Matthew Polk designed the Monitor 10 in 1977. They are very efficient and sound excellent, even on mediocre electronics. The polypropylene woofer uses "Bass Radiator Technology," (passive radiator) tuned to produce deep, musical bass. The tweeter was the then-popular Peerless K010DT soft dome tweeter, also found in many other excellent speakers & studio monitors of the era. Two polypropylene midwoofers completed the design. They have a believably realistic soundstage. A true classic.