Alphacool SL-15 PWM: Low profile does not equal low airflow

Extra tests, Fans | | Ľubomír Samák

Results: Frequency response of sound with a dust filter

There are situations where standard 25 mm fans will not fit. Even the 120 mm format therefore offers lower alternatives. The first thing that naturally comes to mind is that such fans mean a trade-off in cooling efficiency. However, this may not be true and the hassle of thinking about how to fit a thicker fan inside may even be quite unnecessary. A well-designed rotor can achieve fully-fledged results when compared to a thicker rotor, even if it is slimmer.

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.

Noise levels in the tables below -87 dBu (but watch out for the negative sign, -70 dBu is louder than -80 dBu) can be ignored. They are in fact extremely weak and always far below the limit of human perception, and are often defined by the “noise” of the measurement string. Therefore, do not take even the dominant frequencies within the treble band that exceed 12 kHz too much into account.

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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