When Sirens "BITE"

[Daniel]

When I found this beast sitting on the ground in Warrenton, Oregon, the people who removed it from its pole had secured the rotor by tying bailing wire through the port openings.



By the way, it was never reinstalled and I don't know what happened to it. Given that Warrenton is at sea level on the coast, one would think that they would want to keep it.

[Robert Gift]

Daniel, you always have the most interesting photos!

Appears the same red as your German(?) siren.

The stators appear identical.
Is thisingle pitch though two rotor/stators?

A cancellation problem can occur when two sources produce the same pitch.

I wonder how much sound output is diminished by the covers.

Thank you,

[Daniel]

This is a Sterling M-10 from the 1960's, I believe, and has a very high pitch. No cancellation problems at all, in fact I have never heard of this happening on single-tone, dual-head sirens. I suppose if one were somehow out of phase with the other, this could happen. All of my photos were taken in the USA, and the siren in my avitar is not German. It is in the town of Summit City, CA (near Shasta Dam), and I don't know exactly who built it. This is the same kind of siren that is shown in that 1940's photograph of workmen installing one at Pearl Harbor. Some speculated that the Buell company built these, but all I know about Buell is that they made large air horns for municipal warning purposes in the 30's.

[Robert Gift]

Oh, thought it was German. Looks German!

Cancellation can happen simply because two sources produce the same pitch.
The space between the sources may cause their sound waves to coincide
and neutralize one another.

This can happen with electronic vehicle sirens.
I saw an ambulance which had one siren speaker in the lightbar and the
other behind the front grill.
I informed them that was improper and likely produced cancellation.

Had they had an accident, and the opposition had a good lawyer, he would probably make an issue of it.

The vehicle siren speakershould be exactly side by side.

Cancellation also occurs in largelectronic outdoor warning speaker arrays.

Other than having everything coming from one source, next best is to have speakers at slightly different frequencies!

[SirenMadness]

Cancellation should not be of much worry to you if you have two sources, case-specifically of two rotors, producing a high pitch, as high pitches are more organized than lower pitches and therefore would not interfere with each-other too much.
Also, I was too afraid to touch at the rotor from a siren in Zagreb, at the edges, as I was afraid of the chance of an accidental rotation.

[Robert Gift]

Do you mean the siren may start up?

Bicycle sirens often (if not always) had saw-like "teeth" on their stator edges which repelled kids from putting their fingers in the stator ports.
(Worked on me.) (I remember something replusive about a siren
on an aquaintence's bike. When I recently saw one, I noticed the teeth
and now knowhy.)

[AllSafe]

Actually, the Pearson's Majestic bicycle siren was designed that way to intentionally limit the efficency of the siren; i.e. to make it quieter.

[Robert Gift]

Are you sure it was noto repel fingers?
To make softer, I'd expecthem to make the stator openings shorter.

If I am able to afford one, I had already planned to file off the teeth!

A new low!

Robert -XXIV

[Robert Gift]

Peter, I don't see why frequency would matter.

You can still cause cancellation using the same frequency as what is being emitted.

I wish I could experiment with cancellation.
But my tone generators are longone.

[SirenMadness]

Lower frequencies would, theoretically, cancel each-other out more than higher frequencies, because higher frequencies are more in order and are more confined.