Federal Signal Modulator

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A Federal Signal Modulator siren in Bay Head, NJ.

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 more sold on the side of the siren.

General Description[edit]

The Modulator is composed of speaker cells (ranging from one to six) that contain four speaker drivers per cell, although two models (Model 6032 and 6048) can have more drivers. 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.


Modulator model numbers identify the number of cells, as well as the number of drivers. The family of Modulator array are made up 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, which provide the same alerting technology as the original Modulator with the exception of a smaller compact chassis and cylindrical modules instead of elliptical ones.[1]

Warning Tones[edit]

Like Federal Signal's previous Electronic Outdoor Warning Siren series, the Modulator can produce six standard warning tones. The six standard tones are: Steady, Wail, Alternating Wail, Alternating Steady, Pulsed Wail, Hi-lo, and Pulsed Steady.[2] 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. For testing purposes, a Westminster Chime can be played.

Similar Devices[edit]

The Modulator has similar setup to the Whelen WPS 2700, 2800, 2900, and OmniAlert omnidirectional speaker arrays. The Whelen arrays have single driver cells,[3] 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.


  1. ^ Modulator II Siren - Federal Signal (accessed January 26, 2013)
  2. ^ Federal Signal Corporation: http://www.federalsignal-indust.com/default.asp?pageID=4&lookup=2392
  3. ^ Whelen Engineering Company: http://www.whelen.com/_MASSNOTIFICATION/omnisirn.php