SD-10
| Model SD-10 | |
 A Model SD-10 in Atlanta, GA. | |
| Company | |
|---|---|
| Produced | 1954-1987 |
| Type | Omnidirectional Electromechanical |
| Sound output | 109 dB @ 100 ft |
| Frequency | 50/60 Hz |
| Horsepower | 7.5-10 hp |
| Voltage | 208-240/480 V AC 1 or 3 ph |
| Preceded by | |
| Succeeded by | |
| Documentation | Manual |
The Model SD-10 (Special Dual-Tone, 10-Horsepower) is an omnidirectional, electromechanical civil defense siren that was produced by Federal Signal. It was introduced in 1954 as a special-purpose dual-tone civil defense siren, as the Office of Civil Defense mandated that all sirens used for civil defense must be dual-tone.
History
The Model SD-10 was introduced in 1954 by Federal Signal (then Federal Sign & Signal) after the Office of Civil Defense mandated that civil defense sirens were dual-tone and were intended to be used for purely civil defense purposes. These sirens were a popular option, with many being sold across the United States, especially in California and Arizona. The large deflection band utilized by the Model SD-10 was optional between 1954 and 1957 and became standard on all units produced afterward. Some cities such as Fresno, CA, and Tuscon, AZ chose not to use the deflection band. The Model SD-10 proved to be an effective and reliable siren, alongside Federal Signal's other models produced at the time such as the Model 2T22, Model 3T22, and Model STH-10. Even after civil defense sirens were no longer required to be dual-tone, the SD-10 continued to be produced until 1987, when Federal Signal began to streamline its lineup. Despite being intended as a civil defense siren, many SD-10s continue to be used as severe weather or fire sirens, in varying states of repair. Others still sit silently, a reminder of the perils of the Cold War.
Design
The Model SD-10 is a dual-tone siren, with a 9/12-port dual-tone rotor providing 109 dB at 100 ft. The siren has a 50/60 Hz 1 or 3 ph (1 and 3 ph Model SD-10 sirens are named Model SD-10B and Model SD-10A respectively) 208-240/480 V AC 10 hp motor above the rotor/stator assembly, shielded from the elements by a weatherproof cover. There was also an option to use a 7.5 hp motor. The siren has a unique steel shroud intended to evenly distribute the sound 360°, with 4 large "vanes" inside of 2 curved shroud pieces directing the sound. The siren has a large deflection band around the stator, which was intended to pressurize the sound and make the siren louder. This severely harmed the siren's ability to project, however, and the siren is louder without it. The siren's intake is located on the bottom, with a mesh screen to keep debris out, and this is also where the siren's included mounting legs are attached. The Model SD-10 also came in the form of the rotational Model 500-SHTT, which used the Model SD-10's rotor and stator inside of a belt-driven rotational platform. Only the 9/12-port dual-tone models came with the Model SD-10's rotor, with the 10/12 model using its own rotor. These Model 500-SHTT examples can be found in Los Angeles' former civil defense system, sitting inactive on their mounts.
Gallery
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A 1957 Model SD-10 without a deflection band in Tuscon, AZ. Image taken by Delta757.
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The internal components of a Model SD-10A.
