Endorfy Stratus 120 PWM: Efficient fan on a budget

Results: Frequency response of sound with a dust filter

Why spend as much money on one fan as you would on four or five Endorfy Stratus 120 PWMs? There is a clear answer to this, but it may not be interesting to everyone. Especially when the fans are meant to fit well into builds designed with the best possible price/performance ratio in mind. That’s when low-cost fans make sense, and the end-user often dismisses the “imperfections” of the Stratus 120 (PWM) with a wave of the hand.

Results: Frequency response of sound with a dust filter

Measurements are performed in the TrueRTA application, which records sound in a range of 240 frequencies in the recorded range of 20–20,000 Hz. For the possibility of comparison across articles, we export the dominant frequency from the low (20–200 Hz), medium (201–2,000 Hz) and high (2,001–20,000 Hz) range to standard bar graphs.

However, for an even more detailed analysis of the sound expression, it is important to perceive the overall shape of the graph and the intensity of all frequencies/tones. If you don’t understand something in the graphs or tables below, you’ll find the answers to all your questions in this article. It explains how to read the measured data below correctly.

The sound of the 120 and 140 mm fans for the most part operates in the 70–700 Hz band. The bearings and motor operate between 1000 and 2500 Hz. Higher frequencies can be amplified by grilles or plastic filters (typically with hissing). Ignore the frequencies above 7000 Hz, these reflect electromagnetic noise from the measurement chain. This (electromagnetic noise) partially interferes with frequencies below 70 Hz as well, although there is still aerodynamic noise at these frequencies.

Note: For these measurements, a plastic filter is used, which, compared to a situation without an obstacle, bends the sound considerably more than a non-obstructive nylon filter.










Why is there a missing value sometimes? There may be more reasons. Usually it is because the fan could not be adjusted to the target noise level. Some have a higher minimum speed (or the speed is low, but the motor is too noisy) or it is a slower fan that will not reach the higher decibels. But the results in the graphs are also missing if the rotor is brushing against the nylon filter mesh. In that case, we evaluate this combination as incompatible. And zero in the graphs is naturally also in situations where we measure 0.00. This is a common occurrence at extremely low speeds with obstructions or within vibration measurements.


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