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 Post subject: 3 PWM fans and a Slipstream tested with equal airflow
PostPosted: Fri Apr 11, 2008 12:16 pm 
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Here are 4ea brand-new, yet unpackaged fans for testing, and the tool needed to open the Enermax Cluster package:

Image

The fans are the A-C PWM 1500RPM, the Scythe PWM 1200RPM, the Enermax Cluster PWM fan at 1200RPM, and the 1200RPM Slipstream 3-pin fan to provide a reference for the PWM fans. A white spot was added to the plain black hubs so a stroboscope could be used to measure RPM:

Image

First, I tested the four fans to see which pushed the least air at 100% (or 12.00V for the Slipstream). The Scythe PWM proved the weakest by a small margin, with 611sensorRPM at 100%. The Cluster was almost identical, while the A-C needed to be turned down to 82% (as you would expect from a higher RPM part). The Slipstream pushed even more air that the A-C, with a sensorRPM of 848 at 12.00V.
Code:
Kama PWM 100% 48.0dBA .5" 611sensor 1292fanRPM (39.0dBA @5")
          50% 38.4dBA .5" 332sensor  759fanRPM
Clus PWM 100% 48.2dBA .5" 611sensor 1275fanRPM
          50% 35.9dBA .5" 361sensor  794fanRPM
A-C PWM   82% 48.4dBA .5" (note 1)  1198fanRPM
          42% 33.2dBA .5" (note 2)   556fanRPM
Slipstr 6.84V 40.6dBA .5" 611sensor  932fanRPM

A cautionary note: the A-C PWM was the last fan tested. I was getting anomolous sensor RPMs, a small anomoly at first (note 1) and a whopper at the last (note 2), where I measured 474RPM that should have been in the mid-to-upper 300s. I repeated that test 4 times and got 474sensor 4 times. If the fan was really pushing that much air, the fan RPM and the noise level should have been higher... but they weren't.

This 120mm fixture was the first I constructed. The sensor prop shaft was originally taped to the pylon, and since the pylon was not put on completely straight, I just bent the prop shaft. This fixture, and its plastic sensor prop, have seen a great deal of use. I repeat, the problem showed up on the last fan and was much worse on the second of two measurements.

You should know this, and decide for yourself how much trust to put in the above figures. I didn't measure the Slipstream at half-RPM because the noise reading would have been near the ambient (27.9dBA, as usual). And, I measured the Slipstream before I measured the A-C.

My other fixtures - 92, 80, and 60mm - incorporated things learned on the 120mm fixture, esp. re the sensor prop assembly. No bent shafts! I've started building a new 120mm fixture with the same improvements.

Now, pretending that nothing is amiss, note that all the PWM fans had the same noise levels near 100%, but there are definite differences lower down (the A-C is quietest there). All the PWM fans are 7.4 to 7.8dBA noisier than the Slipstream when near 100%. This is something to think about when deciding on 3-pin or PWM fans.

I didn't use a 5" distance for the noise measurements - except one - because the reading is 9dBA lower and would have placed some of the other readings below the ambient noise. Similarly, I couldn't measure the noise levels at 30% PWM.

edit: changed "at" to "with" and "constant" to "equal" in the title.


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PostPosted: Sun Aug 30, 2009 7:48 pm 
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Thanks for the review.

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 Post subject:
PostPosted: Mon Apr 05, 2010 3:20 pm 
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Location: Slovenia
I need three PWM fans (CPU fan header will control all of them). One is for heatsink (HR-01+) and two for intake and exhaust. What would you recommend, Slipstream PWM or A-C 12025? Really important for me is idle noise, so if I understand right, AC would be better on lower RPM's?

Thanks for reply!


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 Post subject:
PostPosted: Mon Apr 05, 2010 3:38 pm 
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I believe that the Scythe PWM will go all the way down to 0 rpm or 300 rpm.

I doubt the Arctic cooling fan can do that.

Fan speed (in a reasonably good brand of fan) is the largest contributing factor to noise.

I think a lot is going to depend on how your motherboard is set up to control the PWM fans.

Start by getting one of each and experimenting.


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 Post subject:
PostPosted: Tue Apr 06, 2010 12:34 am 
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You could use a skythe kama pwm on the heatsink and slipstreams in the other positions. The arctic cooling fans never impressed me, I tried one of their pwm models and it had a fairly noticeable ticking noise at low speeds. The kama pwm is very smooth and it`s more conventional design might be better suited for use on coolers. Another thing to consider is the behaviour of the fan controller. If it ramps up speeds too agressively you might be better of using normal fans and undervolting them manually.

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 Post subject:
PostPosted: Tue Apr 06, 2010 3:17 am 
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Now I have Slipstream for intake and exhaust, running at 650RPM and AC 12025 PWM on heatsink. I'm using asus fanexpert to control PWM behaviour, so aggressive ramping isn't problem.

AC is running 450RPM on idle and it's completely silent, but Slipstreams are too loud for me (sound of air moving). I need better airflow during full load, because I have Q9550 OC'ed at 3.8GHz, but silence at idle, so PWM fans are perfect for me. I'm impressed by AC fan on heatsink, it doesn't make more noise than slipstreams even when running at same (or higher) RPMs, without ticking noise..I have Kama PWM at home but it can't be mounted on heatsink because of closed corners.

But because SPCR's recommendations about Slipstream's noise/airflow ratio, I'm not sure what to get, many people have problems with arctic cooling but mine is excellent! Maybe I just got a "lucky" fan..

Another option would be Slipstreams for intake and exhaust and 12025 PWM for heatink, but different fans on the same PWM connector..


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 Post subject:
PostPosted: Tue Apr 06, 2010 3:56 am 
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axee wrote:
Now I have Slipstream for intake and exhaust, running at 650RPM and AC 12025 PWM on heatsink...
AC is running 450RPM on idle and it's completely silent, but Slipstreams are too loud for me (sound of air moving). I need better airflow during full load, because I have Q9550 OC'ed at 3.8GHz, but silence at idle, so PWM fans are perfect for me. I'm impressed by AC fan on heatsink, it doesn't make more noise than slipstreams even when running at same (or higher) RPMs, without ticking noise..
Gee this is tough. Looks like you might have 1200rpm slipstreams running on 5 volts. Can you confirm the slipstream model and the voltage?

And is isn't the slipstreams making the noise, but the airflow. If it is the airflow, that is pretty hard to quiet. What case are you using?

Experiment with putting the AC on intake and take the intake Slipstream and put it on the HR-01 running at 5v. Then see what happens if you remove the exhaust Slipstream entirely.

Get an Akasa PWM spliter so you can run multiple fans off the PWM header. And also get an Akasa Apache and a Slipstream PWM (which can go down to 0 or 300 rpm)

It would seem some combination of these changes should work. With each mini-experiment, with each change, you will learn something and it will change what you decide to do with the next one.

I think you will learn the most from the first set of experiments that do not require you to buy new fans.


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 Post subject:
PostPosted: Tue Apr 06, 2010 4:50 am 
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Location: Slovenia
Yes I have 1200RPM Slipstreams at 5V and yes, airflow is the one causing noise.

My system:

-Intel Q9550 @ 3.8GHz (1.25V)-> HR-01+, ducted and with AF 12025 PWM, most of time running at 480RPM
-Mushkin Redline 8GB of RAM
-Antec P182
-two Slipstreams running at 620RPM (one at back with cut grills, one on drive cage in front of GPU), top fan hole is covered with acoustic foam
-ATi HD 4670 with Accelero S1 running passive
-Corsair HX 450W with S-FLEX 1600RPM, 99% of time running at 450RPM

I tried HR-01+ passive since it's ducted but temperatures are way to high (75°C +) for my comfort ;)

Since I have problem with idle noise, it might be the best (easiest) solution to use multiple PWM fans, I guess three fans running at 450RPM would be enough for me.. Then the question is: which is better at low speed (RPM), Slipstream or AC? I know that when running at 1000RPM, Slipstreams have more smoother noise..

In the past I have replaced 650RPM slipstream with AC (Slipstream was simply making too much turbolence near heatsink) so Slipstream on heatsink isn't an option. [/b]


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 Post subject:
PostPosted: Tue Apr 06, 2010 5:00 am 
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1. See what happens to your temps when you remove your exhaust slipstream.

2. Then with just two fans (one slipstream on intake and your AC on the heatsink) see what happens if you switch the two fans.

3. Repeat the above, only this time remove your intake slipstream.


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