B&M Siro-Drift

**Type of siren** | Friction
Directional Electromechanical

The **Siro-Drift** is a series of friction and electromechanical vehicular sirens produced by the B&M Siren Manufacturing Company, which includes a wide variety of sirens, including the flagship Super Chief. Like many of B&M's sirens, these sirens are known for their ear-piercing pitch and deafening volume and are stiff competition to other popular mechanical vehicular sirens like the Q-Siren and various electronic sirens. The mechanical B&M sirens lived through 10 generations, and three models are still in production today. B&M will also refurbish any old vehicular siren, bringing it back to factory condition.

## Friction Sirens

B&M produced friction driven sirens from 1913 all the way to the early 1980s. Friction sirens require no electricity to operate, instead, the siren is on a pivoting base and has a friction roller on the back of the siren which makes contact with a motorcycle wheel, engine flywheel, or crankshaft extension. This makes the siren ramp up, and the speed and size of the object driving the siren determines how loud the siren gets. B&M friction sirens were discontinued in the 1980s, as they were obsolete and unsafe for use. There are multiple known incidents of police motorcyclists getting injured from exploding friction sirens. B&M produced these three friction sirens:

### Model MC

The first generation MC is a motorcycle siren, and was B&M's first siren, introduced in 1913 and built until the late 1930s. Being B&M's first siren, it was not the most effective. The 1st gen. MC has a 6 inch stator with a wide "spider-arm" intake and an 8 port rotor with straight, bi-directional vanes. The 1st gen. MC got a slight refresh during production, seeing an improved tighter air intake. In the late 1930s, the MC was completely redesigned, now with a 5 inch 6 port stator and a rotor with curved vanes, meaning the siren operates much more efficiently at a smaller size. The second generation MC could also be equipped with a 90 degree horn, creating smoother airflow and slightly improved forwards projection. It could be mounted above the front wheel or in front of the rear wheel on either side. The 2nd gen. MC was a popular choice for Moto Guzzi motorcycles, but was ultimately discontinued later down the line due to the safety hazards of friction sirens.

### Model 8F

The 8F was an automotive friction siren, introduced in the 1910s and produced until the late 1930s. The 8F has an 8 inch, 8 port stator and a rotor with straight long vanes, though a couple examples with short vanes have been discovered. The 8F had a friction roller made of compressed cotton, being driven by an engine flywheel or extended crankshaft, often on fire engines. One 8F with the large projector off a B&M CS8 siren is known to exist. It is the largest friction siren that B&M produced.

### Model 6FA

The 6FA was an automotive friction siren, introduced in the 1920s and produced into the 1950s. The 6FA has a 6 inch, 6 port stator and a curved vane rotor inside, presumably the same rotor out of the 6GA electric siren. Like the 8F, the 6FA had a friction roller made of compressed cotton, and could be driven by an engine flywheel, extended crankshaft, custom engine fan, or generator pulley. The 6FA was most commonly seen used in police cars and ambulances. It could have been ordered with either a regular intake or a custom horn. The 6FA was discontinued in the 1950s, as automotive friction sirens were becoming obsolete in favor of regular motor driven sirens.