Thermaltake Silent Boost RX-K8



Thermaltake has expanded their product line tenfold in the last few years. A company which originally gained fame with its introduction of the original Orb HSF has now grown into an OEM giant. Thermaltake's product line now includes the following: CPU air-coolers, high-tech/sever style chassis, power supplies, innovative liquid cooling, silent DC fans, several storage devices, a cornucopia of accessories and a introduction of Desktop Media solutions. Thermaltake's rapid growth and cutting edge inventory exemplifies this company has thrown a substantial amount of profit right back into R&D. In my assessment this is Thermaltake's formula for success.

Today we test the RX-K8. This HSF is an all copper cooler based on a reverse flow fan designed to produce maximum air flow with minimal noise. Sadly this cooler has been met with mixed reviews many of which found the “Silent” in Silent Boost to be lacking. Unfortunately this may be one case in which this heatsink's shortcomings mask its true potential. In their desire to build an active cooler featuring near silent operation the heatsink had to be extraordinary in its ability to transfer and dissipate thermal energy. This isn't so much because of the fan's 38CFM rating, there are lower out there of course, but the fan's design almost excludes a "shroud" focusing the air in a more concentrated fashion. If I've done my job correctly we'll discover two important facts which have plagued this particular heatsink and the reviewing process on the whole where noise levels are concerned.

First, criticizing Thermaltake's claim this heatsink-fan emits just 15dBA using an SPL meter in any environment other then an anechoic chamber would be analogous to criticizing the Weather Bureau's data on a Hurricane flood surge by measuring the overflow of your swimming pool.

Second, we cannot expect any degree of accuracy so long as there are no criteria or industry wide standards for sound level tests. After spending years in the High End Audiophile industry there is one thing I know for sure, the number of research level anechoic chambers around the world can be counted on your hands (addition only *hehe*).

As an example, the audiophile loudspeaker industry had been dominated by a single pair of studio recording monitors which are still found today at Abby Road Studios, B&W 801 loudspeakers. These were the most coveted transducers by audiophiles whom could afford speakers costing 5x as much, although B&W 801's sold at around $5,000 and thousands of 20-year old pairs remain in audiophile systems today. The audiophile world saw some dramatic changes between 1980 ~ 2000 with some truly exceptional speakers originating from Canada. The sole reason behind this movement was due to Canada's rapidly expanding NRC Facilities which was built to keep the Canadian economy on the cutting edge and Canadian business competitive in the world market. In particular its anechoic chamber (seen in the article below) has contributed to the success of Canadian loudspeaker companies, such as the relationship described in the following article about Axiom (speakers) and the NRC.

How does all this fit into a heatsink review? In the field of psycho-acoustics our test methods are rudimentary at best and this is not to say we should blindly trust what each company claims in their specifications, only we should be as skeptical of our own. Certainly when we make observations as “Technical Writers” there are those whom entrust in those observations, which is why the description below which violates a few laws of physics is better left unsaid.

As soon as I started up my system the first time, I knew there was a problem. It was the loudest heatsink I’d ever had. It wasn’t so much that the fan was loud; it was that it was vibrating my whole case, and it acted like a sub woofer. I couldn’t leave it running, so I took it out and looked for the problem....

Packaging



As is evident from the photo above the RX-K8 is a fairly compact HSF compared to it's sibling the Blue ORB II which I reviewed here back in January. Admittedly the ORB which supports a 120mm fan is an extra large HSF. RX-K8 packaging is atypical Tt, ready for retail display at your local Computer Shop. The package includes an instruction manual, thermal paste and the RX-K8 itself which is intended to accommodate the Athlon 64, Athlon 64 FX, Opteron and Sempron on Socket-939 / 754.

RX Factor



All fans produce two types of unwanted noise:

1.) Mechanical - caused by the motor, bearings, or blade imbalance.
2.) Aerodynamic - resulting primarily from turbulent air as each fan blade passes over the mounting struts between the fan blades and heatsink cooling fins.

The struts are necessary to secure the motor and blade assembly to the outer shroud. In fact the shroud itself perpetuates turbulence, ironically by doing its job which is to focus airflow down onto the cooling fins. Air from the trailing edge of each blade creates further turbulence which the shroud then refracts back into the environment. Noise created by the spinning blades is characterized in frequency or pitch dependent upon the fan speed, the number of fan blades and the number of struts the fan blade passes over. Multiplying fan speed in rpm/60 (revs per sec) times the number of fan blades times the number of struts each fan blade passes over in one revolution determines frequency of pitch in cycles per second or hertz (Hz).

For example: a fan running at 5000 rpm with 7 blades rotating over 3 struts generates a frequency of 5000/60 x 7 x 3 = 1750hz



Reverse Flow may read like another marketing ploy; however, the design is proven, pragmatic and used throughout the industry. I must confess when I reviewed Arctic Cooling's Slinetium-2 PC-case which utilizes reverse flow technology, was completely unaware of the science behind the fans, which worked well and were very silent. The design works to eliminate aerodynamic noise by eliminating strut turbulence and minimizing shroud turbulence. If there are deficiencies in this design they most likely result from the absence of a full shroud concentrating the air-flow where it needs to be.




Specifications



The RX-K8 fan is rated at 38.7CFM which isn't the greatest amount of air-flow, however; where silence is a goal sacrifices must be made. Removing the fan assembly shows the absence of an atypical shroud. Further details can be found by clicking on the thumbnails below.





Looking at the exposed mounting base and pseudo shroud reveals mounting holes for an 80mm fan, although I fail to see the need for this as it would inevitably increase noise and decrease air-flow compared to its included 92mm fan. I intentionally left the dust particles in place to exemplify the "dead zone" which is the Achilles Heel for all fans mounted in this fashion, albeit reverse flow or the usual fan design. Design alternatives are numerous including the use of vertical mounted fans which move air across a fin assembly in what are much taller units, these are also known as tower coolers and will often integrate heat-pipes. Even with its Achilles’ Heel it seems mounting the fan so air is forced down onto the fins and base plate works best.





The fan mounting enclosure encasing the fin section seems to be made of aluminum, the fin and base plate section is constructed of copper with the exception of an aluminum "riser" bar. This center section which screws into the base plate acts as a spacer between the mounting retention bracket and base plate, it’s there to keep the mounting clip in place.






The retention clip-style mount is about as simple as it gets providing solid footing for the copper base plate and adequate pressure for contact between base plate and CPU IHS (Integrated Heat Spreader).



Finish is always a critical issue as the thermal paste provides a microscopic layer which must fill every striation on the base. If the finish is too rough there's bound to be air-gaps and while their minute pockets they do nonetheless raise temps.

TT’s base-plate finishes have been relatively consistent which is a good thing; however, their finish is representative of a mass production process. I would say this finish is "just" acceptable and if I were to live with this unit for any length of time would most likely lap it. Spending an hour lapping the base plate will lower temps and effectively raise the performance value of your $25 HSF.



After removing the RX-K8 note the perfect spread of the thermal paste. As proven more effective, I applied a single dollop or rise sized grain of thermal paste to the IHS, then mounting the heatsink as usual. This method uses the tension of the mounting hardware to "compress" and naturally disperse the thermal paste rather then "spreading" the paste. Spreading thermal paste will most often incorporate air-pockets into the paste.



Although unlikely in a cooler at this price range, just once I'd like to see an HSF with a base plate recess able to accommodate a thermistor. Since thermistor sizes vary ever so slightly this can easily be solved with the manufacturer purchasing in bulk as usual and mate thermistor to recess. Even more effective would be an impregnated base plate fabricated around the thermistor such that the thermistor is located just a mm or so above the processor’s IHS (Integrated Heatsink) and core. When it comes to thermodynamics in the world of micro-electronics, a few mm's distance from the surface of the processor to its core would be akin to measuring the distance from the Earth to the Sun using a Yardstick.