Electro-Mechanical Sirens vs. Electronic 'sirens'

Regardless of the decibel levels close to the speaker, electronic sirens do not maintain sound intensity at longer distances.  Their sound waves are more easily overwhelmed by background noise and today's sound-insulated vehicles and high-powered stereo systems.  Speaker sound output can vary widely at different angles from the centerline, and speakers are often mounted behind decorative grilles which serve no functional purpose, but do interfere with sound output.

Many electronics are now driven at higher frequencies so that their compact speakers can meet spec for decibel output (at 3 meters).  Higher sound frequencies suffer greater attenuation (sound level loss at a distance) than do lower frequencies.  With an aging population losing its high frequency hearing acuity, the effectiveness of electronic sirens is diminished all the more.  Real electro-mechanical sirens can produce a wide range of frequencies due to the accelleration and coasting of the rotor, which is controlled by the operator.

Simply comparing current draw between electro-mechanical sirens and electronics does not reveal the actual load placed on a vehicle's electrical system.  Electronic sirens draw full current whenever they are making noise.  (From about 14 amps for a cheap, throw-away electronic box, up to 30 amps for one that mimics the 'sound' of a real electro-mechanical siren.)

B&M sirens draw about 60 amps, but only when the motor is running.  While coasting, the siren uses only 1.25  amps to keep the brake released.  During a very heavy 25% duty cycle, (25% on, 75% coasting), the averaged load on the electrical system is 16.25 amps.  A more typical 15% duty cycle brings the average down to only 10.25 amps.