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 Post subject: Enermax Magma and Slipstream1200 tested with equal CFM
PostPosted: Sat Apr 12, 2008 12:07 pm 
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Location: Klamath Falls, OR
The Magma I have (and opened first, I have another) is a "hot" unit, turning 1657RPM at 12.00V here in KF's thinnish air. So, I used the slower unit - the Slipstream1200 - as the reference, as usual.

About the sensor prop: I cropped another, new, 5.82" prop down to 120mm for use as the sensor. My recent problems occured on a very well-used sensor, when trying to measure/set very low sensor RPMs. I think this is friction-related; oiling the plastic sensor prop doesn't work because there's no way to keep the oil in.

So I've modified my test procedures - an improvement, I believe. Once I've used the sensor prop to equalize airflow at the maximum RPMs, I record the fan RPMs. And then I use the fan RPMs to guide my settings when running a lower airflow. After all, the sensor is known to be a little non-linear (no matter at equal settings!), but fan RPMs are by definition linear vs airflow.
Code:
Slip1200 12.00V 856sensorRPM 1262fanRPM 42.0dBA 3" (ambient 28.7dBA)
          5.87V    66.7%-->   841fanRPM 33.3dBA 3"
Magma    10.76V 856sensorRPM 1565fanRPM 46.5dBA 3"
          6.16V    66.7%-->  1043fanRPM 36.0dBA 3"

At 66.7% fan RPM, the Slipstream is 2.7dBA quieter than the Magma. But the fans are both 9-bladed, and there's a lot less open space between the lower-pitched Magma's blades. The higher RPM of the Magma surely produces more pressure since pressure is proportional to the fan RPM squared. Finally, the Magma is rated 100,000 hours at 85C!

I think the Slipstream is the clear choice for an exhaust fan where adequate air intake area is provided (and I make sure my computers do provide lotsa intake area). The Magma looks like it should be the clear choice as a CPU cooler on HSs with closely spaced fins. A filter, in effect, restricts the effective air intake. Depending on the filter characteristics, the Magma might well work better as the exhaust.

I don't see one of these two fans as the winner. I think each has situations that are a natural fit. What do you think?


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PostPosted: Sat Apr 12, 2008 1:12 pm 
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What I'm reading here.....The SS turns your sensor 856rpms @1262rpms. The Magma needs to turn 1565rpms to produce the same airflow? ......And at that rpm is 4.5dBA louder?

If that's the case, I cannot see any advantage to the Magma at all.

:?

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PostPosted: Sat Apr 12, 2008 4:29 pm 
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Location: Klamath Falls, OR
Bluefront wrote:
What I'm reading here.....The SS turns your sensor 856rpms @1262rpms. The Magma needs to turn 1565rpms to produce the same airflow? ......And at that rpm is 4.5dBA louder?

If that's the case, I cannot see any advantage to the Magma at all.

The Magma needs more RPM because it's a lower pitch fan. Lower pitch fans generally do well in higher backpressure situations. A low-pressure fan like the Slipstream can get noisier as the backpressure goes up, as I assume you've noticed when partially blocking a fan with your hand.

If there were no disadvantages to low-pressure fans, then every fan would be even higher-pitched than the Slipstream. I'm suggesting there are tradeoffs in different situations - the filters you need, but most folk don't use, are one special situation.

The Nexus Silent 120mm fan, very popular here at SPCR over the years, is the lowest-pitch 120mm fan I've encountered (in its YL guise). Takes a lot of RPM to push air. But very popular. :?:


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PostPosted: Sun Apr 13, 2008 1:55 am 
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As far as that "low pressure" thing is concerned......your testing is done in free air, without any restrictions to airflow. I suppose this is the normal way fans are tested, and cfm specs published. (marketing tweaking aside)

When you place some resistance to the airflow, the relative differences of the different blade configurations become more obvious....in theory anyway. I've been unable to pick out in advance of testing, the better "pressure" fan simply by looking at it and measuring blade surface and pitch. So I guess I'll just need to try out these new Enermax fans in one of my filtered setups.....

Certainly doesn't look too promising however. :(

_________________
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 Post subject: More fan data
PostPosted: Sun Apr 13, 2008 8:36 am 
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Location: Klamath Falls, OR
Some more data on these two fans:

The Magma starts, using a Sunbeam Rheostat, at 4V (720RPM) and runs at 2V (352RPM). The Sunbeam uses "Darlington Emitter Followers" which means the voltage drops as the current increases, so that's a very conservative starting voltage if you're using a stiffer source.

Scythe rates the Slipstream1200 at 24dBA @ 1200RPM. In Italy, Enermax rates the Magma at 29.58dBA @1500RPM. Now, as I reported, the fan I tested was "hot", so I had to turn the RPM down to match the Slipstream. If you do all the math you'll find the 4.5dBA difference I measured is remarkably similar to the seller-specified 5.58dBA difference at nominal RPMs and CFMs. Apparently you can find honest fan dBA ratings... you just can't in this country. The number Enermax has printed on the impervious Magma packaging arrived direct from Fantasy Island (boss! da plane! da plane!). :oops:


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 Post subject:
PostPosted: Sun Apr 13, 2008 8:50 am 
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Location: Klamath Falls, OR
Bluefront wrote:
As far as that "low pressure" thing is concerned......your testing is done in free air, without any restrictions to airflow. I suppose this is the normal way fans are tested, and cfm specs published. (marketing tweaking aside).

Correct. Normal fan testing, including in my equal-airflow fixtures, is done under zero backpressure conditions. These conditions are ideal for high-pitch fans such as the Slipstreams etc. Everybody is "guilty", including me.

The problem is there are no standards or agreed methods to test under backpressure. How much backpressure? How applied?

I suggested one way to achieve controlled backpressure in the Silent Forum. But who else would salute the flag? Nobody! So it's not worth the net electrons to write up an experment that everyone else will either ignore or hold up for ridicule.

Backpressure is a problem in some (many?) situations, which is why fans with lower pitch than the Slipstreams are the norm. I'm very impressed with the way Slipstreams hold up under adverse (backpressure) conditions. Nine curved blades probably have something to do with that.


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 Post subject:
PostPosted: Mon Aug 25, 2008 8:43 am 
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Do you have an opinion of which of these two fans would be better for an intake fan?

I have the Coolermaster Cosmos 1000 case which draws air from the bottom through a mesh dust filter (although the filter isn't right next to the fan).

EDIT: I'm sorry, I just read now in another thread, the original poster here passed away. That is so very sad to hear, and I didn't even know him.


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