The Dystopian Wail of Air Raid Sirens

Ah, summer. A time for barbecues, Sun-drenched day drinking, violent thunderstorms and, until one physicist's crazy dream of building three 1,000-foot walls in the American Midwest gets realized, tornadoes.

Depending on where you live, you'll have enough of an advanced warning to take cover in the event of a twister. At least, that's the idea behind emergency alert systems, like the siren heard ping-ponging over the city of Chicago above. As public-warning technologies, their cries strike a discomforting, if dystopian chord.

That has always been precisely the point: to prompt an immediate response, to jarr you to ditch that open-air BBQ and find the nearest basement. As if to say, UHM YEAH THERE IS A NASTY WEATHER SYSTEM BLOWING THROUGH AND YOU SHOULD TAKE COVER. NOW.

The origins of the modern tornado siren, of course, stretch back to just before ducking and covering like Bert the Turtle was a thing, to when choruses of WWII-era Chrysler Air Raid sirens blared out over Europe:

An internal combustion engine drove the mighty Chrysler, capable of warning the masses at 138 decibels at up to 100 feet. That is loud. By using an array of tones and on/off sound patterns, it could signal all sorts of alert noises.

Thing is, a lot of mechanical or direct-driven sirens like the Chrysler, which generate sounds via electric motors that drive slotted wheels and choppers that puncuate streams of air at steady rates, have since been folded into broader Emergency Alert and similar warning systems. Taking their place, at first, were electromechanical sirens, like this big ol' Thunderbolt:

You can still see these things in operation. But drive out to the nearest field and you'll likely see some variation of an electronic siren, like the Dutch air raid siren below.

It's often the case that the loudspeaker units on electronic sirens come equipped with horn loading, which can make them bear a certain likeness to big electromechanical alarms. To strike desired pattern controls within the up-down sonic plane, a lot of electronic sirens' horns take on a vertical array design. Essentially, the horns are stacked, one on top of the other, with each individual cell in a loudspeaker's horn being driven by at least one compression driver, usually more.

You'll notice the irregularites in some of these cries. They can be almost comical. That's because, as redditor DiogenesHoSinopeus points out, sirens must "prevent sensory adaptation. In other words, this type of irregular repeating sound can't be ignored. The same way you get sensory adaptation when you suddenly hear how loud your computer was when you finally turn it off and can hear the room without the constant steady humm."

Here's another example of an anti-sensory adapting alarm, Denmark's Dansk Luftalarm:

But not so much, it seems, with Sweden's air raid / war / disaster siren, the Hoarse Fredrik. It carries a fairly flat tone:

Then there are those people, like this guy, who want to show you how to build your own DIY air raid siren. Irregular repetitions? 5:6 (untempered minor third) frequency ratios? Capital-D Dystopian, or small-d dystopian? That's for you to decide! And if the winds and rain sweep you away in the end, just let the timeless moan of fog horns guide you home.