Dimmer for an aspirator (evaporative cooler)

Hello,

I have an evaporative cooler which is too noisy for the application I want to use it for, I'd like to ask if it's possible to use a dimmer for it in order to drastically reduce the noise. Of course I'm aware that decreasing the fan speed will decrease the efficiency of the device, but this is not a problem at all, it's already oversized. My issue is only the noise (around 60dB at minimum...).
In particular I'm talking of this device:

I know there is also a water pump inside, but I can simply disconnect it and run it separately.

Do you think it's a feasible workaround?
Will decreasing the speed to 1/2 or 1/3 of the selectable lowest speed significantly decrease the noise?
Which type of dimmer do I need? one for induction motors, right?

Thanks

I forgot to attach the motor schematics of this device, here it is

motor.JPG

The schematic shows the motor has a capacitor, so it is a split-phase motor, and no, you can't use a dimmer to lower the speed. What is wrong with the three speeds you have now? IF there is still too much air, cut out two opposite fan blades so the fan remains balanced.

Paul

As I already wrote the problem is the noise