How It Works

1st Generation

There are two main mechanisms, and 5 main parts-

Chopper Mechanism (where the sound is made!)
- Rotor (spins at around 3450 RPM, combusts air)
- Stator (stays in place, provides ports for air to exit)
Damper Mechanism
- Damper (controls air flow, rotates to reveal or conceal ports)
- Electromagnet (yeah i mean it's an electromagnet lol)
- Armature (on an axis, connects to a notch on damper & operates it)

**Siren enthusiasts, feel free to skip the below paragraph.

In more complicated terms, there is the rotor (highlighted in yellow), which rotates on a fixed shaft at around 3450 RPM. The rotor has fins inside of it to push air toward open holes (called 'ports' in siren terminology) on the sides. The stator (highlighted in blue) also has ports, which air can pass through. This is how a basic mechanical siren works.

But of course, with the Yamaha Music Siren being a unique siren, it has a unique mechanism that operates a damper. The damper (highlighted in bright red) rides on an axis and conceals the stator's ports when not in use.

When the electromagnet is charged, the armature will lower onto the magnet, and the armature will open the damper, thus revealing the ports and allowing air to flow freely and produce a note.

Different notes are achieved by using different port ratios- a term we siren enthusiasts use to denote the ratio between how many holes a siren has. For example, a 10/12 port ratio means that a section of a siren's chopper assembly has 10 ports or output holes, while another has 12.

Closed position; damper does not reveal stator ports, armature remains suspended above the electromagnet. Air is blocked from exiting choppers.

Open position; damper reveals stator ports, armature lowers onto the electromagnet. Air freely escapes and emits sound.

2nd Generation

Instead of using an electromagnet, the armature is operated via two pneumatic pistons. Air is fed into either piston via a small tube linking to a valve that controls when the damper is opened or closed. The valve leads into another small tube that feeds compressed air from an air compressor at the bottom of the assembly. The valve is operated via a MIDI reader in the siren's control box, which also explains why the siren is so much more on-time than the 1st generation units.

The armature again connects to a notch on the damper, but this time, the damper is inside the stator. A little window is cut where the notch moves accordingly with the stator.

Unlike the 1st generation model, the 2nd generation sirens' chopper assemblies are thrown together in pairs of 4, usually with port ratios of 4/6/9/12 (C3, F3, C4, F4), 6/8/9/12 (F3, Bb3, C4, F4), or others that are usually unique for a specific order. The reason why you hear so many different notes with just these assemblies alone is likely to do with the belt. The rotors in a given assembly are all fixed on a shaft that connects to a wheel on a belt assembly. Some of those wheels may be smaller than others to give the rotors a higher RPM. This would also explain why C3 is often the lowest note on most 2nd generation music sirens.

At the moment, it is unknown how air is fed into the rotor since the stators are bolted onto a stand that holds the entire assembly. Evan Vander Stoep, who is one of the main 'researchers' for the music sirens, believes it may be that the stands have small holes on the sides that may be the intake for the choppers. I have heard other theories where the choppers' air supply may be from under the stand- a hole punched under the stands so air can enter via the bottom. One thing's for certain though, the airflow HAS to be somewhere in that stand.

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