What is a Passive Radiator?
Passive Radiator become quite popular in especially portable speaker systems over the past years. Every speaker usually consists of the same type of components. There are multiple active speaker drivers installed, such as woofer or tweeters, to cover the full frequency range of the human hearing. These drivers are installed in a speaker cabinet, mostly made from wood, such as MDF, combined with either active or passive electronic components such as crossover components or amplifier modules. Most speakers are also equipped with a port or vent for air pressure to pass through.
The audio components combined amplify and recreate sound, while the ports on the back regulate the air pressure created in the cabinet. This is where passive radiators become interesting. In modern speakers, the passive radiator often replaces the bassreflex port tube. Although a passive radiator looks almost identical to an active driver, they cannot replace another, only complement each other.
A passive radiator is identical in design of an active loudspeaker, except that it is missing a voice coil and a magnet. A passive radiator is also not wired to an electrical circuit or power amplifier. Instead, they are powered by the created air pressure inside the speaker cabinet.
Passive Radiator vs Port
Passive radiators, also known as drone cone, make it possible for the active woofer in the speaker cabinet to recreate deep, resonant tones that could usually only come from loudspeakers with a large cabinet and AC power. A passive radiator is an efficient way of getting more power and deeper frequencies out of a compact speaker system. Passive radiators also eliminate the chances of port tube noises, called chuffing, associated with bassreflex port tubes. Furthermore, passive radiators recreate sound to exit the cabinet similarly to a bassreflex port tube, but with one crucial distinction - they permit a larger range of frequencies to be recreated since they lack a resonance frequency like bassreflex port tubes do.