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Stock Fan Measurements
As we mentioned earlier, the fans are attached using metal stands so they lack
the traditional square frame housing found on most case fans. However, the impeller
and blades are similar in size to standard 120/140 mm models. The CNPS9900 MAX
was equipped with a 1600 RPM fan while the CNPS9900DF uses lower speed variants.
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Zalman CNPS9900DF: Stock Fan Measurements
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Voltage
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Speed (Front)
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Speed (Center)
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Combined SPL@1m
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12V
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1060 RPM
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1370 RPM
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32 dBA
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9V
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870 RPM
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1070 RPM
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26 dBA
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7V
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710 RPM
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830 RPM
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20 dBA
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6V
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610 RPM
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700 RPM
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17 dBA
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5V
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520 RPM
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550 RPM
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14 dBA
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Measuring mic positioned 1m at diagonal angle from
the center of the heatsink.
Ambient noise level: 10~11 dBA.
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We're not crazy about different size fans on one heatsink due to possible intermodulation
effects on noise. It's also inefficient if each fan's individual noise output
is significantly different, i.e. one fan drowning out the other when set to
the same voltage/PWM setting. The CNPS9900DF wasn't bad in this regard despite
a 300 RPM difference at full speed. The center 140 mm model was the faster fan
and thus produced more noise, though subjectively, it sounded better.
At full speed the pair generated a pretty loud 32 dBA@1m but if you're noise
conscious, the fans can be reduced down to about 14 dBA@1m through voltage control;
the starting voltage was 4.8V and 4.0V for the front and center fan, respectively.
The quality of noise emitted by the 9900DF was simply put, bad. It generated
tonal peaks at multiple frequencies in the 150 to 1,000 Hz range. It made an
unpleasant, harsh drone. At lower speeds, there was also an underlying "wobble"
to the sound, as if one of the fans was off-kilter. This effect was audible
in each individual fan, but particularly in the front model, so it wasn't a
result of interaction between the two. The overall acoustics were very disappointing
as Zalman's previous model, the CNPS9900 MAX, actually had a fairly nice sounding
fan for a change.
The cooler's mismatched fans contributed to the 9900DF's poor acoustics. Both
fans had noticeable tonality but they also had distinctive noise signatures.
The front fan had a harsher, lower pitch profile, and was the main source of
the aforementioned "wobble" effect. The center fan had a smoother
profile with a higher pitch but it produced a dry, undesirable hum.
Test Results
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Zalman CNPS9900DF vs. CNPS9900 MAX
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Fan Voltage
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CNPS9900DF
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CNPS9900 MAX
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SPL@1m
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°C Rise
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°C Rise
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SPL@1m
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12V
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32 dBA
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43
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41
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32~33 dBA
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9V
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26 dBA
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46
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42
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26~27 dBA
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7V
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20 dBA
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48
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45
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20 dBA
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6V
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17 dBA
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50
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47
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16 dBA
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5V
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14 dBA
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53
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49
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13 dBA
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°C Rise: Temperature rise above ambient (22°C)
on load.
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To our surprise, the CNPS9900DF turned out to be less proficient than its single fan predecessor, the CNPS9900 MAX. Despite its second fan and larger heat dissipation area, the DF performed 2~4°C worse depending on the fan speed.
The main culprit for its disappointing performance was the heatsink's concave
base. Despite tightening the cooler to the point that the bolt threads were
almost completely stripped, the thermal compound pattern left behind showed
poor contact, with large tendrils of TIM all over the surface, which only happens
when there are significant air caps between CPU and heatsink base. When good
contact and pressure is achieved, most of the compound is squeezed out toward
the sides; that obviously didn't happen here.
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