Acoustic Research LST-2

Sixty pounds of acoustic suspension, nine drivers stacked in a vertical line, and a rear-panel switch that changes the balance of the room. The LST-2 is the more attainable sibling of the Laboratory Standard Transducer.

Overview

The LST-2 arrived in 1972 as Acoustic Research's cheaper alternative to the flagship LST. The driver complement shows the family resemblance right away. As DB-Magazine (December 1973, p.27) noted, AR showed their LST monitoring speaker now also available in a smaller model known as the LST-2. The LST used the full AR-3a driver suite - a 12-inch woofer, four midranges, four tweeters. The LST-2 uses a 12-inch woofer, four 1.5-inch midranges, and four 0.75-inch tweeters. That's still a three-way, nine-driver design, still acoustic suspension, still the same philosophy. It cost $450 instead of the LST's $600, which was a staggering sum at the time.

The money bought a floor-standing speaker with a trapezoidal cabinet and angled baffles. It was finished in walnut veneer or, optionally, black vinyl, with a fabric-covered grille that lifts off. Each cabinet measures 689 by 508 by 248 mm and weighs 90 pounds. That's heavy for its footprint, and there are no ports and no passive radiators here. The 12-inch woofer is a long-throw, low-tuned driver in a sealed box, using trapped air as its spring. Low-frequency extension runs down to around 45Hz, which is deep for a ten, and the bass is tight rather than fat. It isn't the loudest bass of its era, but it's among the most articulate.

The sound is open, airy, and very neutral. No peaky presence, no bloated bottom. The restraint is deliberate. This speaker descends from AR's laboratory lineage.

Key Features

Vertical Array of Hemispherical Domes

Four 1.5-inch hemispherical dome midranges and four 0.75-inch hemispherical dome tweeters sit stacked in a vertical line above the woofer. The domes are low-mass and widely dispersive by design. The vertical stacking gives a line-source-like behavior that spreads sound evenly across a wide horizontal arc. In practice the tonal balance stays consistent as you move around the room, so there's no single sweet spot to sit in.

Transformer-Coupled Crossover with Spectral Energy Control

The crossover is passive but transformer-coupled, and it's adjustable. A small switch on the rear panel offers three spectral energy positions: flat, + bass, and + mid/treble. It isn't a tone control in the cheap sense. It's a room-compensation tool, and it uses autotransformer taps so the impedance stays relatively stable across settings rather than swinging wildly and upsetting the amplifier. Owners report that cycling through all three positions should produce an audible and smooth tonal shift. If the change is subtle or gritty, something in the network needs attention.

Ten-Inch Acoustic Suspension Woofer

The woofer is a 12-inch acoustic suspension unit, sealed in the cabinet with no port to tune and no passive radiator to leak. The bass rolls off gradually and transients stay clean, so kick drums pop rather than blur. It also means the speaker needs real amplifier current. Sensitivity is only 89.5dB, and AR's own guidance calls for 60-100 watts from a clean, current-capable amp that's happy into a 4-ohm-stable load. Pair it with something anemic and the LST-2 will just sit there, polite and unimpressed.

Historical Context

AR had built its reputation on the AR-3, and the LST-2 was a culmination of that lineage, a domestic-adjacent version of a professional tool. The Laboratory Standard Transducer concept was aimed at laboratory and commercial applications that required conveniently repeatable, accurately known spectral energy profiles. The LST-2 carried that intent into a $450 package. It found homes in radio stations, recording studios, and the living rooms of audiophiles who valued transparency over theatrics.

Roy Allison, the engineer behind the AR-3a and the LST, had just left AR to found his own company when the LST-2 launched. Some speculate he wasn't fully behind the cost-reduced version, preferring the full LST's six-position control and 12-inch bass extension. Whatever the internal politics, the LST-2 didn't replace the LST. It paved the way for the AR-9, AR's next flagship, which took the LST idea further with dual woofers and a radical new cabinet design.

Collectibility & Value

The LST-2 is a sleeper among vintage AR collectors. It's less flashy and less rare than the LST, but more attainable and more likely to actually get used. A clean, fully functional pair in good cosmetic condition typically sells for $500 - $1,000. Fully recapped, refoamed, and tested pairs can fetch $1,200 or more, especially with original grilles and documentation. Parts support exists: recap kits for the crossovers using MPT film capacitors, replacement woofers, and speaker grilles all turn up for sale, and vintage speaker specialists keep NOS drivers and crossover components in stock.

The maintenance picture is predictable for a speaker this age. The foam surrounds on the 12-inch woofers dry out and crumble - not if but when - and refoaming runs roughly $150 - $250 per speaker depending on labor rates. The original crossover capacitors also degrade, leading to dull highs or uneven response, and a full recap runs $200 - $300. The hemispherical domes are more durable than typical cone midranges, but tears in the dome or voice coil misalignment can kill a driver's clarity. The walnut veneer is prone to edge chipping, and water stains or cigarette burns under the grilles aren't uncommon. One owner on the classic speaker forums reported the red and black speaker terminals on the back of one cabinet had come out, with the other loose. Check before you buy.

Inspection advice: confirm all nine drivers are present and intact, listen for buzzing or rattling at low volume, and if the bass is flabby or one channel sounds weak, assume the woofers need refoaming. Cycle the spectral energy switch through all three positions and make sure the tonal shift is audible and smooth.