Port Ratio?

[Justheretolook]

I just realized my primal interest in sirens but i know nothing about them, what is a port ratio?

[Chicagosiren-hunters]

Port ratio is the difference between the number of slits a sirens chopper have; mainly used on sirens that have two sets of fans. here is an example:

This siren picture is a Sterling M10, and it has two fans, each with 16 ports. Therefore, the port ratio for this siren is 16/16.

[Chicagosiren-hunters]

The second picture is a Federal 76A vehicular siren, and this has one large fan with two sets of ports, ore commonly seen on larger warning sirens. The fans have 8 and 9 ports, so the port ratio would be 8/9.
I hope this made sense, and welcome to the community!
-Cheers

[T-1000]

Yeah, as stated above it is the number of ports on the high tone compared to the number of ports on the low tone (or vice versa,) for example a 2t22 or 3t22 siren would be 10/12 so, 12 ports high tone and 10 ports low tone.

[Justheretolook]

Yeah, as stated above it is the number of ports on the high tone compared to the number of ports on the low tone (or vice versa,) for example a 2t22 or 3t22 siren would be 10/12 so, 12 ports high tone and 10 ports low tone.

So more ports = Higher tone and vice versa?

[T-1000]

Yeah more ports would make the siren higher. And less would make it lower.

[Chem_Boffin_6589]

I always remember port ratio being used for sirens with more than 1 rotor/stator assembly. As Chicago mentioned above that picture of a Sterling M-10 will have a ratio of 16/16 because it has two of the same choppers and stators.

As you watch more siren videos you'll soon be able to know what a siren will sound like from the tone it makes. As you've said, more ports means higher pitch, and certain numbers of ports will make a distinct sound. What I'm basically getting at is that the sound a siren makes will match with a note on a piano, for example. (e.g: an STH-10 which is a 12 port siren will make the note F) and it will make that sound because of the number of ports the chopper and stator has.

[FahmiRBLX]

Port ratios are shortly known as "Ports".

Single tone sirens (Sirens with either 1 chopper & stator or 2 C&S (Why not abbreviate Chopper & Stator with this?) that sound the same pitch) also have port ratios. Example, a Federal Signal 2001-130 has 12 Ports.

Yeah more ports would make the siren higher. And less would make it lower.

The chopper (Fan)'s RPM (Revolutions Per Minute) also accounts for the pitch. Example, you went to record an ACA Allertor 125 siren (9/12 Port (Keys F, B) variant) in [Insert sick unit location]. However, once it sounds, it sounds a lower pitch. Meaning the chopper spins slowly.

The stator hole number mustn't always match the chopper. The Fed. Sig. Thunderbolt has only 1 stator hole, whereas the chopper has more than 1 port holes.

Electronic sirens (Essentially a loudspeaker that blast siren tones. Usually comes with announcement-'blasting') shall not have the term ports. The pitch is measured in Hz.

[T-1000]

Yes, I was just saying that in general a siren with more ports would be a higher pitch, I know motor rpm also accounts for pitch. For example a 3200rpm siren with 7 ports would be a lower pitch than a 3200rpm one with 12.

[Jackson95]

There are also sirens that use Single Ratio or triple ratio. But there are no triple ratio sirens has far has I know.