Fri Nov 24, 2006 8:26 pm
You cannot pump air with a simple rotor-siren; the air gets sucked in by the rotor. A rotor spinning inside a stator does have a certain maximum speed at which it can push out the most air, though spinning a rotor somewhat faster would not hurt. Also, some new sirens just use bigger rotors, to decrease the need for a faster speed of the rotors.
Also, covering some of the ports on the stator would not change the frequency of the sound outputted; look at the fact that any T-bolt only has one stator opening with no low pitch. That is because it is almost solely the amount of ports on the rotor, that matters: what determines the outputted frequency is the speed at which rotor-ports pass through a stator-port, which is what determines the fluctuation of air of every chop, as the more chops you have in a time, the less time the air escaping from a previous chop has to not be pushed by the chop after it, producing that pressure which allows the chopped air to only move so much as the rotor speeds up, to make a smaller fluctuation, resulting in a higher pitch.
~ Peter Radanovic