I tested the decibels of the 140mm fan first. I tested each fan on each speed from a distance of one inch. I also disabled all other fans on my system with the exception of the CPU fan. On the lowest setting (5v), I got a 26.4 dBA rating at a distance of one inch. At the medium (7v) setting, my meter registered 32 dBA. On the highest setting (12v), I got a reading of 34.6 dBA. The airflow was also quite powerful on the highest speed. The medium speed was nothing to sneer at, either, and was a tad quieter. The lowest speed, while the quietest, felt like a light breeze. Maybe good for low power units, but for gaming I would go for a higher setting.
I removed the 140mm and connected the 120mm in its place. I used the same meter and the same distance of one inch to test on all three settings. At 5v I got a 22.8 dBA reading on my meter. On medium at 7v I got 30 dBA. And finally, on high at 12v I got 33 dBA. As with the 140mm fan, the speeds for the medium and high settings were good for a regular consumer or gamer machine, but the low setting should be reserved for a low power machine such as a home theater PC.
The noise differs slightly between the two fan sizes, but the airflow remains pretty linear at all voltage settings. At the lowest setting (5V), the FX-120LB produced 36 CFM (cubic feet per minute). At medium settings, the same fan produced 65 CFM and 89CFM at the highest setting. The larger FX-140LB moved more air at the same settings: 49 CFM, 73 CFM, and 98 CFM respectively. Both fan sizes seem to have the same efficiency; if you can handle a tad bit more noise then you’ll get a little bit more airflow.
My findings were that these fans are pretty much excellent all-around chassis fans. The multiple speeds on the fan are very handy when connecting to the PSU directly, although having to take the side of the case off to change the speed would be a nuisance for those who like to tinker. Most of us prefer fan controls on the front of the case, or at least a rear control. Other than that, I could find nothing bad to say about these fans. Good performance, adjustable, and the price is right.