You’re looking at a rare beautiful set of speakers. They function perfectly and sound great!The NS18 was produced between 1969-1976 - given its rarity on the second hand market, apparently only a very small series. NS18 is a dipole speaker with an asymmetrical 18 x 23 inch woofer/midrange driver with some very special cone material and ALNICO magnet system. Frequencies from 5 kHz up are handled by a bullet-type horn tweeter JA-05036B, the level of which can be adjusted with a three-step attenuater. The cross-over is of a second order, and some EQ is applied to 1-5 kHz. NS18s claimed frequency response is 35-20000 Hz, and the sensitivity 100 dB.Own a set of the famous Natural Sound NS-18 speakers. They are complete, in very good condition, and all drivers function properly. They are a very nice example of a very rare speaker.Yamahas NS-18 speakers are a piece of Hi-Fi history. Introduced in 1967, they were the first of the Natural Sound series of HiFi speakers for the home; and represent Yamahas official entry into the US home audio market. These unique speakers utilize a large enclosure with a fairly shallow depth; housing a large styrofoam diaphragm that was designed to mimic the shape & characteristics of the human ear.