Acoustic Research · Bookshelf · c.1975–1979 (Mk I and Mk II)
When AR retired the AR-3a in 1977, the AR-11 and AR-10π took its place. The AR-11 keeps the same recipe of a 12-inch acoustic suspension woofer, a 1.5-inch dome midrange and a 3/4-inch dome tweeter in a similar-sized box, with new drivers and a new crossover. Instead of the 3a's knobs it has two three-position switches on the back, at 0, minus 3 and minus 6 dB, for the midrange and the treble. The AR logo badge pivots so it reads the right way up whether the speaker stands upright or lies on its side. There are two versions. The Mk I from about 1975 used a yellow-orange cloth tweeter dome, and the Mk II of 1978 and 1979 used a black ferrofluid-cooled one with a revised woofer. It's rated at 4 ohms, and AR said 25 watts into one speaker would reach 100 dB in a large room.
With the grille off
Ask for a photo of every driver with the grilles off, on both speakers. They should match each other and this list.
The foam woofer surrounds will have aged on an unrestored pair, so look for a refoam. The tweeters differ between the Mk I and Mk II and don't swap with AR-3a tweeters without crossover changes.
New to old speakers? How to check a used pair walks through every driver, the crossover and the cabinet.
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