My ignorance of plastics is almost unbeatable, and equaled only by my ignorance of brain surgery. But I've read, several times in SPCR, that brittle fan plastic is bad, transparent fan plastic is brittle, and whatever filler is added to make fans black also moderates the brittleness, resulting in a quieter fan. It seems that brittle plastic exaggerates some fan noises, presumably bearing noises. I have no reason to believe this isn't true.

Fan plastic in general is brittle. Using a pair of dikes (diagonal cutters) on a motor support strut causes the strut to snap before the dikes cut all the way thru, for instance.

Brittle substances are hard, like glass. The word "tough" is not associated with "brittle. I bring this up because some fans are not made of brittle plastic, but "tough" plastic. Very big difference in mechanical properties (I know more about mechanical properties than I do about plastics).

The only fans I know of that are made of "tough" plastic come from SilenX. Their newly-styled small fans, and their older 120x38mm fans, are made of tough plastic. Their 120x25mm fans, which look the same, are made of conventional fan plastic although they share the "titanium dust sheen" physical appearance.

A long time ago, I reported that the bearing noise of the SilenX 120x38 fan was astonishingly low, much lower than any other 120x25mm fan I had including Yate Loon, GW NCB, etc. Later, when attempting to mod that 120x38 fan, I discovered the fan was made of a very different plastic, one that was very tough and not brittle at all. I also said I didn't know if the very low bearing noise had anything to do with that plastic. I still don't know.

But I have a couple of new SilenX 60x25mm fans, which I will shortly test vs Vantec's 60mm stealth and some other 60mm fans. And I just discovered these SilenX fans are made of the same tough plastic.

If "brittle" equals more noise, it would seem logical that "not brittle" equals lower noise. I said "seem"; I don't know and I don't want to make a wild guess. But I do want to see if testing shows anything interesting... and I have superglue drying on a 60mm fan test fixture right now.

It would "seem" that a lot of what SilenX does makes quieter/better fans - larger fan blade sweep, smaller fan hubs, and apparently tough plastic. In reality, what are SilenX fans? Horrible.

While in theory they are great, in reality they suck; you should keep that in mind when you test these brittle vs. tough plastic tests.

They only suck when, after testing, it is concluded so.
Most of us here do know the history of SilenX though

I trust Felger to do some unbiased experiments on the fans in question!

You know they suck because... ?

I admit that I've been a happy customer WRT SilenX's 92mm fans since Jul 2005, a time when I had not even heard of SPCR. I still have 3 of the 4 92mm fans I bought back then and I did once own a Nexus 92mm 1500RPM fan; I preferred the SilenX fans by a large margin. Within a week or so I should have some objective measurements.

Since that time SilenX has changed the design (and plastic, it would seem) of their 92mm fans. I guess you'd call the 3 fans I have "legacy" fans.

I made my first series of tests on the 60mm fixture and I don't like the results. I compared the SilenX against 3 other contenders. One was the Vantec Stealth, which is 25mm thick like the Silenx. But when I took a closeup look at the Vantec, it has lotsa little short stubby fins for fan blades. No way was that fan gonna push much air at the same RPM as the SilenX, and it didn't. The other two were thin fans, one a 12mm out of a Logisys HC102, and the other a 10mm HC102-alike fan with sleeve instead of ball bearings. All three fans had clearly audible whines when spinning the sensor prop at 1000RPM. The SilenX spun the sensor prop in dead silence (to my ear) and 14.2dBA quieter than the best of the other 3 fans as measured by the SLM.

This is not a victory for the SilenX, it's a bad goof on my part for not providing at least one competing fan with normal blades (like the SilenX) and sleeve bearings (like the SilenX). Frankly, I don't know of such a 60mm fan on the US of A market.

Until such time as I do find reasonable "opponent" fans, I'll put the 60mm fixture on the shelf.
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Note: in my review of the HC102, I wanted to see if the device could cool an HDD adequately while being inaudible to the ear at a reasonable real-world distance. It could. But that's a very different test.

Last week, I ordered a 92mm and 80mm SilenX fan with "tough" plastic, to see if the cooling/noise ratio differed. The 80mm arrived and the 92mm is still in the system, so I'll provide the 80mm results.

I've improved the 80mm fixture since its first use. I discovered a far better, as in more stable-RPM, sensor-prop.

I used 12.0V on the lowest-airflow fan to provide a baseline. The sensor prop turned 699.7RPM, which I call 700. I included the Sunbeam Silent Core fan, which in a previous test measured exactly the same as the brittle-plastic SilenX. I did not measure fan RPMs (so I could leave the strobe set to 700); I recorded fan voltages instead.

Ambient noise was 30.1dBA (20 dBA range on SLM). On this second test, with a different and more stable sensor prop, the SilenX-Sunbeam difference changed 0.2dBA. I recorded the range the SLM was on because the ranging is manual and the wrong setting can bite. What I really wanted was the brittle-tough noise level difference, and the 80mm tuff fan was exactly 2dBA quieter (number of samples = 1).

When the 92mm fan arrives, I'll be able to compare it to 3ea of the old-style brittle-plastic SilenX fan.

The first two fans on this list are 2.5 years old, and got a lot of use the 12-15 months. The new-style SilenX fan with the tough plastic just came this afternoon. The GW is not only new but a newly released product. The Arctic Cooling 92x25mm fan is 2000RPM nominal; I just bought it. Data is fan ID, fan voltage, fan noise level at 1/4" from center of intake hub, the sensor RPM, fan size, and the range used for measurement on the manually ranged SLM.

Under my self-imposed rules (to not be affected by traffic noise) I could have (and probably should have) awarded a 40.1dBA to the "tuff" fan, becuz it hit that reading 3 times. But the fan spent more time at 41.0dBA, so that's what I wrote down. Noise floor right at 30dBA (20dBA range).

Do you see how quiet this 92mm fan is at equal airflow to the other "brittle plastic" fans? I suppose it's possible the plastic isn't what makes the difference, but in 3 examples, that plastic is associated with very low noise, lower than the noise from comparable products.

I think it's worth looking into for anybody who's really serious about fan noise. You can't tell me the regular fan plastic is noisier just by leaving out the color "filler", and then tell me the vastly different plastic SilenX is using in most of its product line now makes no difference at all.

If you want the cheapest "tough plastic" fan to experiment with, Newegg sells a 60mm SilenX for $9. The fan has open ears, so you can use dikes (diagonal cutters) to nibble-away at the front 4 ears without destroying the usefulness of the fan. Warning: the 120x25mm SilenX fans may or may not be using "tough plastic" these days.

Felger Carbon --

Your testing here is very interesting, but as you say, it's really difficult to attribute the sound difference to the tuff plastic alone. The trouble is that it appears there are very few fans made of this "tuff" plastic, which means the range for comparisons is simply too small. I think a call needs to go out to all fan nutters (I say that with humor ) on the forums, asking folks to identify any fans they think are made of similarly tough plastic like the silenx you mention. Maybe you can take some close up comparison photos? Or close mic high quality recordings? Finally, is there any indication of who is the real manufacturer of these silenx fans?

It's not clear to me what a photo would show that's applicable to the brittle-tough issue. Although I can take closeups - my camera has macro(?) capability, which I've used - I have no idea what to photograph. I'm not an audio or video person; I'm a text and still photograph guy. I don't have a microphone (other than the one on my SLM, and the SLM does not seem to have an audio output).

The difference in noise level under equal airflow conditions of the new 92mm SilenX fan is HUGE. Something is causing it. Whatever is causing it, I'd think any serious student of quiet fans would want to know what! I've identified an issue; now it's time for others who're interested to pursue this (is there a plastics expert in the crowd?). I emphasize "who're interested"; I suspect most aren't.

I'll just put my oar in to clarify a few things.

From a strictly engineering sense:

Toughness: The amount of kinetic energy a material can withstand before breaking.

Brittle: A material which breaks with little to no plastic deformation (think broken pottery).

Neither property IMHO would directly influence the performance characteristics of the fan. However I wouldn't be suprised if this 'tougher' (it sounds like they're using at as marketing term rather than an engineering one) plastic is also stiffer which would reduce the amplitude of any vibrations in fan. Smaller vibrations would result in a better balanced fan, cleaner airflow and reduced noise.

P.S. Not suggesting the Felger Carbon isn't using any terms incorrectly, just making sure everyone knows exactly what is being discussed.

To clarify: SilenX does not mention the plastic in any of its literature to the best of my knowledge. Here's how this came about:

A) I bought a 120x38mm fan so I could truthfully say I had two 120mm fans within an inch of the Ninja I was using. I bought SilenX because I had had very good luck with their 92mm fans.
B) I discovered this new fan had fantastically low bearing noise. Lotsa whoosh, but really really low bearing noise.
C) Much much later, I decided to try modifying the 120x38 fan for use in my TT MaxOrb HSF (along with some other fans). This required me to cut away the regular fan housing. When I did so, I was surprised to discover the plastic had very unusual properties. I was modifying other fans as well, so I knew what to expect when cutting the housing away - and what I expected was not what I got!
D) While I don't know plastics, as an engineer I know a little about material properties. Regular fan plastic is brittle - it snaps. The plastic SilenX is using in its new fans will deform rather than snap - the difference between steel and glass. The words "tough" and "brittle" are mine.
E) I developed my equal-airflow fan testing fixture(s) for testing all conventional 25mm-thick fans. I tested SilenX because I own some of them. I discovered the ones made of the tough plastic are also pretty quiet, and then the 92mm fan I just got yesterday via UPS proved to be very quiet indeed.

As you can see, I fell into this "brit"-"tuff" thing purely by accident. SilenX either doesn't think the plastic is important, or is keeping it as a trade secret. I have not encountered this plastic in any other fan brand.

I don't know either, I'm just suggesting avenues to explore the differences. Maybe there is something visible. If you don't have a mic, you should by now, what with all the experiments you've been doing with fan acoustics!

Ok, I guess it's time for the chemist to weigh in.

Plastics are generally categorized by two main factors. Tg and modulus. Tg is the glass-transition temperature, or the temperature the plastic will begin to turn clear before melting. Modulus can be though of as the hardness, stiffness, or plasticity of the material.

A high Tg leads to a more brittle plastic as the crystalline structure is more tightly compacted, but this has little to do with its strength. Conversely, a low Tg will make a softer plastic, but not make it any stronger.

Modulus is determined more by the strength of the polymer bonds. And this strength is translated to the molds.

The adding of pigment particles to a plastic resin, spaces out the crystalline structure of the resin, allowing more molecular freedom, making it less brittle. It sometimes has the added effect of increasing the density slightly due to the small particle size of most pigment particles. Increased density of the plastic might reduce resonance somewhat, making the fan sound less "pingy".

FYI, the plastic in these fans will most likely be an acrylic of some sort.

I spent some time earlier Tue nite tapping on the SilenX fans, examining them etc. Suddenly it hit me: besides being "tough", what the new plastic brings to the party is a shiny, mirror-smooth surface finish. Gaah! Is all this effort just for cosmetics? Regular fan plastic has a pebbly surface. Small pebbles, but definitely pebbly and not shiny.

Which would mean the quietness the new fans provide is likely due to the things SilenX does advertise - quiet bearings, advanced fan blade design...

I'm not totally embarrassed; I don't pay much attention to superficial cosmetics most of the time. This is one time I'd be pleased if I was wrong (again); I'd rather the different plastic had something to do with quietness.

As I have cut the "closed corners" out of a couple of Nexus (Yate Loon) fans I can happily say that the plastic they use is bloody hard stuff (compared to many other plastic items I have broken/ destroyed/ cut in the past.

It is not "brittle" even compared to "other fans" that I have handled, screwed into cases, dropped, thrown across the room, hit with a hammer etc etc..... Come to think of it I cant think of a single fan I have personally used I would consider brittle that is "black". All and every "transparent" fans I have ever used felt brittle and makes a vastly different sound when I put it down on my hard (plastic) desk.

You might very well be onto something with your theory of the plastic affecting the overall fan noise, but as Mike pointed out you cant test 1 "tough" fan vs dozens of not so tough fans.

To give your testing more validity you either need to find more "tough" fans to add to the group, or identify how "tough" the plastics of various fans are, it would be interesting to find a linear line of silence that matches fan "toughness".


Andy

I now know, for sure, why the 92mm SilenX is so quiet. It's a small Scythe Slipstream! Both the 120mm Slipstream and the new-design 92mm SilenX have very high fan blade pitches. I've got the data to prove it, and by tomorrow afternoon I'll post it in the User Review forum (I'm getting a tad sleepy right now).

It's a shame the "tough plastic" had nothing to do with it. It would have made a fascinating design example (sigh).

That was a cool interview :: thanks for posting it