Acoustic Research AR-3a
Twenty-five inches of sealed walnut that made a generation of ported speakers sound like they were guessing.
Overview
There is no clean fact sheet behind this page. The research file came back empty, and the only hard documentation on hand is a set of period magazine pages and a Heathkit catalog listing that names the AR-3a by its drivers. So everything below is what the contemporary record says, not a full technical profile. The record is unusually consistent on one point: by the late 1960s the AR-3a was the speaker other speakers were measured against, and it stayed there for the better part of a decade.
The clearest description of the design comes from a Heathkit catalog. It sold a kit version (the AS-103A) built around three Acoustic Research AR-3A drivers in an oiled walnut veneer enclosure: a 12-inch acoustic suspension woofer, a hemispherical dome midrange, and a hemispherical dome tweeter. The listing also notes midrange and tweeter level controls, a rated response of 30-20,000 Hz, a 4-ohm impedance, and a minimum amplifier requirement of 25 watts RMS. The cabinet is given as 25 inches high, 14 inches wide, and 11¾ inches deep, with a shipping weight of 64 lbs. Those are Heathkit's figures for the kit, so treat them as approximate for the factory AR-3a. They do line up with the dimensions and price structure the audio press reported independently.
High Fidelity (January 1968, p.50) described the AR-3a as a full-range speaker system in an enclosure measuring 25 by 14 by 11⅝ inches. It was priced at $250 in walnut, oiled walnut, cherry, or oiled teak, $240 in mahogany or birch, and $225 in unfinished pine. The unfinished-pine version existed so a buyer could save money and finish the cabinet themselves. The same review credited the redesign with lowering the bass crossover point and keeping low frequencies out of the midrange driver. It also noted that the changes to the midrange and tweeter were made to improve dispersion. That is a period reviewer describing a deliberate engineering revision, not a cosmetic update.
The acoustic suspension principle is what sits underneath the AR-3a. Sealing the cabinet and using the trapped air as a spring let a 12-inch woofer produce deep bass from a box that would have been considered absurdly small for the job a decade earlier. The trade-off is that a sealed, low-sensitivity system is hungry. The 25-watt minimum in the Heathkit listing is a floor, not a recommendation, and the 4-ohm nominal impedance means an amplifier rated into 8 ohms will be asked for more current than its spec sheet implies.
The professional adoption is the best documented part of the story. High Fidelity (January 1970, p.11) ran a piece noting that AR-3a systems were working tools for composer and arranger Don Ellis. His studio rig paired a pair of them with an AR turntable, a Bogen-Lenco B62, an AR amplifier, a JBL 630 amplifier, a Koss Pro 600A headset, and Revox and Crown tape recorders. The same advertisement-style notice appeared in Audio (July 1969, p.5), DB Magazine (June 1969, p.43), and HiFI-Stereo (July 1969, p.106). That reads as a coordinated campaign, so take it as marketing rather than independent verdict.
None of this substitutes for a proper fact sheet. Driver part numbers, crossover topology, sensitivity figures, and production end dates are not documented in the sources available here, and this page does not guess at them. What can be said is narrower: the AR-3a was a sealed three-way with a 12-inch woofer, built in a 25-inch cabinet, sold between roughly $225 and $250 depending on finish, and used in at least one documented professional studio alongside an AR turntable and AR amplification.
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