Xigmatek Achilles Plus SD1484 Heatsink Prototype

One of the benefits of testing computer hardware is that you occasionally get to look at a new product before it's introduced to the market. In my time at Benchmark Reviews, I've been fortunate enough to be able to review computer cases and CPUs before they were generally available (or in some cases, before they were even announced). Recently Benchmark Reviews was given the opportunity to evaluate a prototype of Xigmatek's forthcoming Achilles Plus SD1484 CPU cooler, and I tested it to compare performance against a variety of air and water coolers.

While all-in-one water coolers have become more popular recently, their performance in most cases still can't compete with that of the best air coolers. Air cooling will remain the norm for most rigs, and as Intel and AMD transition to 32nm and smaller processes, the amount of heat their CPUs produce will go down, as we've seen with testing of Intel's Sandy Bridge processors, which even when heavily overclocked simply don't require the likes of a ProlimaTech Megahalems to keep them cool.

The sample Benchmark Reviews received is, officially, a "Xigmatek Achilles Plus SD1484 Prototype Sample". There was no retail box, fans, fan mounts, or even marketing specifications, so all we can do is show you pictures and report the performance we observed.

Manufacturer: Xigmatek
Product Name: Achilles Plus SD1484
Price: $39.95 MSRP

Full Disclosure: The product sample used in this article has been provided by Xigmatek.

Normally, we'd put the product's official specifications and features here, but we have none, so let's get on with the closer look and performance testing.

Closer Look: Achilles Plus Prototype

Here's what we received from Xigmatek: the actual heat sink, a universal base plate and mounting hardware, and a printed booklet that seems to be for Xigmatek's existing SD1284 cooler. The mounting system described in the booklet largely matched what we had.

The Xigmatek Achilles Plus SD1484 Prototype Sample is a fairly standard-looking heat pipe cooler. 46 aluminum fins are pierced by four U-shaped heat pipes. The heat pipes are unusually thick at a measured 8mm. The heat sink measures about 6.5" high, 2 3/8" deep and 5 5/8" wide.

The base of the cooler is aluminum, with the four heat pipes exposed in what Xigmatek calls a "heat-pipe direct touch" design. While the theoretical advantages of this design seem obvious (you're eliminating a material transition that the heat has to cross), some of the very best air coolers do without it. The base finish has the typical grained look of this design, since the heat pipes must be ground down to be flush with the rest of the base. Using a straightedge, I noticed that while the base was perfectly flat front-to-back (i.e. across the heat pipes), it was very slightly convex side-to-side, with the center of the base bulging a fraction of a millimeter out from the sides.

The mounting system comprises a base plate with a relatively thick foam rubber pad that accommodates Intel Socket 775, 1155/1156, and 1366 as well as AMD Socket AM2/AM2+/AM3. Long screws thread through the base and are secured by knurled nuts, which form supports for the main mounting brackets. The mounting brackets and the pressure bar, are secured with hex nuts. Xigmatek supplies a small wrench to tighten the nuts. Assembled outside a case, it looks like the image below. The thick foam on the base plate makes mounting the system a little difficult; you need to be careful to tighten the knurled nuts as tightly as you can to compress the foam as far as it will go. I'd prefer to have seen a thin layer of insulating plastic or perhaps Teflon washers used here.

According to the included booklet, two small pegs on the bottom of the pressure bar that secures the heat sink to its mount should fit into matching holes on the heat sink base. The SD1484 Prototype Sample instead had a "stair step" base as shown below. This didn't affect the mounting.

Lacking any official specifications, I didn't know what kind of fans the retail cooler would include, or if it would include fans at all. Normally, relatively thin coolers like this work best with two fans, but for the results to be comparable with the other coolers I used the same "stock" and "high speed" fans that I used in previous tests. While the high speed fan results are directly comparable, the stock results will probably be different from those of the retail version.

So let's get on with the testing...

Heatsink Test Methodology

Benchmark Reviews is obsessed with testing CPU coolers, as our Cooling Section has demonstrated over the past few years. We've solicited suggestions from the enthusiast community, and received guidance from some of the most technical overclockers on the planet. As a result, our testing methodology has changed with every new edition of our Best CPU Cooler Performance series. Because of this, each article is really its own stand-alone product, and cannot be fairly compared to the others. Benchmark Reviews continues to test CPU coolers using the stock included fan (whenever applicable), and then replace it with a high-output fan for re-testing.

Manufacturers are not expected to enjoy this sort of comparison, since we level the playing field for all heat sinks by replacing their included fan with a common unit which is then used for every CPU cooler tested. Many manufacturers include fans with their heat sink products, but many 'stock' fans are high-RPM units that offer great airflow at the expense of obnoxiously loud noise levels, or, conversely, quiet fans that sacrifice performance for low noise. By using the same model of cooling fan throughout our heat sink tests, we can assure our results are comparable across the board. This is one of the more significant changes we have made to our test methodology, since many of the benchmark tests we have conducted in the past have compared the total package. Ultimately we're more interested in the discovering the best possible heat sink, and we believe that you'll feel the same way.

For each test, ambient room temperature levels were maintained within one degree of fluctuation, and measured at static points beside the test equipment with a digital thermometer. The Corsair H70 and the comparison coolers used a common Thermal Interface Material of our choosing (listed in the support equipment section below) for consistency. The processor received the same amount of thermal paste in every test, which covered the heat spreader with a thin nearly-transparent layer. The heat sink being tested was then laid down flat onto the CPU, and compressed to the motherboard using the supplied retaining mechanism. If the mounting mechanism used only two points of force, they were tightened in alternation; standard clip-style mounting with four securing points were compressed using the cross-over method. Once installed, the system was tested for a baseline reading prior to testing.

At the start of each test, the ambient room temperature was measured to track any fluctuation throughout the testing period. AIDA64 Extreme Edition is utilized to create 100% CPU-core loads and measure each individual processor core temperature. It's important to note that software-based temperature reading reflects the thermal output as reported from the CPU to the BIOS. For this reason, it is critically important (for us) to use the exact same software and BIOS versions throughout the entire test cycle, or the results will be incomparable. All of the units compared in our results were tested on the same motherboard using the same BIOS and software, with only the CPU-cooler product changing in each test. These readings are neither absolute nor calibrated, since every BIOS is programmed differently. Nevertheless, all results are still comparable and relative to each products in our test bed (see The Accuracy Myth section below).

Since our test processor reports core temperatures as a whole number and not in fractions, all test results utilize ADIA64 to report averages (within the statistics panel), which gives us more precise readings. The ambient room temperature levels were all recorded and accurate to one-tenth of a degree Celsius at the time of data collection.

When each cooler is tested, Benchmark Reviews makes certain to keep the hardware settings identical across the test platform. This enables us to clearly compare the performance of each product under identical conditions. Benchmark Reviews reports the thermal difference; for the purposes of this article, thermal difference (not the same as thermal delta) is calculated by subtracting the ambient room temperature from the recorded CPU temperature.

Please keep in mind that that these test results are only valid within the context of this particular test: as the saying goes, your mileage may vary.

Intel Test System

• Processor: Intel Core i7-950 Bloomfield 3.06GHz LGA1366 130W Quad-Core Processor Model BX80601950, core voltage set to 1.35V
• Motherboard: ASUS Sabertooth X58 Intel X58-Express chipset) with BIOS 0603, BCLK set to 175MHz for a processor speed of 4025MHz

Support Equipment

• AIDA64 Extreme Edition version 1.50.1200
• MG Chemicals Heat Transfer Compound 8610-60G
• Stock fan (for heat sinks without fans): Thermalright TR-FDB-12-1600 (63.7CFM advertised)
• High-speed fan: Delta AFC1212D (113CFM advertised)

All of the tests in this article have been conducted using vertical motherboard orientation, positioned upright in a traditional tower computer case. Air-cooled heat sinks are positioned so that heatpipe rods span horizontally, with the fan blowing air out the top of the chassis. The radiators of water coolers are mounted as per manufacturer instructions. In both cases, fans are connected directly to the power supply (rather than motherboard headers) and run at full speed during the test. At the start of our test period, the test system is powered on and AIDA64 system stability tests are started with Stress CPU and Stress FPU options selected. AIDA64 loads each CPU core to 100% usage, which drives the temperature to its highest point. Finally, once temperatures have sustained a plateau (no observed change in average temperatures for 5 minutes), the ending ambient room temperature and individual CPU core levels are recorded thus completing the first benchmark segment. The time to reach stable temperatures varied between 10 and 20 minutes for the heat sinks in this test; larger heat sinks typically take longer to stabilize.

The second test segment involves removing the stock cooling fan and replacing it with a high-output 120 mm Delta AFC1212D cooling fan, then running the same tests again.

Note: Both the Antec KühlerH2O 620 and the CoolIt Vantage A.L.C. are designed to drive their own RPM-controlled fans directly; in the case of the Vantage, an alarm will sound continuously if there is no fan connected. For these coolers, the fans were left connected as designed during stock fan testing. For high-speed fan testing, the Delta fan was connected directly to the power supply (and the alarm on the Vantage ignored).

The Accuracy Myth

All modern processors incorporate an internal thermal diode that can be read by the motherboards' BIOS. While this diode and the motherboard are not calibrated and therefore may not display the actual true temperature, the degree of accuracy is constant. This means that if the diode reports 40°C when it's actually 43°C, then it will also report 60°C when it's truly 63°C. Since the design goal of any thermal solution is to keep the CPU core within allowable temperatures, a processor's internal diode is the most valid means of comparison between different heat sinks, or thermal compounds. The diode and motherboard may be incorrect by a small margin in relation to an actual calibrated temperature sensor, but they will be consistent in their margin of error every time.

Testing and Results

For this test, I used the following heat sinks in addition to the Xigmatek Achilles Plus SD1484 Prototype Sample:

• Thermalright Venomous X
• Cooler Master V6 GT
• CoolIt Vantage A.L.C.
• CoolIt ECO A.L.C.
• ProlimaTech Super Mega
• Corsair Hydro Series H50
• Corsair Hydro Series H70
• Antec Kühler H2O 620

For heat sinks without a stock fan (including the Achilles SD1484), I used a Thermalright TR-FDB-12-1600 fan, which puts out 63.7CFM at 28dBa according to Thermalright. This mid-range fan provides good air flow and reasonable noise levels. For "apples to apples" testing, where each heat sink is tested with the same fan, I used a Delta AFC1212D. This high-performance PWM fan is rated at 113CFM at a claimed 46.5dBa at full speed...which means that while it moves quite a bit of air, it's very loud.

The Intel Core i7-950 I used in this test runs much hotter than the Core i7-920 I'd used previously. At 1.35 volts, with a BCLK of 175 MHz, the 4,025 MHz CPU pumped out enough heat to stress the very best heat sinks. AIDA64 would report throttling once any single core reached 100 degrees Celsius; any throttling resulted in cancelling the test and recording a "FAIL". Although this overclocked and overvolted Core i7-950 represents an extreme, these are expensive, high-end heat sinks.

The chart below summarizes the results with the stock fans (hotter temperatures towards the top of the chart, and cooler temperatures towards the bottom). The twin-fan Cooler Master V6 GT and Corsair H70 have a real advantage here, since their dual fans move more air than the stock single fan of any of the other units.

Stock Fan Tests

With its dual fans providing an aggregate airflow of over 180CFM, the Cooler Master V6 GT takes the lead here, keeping the blistering hot Core i7-950 almost 8 degrees cooler than the Achilles Plus prototype. But the Xigmatec acquits itself pretty well here, coming in only 1.8 degrees hotter than the ProlimaTech Super Mega and 4 degrees cooler than the CoolIt Vantage A.L.C. This four-degree break is the largest difference between adjacent coolers in this test. Xigmatek's existing Achilles II SD1284 cooler comes with an 85CFM fan; if the retail Achilles Plus SD1484 comes with a similar fan, the temperature results in this test would be somewhat better than the ones I obtained with the 63.7CFM Thermalright fan.

Delta High Speed Fan Tests

With more airflow, courtesy of the Delta 113CFM fan, the lineup changes. The Corsair H50 and CoolIt Vantage A.L.C. betray their first-generation designs with bottom-of-the-pack performances, while the Xigmatek Achilles Plus prototype manages an 8-degree improvement, which brings it to within 3 degrees of the top-performing cooler in this test, and only 1.6 degrees short of the Cooler Master V6 GT. This is an excellent result considering the other air coolers are either almost twice the depth (the Super Mega and the Venomous X) or have two fans with much more airflow (V6 GT).

CPU Cooler Final Thoughts and Conclusion

There's really only so much you can do to improve the performance of an air cooler. After testing a couple of dozen coolers for Benchmark Reviews, I think the important points are:

• Physical size of the cooler (more mass absorbs more heat)
• Airflow through the cooler (a combination of fans and fin design)
• Clamping force (how tightly is the cooler pressed against the processor)

There are probably other significant factors like the internal design of the heat pipes, but these three are some of the most important. It's interesting to watch the design variations manufacturers come up with to trade off various factors. For example, the Cooler Master V6 GT is, like this Xigmatek prototype, a relatively "thin" cooler compared to the Thermalright Venomous X or ProlimaTech Super Mega, but Cooler Master compensates for this by pushing more air through the cooler using dual high-speed fans.

The Achilles Plus SD1484 Prototype Sample seems to be physically very similar to Xigmatek's existing Achilles II SD 1284 cooler; it has 46 fins instead of 52, but the oversize appears roughly the same and both units use the large 8mm diameter heat pipes. The SD1484 prototype's heat pipes seem to expose more surface area to the CPU than do the heat pipes of the 1284, judging from photos on Xigmatek's web site, but without actually measuring them it's hard to be sure.

As I noted earlier, the "fit and finish" of the prototype was rather rough, but its performance was quite good. The existing Achilles II SD1284 cooler can be found for under $50 with an 85CFM fan, if the Achilles Plus SD1484 comes in near this price, it'll offer an excellent price/performance ratio and should definitely be something to consider if you're in the market for a high-performance air cooler.

Questions? Comments? Benchmark Reviews really wants your feedback. We invite you to leave your remarks in our Discussion Forum.

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