in terms of 80mm fans what is dba and how does the meserment work and what is cfm in terms of air flow (i know this is n00b, but i need some help)
dBA is the measurement of ambient noise with a standard A-type contour filter applied. If that doesn't help you, try looking at this page:http://hyperphysics.phy-astr.gsu.edu/hbase/sound/acont.html All you really need to know is any measurement in decibels (dB) is telling you how loud something is. For fans, lower dB rating is quieter and more desireable, but low noise fans often don't push as much air (CFM). As for the measurement of the noise levels, a microphone and a decibel-meter is all that is needed, but the real question is how far away from the object were the readings taken from....Notice how companies don't tell us that
all you really needed was to in particular: www.onelook.com http://www.onelook.com/?loc=reg2&w=cfm http://www.onelook.com/?loc=reg2&w=dba
How long is a piece of string? What you need to decide is what is important in your case: performance (CFM), silence (a dBA of 25-ish or lower), or a balance between the two. More performance (CFM) inevitably means more noise. Anything above 30 dBA becomes pretty annoying. Also keep in mind that bigger fans can produce more airflow with less noise. So a 120mm fan is desirable over a 80mm fan if the space is there to accomodate it. Even when a 120mm fan is loud-ish, it makes a lower frequency noise than a 80mm fan, and most people find that less intrusive.
25 ish you can't even hear, 30 is a whisper, the human ear can't hear a 25dB noise. The way that dB's work is say you have something that is 55dB and you put 2 of those than the total dB rate is 58dB's. The level goes up 3dB for each time the noise doubles. most high end speakers go up to about 107dB or so and standing outside while a commercial airliner takes off is about 130 dB's
It all depends on the scale, dbA dbC, unweighted, then you have the setup on sound systems, where -20 db would be line level, and 10db would be clipping. So it does matter a lot what scale it is on. The way most fans are measured you can definitely hear a "25db" fan from a meter or further away provided you are in a quiet room.
I can definitely hear my 21dbA fans. Moreover I have five of them, plus the PSU fan, and that all starts to add up. And the case can act like an echo chamber. Furthermore as Conkbot points out, measurement can be a fluid concept and you will find that manufacturers are a bit generous with their specs. Their fans are never quite as quiet or powerful as they promise.
