ASC Electronic Siren Controller In Low Tone Mode

[DJ2226]

Over the past several years, I've accumulated parts to build my own electronic siren. It's been a stop-and-go type of situation where I've picked up this project, worked on it for a few weeks, and then would put it away for months to collect dust. Earlier this year I decided to end the hiatus and finally start putting it together. The result was a mini Alertronic/Whelen type array, originally consisting of 8 100-watt police siren horns sourced from LEDEquipped and Abrams and then expanding to 16. Effectively, I built my own miniaturized AL-2000 and AL-4000, respectively. Powering this setup is an ASC CompuLert generation 3 logic board, the same logic board that comes standard in current ASC electronic sirens such as the Clarity and I-Force ; ASC does have newer NextGen boards available that are a bit more customizable and have additional bells and whistles for customers that want more features with their system. The controller feeds audio into four Whelen amps (Powermaster 1 70VAC amps from WPS-4000/2800/2900 series sirens) and triggers them via the bias input. The amps are then connected to the horns, which are wired in a series-parallel configuration like a Modulator or DSA to compensate for the voltage, roughly 78VAC while running under load, and the impedance of the compression drivers, which is 11 ohms.

As you will hear in the videos, I have the logic board wired to run in low tone mode. From the factory, these CompuLert boards are actually dual-tone with a 6/7 ratio, a feature that ASC carried over from the CD era with the original Alertronic series. Over the years, ASC has stopped using the feature; however, they never actually removed it from their controllers, meaning that even the current sirens produced today can technically run in dual tone with the modern controllers. On the board, there are two audio outputs for the tones, which are found on header J102. Currently, ASC wires the amps in their sirens to the high tone side of the tone generator, which is output on pin 8 of the header. The low tone output is on pin 7, while the common/ground connections are on pins 1 and 2. For my system implementation, I connected the amps to pins 1 and 7 to strictly use the low tone side of the controller. I also had the board reconfigured from its original state as a mechanical siren controller to function as an electronic siren controller and had it loaded with the 6 tones: alert, attack, air horn (pulse), hilo, HAZMAT (whoop), and wail (fast wail). Additionally, I had the cancel button reprogrammed to send a slow-cancel command to the controller, which gives the controller a proper wind down on all of the tones except air horn and hilo, unlike what we see with most ASC electronic controllers that receive a hard cancel and abruptly stop mid-tone. The resulting pitch shift causes alert tone to peak at 575 Hz, attack/air horn/wail tone at roughly 635 Hz, HAZMAT peaks at around 729 Hz, and HiLo tone at 489/635 Hz. While my controller isn't programmed to run scream, fire (long cycle attack), or chimes, they would peak at 729, 635, and 457 Hz respectively. The controller is augmented with an Arduino, which operates a relay board to do remote activation in order to run a custom preset routine that mirrors what Columbus, GA's system runs for testing. The Arduino is also connected to a SparkFun MP3 trigger board, which it communicates with using serial bit transmissions. The MP3 board's audio and the CompuLert's tone output are run into one of the relays to separate the two using the NO/NC connections as a three-way switch to keep the preamps on the boards from fighting each other.

The overall SPL of the siren in its 1600-watt form is north of 102 dB at 100 feet, as it exceeds the SPL of the Model 2 on axis with the siren's horns. It's not quite on par with a proper 1600-watt siren, but it definitely packs a mean punch. Given that the horns are mostly made for a vehicular siren application, they would benefit with a higher pitch compared to what the CompuLert produces, especially in this low tone mode I have it set for. I'd imagine that with an array design like the I-Force, the SPL drop from the lower frequencies would be much less impacted. The Clarity would probably struggle even worse with these lower-pitched tones since the horns are even smaller than these, and they use a straight design vs reentrant.

Enough text, on with the videos. The first two were from the siren in its 800-watt form, AKA AL-2000. In those videos, I run all of the tones and the test routine minus the voice messages (made before I integrated the MP3 board into the mix). During that particular test,t Columbus's system failed to run, so the siren got a good solo run. In the second set of videos, I set the array up to run at 1600 watts, hence the AL-4000 title. Columbus's system actually ran for that test, so in the second video, you hear how it sounds with the surrounding Whelens. Since two of the nearby 2810s run at 560 Hz in alert, their tones clash with the tone from the "Mini-tronic", creating a dual tone type of sound reminiscent of most European electronic sirens, albeit at a higher pitch. I also placed the siren on top of our shed to allow the sound from the horns to pass the fence since the wood blocked a good amount of the sound from the first run; the horns throw a much more directional beam of sound than the mechanical sirens which tend to scatter the sound they produce more sparatically allowing it to make it pass the fence easier.

https://www.youtube.com/watch?v=4rqqc9ClSD0
https://www.youtube.com/watch?v=iURpb85dxxU

https://www.youtube.com/watch?v=XHHnKZh4mAk
https://www.youtube.com/watch?v=9qhCRZ2mj70