Scythe Slipstream vs S-Flex observations

jeffc · Post by **jeffc** » Fri Mar 28, 2008 10:52 pm

[Hope this hasn't been covered much before. I did a forum search and didn't find an obvious thread comparing them directly.]

I got a couple S-FLEX SFF21F 120mm fans based on the SPCR recommended list and thought they were not truly silent. I hear a thrum (beating) at any speed, but moreso as speeds increase. These are rated as 1600 RPM, 64 CFM fans.

At Mike's suggestion I tried the Slipstream. Got a couple of the 1200 RPM, 68 CFM-rated SY1225SL12M. The Slipstream does seem quieter at all speeds. In open air the S-Flex seems to flow somewhat more air at 12V than the Slipstream, but I haven't tried them in an actual case yet. The full speed airflow seems pretty close between them.

Both are very quiet, nearly silent at 5V. I have not connected either to a fan controller yet, but have run them at 5V and 12V.

A couple thoughts: I hear an occasional click, maybe once every few seconds, from the Slipstream. I'd probably assume it's some kind of bearing-related sound. Very minor and probably livable, but audible right at the fan. Have not tried the other sample Slipstream yet.

Saw some other comments about strut shape. The Slipstream, in addition to having more numerous, longer, thinner fan blades, has curved struts. The struts correctly curve opposite the curve of the fan blades, so when the blades are sweeping by the struts, there isn't s sudden pressure wave hitting along the length of the blade or strut. Instead they would pass each other gradually tracing a outward-expanding spiral line. Clearly it should be better for struts to not line up with the blades, so having the blade and struts angled in different directions is good. Having them curved should be even better since they can't possibly overlap entirely at the same time.

The S-Flex on the other hand has straight struts that approximtely line up with the blades. This could very well be the source of the thrumming I'm hearing. The thrumming is of a lower frequency than the general noise of the blades. Since there are 4 struts and 7 blades, that would also make sense.

The Slipstream has 9 blades and 4 struts. As others have noted it also has a smaller motor hub, which should be an advantage in terms of aerodynamic efficiency. Not sure what effect (if any) it has on motor efficiency though.

So I'm definitely leaning towards using the Slipstreams for sound versus flow, but I suspect the S-FLEX may have more reliable bearings.

Does anyone know if the Slipstream, with their sleeve bearings, are ok to use horizontally?

Bluefront · Post by **Bluefront** » Sat Mar 29, 2008 1:48 am

I also have both of the fans you mention, and find very little difference between them when running at similar rpm. The sounds you hear may well be due to sample differences. And the theory is that sleeve bearing fans will last longer if mounted vertical......although these fans are too new for any long-term observations.

Frankly....I mount fans all sorts of angles without regard to the bearing types. Never had a problem.

jeffc · Post by **jeffc** » Sat Mar 29, 2008 1:56 am

I think you're probably right about similar sound at similar rpm, especially from reasonably far away where the clicks and thrums are harder to hear and especially at lower to middle rpms. At higher rpms, the thrumming on the S-FLEX is very noticeable to me. However at a given rpm, the Slipstream appears to have more airflow. If so, it would seem to beat the S-FLEX on noise per airflow.

I guess my main impression is that these fans are very good, but not perfect. If they put the S-FLEX bearing on the Slipstream fan and struts, then that new combination may be better than either of them.

nafets · Post by **nafets** » Sat Mar 29, 2008 4:27 am

Post by **NeilBlanchard** » Sat Mar 29, 2008 5:13 am

Hello,

Even the 1200RPM Slipstreams are louder than they should be for a quiet computer. I would hope that folks try the 800RPM Slipstream, for a truly quiet fan.

For situations where you need more air speed/volume, then try the 1200RPM (which starts at very low voltages) -- but the 1600RPM or faster is too much fan, and please change whatever you need to have to change in order to be able to use a slower fan!

BTW, the 800RPM Slipstream at 12v is approximately equal noise to the Nexus at 7v, and it blows a bit more air -- check the Copper Ninja review.

Bluefront · Post by **Bluefront** » Sat Mar 29, 2008 7:19 am

Neil....I look at that somewhat differently. If you need a certain amount of airflow to keep your CPU (for instance) at 50C, what difference does it make to use an 800rpm S-Flex @ 700rpms, or a 1600rpm S-Flex @700rpms?. The faster S-Flex sounds about the same running slower, and gives you the ability to push more air if conditions warrant.

These Scythe fans all run slow at low voltages, and start at low voltages. The only exception I've found.....the 100x12mm Scythe, which needs about 8-9V to start and keep running.

Das_Saunamies · Post by **Das_Saunamies** » Sat Mar 29, 2008 8:58 am

This just from my very limited experience and reading the SPCR fan tests, but don't the faster motors make a noise different to a low-range one? I know for sure there was a definite difference in the tone my Blacksilent XL2 had compared to my current XL1 - medium vs. low in this case. Similar effect with Noiseblocker's 92mm fans, of which the XE1R is recommended by SPCR.

The degree of this probably varies by fan make and model, but the mechanics are certainly different. And as you said Bluefront, "sounds about the same", which I take to mean "it sounds different". I agree with your logic though: I have a 1200 RPM exhaust and not an 800 RPM one precisely because of flow headroom.

jeffc · Post by **jeffc** » Sat Mar 29, 2008 2:58 pm

nafets wrote:The Slipstreams are smooth and bearing noise-free at 12V, but when you start undervolting them through a fan controller, a random bearing chatter is introduced and is easily noticable listening up close. It's possible I had bad samples, but I was a bit disappointed by this.

The S-Flex was smooth and bearing noise-free at 12V and while undervolted. There is a bit of that "thrumming" noise, but it's masked a bit better when undervolted. Since I had a few spots where the fans would be running horizontal, I went with the S-Flex's all around.

I think nafets is right about both issues. The clicking only happens when the Slipstream is undervolted.

I don't hear any bearing noise on the S-FLEX at any speed, but I do hear the thrumming (blade and strut noise) at all speeds. The thrumming is much less loud at lower speeds. It's very noticeable to me at high speeds.

So again I'm going to conclude, on very partial information, that the Slipstream strut and possibly blade design is better, but the S-FLEX bearing is better.

Post by **NeilBlanchard** » Sat Mar 29, 2008 6:13 pm

Hello,

My point was that if you need 1600RPM to keep it cool, there is no way that this will be quiet, and there has to be another way to keep it cool that uses a slower fan. If a 1600RPM fan is noisy at that speed, then why use it at all? I can't think that even the 1200RPM model will be quiet enough at 12v -- so why use it?

Besides, someone mentioned that the 1600RPM didn't start at a nearly as low a voltage as the 1200RPM; which starts at an amazing low voltage.

The 800RPM Slipstream is in the sweet spot, I think -- decently quiet at 12v, and starts and runs at 5v, which is ~400-450RPM, I think.

jeffc · Post by **jeffc** » Sat Mar 29, 2008 6:28 pm

My reason for using a 1200 RPM Slipstream and 1600 RPM S-FLEX is that I can undervolt them for slow, quiet operation most of the time and turn them up to higher speeds for cooling if needed, for example during gaming. (However my system is water cooled, so the stuff inside the case mostly doesn't get hot anyway. The heat gets taken out of the case by the water cooling and external radiator.)

The two fan models have similar airflow specifications (about 64 CFM) at full speed. I certainly agree that from a noise point of view it's better to run them slower, and that's what I do most of the time. I also agree that 64 CFM may be too much flow.

NTNgod · Post by **NTNgod** » Sat Mar 29, 2008 6:35 pm

jeffc wrote: I think nafets is right about both issues. The clicking only happens when the Slipstream is undervolted.

One of the two 1200RPM Slipstreams I have, which are about a week old, had the same sporadic clicking when undervolting (attached to a Sunbeam rheobus). The clicking disappeared after a few days, though.

I mention that because there was another post or two on here that had the exact same experience that I did (clicked occasionally for the first few days, then stopped).

jeffc · Post by **jeffc** » Sat Mar 29, 2008 6:37 pm

NTNgod wrote: One of the two 1200RPM Slipstreams I have, which are about a week old, had the same sporadic clicking when undervolting (attached to a Sunbeam rheobus). The clicking disappeared after a few days, though.

I mention that because there was another post or two on here that had the exact same experience that I did (clicked for a few days, then stopped).

Thanks much. Could be a case of the lubricating oil having settled somewhere during storage, etc. and needing to be stirred up by running for a while.

tutu · Post by **tutu** » Mon Mar 31, 2008 4:05 pm

How should I "run them in" at 12v or 5v? Or does it not matter. Got my Slipstreams today and hooked them upto a fan controller (Zalman MFC-1 Plus).

I have the 1200 as exhaust, 800 as intake and 800 on CPU (TBD waiting on TRUE UK stock).

1200@12v is audible and shifts a lot of air (unlike some manufacturers who fudge their results I believe these). At 1200@5v its practically inaudible. I still have the stock 8400 heatsink/fan so It's not so easy to tell if it's "silent" yet.

The 800 at 5V sounds just like it does at 12V to me!!!

But WOW my PC is dead silent now (with ambient noises!). Such a major difference to the stock fans and boy oh boy what a difference the whole system is to my old one (which was a Lian-Li aluminium case with very thin side panels, raptor HDD, stock fans at 12V)

Thanks to everyone for helping me out!

My friends think I'm nuts to be so obsessed in making a silent computer btw

jeffc · Post by **jeffc** » Mon Mar 31, 2008 10:22 pm

Glad to hear the Slipstreams are working well for you.

It's nuts to be irritated by a noisy computer.

Silence is golden....