The Siren Board

Discussion of Outdoor Warning Systems
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 Post subject: Scale model Carter
PostPosted: Tue Dec 24, 2019 4:11 pm 
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Real Name: Drew
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


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 Post subject: Re: Scale model Carter
PostPosted: Wed Dec 25, 2019 8:01 am 
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Real Name: Zachary Salman
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Location: Berkeley Springs & Shepherdstown, West Virginia
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.

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Historic preservation college student in northeastern West Virginia.
Interested in the acoustical properties of mechanical sirens from a scientific and musical perspective.
West Virginia State-wide & Western Maryland Siren Map


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 Post subject: Re: Scale model Carter
PostPosted: Thu Dec 26, 2019 4:13 am 
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Real Name: Drew
Doing that math then it equates out to 14.767 and 12.232, which really isn't sticking with that 5:6 ratio


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