Used one summer, excellent condition Harman's patented (US patent #7,548,631) Plus One™ polypropylene cones provide more overall speaker-cone area than other cones in its class — the result is higher sensitivity, increased low-frequency output and greater musical character.The GT7 component systems feature external crossover housings, which provide extra space for true high pass and low pass sections - a step up from the coaxial models -smoothing out the critical midband response where most of the music occurs. There's also a tweeter level control, which allows fine adjustment to suit varying listening tastes and to accommodate different placement.