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.
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?