The F/XiA4's engine is the dual Dynamic Balance 1-inch dome tweeter design and a 5 1/4-inch Dynamic Balance driver that produces believable real-life effects at prodigious volumes. The selectable bipole/dipole function allows you to configure it to your space and 7.1 systems. The smaller cabinet enables it to fit in more places.F/XiA4 Features: The trapezoidal shaped cabinets aim the drivers and tweeters in opposing directions to produce a more realistically diffuse wavefront and wide, lifelike imaging of surround sound. Keyhole slots make mounting a snap. With the flip of a switch, our dipole/bipole circuitry changes the soundfield from direct to indirect radiation patterns enabling you to place the surround speaker beside or behind you depending on your listening room setup. Klippel motor optimization uses laser measurement technology to ensure a smooth excursion path at either end of the volume spectrum for uniform performance at both low and high volumes. Polk's proprietary, patented Dynamic Balance technology allows our engineers to design out distortion-causing driver and system resonances, so you only hear the good sounds. Durable, computer-modeled, injection-molded butyl rubber surrounds suppress unwanted cone resonances for a lifetime of reliable sound. The F/XiA Cascade Tapered Crossover eliminates the comb filtering and beaming, common to multi-driver speakers, which degrades the quality of the audio and collapses the soundstage. Patented Acoustic Resonance Control (ARC) technology suppresses cabinet resonance that causes distortion to ensure clear and natural sound. Computer-modeled anti-diffraction grilles enhance the good looks while minimizing sonic interference. All Polk loudspeakers are timbre-matched within their series, designed with the same components throughout, to achieve seamless speaker-to-speaker blending effects in multi-channel systems. Gold-plated, professional-style 5-way binding posts offer the most secure connection options.