The VR-M60 is a full-range two-way system utilizing Boston's most advanced technology. Inside is a 1-inch aluminum tweeter with AMD. AMD stands for Amplitude Modification Device--an ingenious method of producing lifelike, smooth high frequencies without resorting to signal-degrading electronic circuitry. The VR-M tweeter is joined-literally-by a Boston computer optimized 6-1/2-inch bass unit. Their closeness creates a "point source" image, which means your ear cannot discern where highs end and lows begin, for sound that's seamless and natural. The VR-M DCD Bass unit features a rigid die-cast aluminum basket that keeps the driver's moving parts in precise alignment for the cleanest, smoothest response.