View Full Version : Fan RPM vs. Volume? What's the relation?

03 March 2003, 11:13 PM
Btw, I took my old heat sink and fan and threw it onto my bro's 1.2GHz Athlon T-Bird.

His case is hidden in his table in one of those compartments built for computers so u can hide them away. So naturally... the temp is a bit high. His case stays @ about 75-80*F. The CPU metal contact die temp with my old heat sink and fan is about 50*C.

So the question is:

The fan is one i jacked from another Cooler Master copper block fan. For some reason, it will not go past 3000RPM. However, the fan looks very tall, big, so I assume it will get more air through per cycle.

The original fan was a fan that came with the coxed CPU. It's an AMD. I took that fan and stuck it with another heat sink, a copper one from Cooler Master. That fan goes @ like 4500RPM!

So should I combine the large copper block with the tall slow fan that goes @ 3000 RPM or with the small thin fan that goes @ 4500RPM

03 March 2003, 12:28 AM
Actually, scrub that. I got my laziness away and worked on his system and it turns out the damn cooler master wasn't working as well as it should have... not only will it not work with the BIOS to give a reading on its RPM, it doesn't cool that well. The CPU temp hit 50*C easily and the boxed fan from AMD kept it @ about 48*C... not much of a difference, but where that guy has his case, every bit counts.... I even spent some time to re-arrange the fans and get this circulating correctly including the addition of a bay fan for the hard drive which runs pretty warm too..... aren't i so considerate? 0=D

03 March 2003, 12:49 PM
Fan rpm is not indicative of performance...or noise.

A smaller faster spinning fan, produces more noise then a larger slower spinning fan. It also produces less airflow.

One of the biggest movements in the heatsink market of late is to 80mm sized heatsinks. Heatsinks like the thermalright AX7, SK7, and SLK800 have moved from the traditional 60mm cooling fan's to 80mm's (and 92mm with the 900).

This allows for the fan rpm to be significantly less (2500 rpm instead of a delta's 6800), which results in a greatly reduced noise level...WITHOUT a performance penalty.

Here's a quick rule of thumb.

The higher the rpm, the louder the fan.

With fan size as a constant, the higher the rpm, the more airflow produced.

The smaller the fan, and the higher the rpm, the higher the pitch of the noise. (A delta produces an infamous whine)

With rpm as a constant, the larger the fan, the more noise and airflow produced.

With airflow a constant, the larger the fan, the lower the rpm has to be to produce the same amount of flow.

There are some fan's which throw a slight wrench into this whole mix. Like YS-Tech's T.M.D. fans. They run at a mid range rpm (5000) but produce significantly less noise then fans of similar size due to a widely different method of driving the fans.

03 March 2003, 06:39 PM
Thanks for the nfO Greg. I finally took a look @ those fans on my bro's system and it turns out the coolermaster was all defunct or something. On my workstation, it only ran about 3200 RPM max. On my bro's system, it won't even give me a reading. So I put on the original boxed AMD fan onto the heat sink (which was much smaller but much faster) and I managed to keep the contact die temperature @ 48*C. The coolermaster which was big but slow, easily let the temp go past 50*C.

As for my own system, that Vantec Aeromaster r0xurz!! My contact die temp has gone down from 61*C to 51*C!!!!!! The thing sounds really sweeeet too. The coolermaster i originally used was much quieter but this one actually has a nice sound... like a humming of a jet engine? something like that... it sounds coooooooL.....:drool:

but argh, the Antec drive bay cooler I'm using has a very irritating annoying sound... -.-"

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