The Siren Board

Well, the clearance between the rotor and the stator is quite big, which could explain the lack of sound from the ports in relation to the front of the siren.
I believe that the sound is coming from the intake because the air that is getting sucked into the rotor pulsates in synchronization with the air being expelled out the rotor, to equalize the pressure, causing sound to form in the intake, and since the frequency of the air falling into the intake is the same as the frequency of bursts of air from the rotor, the sound from the intake is generally the same in pitch as the sound from the stator.
This is a little theory of mine I've had for a year or so.

In regards to curved/angled blades, at least with some vehicular sirens,
Q series curved
C5A angled/curved
B & M angled/curved
77 doubletone straight
28 straight
Sterling M30 straight



Clockwise from top left, Model 28, 77, Q, Sterling


C5A

Those are quite aggressive curves on that Q rotor; I bet it helps quite a bit with efficiency.

Ok guys check this out, I have finished modifying my little grey siren and here is the finished product, installed in its own housing. I have uploaded test videos on the Audio/Video forum.



List of things I have done:

Removed those annoying finger guards

Cut the "daisy" design out of the top to allow more air flow

Painted the inside of the stator with a HEAVY coat of paint to reduce the rotor/stator clearance and increase output

Painted it Ace Hardware Safety Yellow and added the cover (I'll let you guys figure out what the cover is )[/img]

I'm gonna go with roof vent topper.

Adam Pollak wrote:I'm gonna go with roof vent topper.

Yep

I like the vent cover. Has this changed the sound, along with your modifications?

The vent cover has changed the sound by deflecting any sound that is coming out of the top of the siren back towards the ground.

i was gonna say it looks like the top of a bird feeder.

I'm going to say that the space between rotor and stator helps explain why the sound output is attenuated when air if blown into the intake. The hypothesis goes like this: the forced air is getting into the annular space between the rotor and stator and interfering with air chopping.

This is an experiment that may help prove or disprove the hypothesis: blow air into the intake through a small diameter hose pointed right in the center of the intake, to avoid air getting into the rotor/stator space as much as possible. If the sound improves compared with nothing and using a shop-vac still hurts output, that might be the answer.