Infinity Qa

A 57-pound acoustic suspension loudspeaker that brought Infinity's state-of-the-art driver technology to a price the working audiophile could actually afford.

Overview

The Infinity Qa weighs 57 pounds and stands 22-1/2 inches tall. It is American loudspeaker engineering from the mid-1970s, when Infinity was making its name with exotic, expensive reference designs and trying to get that technology to listeners who couldn't stretch to four figures. The Qa was the answer, and it is one of the most interesting "affordable flagship" designs the company ever produced.

The Qa is a 4-way, 5-driver acoustic suspension design, per the original factory brochure. That sets it apart from the typical two-way bookshelf speakers that dominated the budget and mid-priced market at the time. Infinity packed two 12-inch woofers, a 4-1/2-inch midrange, a 2-inch Mylar dome tweeter, and a 1-inch Mylar dome super-tweeter into a cabinet measuring 22-1/2 inches high by 15 inches wide by 12 inches deep. That is a lot of driver surface area in a small enclosure, and it explains the weight.

Infinity's advertising compared the Qa directly to its $1,200 Quantum Line Source. It claimed the modestly priced newcomer delivered "accurate, transparent mid and high frequencies as high as your ear can follow - and beyond - to 32,000 Hz." That was a bold claim for a speaker that retailed at $145 east of the Mississippi.

Key Features

Dual 12-Inch Woofers in Acoustic Suspension

The foundation of the Qa is its pair of 12-inch woofers in a sealed, acoustic suspension cabinet. This is the classic American approach to bass. It requires amplifier power, and it rewards that power with a tight, controlled low end. The brochure specifies a frequency response of 38 Hz to 32 kHz, which was respectable for the era, though owners report the speaker is "a bit light on deep bass below about 50 Hz." That's the acoustic suspension trade-off: accuracy and control rather than room-shaking quantity.

Mylar Dome Tweeter and Super-Tweeter

At the top end, Infinity used its Mylar dome technology in both a 2-inch tweeter and a 1-inch super-tweeter. This is what gave the Qa its reputation for air and transparency. The crossover hands off between the two domes at 7,000 Hz, and the super-tweeter extends response out to 32 kHz. That is beyond the range of human hearing, but it still shapes cymbals, strings, and room ambience.

Complex 4-Way Crossover at 400, 4,000, and 7,000 Hz

The Qa's crossover is a study in 1970s engineering ambition. As Audio (November 1977, p.45) noted, the Qa was conceived with much of the technology of the company's flagship Quantum Line Source. Splitting the band at 400 Hz, 4,000 Hz, and 7,000 Hz across five drivers is a complex proposition, and it's the reason the Qa needs serious amplification. The audiokarma.org forum post that quotes the factory brochure puts it plainly: the Qa "really need a big amp" and are "power hungry." With a rated sensitivity of 88 dB SPL at 1 meter for 1 watt input and a power handling range of 10 watts minimum to 100 watts maximum, these speakers want current and headroom. They'll play with a modest receiver, but they come alive with real power behind them.

Collectibility & Value

The Qa has a devoted following among vintage Infinity collectors. The same forum source that warns about the power requirements also calls the Qa "a wonderful speaker - it does most everything well."

Current asking prices put the Qa among the respected but not hyped vintage designs. A Canuck Audio Mart listing from March 2023 asked $275 USD for a pair described as "well maintained and excellent sounding," with "beautiful walnut cabinets" and surrounds freshly replaced. The seller noted the pair was "one owner for 40+ years" and that they "sound great without being overly bright." A US Audio Mart listing asked $300 for a pair in "excellent condition" with "all original drivers," also from the first owner.

That sub-$300 price point makes the Qa an approachable entry into vintage Infinity ownership. You're not paying for a name or a collectible halo — you're paying for a genuine piece of 1970s engineering that still delivers a transparent, musical presentation. The cabinet construction is solid, and the acoustic suspension design means no port noise or tuning issues to worry about.

Driver configurations in online listings conflict. A Canuck Audio Mart listing describes the Qa as a 2-way with a single 12-inch woofer and a 1.25-inch dome tweeter crossing over at 1,900 Hz. That contradicts the factory brochure's 4-way, 5-driver specification entirely. The brochure is the authoritative source here, and the dealer listing appears to be simply wrong, possibly confusing the Qa with a different model. Check the driver complement against the brochure specs before buying.

As with any vintage speaker of this era, inspect carefully. The Mylar domes should be intact and free of dents, the woofer surrounds should be checked for deterioration (though many have been replaced by now), and the cabinets should be examined for water damage or delamination of the veneer. A pair with original drivers and fresh surrounds, like the ones that have been changing hands recently, is the best value.