Mechanically how do sirens work?
could someone translate joans answer into layman for me.
- MarkGLv 71 decade agoFavourite answer
Check out the link.
A mechanical siren is like a fan. A revolving impeller with fan blades draws air into the center of the rotating impeller. The spinning blades(Vanes) sling or push the air to the outside diameter of the impeller.
The impeller is spinning in a cylinder which has a series of slots cut in it. The Air that is being compressed by the impeller is allowed to exit out of these slots when the vanes line up with the slots (there are also tabs at the end of teh blades that are sized to cover the slots). When the vanes don't line up with the slots the air is compressed until it lines up with the next slot. The baldes are spaced so that they are twice as far apart as the lenght of the slot.
All sound is basically rapid changes in air pressure. Like a guitar string being plucked, the vibrating string moving back and forth causes changes in air pressure that move outward from the source until they reach our ear. The faster the vibrations the higher the frequency or pitch sound is produced
So the mechanical siren is creating a series of high frequency(rapid) air pulsations. The impeller is spinning at 1000's of rpms compresses air and when the openings in the impeller line up with the slot a puff of air is released. The slots are just as quickly covered up blocking air from leaving and allowing it to compress for the next opening.
So you get a series of air puffs happening at a very fast rate which gives you sound.
- Anonymous1 decade ago
By vanes moving in close proximity to fixed vanes so creating resonances.