I bought a new akasa apche to test it's sound level. I tested it for about 5 minutes... not silent, louder than the Noctua NF-P12 (though more cfm and pressure too).
How can you compare the two.
The AKASA is a PWM fan with a relatively low (for a PWM fan) top speed of 1500. The Noctua operates at something like 800 to 1200 rpm spending on what speed you set it to run. I think maybe the only competition for the Akasa are the PWM slipstreams. The slipstreams appear to be able to run slower... though I suspect they are not so good when faced with high static pressure... where maybe the Akasa might be good.
Would you mind telling us a bit more detail on what speed each was running and on what circumstances?