These are the authentic Acoustic Research LST speaker system and NOT the smaller version LST-2 speakers. These were the company’s most advanced speaker system, designed for professional uses. That require repeatable, accurately known spectral energy profiles, including. Most striking are the LST’s angled sides, differentiating this pair from other AR speakers. Each speaker is equipped with a. 12-inch acoustic suspension woofer, four 1 1/2-inch mid-range hemispherical radiators and four 3/4-inch hemispherical tweeters. I’ve owned these speakers for 25 years and just had several tweeters professionally replaced. Type: 3-way, 9 driver loudspeaker system. Crossover Frequency: 575, 5000Hz. Bass: 1 x 12. Midrange: 4 x 1.5 hemispherical. Tweeter: 4 x 0.75 hemispherical. 27 x 20 x 9 ¾ inches.