After this experience, Amar came to the conclusion that the audio system measurement techniques of the time (such as measuring distortion and frequency response) were not effective ways to evaluate the goal of natural sound reproduction. Amar argued that the best measure of audio quality is the listener's perception. Also in 1968, the company introduced the Bose 901 stereo speaker system, which used eight mid-range drivers pointing towards the wall behind the speaker, and a ninth driver towards the listener. The purpose of this design was to achieve a dominance of reflected over direct sound in home listening spaces. The design used in the 901 is unconventional compared with most systems, where mid-range and high-frequency speakers directly face the listener. The 901 was an immediate commercial success, and Bose Corporation grew rapidly during the 1970s. The Bose 901 model name was a mainstay of the Bose line-up for many years, being produced from 1968 until 2016.