The ESS 689-10P 10" passive radiator is engineered to match ESS active woofers cosmetically while helping the speaker system achieve excellent bass response. A treated paper cone with half-roll rubber surround provides a fast, well-damped structure that offers an extended lifetime of service. Passive radiators are a viable alternative to traditional ducted ports. Their diaphragm is a mechanical substitute for a port's air load, and tuning is achieved by adding mass instead of adjusting port diameter and length. Passive radiators are especially useful when a speaker's projected optimum port length exceeds available cabinet depth.