Last November I was in Illinois to take some courthouses photos. My first stop was in Danville, and I was struck by the twelve-story First National Bank Building downtown. Actually, it was the siren song coming from its apex that snagged my attention. See that yellow thing up top? It’s a Federal Signal Thunderbolt 1000T. Sixty-year-old examples like this are getting harder and harder to come by these days! Unfortunately, it was mute; I guess it has been since sometime prior to 20081. No actual siren song for ol’ Teddo.
As I am with pizza robots, I’m drawn to tornado sirens in my adulthood even though I was terrified of them growing up. I’ve always had a thing for hidden infrastructure, though: whether we were at Big Lots, Ames, or Hills I always made a point of identifying the electric eye that opened the doors automatically. I felt like an expert spy when I found that the older Marsh supermarkets used a hidden pedal like the one on my mom’s sewing machine to advance their check-out conveyors. It was the same with the oft-heard but never seen sirens- I’d proudly made a mental note when my mom pointed out the one atop Muncie’s 1969 county courthouse, but as far as wantonly looking for or researching any of its counterparts, though, forget it. Too scary. That is, until I moved within a thousand feet of one and noticed them begin to pop up in my photos here.
Muncie’s courthouse is hardly exceptional when it comes to having a noisemaker affixed to its rooftop. Even today, 56 percent of Indiana’s feature one in the form of a clock tower or belfry. These elements originally served multiple functions: First, a ticking clock or a chiming bell during the victorian era told residents what time it was! For those too far away to actually see or hear the clock, the added height of the tower advertised the county’s prosperity and amenities to weary travelers or out-of-town businessmen. Finally, towers and belfries served the practical
porpoise purpose of alerting residents to disasters like fires. Of course, that’s hard to do when the courthouse itself is engulfed in flames, with is something that’s happened at least forty-two times in Indiana2. Around the turn of the century, the electromechanical siren was invented and local governments bought the crap out of them. I wanted to say that every county in Indiana has a siren at its courthouse square, but that’d be data pulled ex recto. Closer inspection shows that thirty Indiana county seats still have a siren within a block of the courthouse. More often than not, they’re jacked into a countywide emergency management system and tested somewhat frequently.
Thunderbolts like the one in Danville are cool. They’re old, and they sound absolutely terrifying when they wind up. Federal Signal started producing them during the 1950s as civil defense sirens to alert communities to an impending Soviet attack. Just about everywhere I’ve lived is said to have been on Khrushchev’s hit list at one time or another and In Muncie, six Thunderbolts arrived on January 9, 1958 at the order of Marshall Sipe, Delaware County’s new Director of Civil Defense. Promising a circular mile of audible coverage, the sirens were installed around town atop three schools, a forge, a dairy, and a downtown department store. I’d imagine that many cities followed a similar trajectory of putting their own sirens in, while many smaller towns eventually hooked their old fire call signals -often old Darleys or lesser Federal Signal models with two or five-horsepower motors— up to their county emergency systems.
Several of these sirens have inadvertently made it into some of my courthouse photos, though sadly, no Thunderbolts are among them. The 1958 Crawford County Courthouse has got a Federal Signal 2001-DC jacked up on a tower behind it. The 2001 is the model that replaced the Thunderbolt, and Federal Signal’s been cranking versions of them out since 1988. You could buy one new today.
The modern Perry County Courthouse has no siren, but Tell City’s city hall -originally built as a prospective courthouse in 1895 to try and steal the government away from neighboring Cannelton- has a Federal Signal 3T22A on its roof. It’s painted white to match the building’s belfry.
The 1929 Harrison County Courthouse in Corydon was designed to be classical in influence but minimalist in execution so as not to distract from the 1816 statehouse in its front yard. Fittingly, a tiny bit of a modern Federal Signal Modulator 3012 peeks out from behind the building’s parapet. Modulators are not electromechanical sirens; they reproduce warning signals and messaging through electronic amplification. They’re essentially a series of big speakers.
So how do mechanical sirens work? Well, they’re usually activated by a series of tones transmitted via dispatch radio. Once a Thunderbolt gets word to start screaming, three assemblies called a blower, a chopper, and a rotator go to work. The blower is a supercharger that sends air up a pipe into the chopper, which consists of a high-speed, axial fan called a rotor within a stationary element called a stator. The spin of the rotor opens and closes a series of integrated holes called ports, which causes the blower’s air to project into the big trumpet at the end (called an “exponential horn”) in a series of waves that create a tone. That tone varies depending on how fast the rotor is spinning along with how many ports are in the rotor. Finally, a separate assembly allows the horn to spin in a circle for omnidirectional coverage. Modern electromechanical sirens work the same way, albeit without the blower.
Other sirens may vary in appearance but generally work the same. There’s no exponential horn on the Banshee atop the County Building in Muncie, but it’s still good for 119 dB from a hundred feet away. That’s like standing next to a jumbo jet taking off.
Rotating at top speed, a Thunderbolt is capable of generating sound in an overall frequency range of approximately 128-700Hz. They’re powerful sirens; single-tone units can hit 127dB at 100 feet away. That’s hella loud! Thunderbolts typically produce two tones, “alert” (a steady signal) and “attack,” a wail. Federal Signal’s newer SRNs produce three sounds: a “steady” 790Hz tone, a 470-790Hz “wail” tone that oscillates up and down between frequencies every ten seconds, and a “fast wail” that goes from 600-790Hz every 3.5 seconds3.
Unfortunately, I’ve never been in a big enough apocalypse to hear wail or fast wail cycles through a mechanical siren. A couple of miles away from my house, Ball State University has three electronic Whelan WPS 4004s that they’ve tested on “wail” every Friday for the past few months. These sirens are like Corydon’s Modulator and create sounds via four 400-watt drivers4. They’re easy to discern as their wind-down ends abruptly. Pop! No more siren noise since there’s no need for the rotor to slow. Universities probably prefer electronic sirens because they can plug a microphone into them and customize the message they play. They have more practical usability that way.
Along with Ball State, Delaware County does a twenty-second test of its sirens at 11:00 a.m. every Friday. I can hear six of them from here. I know this because one Friday I recorded them from my balcony with an omnidirectional mic and established their locations by using a map, a stereo visualization plugin, and a spectrogram in my recording software. Over the course of the next six weeks I went to each siren shortly before 11:00 and recorded each with a USB condenser mic stuck through the sunroof of my car. I mixed the results into a Friday morning alarm for my phone and watch. Anything worth doing’s worth doing to excess, I say!
Unfortunately, the sirens around here -including the one a thousand feet from my house- are mostly boring 2001s. In fact, 2001s are the sirens around most of everywhere. According to a Google Map made by Spencer Harman, Tyler Noie, Brandon Mendel, Ian Tate, and Matt Hackler that tracks them all, there are 2348 sirens in Indiana and 43.9% of the Hoosier State’s sirens are different forms of 2001s. No other style comes close to that sort of widespread use. There are twenty-six Thunderbolts in Indiana, good for 1.1%. Banshees like the one on the County Building downtown are even scarcer- only six remain across the state and three are in Kendallville. They must have gotten a great deal!
It’s sort of fun to look around for our outdoor warning sirens- a little bit like a treasure hunt. Unfortunately, if you go searching and live in Marion County, your bounty will consist of a lot of suck. Officials there replaced all of their old sirens with SRNs around 2009. Your best bet on finding some cool ones is to go to a local fire department out in the middle of nowhere, though Zionsville’s nearby and has a trio of older STH-10s.
Here’s a quick video I made from my redundant 11:00 siren alarm recording. The footage on the left was taken from my balcony the day I recorded the reference audio. The map on the right illuminates new siren when they chime in via their actual locations and the data I got from my stereo imager and spectrogram. Though four of the featured sirens are SRNs, a few things affect how they can be individually heard; namely their distance from me and the direction they’re set to rotate. A few harmonics ping out here and there. The Thunderbolt note is obvious, and I added in some neighborhood noises that I’d eliminated from my actual alarm. It’s not totally perfect, but it’s absolutely representative of what we hear in my neighborhood on a Friday morning if the trash truck’s already gone through!
I could 3D-print a tiny, working replica but my printer’s sized just right for ABS replacement joints for my Billy Bob robot and not much else. But like I said last week, the best way to deal with your fears is to confront them head on, which means that I must acquire my own air raid siren, although a department store electric eye or a sewing machine pedal would be cheaper. Or another pizza robot! For now, I’m waiting for the right example to pop up on eBay and enjoying the confluence of my interests through seeing a handful of sirens poke through in my courthouse pictures.
1 Bailey, Jennifer. “City to review warning system” The Commercial-News [Danville]. June 19, 2008. Web. Retrieved 3/17/21.
2 Enyart, David. “Fires and Tornadoes” Indiana County Courthouse Histories. ACPL Genealogy Center, 2010-2018. Web. Retrieved 3/186/21.
3 “Service Manual” Thunderbolt Siren. Signal Division, Federal Signal Corporation [Blue Island]. Print.
4 “WPS4004 Four Cell” Mass Notification Literature. Whelen Engineering Company, Inc. [Chester]. Web. Retrieved 3/19/21.