Testing
The Zalman Reserator is designed for completely silent running at stock CPU speeds. Overclocking, if any can be achieved, is a secondary consideration. Given those caveats, testing was carried out using a stock clocked Athlon FX-51 system using an ASUS SK8V motherboard. Opposition comes in the form of the stock FX-51 air cooler supplied with the processor and Cooler Master's recently released Hyper-6 (full review of that on its own soon).
To test the noise side of things I used my good old ears. To limit the affects of ambient noise in my wholly unscientific listening tests, I equipped the system with a Gainward SilentFX graphics card and a very quiet Tagan power supply. The SK8V comes without a discrete fan on the K8T800 bridge so things were eerily quiet. More on the noise shortly.
To monitor temperatures I used Motherboard Monitor with the default SK8V profile. Temperatures were pre-tested to get a quick idea of the maximum and idle temperatures for each cooler, before a half an hour run of the HEXUS SETI benchmark was used to generate CPU load and therefore heat. After the half hour was up, the SETI instance was closed and drop-off temperatures were recorded, giving a full spectrum of results for idle, quick load, constant load and load drop-off, over a 30 minute period. Ambient temperature throughout testing for all coolers was a nice 18°C
Temperature Testing
Given the Reserator's design and water volume, you'd maybe expect idle temperatures to come close to that of a good air-cooler, but perhaps slightly higher overall due to eventual water warming. You'd then expect a higher load temperature and a much longer drop off period to get back to idle, after load, as the system has no fan to actively shift air over the cooling fins on the unit. Pretty logical stuff, so let's see how it panned out against the stock AMD cooler and the Hyper-6.
Base-line idle for the Reserator sits usefully lower than the stock heatsink, but a fair bit higher than the Hyper-6, a fairly hardcore air-cooler. Temperature climbs steadier than the stock heatsink, a testament to the design with the water volume holding a large amount of transferred heat and the Reserator doing a decent job of moving it on, if slowly due to no active cooling of the fins.
The interesting thing to note is the slow drop-off performance of the Reserator. It takes a long time for the temperature recorded for base-line idle to return, following a period of extended load. The graph doesn't show it, but it took a full two hours to drop back to the 39°C idle temperature it posted.
Both tested air-coolers dropped back to base-line idle fairly quickly, within a matter of minutes. The Reserator holds onto its heat for a lot longer. It's that which causes problems when overclocking, since latent heat captured from the processor when loaded keeps CPU temperatures quite high when subsequently idle. So while the Reserator has no problems dealing with a loaded FX-51, it might not fair so well, even at stock clocks, with something like a 3.4GHz Prescott.
For what it's worth, the Reserator was happy with a simple 100MHz overclock on the FX-51, at 2300MHz and 1.6V (1.5V standard), but any more than that would cause eventual issues after a few hours of running.
Noise Testing
This was the good bit. The Reserator is completely silent, unless you make things really hard for the pump and it has to pump against gravity. Even then its increased noise isn't much cause for aural concern. It's erk-have-I-suddenly-gone-deaf-because-I-can't-hear-jack quiet, much more so than any cooler I've ever had the pleasure of bearing witness to, passive or otherwise. Put your ear up against the base of the unit and you'll hear it purring, but otherwise I challenge you to pick it out amongst the rest of your computer system and definitely against any background noise that will probably be around.Utterly brilliant and I love it to death for that reason. With the SilentFX graphics card and the Tagan, only the seek noise from my hard drives would rise above the tap-tap of my keyboard actions. If silence is your aim, Zalman certainly have the toys for you.
