasing noise. "Enough airflow" is not a constant, of course, it varies for each system of components."

FYI,
Dave