By Alan M. Petrillo
Fire departments tend to be traditional in many ways yet often take time to embrace new technologies.
But when it comes to sirens-audible warning devices for fire apparatus-a mix of old and new technology can be found on many fire vehicles. It's not unusual, for instance, to see a new first-due pumper outfitted with both electromechanical and electronic siren systems.
Electromechanical Sirens
Vic Hilbert, owner of Eagle Sirens Inc., makes traditional electromechanical sirens that he says use a forward projection of sound instead of a wall of noise. "We focused the sound from our sirens to send it forward," Hilbert says, "and also off on a 55-degree angle to each side to get great penetration at intersections. A lot of other sirens put up that wall of sound, which puts the noise out front but also has a backwash that penetrates backward into the cab of the fire truck."
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Eagle Sirens Inc. makes the Screaming Eagle electromechanical
siren, shown here pedestal-mounted on an extended bumper. The
siren also can be flange-mounted and nested in a hidden mount.
(Photo courtesy of Eagle Sirens Inc.)
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Hilbert's company makes the Screaming Eagle siren in one model available in three mountings: a pedestal mount (for apparatus with extended bumpers), a flange mount, and a hidden mount where the siren is nested behind a vehicle's bumper.
Hilbert points out that Eagle Sirens uses a pure silicone formula for all of the noncontact sealed bearings in its sirens. "The silicone makes the siren run much quieter and longer, and it has an anti-vibration effect," he says.
Kevin O'Connell, owner of B&M Siren Manufacturing Co., says B&M has five models of electromechanical sirens in its line: two direct-driven Super Chief versions and three Siro-Drift models. O'Connell maintains that electromechanical sirens move traffic better than electronic sirens. The electromechanical signal sent by a siren depends on the number of ports it has and how fast the air is moving through the ports, he notes. "The faster you run the siren, the more it sounds like you're stepping on a cat's tail," he says.
O'Connell says a siren's spinning rotor is very similar to that of a centrifugal pump. It draws air in at the front of the siren; compresses it slightly; and, as the air escapes out of the ports, the siren pops with sound.
One of the advantages of a mechanical siren over an electronic one, he points out, is that the mechanical siren emits a lower-frequency signal, which travels much farther. "The lower the frequency, the farther the sound travels, which is why air raid sirens operate at a low frequency," he says. "There's no beating a mechanical siren for attracting attention down the road," O'Connell says.
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Code 3 has developed the Banshee, an electronic device that can
be attached to any siren in the industry to produce attention-
getting low-frequency tones among its 25 tone combinations.
(Photo courtesy of Code 3.)
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Timberwolf Siren Technology also builds an electromechanical siren-the Timberwolf 45, which develops a 123-decibel sound level from a 12-volt, 28-amp power source. The Timberwolf 45 uses an angle-designed rotor that the company says won't lose acoustic energy because the sound is d