In the case of an axial fan, the air is always obstructed by the PCB, and has to take a "90 degree turn", the same applies to AMD's "new" cooler. The only thing we have to focus on is how much total heat is going out either way, not the amount of air in CFM. If the CFM in the back fan is half of the front, it may still carry the same amount of heat energy due to absorbing more heat under time of contact with the fins. They would not have put a fan there if the amount of heat dissipated was miniscule. Of course this would be optimal in a positive pressure case, and of course a negative pressure case could have a very negative impact on this type of setup. As I see it, the more heat you could push out as fast as possible, the better. There is nothing positive recirculating hot air inside the case. Nvidias half'n half aproach still makes a ton of sense.View attachment 29903
The front fins are tied into the vapour chamber, but the stack height is much smaller than the rear fan. Even if the airflow wasn't obstructed by the PCB, you would need greater airflow to provide the same cooling through the front fin array, which means more RPM and thus more noise. The airflow is obstructed by the PCB and the shroud though, and has to take a hard 90 and travel in that thin stack between the fan and the board, along all the high z-height components, and the up and around the HDMI ports and out the back. If you tried to provide equal cooling, the exhaust air will be a loud, high velocity turbulent mess and the fan will be spinning like a banshee trying to force it all through while the back fan spins slow and easy. The best compromise for low acoustics would be to have both fans run in a way that produces the same amount of noise, as long as thermal constraints on all the subsystems are met.