The Siren Board

I'm looking to make a scale model of a Carter Type 1H air raid siren out of a bench grinder. Can anyone help as far as telling me how can I make it sound the same? Especially since it turns about 3600rpm instead if 2840rpm

Though I've never built a model siren, I can help with the math. Divide 2840rpm by the number of ports to get the frequency, then divide 3600 (or whatever the exact rpm is) by the frequency and round to the nearest whole number to get the most accurate-sounding number of ports.

The tough part is that, with dual tones, the ratio between their port numbers has to be the same. So with a 10/12 siren, the ratio is 5:6 (a minor third), so you'd have to make sure that the new port ratio also divides evenly into 5:6.

If there's no good way to make the math work out on that, it may be best to simply use the original port numbers and accept a higher tone than the real thing has. Or, err on the side of a lower tone than original, which would certainly be (slightly) easier on the ears.

Doing that math then it equates out to 14.767 and 12.232, which really isn't sticking with that 5:6 ratio