Scythe GlideStream, Slip Stream XT, and Grand Flex Fans

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Scythe GlideStream, Slip Stream XT, and Grand Flex Fans

October 1, 2013 by Lawrence Lee

While Scythe's North American distribution is still in abeyance, its global business seems to go on as usual, with new products like the Mugen 4 and Ashura heatsinks. A key ingredient in Scythe's coolers both past and present has been acoustically superb fans. The new GlideStream series now shipping with their newer cooling solutions follows in the footsteps of the Slip Stream family, providing a smooth sounding experience right out of the box. For noise conscious enthusiasts, this gives them a leg up on most of the competition.

The GlideStream 120/140 is part of a new lineup of fans along with the Slip Stream 140XT and Grand Flex. These models have very different designs, and its likely each is suited for a specific application, though Scythe has not made any usage recommendations, i.e. whether one line is better than the other as a case fan, a heatsink fan, or a radiator fan.

The 7 Scythe fans tested in today's roundup.

Like their predecessors, each fan model is available in wide variety of speeds but they are now more easily differentiated by color-coding on the packaging. A large assortment was sent to us from Scythe, but only the seven pictured above were picked for testing. They were chosen based on how well they represented the other models in their respective families, based on their acoustics at various speeds.

Two samples of each model were provided. More often than not, each pair would have differing sounds, so the more pleasant of the two samples was used for testing. Any acoustic inconsistencies between the samples, which were mostly minor or only noticeable at close proximity, were noted. It's not a perfect process but with the limited sample size, we felt this was the best way to proceed.

The following is a summary of our current fan testing methodology; for more information as to our reasoning behind all this, it's described in great detail in our last fan roundup.


  • i7-1366 CPU die simulator with embedded T-type Thermocouple wire -- A generous contribution from Thermalright. It can handle up to 150W, but its heat distribution is somewhat more even than a typical CPU. The main thing is that it gets hot enough, with extreme consistency, and there are no worries about a CPU or motherboard breaking down.
  • Thermalright Archon heatsink -- It's a good performer like most Thermalright CPU heatsinks, and it can fit very large fans. It is also quite responsive to the size of fan used due to its big mating surface area for the fan. Given the same RPM, for example, a 140mm fan always results in lower temperature than a 120mm fan. For a fan test platform, this is as it should be.
  • Mastech 6030D DC Regulated Power supply, 0-64V/3A -- It heats up the CPU die simulator with power up to 137W.
  • For Voltage fan speed control, we use a custom built 0~12 VDC Regulated Voltage Fan Controller -- The same one used for years and years. It is sometimes used for PWM fans when the lowest test speed is not achievable on the PWM fan controller.
  • For PWM fan speed control, Fan Xpert 2 utility in Asus P8Z77-V Pro motherboard -- A great board to work with to test fans. You'll appreciate the detailed data summary it generates. It also incorporates a voltage regulation circuit for its non-CPU 4-pin headers, which allows 3-pin non-PWM fans to be analyzed using its auto-tune function, and to run the entire test on the fan when appropriate. It has too conservative a definition of "safe starting speed", which prevents many 3-pin fans from running at very low (but still safe) speeds.
  • Kanomax 6803 Vane Anemometer -- ±1% accuracy rating, which is believable. This is by far the most accurate of the handful that we've acquired over the years. Ironically, it is used not as a primary tool, however, but a secondary one as we're not concerned about airflow per se, but its thermal effects in a cooling system.
  • Mannix DT8852 Dual Input Thermometer (K, J or T Thermocouple input) -- Supposedly 0.1% accurate. This is to monitor the temperature of the CPU die and the ambient air ~6" in front of the fan intake
  • High accuracy general purpose Multimeter
  • Guangzhou Landtek Instruments Scroboscope DT2350P (primary tachometer) -- This is supposed to be accurate to 0.1%.
  • Laser digital tachometer by Neiko Tools USA (alternate tachometer) -- This is supposed to have 0.05% accuracy, but I don't trust it as much as the strobe, it requires a reflective tape to be stuck on a blade, often gives false readings (like 9687 RPM when measuring a fan spinning at ~700 RPM)) and doesn't work well with light colored fins.
  • SPCR hemi-anechoic chamber and audio analysis system.


Our die simulator is heated up to maximum capacity and fans are strapped on and run at a variety of predetermined speeds. We record airflow, noise, and temperature rise, that is the difference between ambient temperature and the temperature of an object under thermal load. Better cooling results in lower temperature rise; worse cooling results in higher temperature rise. In this case, the ambient is the temperature of the air 6" in front of the fan, and the thermal load temperature is that of the CPU die simulator.

The fans are tested at top speed and 1500, 1100, 900, 700, and 550 RPM if possible (most fans can hit at least three or four of these speeds, giving us a nice cross-section for comparison). Long experience has shown that neither noise nor cooling is affected by changes in fan speed that are lower than ~50 RPM. We did not sweat to make the targets exactly, but they were always better than 50 RPM within target, as measured by the stroboscope.

Using RPM has an important, practical advantage: For most computer users, RPM is the fan/cooling data that is most readily accessible, and controllable. Almost every fan in computerland these days offers RPM data output, and every motherboard has the ability to monitor it. If you set the speed of your selected fan at one of our test points, you know exactly what noise level (within a decibel or so) will obtain. There are many ways to adjust fan speed: Most motherboards are equipped with speed controllers for their fan headers, and monitor fan speeds for any standard 3-pin fans or 4-pin PWM fans, and the RPM can be displayed right on the desktop using any number of fan and/or thermal utilities.

Scythe GlideStream 140

Specifications: Scythe GlideStream 140
Manufacturer Scythe Power Rating 4.2 W
Model Number SY1425HB12M Airflow Rating 84.5 CFM
Bearing Type Sleeve Speed Rating 1200 RPM
Frame Size 140 x 140 x 25 mm Noise Rating 29.5 dBA
Hub Size 40 mm Header Type 3-pin w/ molex adapter
Blade Diameter 129 mm Fan Mounts Screws
Cable Length 50 cm Weight 140 g
Starting Voltage 3.0~3.5 V Number of Samples 2
Corner Type Open Retail Availability Yes
Extras: 20 cm molex adapter with 30 cm 3-pin RPM sensor cable, dampened mounting holes

We kick things off with the GlideStream series, which shares many of the same basic elements of the acclaimed Slip Stream line. It has a multitude of long, thin blades, struts curving in the opposite direction to produce a desirable intersecting angle with the fan's trailing edges, and a very small hub to limit the size of the dead spot at the center.

The 140 mm GlideStream is available in speeds of 800, 1200, and 1600 RPM as well as a single 1300 RPM PWM model. We only received samples of the 800 RPM "L" and 1200 RPM "M" variants. After a cursory comparison, we ended up going with the "M" model as it produced roughly the same sound as the "L" except it didn't click as much when both were set to equivalent speeds. The extra rotational speed also makes it more versatile.

The limited sample size didn't give us good idea of consistency/quality. One of the "L" samples was slightly clickier than the other, while the two "M" samples sounded identical.

The 140 mm GlideStream has a rounded octagonal/square frame and 120 mm mounting holes for compatibility purposes. Along with the grooved blades are ridges running along the exterior of the casing.

The rubber dampers provide soft mounting points and increase the thickness of the fan slightly to make for a tighter fit.

A head-on shot of the GlideStream 140 "M". Compared to the Slip Stream, the GlideStream's blades are twisted more aggressively near the base. Also, the tips of the leading edges have an unusual concave shape.

This is the screen capture of Fan Xpert 2's auto-analysis of the Scythe GlideStream 140 "M".

Acoustic analysis of the Scythe GlideStream 140 "M".

SPCR Test Results: Scythe GlideStream 140-M
Fan Speed (RPM)
Thermal Rise (°C)
Airflow in/out (FPM)

The GlideStream 140 is one of the better sounding fans in this roundup. Above 1000 RPM it's turbulent and slightly buzzy, while at 900 RPM it settles down, becoming mostly smooth with some droning. At lower speeds, it's quiet and innocuous. Buzzing is evident at close proximity at all speeds but it should be imperceptible in most situations.

The measured airflow was surprisingly high, though as we've seen in the past, this didn't translate into superb cooling performance. The numbers we observed were not particularly impressive for a 140 mm fan.

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