With the airstream fan aquacomputer offers an alternative to papst fans.
The airstream fan is a 120mm fan (120mm x 25mm) with a maximum of 1.200rpm at a sound level of 24dB. The fan has good controlling properties and can be used with a rpm value below 500. In a few tests aquacomputer was partially able to go down to ~250rpm. The fan can start with a voltage of 5V.
In this case the fan is working almost noiseless and gives a good cooling performance. Aquacomputer means the fan is a bit quieter than a papst 4412F2GL.
The fan is using a hydro-slip-bearing.
The connection cable is sleeved and has a length of 50cm.
Info for aquaero 3.07 users: this fan has no problems with the PWM signal and can be controlled without any strange noise like ticktack etc.
But now the best: it only costs 6.99 Euro.
Two pictures: