Acoustic Research 312-HO (1996)
A 97 dB floorstander with a side-firing 12-inch woofer — the loudspeaker that finally put Acoustic Research on the efficiency bandwagon.
Overview
Acoustic Research built its reputation on acoustic-suspension speakers that traded efficiency for deep bass — the AR-1, the AR-3, the whole lineage that made the company's name. So when AR introduced its High Output series at the 1996 Winter Consumer Electronics Show, it was a deliberate about-face. The flagship of that line, the 312-HO, carried a rated sensitivity of 97 dB at 1 meter with 2.83 V rms applied, a figure that would have been unthinkable from the company a generation earlier. Audio (May 1996, p.14) flagged it as the head of a ten-model range that also included a center-channel speaker, an indoor/outdoor model, and three subwoofers.
The 312-HO was a three-way floorstander with a 12-inch woofer in a vented enclosure, two 5¼-inch cone midranges, and a 1-inch dome tweeter. The tweeter was molded from low-mass, closed-cell foam, and the midranges were arranged symmetrically above and below it in what AR called a "focused array configuration" — a D'Appolito-style layout. The nominal crossover between woofer and midranges was a low 180 Hz, with the midrange-to-tweeter transition at 2.5 kHz.
The most distinctive thing about the cabinet was its proportions. It was nearly twice as deep as it was wide, giving it a tall, narrow profile — the narrow baffle and rounded front edges were intended to minimize diffraction and reduce blurring of the aural image, as Audio (December 1996, p.62) noted in its equipment profile. The baffle itself was an unusual piece of engineering: made from reticulated foam of varying density and thickness, it was designed to absorb energy that would otherwise radiate off the cabinet surface. The cabinet was built from ¾-inch medium-density fiberboard, braced internally to control wall flexing. Heavy molded-plastic rails on each side of the bottom broadened the footprint for side-to-side stability on carpet; threaded nylon screws could be extended as leveling feet on hard floors and swapped for spikes (not supplied). At 70 pounds each, the speaker was heavy but manageable.
The side-firing woofer was a deliberate choice. Mounting the 12-inch driver on the side allowed a narrow front baffle, and AR positioned it to fire toward the wall for better coupling to the room. Audio measured the on-axis response in a large anechoic chamber and found that, with the grille removed, the 312-HO fit a tight 5.5-dB window between 130 Hz and 20 kHz. Above 200 Hz the response was flat and extended, with only slight roughness above 7 kHz. Below 130 Hz, output diminished — from about 100 Hz down to 50 Hz the average level sat roughly 5 dB below the region above 200 Hz, then rolled off. The reviewer suspected this was deliberate, compensating for the bass augmentation that a side-mounted woofer would get from wall proximity.
The rated frequency response was 30 Hz to 20 kHz, ±2 dB. Audio's measurements put the true woofer-to-midrange crossover at about 120 Hz rather than the claimed 180 Hz, based on a sharp 25-dB null at 120 Hz when the woofer polarity was reversed. Averaged from 250 Hz to 4 kHz, measured sensitivity came in at 93.7 dB — 3.3 dB below AR's rating, but still unusually high for a home speaker. The reviewer's take was blunt: using the ARs instead of less sensitive speakers was like getting a more powerful amp for free.
Impedance was rated 8-ohm compatible, though the measured curve was more complex than that suggests. It ranged from a high of 11.4 ohms at 16 Hz down to a low of 2.6 ohms at 158 Hz, with a maximum above 20 Hz of 9.6 ohms at 50 Hz. That 3.7-times variation, combined with phase swings from +33° inductive at 180 Hz to −56° capacitive at 59 Hz, made the 312-HO a moderately difficult load for receivers rated only for 8 ohms. Amps without that limitation, used with low-resistance cable, drove it well — and the high efficiency meant the amplifier's output capabilities were rarely taxed.
Bass output was a strong point. Audio found clean output from 30 Hz up, with the woofer handling very high levels — in excess of 20 volts rms (100 watts into 4 ohms) — even at 20 Hz, without undue strain. The woofer's excursion capability was ¾ inch peak to peak, and it overloaded gracefully. With room gain, maximum peak SPL started at 104 dB at 20 Hz, passed 110 dB at 30 Hz and 120 dB at 50 Hz, and reached a local maximum of 125 dB at 70 Hz — placing the 312-HO in the top 5% of all speakers and subwoofers the reviewer had tested. At 1 meter in free space with a 200-watt input, it generated 103 dB SPL at 41.2 Hz.
There were flaws. The fabric covering the port generated significant noise from vibration at high levels — a distorted sound the reviewer traced to the cloth flapping, which pressing the center of the fabric with a finger cleaned up. A cabinet wall resonance around 230 Hz showed up on the top sides next to the midranges. And above 2 kHz, peak input power dropped sharply to a low of 250 watts at 5 kHz; at higher levels approaching 120 dB SPL, the sound turned harsh and restricted. The reviewer suspected a saturating inductor core in the tweeter's crossover branch — bypassing the crossover and driving the tweeter directly improved the sound and raised its power capability to the 2,500-watt range. The grille also roughened response significantly above 2 kHz, with peak deviation in the 1-to-2 dB range.
Power handling was rated 25 to 250 watts. Dimensions were 43¾ inches high by 10½ inches wide by 19⅛ inches deep (111 cm x 26.8 cm x 48.6 cm). Price was $1,199 per pair, available in black ash, maple, or cherry vinyl. Audio (May 1996, p.14) listed it at $1,099 per pair in its new-products column; the December equipment profile gives $1,199, so the figure moved between announcement and review.
The 312-HO's close-up perspective — the way it rendered detail at near distances — was judged exactly right for home theater use. That, combined with the high efficiency and the magnetic shielding implied by its placement in a home-theater-oriented line, positioned it as a dual-purpose speaker for music and film. Production years beyond the 1996 introduction are not documented in available sources.
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