Testing PWM Fan Combinations on the NH-D14

Here we will look at a variety of 120 mm PWM push fans on the Noctua NH-D14 while using two different 140 mm PWM fans in the center. Noctua has sent three PWM fans so we finally have what I need to make some comprehensive comparisons. Those of you who have PWM-only control of your CPU fans (most of you) can now control fans on your NH-D14 with your motherboard. When your CPU is idling your CPU heatsink fans will be running slowly. When your CPU loads up, your heatsink fans will speed up. In this study you will see the amount of noise these PWM fans make when they are running flat out. This is the loudest they will be when the CPU is running its hardest. Most of us never stress our CPU’s to the max, so the noise you see below is likely more than your D14 will ever make. But even at the max, this cooler is quiet. Noctua designed it to be quiet, and you really have to work to make it noisy.

Fans

The eight PWM fans above are:

• Akasa Apache
• Arctic Cooling F12 PWM
• Cooler Master Blade Master
• Coolink SWiF2 120P
• Noctua NF-P12 PWM
• Scythe Slip Stream (sent with Mugen 2)
• San Ace 9S1212P4M011 (San Ace “Silent” medium)
• Titan Kukri

Since PWM fans run up and down the speed spectrum, we want to know how they sound at different speeds. I compared them at five PWM duty states to check the quality of the fan noise. A PWM duty state is the percentage of time the PWM controller sends a 5-Volt signal to a fan. You can get 100% simply by supplying 12 Volts and not connecting the fourth wire. You can get a 0% duty state by grounding that fourth wire. To get something in between you need a PWM controller. In this case I used a PWM Mate to produce approximately 25%, 50% and 75% PWM duty. So we can see what these fans will do across their duty states, from zero to 100%.

The table in the scroll window shows the fans running in open air. Because of limitations in the environment I was unable to measure sounds less than 32 dBA, so the equivalent sound pressure level (SPL) at 1 meter could not be assessed at less than 12 dBA. Where the manufacturers or brand sellers specify the minimum and maximum speeds their fans are supposed to reach at 0 and 100% duty, I show those specs along with the sound pressure levels they claim (actually, the only fans here sold by their actual manufacturers are the Gentle Typhoon AP-30 and the San Ace). I modified (“modded”) the AP-30 to get at the node in its PCB that changed it to a PWM fan. It was fun to do. We will start with the key to the sound quality codes then follow with the main table.

Note that the Arctic Cooling fan had some trick that caused it to go full speed when the PWM duty was zero. The only fans that didn’t click at all were the three Noctua fans, no matter what the speed. I guess I was surprised that all the non-Noctua fans — even the San Ace Silent PWM — produces loud clicking at some speeds. I have another PWM fan that clicks at every speed. It’s an industrial NMB fan, clearly not meant for consumers. So if you want full freedom from clicking, only the Noctua fans supplied it.

Test Methods

By now, the NH-D14 has been in place for more than a year so that temps can be compared between fan runs separated by months. When identical setups are periodically tested, the results are very close to each other.

The TEMPer USB Thermometer is set 30 cm in front of the intake finstack. The thermometer software records a log that is saved as a spreadsheet. A mean ambient temperature during each run is calculated and recorded to the nearest tenth of a degree centigrade.

OCCT acts as a front end for Intel’s Linpack, which was written by their engineers to maximally stress their chips. OCCT also records a log that can be saved as a spreadsheet. Since Linpack tests the CPU in bursts, the hottest core temps are harvested and a mean CPU temperature is calculated, and reported to the nearest tenth of a degree centigrade. Temperature Over Ambient (TOA) is calculated by subtracting the mean Ambient temp from the mean Core0 temp (Core0 is the hottest core for this chip).

The Tenma SPL meter can measure SPL in the A and C scale. I recorded measurements in the A scale, notated as dBA. The SPL was measured at 10cm from the side of the center fan (or where the center fan would be). This allowed for a measurement position that was consistent regardless of fan setup. The 10 cm SPL’s were then correlated with 1 m SPL’s by subtracting 20 dB. The results are reported as if the sound levels were measured from 1 m. This allows you to compare sound levels with those in other reviews. Results are reported to the nearest half dB.

My rule of thumb scale for noise:

Testing PWM Fan Combinations on the NH-D14

What you will see below is a pair of charts. The first shows a set of 120x25mm PWM fans placed in the front (push position) of the heatsink with a new Noctua NF-P14 PWM in the center between the fin stacks. The next chart shows the same push fans put through their paces with a Thermalright TY-140 in the center. Do recall that the CPU is an Intel i7 860 running at 4 GHz. It was loaded with Linpack, the software the engineers at Intel wrote to maximally stress their CPU’s. Unless you run Linpack you will never push your CPU this hard. The term TOA represents the average temperature of the hottest core, less the ambient temperature.

The charts set out the fans, their speeds, the SPL measured 10 cm from the center fan, and the TOA of each fan combination. Note that the TY-140 is a PWM fan.

Conclusion

Slip Stream fans tend to do well on heatsinks. Their drawback is their sleeve bearings. If you use them you should lubricate these fans before mounting them, and re-lubricate them twice a year or so (a how-to is here). Too bad they don’t come with ball bearings or fluid dynamic bearings (FDB).

If you can get San Ace fans and put plugs on them, they cool well with little noise at relatively low RPM. They function better on a heatsink than they seem in free air. but these are not consumer-friendly fans.

For an FDB fan that performs well with both 140 mm fans, the Arctic Cooling F12 PWM is worth a look. Its cable incorporates a “PWM Sharing Technology” that allows you to daisy chain PWM fans and see the RPM of each. Pretty clever design.

While none of the fans click obnoxiously, they all click a little — except the three Noctua fans. Noctua made the only non-clicking fans in this lot.

Adding a third fan when you already have a fan in push generally doesn’t get you much better cooling. The example above, with an NF-P12 PWM + TY-140 + NF-P12, is typical: 0.3 °C better cooling. Now, why the combination of three fans produced 1 dB less noise has to be from some odd acoustics. Usually a third fan just adds to the noise.

Of course, whichever fan you use, the NH-D14 makes it a winner. Heck, it even comes with quiet fans of its own. It’s a fine, fine heatsink.

– ehume