Noctua NF-A14x25 G2 PWM Sx2-PP 1500RPM 140mm Next Gen Push-Pull Fan Set\n\n[features] The NF-A14x25 G2 PWM Sx2-PP is a set comprising two NF-A14x25 G2 PWM square-frame 140mm fans with slightly offset rotational speeds. This design is particularly advantageous for push-pull configurations and scenarios where two fans operate in close proximity\u2014such as in case cooling applications or on 280mm water cooling radiators. When two fans run at nearly identical; constant speeds in a push-pull setup\u2014or; to a lesser degree; side by side\u2014their acoustic interaction can give rise to undesirable harmonic effects. These include intermittent vibrations and periodic humming caused by interference; which may manifest as beat frequencies. To mitigate such phenomena; the two fans in the Sx2-PP set are deliberately offset in speed by approximately \u00B125 RPM. This fine-tuning is made possible by the fans' innovative etaPERF motor in conjunction with the NE-FD6 driver IC; which allows for ;