Even if you are not familiar with passive radiators, you have most likely heard a speaker that includes one. Passive radiators (originally called drone cones) are used in many speaker systems to allow woofers to more efficiently reproduce low frequencies. A passive radiator is a device that looks like a woofer but acts similar to a port. Like a woofer, a passive radiator has a cone with suspension and has a resonant frequency that is determined by compliance and mass. Also, a passive radiator is a resonant device that is driven by the air pressure changes inside an enclosure, like a port. With today’s constant push towards smaller systems and higher displacement, passive radiators are commonly used in many speaker designs. The biggest advantage of a passive radiator is that they give you the capability to tune enclosures lower than possible using a reasonable-sized port (more on this below). Also, we have to admit it… a system that includes active woofers and multiple passive radiators looks pretty cool.
