Here’s a video I took of the tornado siren test that took place on Tuesday. The siren seems to drone an Ab concert. Every siren in Stillwater is a Federal Signal Modulator, though the number of modulation… bowls? Is that what they’re called? Anyway, the number of them varies throughout town.

They can be referred to as cells. Each cell has 4 speaker drivers on the inside, and the sound is projected down onto the disc below (This means that the bottom disc does not have drivers in it, rather it is used to deflect the sound from the cell above). There are 7 Modulator variants:

(With each of these subtract one cell and you have how many cells actually have drivers)

MOD-1004 2 cells.

MOD-2008 3 cells.

MOD-3012 4 cells.

MOD-4016 5 cells.

MOD-5020 6 cells.

MOD-6024 7 cells.

MOD-6048 This one has 7 cells, but each cell has 8 drivers rather than 4, these can be identified by having two sets of control boxes.

The Modulator series has since been phased out and replaced with the Modulator II series, which has a newer driver arrangement that allows the same, if not more amount of sound, in a more compact design. These can go up to 9 cells, but there is no 8 cell model available.

Hope this helps!