The next graph shows how much noise AMA’s coolers produce in the entire speed range of their default fans.
AMA’s coolers are not quiet overall. Although the Elf and Phantom have the same fans, they differ greatly in terms of noise. The same goes for the Orc and Stormblazer. The AMA Phantom is the quietest of the four, its noise being comfortable up to 1500 RPM. The fan does not rattle and the heatsink fins do not clank at any speed. The Elf is louder than the Phantom but does not produce parasitic sounds, either. This cooler is acoustically comfortable up to 1350 RPM.
The coolers with 120mm fans are louder than the Elf and Phantom. The Orc and Stormblazer are only comfortable up to 1100-1150 RPM. After that speed, they differ from each other. The Stormblazer’s heatsink fins begin to rattle and clank because they are not soldered up. That’s why its noise graph is not linear.
The bottom speed of each cooler could be achieved at 6 V. When the voltage was reduced by 0.5 V more, each fan would slow down twofold (to 450-500 RPM) and produce a distinct hiss.