Seasonic X-1050 PSU: Gold at Kilowatt+

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7. TEMPERATURE, COOLING & NOISE

Our X-1050 sample exhibited no audible high pitched noise, hum or buzz at any time during testing. It may have been there during high power loads, but the fan would have masked it. At <700W, no trace of this kind of noise was heard, at least not from >6" away. I pressed my ear up to the unit at 200W in hybrid mode with every fan in the anechoic chamber turned off and maybe heard a trace of... something. This is the lowest electronic noise I've encountered in any PSU I tested or used in the last 10 years. Outstanding. We can all hope that this is typical of X-1050s... and perhaps all new production runs of X series models? (There have been some user reports of electronic noise in X series PSUs.)

Seasonic explains the switchable cooling modes on the X-1050 with the following graphic. Basically, in Normal mode, the fan starts at a very low speed and does not run faster until about 50% load (525W) is reached. In Hybrid mode, the fan does not start till about 30% load, but behaves the same as in normal model after it starts spinning. Since the fan speed is controlled by a thermal sensor rather than a load sensor, these trigger load numbers are based on Seasonic's estimates of temperatures in typical use situations; i.e., the trigger points may occur at higher or lower power, depending on thermal conditions, which include not only the computer but the ambient room temperature.

In Normal mode, the fan started immediately at the very quiet level of 16 dBA @1m when our sample was powered on. The fan on our sample was just as smooth and unobtrusive at this speed as the other Sanyo Denki fans Seasonic has used in its X and M series for the last couple of years. True to Seasonic's explanation, the fan speed did not change until well above 500W. Given that the ambient test room temperature was just 22°C, you can expect the fan to speed up at a lower load in summer, hotter climates, or in a computer where the PSU fan draws air from inside the case.

In Hybrid mode, the fan actually began spinning at around 200W, much lower than the 30% load indicated by Seasonic. But before you claim foul, it should be explained that the fan spun up for only perhaps 10 seconds, and never reached the same velocity or noise level as in Normal idle mode. It spun up, then turned off almost immediately, so the impact on overall noise was virtually nil at first. This was the behavior — a short period of spin-up followed by a longer period of no motion — between 200W to around 500W. The periods of no fan motion got shorter and shorter as the load was increased so that by 500W, the fan was running steadily at the same speed as in Normal idle mode. As our measurement tables indicate, the noise rose gradually in level. You might wonder reasonably whether the fan on-off cycling was audible or annoying. My assessment is that because the fan spun for such a short time, the noise level was too low to be easily noticed. By the time the noise rises to an audible level (say >400W), other components in your PC, such as the CPU and video card fans, will make considerably more noise than the X-1050.

Seasonic X-1050: Power vs Noise
Load (W)	SPL (dBA@1m)	Exhaust (Hybrid)
20.9	0 / 16	22°C
38.9	0 / 16	23°C
65.3	0 / 16	25°C
89.8	0 / 16	29°C
146.8	0 / 16	34°C
199.6	12 / 16	39°C
251.0	12 / 16	46°C
301.3	13 / 16	46°C
399.6	14 / 16	42°C
499.4	16 / 16	44°C
699.8	26 / 26	45°C
1047.6	40 / 40	46°C

Another phenomenon to note is that the reported exhaust temperature is the highest seen at each power level in Hybrid mode, but the fan cycling behavior in this mode should have tipped you off to the fact that it actually varied quite a lot. When the fan was not running, our thermal sensor at the exhaust vent of the PSU displayed ~35°C, even at 400W load. It was when the fan did its brief spin-up that the temperature rose to the above cited levels. So what is happening is that at 200~500W load, some components in the PSU get hot enough to trigger the fan turn-on, which forces the heat out of the PSU, and resulted in the 46°C peaks at 250W and 300W. But those components cool off fast so that just a few seconds of the cooler ambient airflow is enough to trigger the fan turnoff. Note how the peak temperature dropped to 42°C at 400W; this was when the fan was spinning for longer periods.

The fan sped up enough between 500W and 700W that the measured SPL rose by 10 dBA, making it plainly audible, though not particularly annoying. The fan's basic acoustic signature is quite smooth. It's unreasonable at this point in technological development to expect silence from an ATX power supply outputting 700W. Maximum noise and fan speed was reached at around 800W. No matter how you slice it, 40 dBA is noisy by our definition, but there isn't a PSU out there which is quieter at >1000W load. What's important at this power level is to keep the components from overheating. If you have a system that can draw a kilowatt, every other fan in the PC will be screaming louder anyway.

IN THE HOT BOX

In the hotbox, the X-1050 fan behaved almost the same as outside the hotbox. The basic difference was that the fan starting spinning steadily at a touch lower power level, and also got slightly louder at 700W load. Higher efficiency models invariably fare better in the hotbox, because they create less heat.

Seasonic X-1050: In Hotbox Vs Out
Load (W)	Hotbox (dBA@1m)	Out (dBA@1m)
20.9	0 / 16	0 / 16
38.9	0 / 16	0 / 16
65.3	0 / 16	0 / 16
89.8	0 / 16	0 / 16
146.8	0 / 16	0 / 16
199.6	12 / 16	12 / 16
251.0	12 / 16	12 / 16
301.3	13 / 16	13 / 16
399.6	16 / 16	14 / 16
499.4	16 / 16	16 / 16
699.8	28 / 28	26 / 26
1047.6	40 / 40	40 / 40

COMPARISONS

The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the hotbox. It's difficult to rank them, as the measured SPL varies with power load. The units which are quietest at minimum load are not always the quietest at midload (100W~300W), which may make them louder in actual use. Then there's the noise level at 400W and up, which will determine the quietest PSUs for high power gaming rigs, during actual gaming.

The Seasonic X-1050 acoustics in the hotbox is up near the top of the pack, aside from the best fanless models. At every load up to its maximum, the unit is quieter than all other tested fan-equipped PSUs. At 6~700W, it is by far the quietest.

PSU Noise (dBA@1m) vs. Power in Hotbox/Anechoic Chamber
Model	90W	150W	200W	250W	300W	400W	500W	6-700W	850W
Seasonic X-400/460 Fanless	<10*	<10	<10	<10	<10	<10	<13	n/a	n/a
Kingwin STR-500 Fanless	<10*	<10	<10	<10	<10	<10	<13	n/a	n/a
Seasonic X-1050	<10*	<10	12	12	13	16	16	28	40
Kingwin Lazer Platinum LZP-550	<10*	<10	<10	<10	<10	16	22	n/a	n/a
Silverstone ST50NF Fanless	11	11	11	11	15	15	16	n/a	n/a
Enermax Modu/Pro87+ 500	11	11	11	11	14	20	23	n/a	n/a
Corsair AX850	<10	<10	12	15	18	25	35	38	39
Seasonic X-650	<10	<10	12	14	16	31	31	32	n/a
Nexus Value 430	11	11	16	18	18	19	n/a	n/a	n/a
Nexus NX-5000	11	11	12	14	22	24	25	n/a	n/a
Antec CP-850	12	12	12	14	14	26	40	44	45
Enermax Eco80+ 500W	<11	12	16	19	26	32	33	n/a	n/a
Seasonic M12D 850W	14	14	14	14	14	24	37	42	42
Antec TP-750	12	12	14	14	18	33	40	40	n/a
Chill Innovation CP-700M	15	15	15	15	17	30	34	34	n/a
Antec Signature 650	15	15	15	18	18	28	36	47	n/a
Coolermaster M700W	14	14	18	21	25	27	34	34	n/a
Cougar GX-700	15	15	18	20	25	32	35	36	n/a
SilverStone DA700	18	18	18	18	23	32	35	41	n/a
Nexus RX-8500	14	14	17	22	28	32	32	33	33
NesteQ ECS7001	22	22	22	21	23	25	36	37	n/a
PCPC Silencer 610	20	24	24	24	24	30	40	50	n/a

Caution: Please keep in mind that the data in the above table is specific to the conditions of our test setup. Change the cooling configuration, the ambient temperature and any number of other factors, and you could change the point at which the fans start speeding up, as well as the rate of the rise in speed. The baseline SPL is accurate, however, probably to within 1 dBA.

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