constructing

[constructing]

Hello air raid sirene interested people,

First sorry for my not total correct writing English. I´am from holland.

I want too try too constuct an air rad siren by my self.

Most off my constuctions i do whitout drawing.

It would be nice if some here could help me out with some drawings too start.

Best regards greetings from Holland

Your constructor

[Ohio_Man]

Awhile back someone on the board made this and posted it to Thingiverse. I do not know if you have a 3d printer but you could use a CNC machine to make some of these parts possibly. Even if you do not they are 3d models.

https://www.thingiverse.com/thing:2817352

What tools do you have at the moment?

[HX56]

Hello! Welcome to the board as well!

If you have time, there are a few very good DIY siren videos on YouTube. I'll link some here for you.

https://www.youtube.com/watch?v=ncBKC8gtT2k
https://www.youtube.com/watch?v=XAfvOjdZpkg
https://www.youtube.com/watch?v=AhJ3yBgXnAA

[AcousticTheory]

To construct a siren, there are a few things to know first.

1) A mechanical siren or pneumatic siren produces a tone using a rotating disc or cylinder with ports that open and close, which chops a stream of air into pulses having a frequency equal to the number of times the ports open every second. The frequency produced by a siren is equal to RPM * (1/60) * number of ports. For a 3600 RPM motor, a siren with 8 ports will produce a tone at 480 Hz. The rotating part of a siren is called the rotor, while the stationary part of a siren is called the stator, and the opening and closing action of the ports occurs every time the rotor openings align with the stator openings.

2) A stream of air needs to be provided; most sirens produce this airflow using blower vanes in the rotor of the siren, but some other sirens have been produced that used compressed air, or a stream of air from a more powerful external blower. If the air stream has a high pressure at the port exits, acoustic horns can be added to the ports of the siren to increase efficiency, but if the siren is large and has a lower working pressure, horns are less useful and are not needed. (This is why you will see that many modern sirens use horns.)

3) To have efficient operation, the physical clearance between the siren rotor and the siren stator should be kept to a minimum. This is the hardest thing for fabricators to get right; the rotor and stator need to be very concentric with each other and the motor shaft, so there is as little air leakage as possible when the ports are "closed". This also makes sirens dangerous; the opening and closing of the ports, backed by the rotational inertia of the rotor, can easily chop off a finger. 3D printing is good, but if it's possible to turn metal parts on a lathe, that's even better.

These basics should help you get started making an effective siren.

Another safety note: Because sirens spin at high speeds, they contain a lot of energy. The rotating assembly should be carefully balanced, and should be constructed in a way that it will not fly apart. It should also be tested for a good long period of time before you consider it to be 'safe'.