Collecting Allertors

[kx250rider]

It wasn't ACA's thinking it was Biersach Niedermeyer.
The original name for that siren was the Mobil Directo.
This ad was in the Sept. 1953 issue of Fire Engineering.
Notice in the ad the little arrows coming out of the top horn.

GREAT AD!!!!!!!!! I didn't know until now that anyone other than Chrysler made a gas powered siren. I wonder if any of the gas Mobil Directos still exist?

Charles

[Robert Gift]

Yes, I know the top horn is the output. Thanks.

It seems that sound waves inside that "ring" around the stator would be cancelling.

Remember, though this monstrosity reminds me of a vacuum cleaner,
the sound waves inside are not just pumped out by air pressure.
Sound waves are very delicate creatures bouncing around and when getting out of phase, possibly in that chamber, cancel each other.

I would aim the horn to the rear to minimize cancellation between
the flare (intake) and horn.
I think it was a mistake to have them in the same direction.

Then, I'd cut off the horn and cut the front half of that ring away to make an open "reflector" out of it.

Maybe it would be louder.

I know, th.is "blast"phemy!

[Conky 2000]

The top horn reminds me of a vacuum, and the bottom horn looks like a pot.

[kuhlman3737]

I have heard other allertors and they do sound terrible, the ones in our system now being replaced as I speak with FS 2001's sound exactly like a 1000T there was a sound clip posted in the old message board from a tornado warning someone thought they were T-bolts.

[Robert Gift]

Crap! - just spent much time posting a reply and it disappeared.

I also do not like the Allertor sound. But have never heard one live - only through the computer thanks to you guys. I appreciate what you do and your photos.

That Allertor design looks like an efficient pump, but you can't just "pump" sound waves.
They must be carefully guided and coupled to air.
The best way I know is an exponential horn. The more gradual the flare, the better. The bigger the horn mouth, the better lower frequency output.

I could be totally wrong, but it appears to me that much cancellation can
occur in that ring around the stator.
I see no reason why sound waves would be efficiently guided around that ring and into the horn.

As an experiment, I'd carefully measure the output.
Then remove the horn and the side of thentire ring torwards the front,
then measure again.

I bet it would be louder.

Does anyone know what the best siren is dB/watt?

I bet the FS 2001.

Air is pulled from behind (under) so no cancellation between stator output
and rotor input.

The outside projector and inside motor cover form an exponential
channel to morefficiently couple sound.

One projector (which turns 360)
With two or more projectors (speakers), cancellation occurs as their sound waves intermingle and cancell.

In speaker sirens, this cancellation can be avoided by each producing a slightly differnt frequency!
Wonder whathat wound sound like?

In place of the straight cones, I'd like to replace our 2t22 cones
with exponential horns to see if it would be louder.

[AllSafe]

I wonder if any of the gas Mobil Directos still exist?

Actually, they do. Someone posted about one on the old board that was powered by a 10hp Wisconsin engine.[/quote]

[SirenMadness]

Yeah, longer waves require longer horns to be directed out of a siren efficiently, because every wave needs to be controlled up to an acceptable point. So, to compensate a certain volume of physically larger waves, you need a longer horn.
I remember saying this on the old board and not getting too many agreements.

Also, the cancellation of sound-waves isn't the sole phenomenon for making some dual-tone mechanical sirens with one rotor be quieter than ones with two rotors, but rather less efficiency for one row of ports, if the rotor has only one opening for air. As a matter of fact, I think that it is the large spacing between the two rotors on a 2T22 or 3T22 that makes them as loud as the STH-10. If the two rotors would be closer to each-other, the medium of carrying the sound would be much smaller, and therefore, have the sound go up by about two decibels at the standard measuring-length. Not worth it, but theoretically possible.

Yeah, exponential horns have less physical volume than the cones of that 2T22, but efficiency does sometimes have to sacrifice good looks; I hate the shape of trumpet-style horns.

[Robert Gift]

Yeah, longer waves require longer horns to be directed out of a siren efficiently, because every wave needs to be controlled up to an acceptable point. So, to compensate a certain volume of physically larger waves, you need a longer horn.
I remember saying this on the old board and not getting too many agreements. :)

It's all a matter of physics and math, blah.

Also, the cancellation of sound-waves isn't the sole phenomenon for making some dual-tone mechanical sirens with one rotor be quieter than ones with two rotors, but rather less efficiency for one row of ports, if the rotor has only one opening for air. As a matter of fact, I think that it is the large spacing between the two rotors on a 2T22 or 3T22 that makes them as loud as the STH-10. If the two rotors would be closer to each-other, the medium of carrying the sound would be much smaller, and therefore, have the sound go up by about two decibels at the standard measuring-length. Not worth it, but theoretically possible.

Yeah, exponential horns have less physical volume than the cones of that 2T22, but efficiency does sometimes have to sacrifice good looks; I hate the shape of trumpet-style horns.

Yes, I'd have to agree with you. I wouldn't like that modern
"technically correct" look. But would be fun to try to see if any
appreciable difference.

[va_nuke_pe]

If they were both gozoutas - there might be a sound cancellation issue. But one hole is the gizinda (air intake) and the other is the gozouta (where the noise comes out).

[Robert Gift]

If they were both gozoutas - there might be a sound cancellation issue. But one hole is the gizinda (air intake) and the other is the gozouta (where the noise comes out).

Thanks, nuke, for the new terminology.
I shall add it to my lexicon.

Is is possible that sound waves coming out of the gozinda
will cancel some of the gozouta waves.

If you were to reverse the gozouta direction and stand near the gozinda, you would still hear sound. (I would love to hear how much can be heard
from "behind" the rotors.)

But my greater concern isound cancellation occuring INSIDE the gozouta chamber where reflected waves inside that ring chamber may cancel.

I think it is a terrible design and a big mistake.
Would be interesting to know amps/dB ratio compared to other sirens.

It appears to be an efficient squirrel-cage air pump, but remember, we are creating sound waves, not pumping air.
You can't pump sound waves.
The best way to couple sound waves to the atmosphere is an exponential horn, which the Allerter gozouta still does not form.

If wrong abouthe Allerter engineering, please correct me.

I'd love to cuthe intake half of the gozouta chamber off (so that it could be reattached!) and see if the output is greater.
before -9 now -7