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 Post subject: Two fans at 1028RPM - One 12cm and one 13cm dia
PostPosted: Tue Aug 01, 2006 1:56 pm 
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Joined: Thu Dec 15, 2005 11:06 am
Posts: 2049
Location: Klamath Falls, OR
Got a new fan in - the new SilenX 120mm "11dBA". Decided to test it and the old Thermaltake "Silent Wheel" with Halloween Orange 13cm blades.

The blade gap on the SilenX is the same as the UC-12EB, about 2/3 the gap on the YL D12SL-12. The case itself is strange in its simplicity: the inside of the case is a perfectly straight 1" thick barrel. All other cased fans I know of have substantially beveled entry and exits. The hub is the smallest in dia I've seen on a 12cm fan.

After a 15 min warmup (my standard), it took 8.24V to run the SilenX at 1028RPM. The fan started at 3.79V. The motor noise was slightly higher than the YL, so I compared it to the GW NCB, which was the same. The motor noise seemed the same in either direction. Listening to the motor noise on the intake side, there was a little more whoosh sound than with the YL or GW fans, which I assume was due to the smaller hub.

SilenX has a bad rep here at SPCR, primarily due to the actions of one person. Also, their method of measurement has some controversy. I'd like to address these two issues: I don't care if the company executives eat babies for lunch. What I was doing was evaluating a fan (which I assume is a vegetarian).

I have read here that SilenX does not reveal the way they measure the (in this case) "11dBA". This is flatly false. SilenX does indeed state how they measure, and always have in the year I've been dealing with them as a paying customer. Here's the statement on the installation sheet that came with this particular fan:

"Noise measurements are taken in an anechoic chamber from a distance of 1m along each of the 3 axis. The geometric means is used to determine the rating.", followed by some legal boilerplate about obstructions, temperature, and normal variance. Do I have a problem with this statement? Yes. The word "axis" is singular; it should be "axes".

It's your money. You can spend it - or not - wherever you wish. It'd cost you about $25 for this particular SilenX fan.

Now we come to the Silent Wheel, which I've had ever since it came out. The blades say it's a 13cm fan but the mounting holes match a standard 120mm fan. Can I mount it in my chassis as an exhaust fan? No, it's too big. Can I mount it on an XP-120? I did once, but there wasn't any rubber strip buffering the fan case from the XP's cooling fins. Can it be mounted on a Ninja? Sure, as long as you don't insist it be easy.

I compared the YL to the Wheel, both at 1028RPM. The Wheel motor noise was a little greater, but not much. I turned the Wheel around, and with the exhaust blowing at me, I noticed two things: the motor noise was actually a tad higher, the first time I've run into this. Also, a lot more air was being blown at me by the Wheel than by the YL.

This was expected; the Wheel fan blade tip speed is 13/12 faster and the ratio of blade area was 13^2 vs 12^2. The Wheel required 8.66V to run at 1028, so I decided to run it at 7.38V. At this voltage, the Wheel was noticably quieter than the YL WRT motor noise, and the breeze blowing at my head seemed the same from both fans (the YL still at 1028RPM). Oh, yes: this particular Wheel needed 5.38V to start.

The YL is still the low motor noise champ of my standard 120mm x 25.4mm 7-blade fans. But I've now found two odd ducks that seem to push the same amount of air more quietly: the 38mm SilenX, and the 13cm Wheel.

I'll let you decide whether running the Wheel at 7.38V during a comparison was a good move.


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 Post subject:
PostPosted: Tue Aug 01, 2006 4:09 pm 
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Joined: Tue Sep 20, 2005 6:55 am
Posts: 5085
Location: UK
Quote:
The YL is still the low motor noise champ of my standard 120mm x 25.4mm 7-blade fans. But I've now found two odd ducks that seem to push the same amount of air more quietly: the 38mm SilenX, and the 13cm Wheel.


Surely these results are not very surprising? The fan laws state that CFM scales proportional to the cube of the fan diameter and RPM, so you would expect a larger diameter fan to move more air for the same RPM, and noise is largely determined by RPM so no change in RPM equals no change in noise.

http://www.vent-axia.com/sharing/fanlaws.asp

http://www.rotronmilaero.com/fanLaws.cfm

Presumably the greater depth of the 38mm SilenX allows it to approximate the performance of a much larger diameter fan.

I also don't care if SilenX execs eat babies for luch; my main beef is that you are paying $25 for a fan which does not outperform the $4 Yate Loon, it's a price/performance thing.


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 Post subject:
PostPosted: Tue Aug 01, 2006 5:19 pm 
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Joined: Thu Dec 15, 2005 11:06 am
Posts: 2049
Location: Klamath Falls, OR
jaganath wrote:
I also don't care if SilenX execs eat babies for luch; my main beef is that you are paying $25 for a fan which does not outperform the $4 Yate Loon, it's a price/performance thing.

I bought this fan because the 38mm-thick version has the lowest motor noise at 1028RPM of any 120mm dia fan I've ever heard, by a large margin. It turns out that particular characteristic is not shared by its 1" thick sibling, but somebody had to give the fan a try, no?

I don't have mechanical mental telepathy. If I did, these fan reviews would be a lot easier and cheaper to write! :D


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 Post subject:
PostPosted: Sun Aug 13, 2006 4:03 pm 
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Joined: Sun Aug 13, 2006 3:30 pm
Posts: 8
Location: Valencia, Spain
Its is important to understand that many fans are too loud just beacuse of badly designed support structure. If you want to make a fan more silent cut the motor hub from the ribs holding it and listen to the noise. In the case of Silenx fans the noise is just the air woosh
and thats about as silent as you can get.
The point is that many fans have extra noise hum because the ribs holding the motor hub
are too close to the fan blades and by adding a few more millimeters distance the hum will disappear.
If you hack off the hub and hold up the whirling fan, listen to the noise as you bring your
finger tips, or any thing else, closer to the whirling blades.
If you get a small ring of wood or plastic, or anything, with the diameter of the hub and bore four holes in it, then fit in four new ribs made of knitting needles, etc, and glue it all together with some binary glue its very easy to have a much better fan.
Another point is that the ring surrounding most fans might also be just a little too small and
another mm or two might also make a big difference.
I am putting my computer in a small 41x32x8.5 cm space and find I have to completely
redesign the fan housings to make the noise disappear. Most people wouldn't think of rearranging the design of all these fans and heatsinks but with a little bit of effort the
results are amazing. And Silenx fans are now really silent!!

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PostPosted: Sun Aug 13, 2006 4:40 pm 
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Joined: Sun Aug 11, 2002 3:26 pm
Posts: 580
Location: USA (Phoenix, AZ)
These fans look pretty wild with a large range of sizes. They should send a bunch over to SPCR for review.

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