Noctua NF-A12x25 G2 PWM Sx2 PP chromax.black 12V 2nd Gen Quiet 120mm Fans\n\n[features] The NF-A12x25 G2 PWM Sx2-PP is a set of two NF-A12x25 G2 PWM 120mm fans that are offset in speed; which can be beneficial in push-pull operation as well as in situations where two or more fans are operating side by side; such as in case cooling applications or on 240 and 360mm water cooling radiators. When two fans are running at almost the same; constant speed in a push-pull configuration or; albeit to a lesser extent; side by side; their acoustic interaction can lead to undesirable harmonic phenomena such as intermittent vibrations or periodic humming due to interference; which can be heard as beat frequencies. The two NF-A12x25 G2 PWM fans contained in the Sx2-PP set are slightly offset in speed (+/- \n50 RPM) in order to avoid such phenomena. This fine-tuning is made possible by the fan's novel etaPERF motor and its NE-FD6 driver IC that achieves extremely precise speed control and; thanks to ;