Federal Signal was approached by the towing industry to create a low cost light bar available to outfit their rigs. Federal came up with the idea to change the metal speaker trays to plastic. They also changed the stainless steel speaker cover to Aluminum. They deleted the stainless steel strips across the front or rear of the light bar. Taking these items away made the Twinsonic an economical light bar for this industry.
The first model was the model 12E. This light bar had the outer rotators of the model 12, it had the motor mounted to a plate on the drivers side. There were no mirrors or other lights mounted in it and it also deleted the passenger side mounting plate.
The Twinsonic model 12EV was an economy series with a single V mirror on each side which produced extra flash of light to the front and rear.
The Twinsonic 12EF featured two front and rear flashing par 36 bulbs. The flasher for these was a Tung Sol 537 can style flasher and was mounted to the mounting stud on the gear cage.