ACA's unique style of stator...

[Nelso90]

A post in another topic made me think a little bit, and, I don't smell anything burning, so it must be a good question. Why did ACA use those backwards inclined ports, not just on a few sirens, but in almost their whole lineup! Nobody else did it? Were they on to something?

[SirenMadness]

I think that it was to improve efficiency more in the distance that the sound travels in. I think that they put those flaps the way they did because putting them at an angle other than an angle agreeing with the diameter, they could increase their size, while not having them going out too much. So, it was basically for top efficiency, I think.

[Robert Gift]

Thanks for the great photo.

Well, what was their dB output per watt?

Maybe that angle helps the air shockwave boundry "roll" away without
disintegrating and cancelling itself as much.

If more efficient, then more sound per watt and maybe even lesstator material.

Would love to learn more about this.

Interesting question!

Thanks

[Robert Gift]

Oh, from what I now see upon second look,
is each stator port a miniature cone?

It appears that the opening walls flare as they go.ut.

Fascinating!

[Travis]

I believe this is refered to as "fluting" the stator. In any case, it looks a lot cooler.

[Robert Gift]

I believe this is refered to as "fluting" the stator. In any case, it looks a lot cooler.

Thanks for the term.

Cooler, schmooler.
I'd want to get every bit of dB out of it possible.

If I owned one, I'd remove the screen.

The Chinese sirens do not have screens.
They know not to stick their fingers in.
Also, their sirens "park" with the rotors blocking the stator openings.
I presume they have a magnet which pulls the rotor closed.

So, does the ACA rotor turn clockwise, same direction that the openings
point? I'd expect so, but just like it to be opposite for some reason,
which would negate my "roll-off" theory.

[Daniel]

I doubt that siren manufacturers are thinking of amputated fingers as much as birds, insects, and bats when they put screens on the ports. Perhaps Chinese builders are using such creatures as a kind of lubricant. The ACA port shape seems like an inexpensive way to make a sort of projector horn out of a single cast part instead of bolted-on horns. Some of the old 1930's Hedberg sirens had an integrated megaphonic projector something like the ACA.

[Hacksaw]

Hedberg's old Foreman told me that they had to pull out chopped up bird's nests & birds out of sirens, so that's the main reason for screens.

[Robert Gift]

Daniel, knowing the Chinese, I wouldn't be surprised the'd make use of livery to lublicate their sirens if they could.

But, their siren rotors "park" blocking the stator ports!
It felt like a magnet pulled the rotor to align it closing the ports.
So no need of screens, which I bet lower the sound output very slightly.

Being the idealist that I am, I'd seek to gain every advantage in sound output possible, and remove any screening.

[SirenMadness]

So the motor must be always on, at one polarization, right?
Mesh around the rotors does not affect the sound to any level that would cause worrying.