Antec Phantom 500

Power
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5. FAN, FAN CONTROLLER & ACOUSTICS (TEST RESULTS, continued)

At the "3" setting where all the tests were conducted, the fan is supposed to turn on when the internal temperature reaches 55°C. We didn't have access to the internal thermistor; our standard temperature probes were used to determine the trigger temperature.

In our test setup, the fan turned on when the intake or internal case temperature reached ~33°C. The fan stayed running until the intake temp dropped to 32°C. The 33°C temperature was reached after running the power supply at 150W output for more than half an hour, in a 24°C ambient room.

This is surprising, given that the fanless Phantom 350 runs without a fan all the way to 350W output. It was questionable enough that we contacted Antec to find out whether this was normal fan controller behavior in this unit.

Antec's answer was that the Phantom 500's fan is set to turn on at the "3" setting when the load reaches ~200W. This calibration is imprecise, because it is an estimate based on temperature. In other words, the internal thermal sensor reaches 55° at ~200W load in a system with a level of airflow deemed suitable by Antec engineers. They could not tell me what "intake" temperature this correlates to.

The fan began spinning at a low level, putting out a quiet-but-not-silent 24 dBA/1m. The noise is a fairly pure tone that is higher in pitch than most quiet 80mm fans, but at 24 dBA/1m, it is easy to ignore. As the temperature rose (in responsed to increased output), the fan ramped up fairly quickly. By 35°C intake temperature, the 30 dBA/1m noise level, which we consider the upper limit of "quiet", was breached.

It was difficult not to notice that slight variances in temperature and airflow caused the fan controller to go up or down almost immediately. All airflow through the test rig can be stopped by turning off the fans. This reduces the flow of hot air from the loaded resistors in the PSU tester, causing a temporary reduction in the air temperature at the PSU intake. It caused the fan controller to audibly ramp the fan speed down within a second or two. Turning the test system fans back on immediately caused the PSU fan to ramp up again.

This observed behavior suggests that the fan controller has two states:

  • Below the trigger temperature, the voltage fed to the fan does not vary with temperature; it is fixed at 0V.
  • Above the trigger temperature, the relationship between fan speed and temperature is linear, and there is very little hystersis. In other words, every change in temperature results in an immediate proportional change in fan voltage (along with its speed and noise).

Phantom 500 fan speed/temp curve

Other PSU fan speed/temp curve

The basic shape of the curve in the above right chart should be familiar to regular SPCR visitors. It is the same one used in many PSU fan controllers. The starting / default fan voltage is usually somewhere between 4 and 5 volts, and the fan spins at a slow, quiet rate. At the trigger temperature, the fan begins to ramp up, often in a linear fashion. The best fan controllers have a some of hysteresis in the latter portion of the fan controller's curve so that small changes in temperature do not lead to instant and rapid changes in fan speed and noise.

The chart on the left illustrates how the Phantom 500 fan controller works. The main difference here is that instead of 4~5V as the starting voltage for the fan, the Phantom 500 starts at 0V. Hysteresis is non-existent in the linear (sloped) portion of the fan controller's operation.

The irregular nature of the fan controller was most pronounced at lower fan speeds; on our test system this was at about 200W output. In fact, the effect made it impossible to make reliable measurements of the noise level. Even more than usual, the above SPL measurements should be considered approximations of what we heard.

Here is a recording of the noise we refer to. It was difficult to capture because of higher than usual ambient noise in the neighborhood, and because the thermals in the test box had to be varied a bit to cause the fan variances. You may have trouble hearing it. The SPL was not monitored during this recording, as we were also busy quietly turning the test box fan on/off. Our guesstimate is 24~26 dBA/1m. The load was 200W.

MP3: Antec Phantom 500 - variable fan noise at 200W load, with small changes in operating ambient temperature.

Finally, there was a small amount of buzzing that could be heard at times from under two feet disatance, directly behind the back panel. This buzzing did not appear to be directly related to load.

Sound Recordings of PSU Comparatives

Seasonic S12-430 @ 200W (22 dBA/1m)

Nexus NX4090 at 200W (30 dBA/1m)

Enermax Noisetaker 600W (2.0) @ 200W (30 dBA/1m)

Nexus 92mm case fan @ 5V (17 dBA/1m) Reference

HOW TO LISTEN & COMPARE

These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during most recordings was 18 dBA or lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.

ACOUSTICS VS. COMPETITORS

It would be instructive to compare the noise of the Phantom 500 against similar power competitors tested by SPCR in recent months. The ambient temp for every PSU test on this table was 21°C, except for the FSP Blue Storm, which was tested at 20°C.

NOISE AT VARIOUS POWER STATES COMPARED (SPL in dBA @ 1m)
DC Output (W)
65
90
150
200
250
300
400
500
Antec Phantom 500
n/a
n/a
n/a
24
29-31
35
36
37
FSP Blue Storm AX500
26
26
29
36
42
43
45
45
Enermax Noisetaker EG701AX-VE 2.0
23
23
27
30
n/a
35
42
45
Seasonic S12-430
18
18
19
22
26
31
32
n/a
Nexus 4090
21
21
24
30
n/a
38
38
n/a

Please note that although this data is accurate, it is within the context of SPCR test rig setup, which simulates a typical low-noise, low-airflow setup of the kind we most often espouse. Results will definitely vary based on case airflow, system components, applications and ambient temperatures. The audibility of the sound levels will also vary depending on your hearing sensitivity as well as ambient noise.



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