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AMD’s flagship HD6990: is silent air cooling possible?

When AMD released the HD6990 it claimed the ‘fastest video card' title and has held it since March this year. While we love the product we absolutely loathe the reference cooler – AMD's choice of tiny red fan has been a bone of contention for me now for years and it doesn't seem to be changing anytime soon. Thankfully Arctic have a firm grasp of the enthusiast sector and released the Accelero Twin Turbo 6990 – an expensive, but class leading cooling solution for AMD's flagship. Since our review went live a few days ago we have been inundated with emails asking if it would be possible to improve, or swap out the twin 120mm fans for something better.

Arctic Cooling are using good quality 120mm fans (1100D), made in Switzerland. These are built into a plastic shroud specially for the Accelero Twin Turbo 6990 Cooler. If you missed the review be sure to check it out before reading further into this article.

Removing these fans is straightforward, but you need to be careful. We recommend using a flat head screwdriver to prise the plastic clips from the aluminum fins underneath taking care not to snap them. When each side of the shroud pops up, pull them away from the fins. Repeat for both fans. Disconnect the single cable from the HD6990 PCB. Store this in a safe place.

The Accelero Twin Turbo 6990 cooler is a great product – it combines decent levels of airflow, with low noise emissions. Our review highlighted that it dropped temperatures by around 20c, while reducing noise from a maximum of 48.5 dBa to 33.4 dBa.

That 33.4 dBa rating is when both of the 120mm fans are spinning at 100% (or 1,500 rpm each). This is significantly lower than the tiny reference fan solution …. but it still isn't silent. At a distance from a few feet, even within a closed case, the fans can be heard.

What we are aiming for today is to achieve similar temperature results, but to lower the noise even further, to around 30 dBa (or less) when under full load. Several months ago we wouldn't have considered this to be possible, but by using the Arctic Cooling Accelero Twin Turbo 6990 we hope to achieve this goal today.

Performance freaks may be disappointed, after all by adding a few 120mm Delta fans it may be possible to lower the temperature by another 10c. To us however this defeats the purpose of the Accelero Twin Turbo 6990 cooler – we want lower temperatures, but it is also important that we reduce the noise levels even further.

Behind the scenes we tried around 5 sets of 120mm fans but weren't happy with any of them. A few fans created more noise, while reducing the temperatures by a few Celsius while others were silent, but temperatures rose to 80c+ again. Arctic Cooling clearly did their research and opted for two quality fans with a balanced air flow/noise dynamic.

It was clear we needed to think ‘bigger'. I mean literally, bigger.

Could the Accelero Twin Turbo 6990 cope with two 140mm fans? The basic idea sounds good – bigger fans produce greater airflow, while spinning slower. Obviously it isn't quite as straighforward as just ‘slotting in a few larger fans', because the quality of the motor and internal design is still massively important.

We were recently sent two of the new Xigmatek XAF F1451/F1452 fans. These are copper bushing axis fans. According to Xigmatek – “Copper bushing axis can guarantee exceptional running smoothness and provide excellent long-term stability.”

These fans are using an Aeronautical Oil System Bearing and push 90.3 cfm of air each, while being rated at less than 18dBa. They do ship with a 4 pin header, but also have a 4 pin to molex adapter in each box, making them ideal for a variety of systems. Just be aware that if you use the 4 pin headers to ensure that the motherboard won't consider them chassis fans, effectively slowing them down when you least want it.

Xigmatek rate the RPM from 800 to 1,300 rpm with a 150,000 hour life span, which is already slower than the 120mm fans that Arctic Cooling supply with the Accelero Twin Turbo 6990 cooler. With the extra 2cm on each blade and the quality internal design could we mount these without a problem?

We used a combination of thick cable ties and wire to mount the 140mm fans to each side of the cooler. We ensured that the bigger fans didn't protrude too far down and block the fitting of the card at the PCIe slot. Looking directly down it was easy to align the outer shell in place.

Each of these fans is supplied with a molex adapter which will prove useful with motherboards which don't have spare headers. The only downside is the untidy mess they make. We stuck a plastic grip to the top of the outside fan, tidying up the cabling a little. Obviously our fan mounting system could be cleaner, but each of the 140mm fans was held in place perfectly, without any movement.

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