Federal Signal Modulator

Federal Signal Modulators (also known as Modulator Speaker Arrays) are electronic warning devices produced by Federal Signal Corporation that are used to alert the public about tornadoes, severe weather, earthquakes, fires, lahars or any other disaster. They are identified mostly by their distinctive stacked "flying saucer" design. The Modulator II is sold based on the more compact chassis of the siren compared to the original Modulators.
General description.
The modulator is composed of speaker cells (ranging from two to eight with the exception of seven) that contain four speaker drivers per cell, although two models (model 6032 and 6048) had additional drivers available when they were still available. Modulators have an inactive (dummy) speaker cell on the bottom of the stack that is used to help project sound in all directions. Without the inactive cell, because of the design of active cells, there would be unbalanced sound distribution. Modulators that are being made now use the UltraVoice controller. When they were first made, they were used with Modulator Control Plus and basic/standard Modulator Controls.
Models.
Modulator model numbers identify the number of cells, as well as the number of drivers. The first family of modulator arrays consisted of eight different models, as follows: 1004, 2008, 3012, 4016, 5020, 6024, 6032, and 6048.
In January 2013, Federal Signal released the Modulator II sirens, consisting of the 1004B, 2008B, 3012B, 4016B, 5020B, 6024B, and 8032B. They provide the same alerting technology as the original modulator with the exception of a smaller compact chassis and cylindrical modules instead of elliptical ones.
Warning tones.
Like Federal Signal's previous Electronic Outdoor Warning Siren series, the modulator can produce seven standard warning tones. The seven standard tones are: Wail, Alternate Wail, Pulsed Wail, Steady, Alternate Steady, Pulsed Steady and Westminster Chimes. If properly equipped, the modulator can also employ voice notification to give specific information or to give a more clear understanding of an emergency situation. They have also been known to play Star Spangled Banner during tests on or near the 4th July, and also on military bases that have the sirens there.
The sirens can be activated by radio using single tone, two-tone, DTMF, MSK or POCSAG over analog, digital and trunking systems, or by satellite, cellular, landline or IP. They are also capable of being activated automatically by the Emergency Alert System.
Similar devices.
The modulator has a similar setup to the Whelen WPS 2700, 2800, 2900, and OmniAlert omnidirectional speaker arrays. The Whelen arrays have single driver cells, while modulators have multi-driver cells. Another siren that is similar to the modulator is the American Signal I-Force siren, which uses stacked, elliptical speaker cells that provide omnidirectional sound output, just like the modulator.
Notable locations.
The modulators in Chicago's siren system run on the noticeably different and somewhat off-putting Alternate Wail tone during tornado warnings in order to vary from emergency vehicular sirens, often mistaken for being broken, malfunctioned, hacked, etc... Recordings of the siren have been uploaded to YouTube, with the videos reaching millions of views. Many people refer the Modulator as the "Chicago Siren", "Scary Tornado Siren", "Cthulhu and "Siren Head" due to the unsettling nature of the tone. However, in O'Hare International Airport, their systems are different. Instead of using the main UV Wail or Attack, they use an Eclipse 8 (possibly) sound card doing attack. Before that is the Westminster Chimes.
Moore, Oklahoma is well known for their modulators being placed close together compared to other cities. They are placed only a half-mile from each other in some parts of the city. Until 2017, some sirens ran on a major third dual-tone alert.
Baytown, Texas is one of only a few cities in the United States to have a whole system of modulators. They use just over 20 5020's and 5020B's, and use them primarily for chemical releases. The warning tone is a custom Hi/Low signal.
The modulators in Olmsted County, Minnesota are known for their pre-test and post-test voice announcements, and also for only being located in parks.
The modulators in Monroe County, Michigan are known for their pre-test voice announcements. There is a unique "rainbow" modulator located in Monroe County as well.
Eden Prairie, Minnesota has a uniquely mounted Modulator 5020 on top of a parking garage which has a custom attack tone that cannot be found on other modulators. This modulator has never done a voice announcement, which is one of the primary reasons that some cities invest in them.
Additionally, in Cape Town, South Africa, several modulator sirens are installed which use their standard wail tone to alert citizens in the Melkbosstrand (of which Van Riebeeckstrand is part of), Duynefontein, Blaauwberg (of which Bloubergrant, West Beach, Blouberg Sands, and Sunningdale are part of), Table View, Robben Island, Atlantis, Philadelphia and Parklands areas in case of any emergency which can occur at the Koeberg Nuclear Power Station. These modulators are tested for about an hour annually on the first Wednesday of March during a so-called "Full Volume Siren Test" using a preset female voice (which reads "This is only a test; there is no need to take any action. This is only a test; there is no need to take any action. I repeat: this is only a test; there is no need to take any action. Listen to Good Hope FM or Kfm for further information") and live voice announcements (which are read by people and are often cite similar things said by the preset voice), other than the typical wail tone of the modulator.
The Modulators (MOD-2008) make up nearly all the warning sirens in the Netherlands, which are tested on the first Monday of the month at noon.