Polk Audio SDA-1 Speakers

Description

The Polk Audio SDA-1 is one of the most historically significant loudspeakers produced by Polk Audio. Introduced in the early 1980s, it was among the first commercial implementations of Polk’s revolutionary Stereo Dimensional Array (SDA) technology, a system designed to overcome the acoustic limitations of conventional stereo by reducing interaural crosstalk and creating a soundstage that extends well beyond the physical locations of the speakers. The result, when properly set up, can be an exceptionally wide and immersive presentation that remains one of the most distinctive characteristics of vintage Polk SDA speakers.

The original SDA-1 was a large four-way floorstanding design measuring approximately 43½ inches high, 16 inches wide and 12 inches deep. Each cabinet used multiple mid/low-frequency drivers, two SL1000 high-frequency drivers, and a 12-inch passive radiator. The original manual specifies four mid/low-frequency drivers, although surviving examples can differ somewhat because Polk made revisions during the SDA-1’s production. The speaker’s nominal DC resistance was approximately 5 ohms.

The heart of the SDA concept is the interconnect cable joining the two speakers. The dimensional drivers reproduce specially derived out-of-phase information that reduces the amount of left-channel information reaching the listener’s right ear, and vice versa. This allows the brain to perceive a much wider stereo image. Unlike a conventional speaker that generally confines the soundstage between the cabinets, the SDA-1 can produce images that seem to originate considerably outside the speakers.

Contemporary reviews were enthusiastic about the technology. Stereo Review reported that SDA produced “a new dimension in stereo sound”, while another published assessment concluded that the result was better than conventional speakers and described the effect as “spectacular.” The same evaluation praised the SDA-1’s broad, precisely defined soundstage and exceptionally strong bass.

The SDA-1’s bass performance was another strong point. Contemporary measurements described the low-frequency output as exceptionally strong, extending roughly an octave deeper than many similarly sized speakers. The speaker was also unusually efficient, with a published sensitivity of approximately 95dB at one meter, although its electrical load and SDA circuitry mean that amplifier compatibility remains important.

Owner experiences reinforce the speaker’s ability to create a huge soundstage. One long-time SDA-1A owner described the presentation as a “wall of sound extending beyond the speakers on either side.” Another owner praised the speakers for their “very coherent detailed sound”, tight bass and excellent overall balance.

The SDA-1 does have some important caveats for today’s vintage buyer. Placement is critical: the speakers generally need substantial space from the side walls and between the cabinets to allow the dimensional effect to develop properly. The interconnect cable is also essential. Furthermore, original SL1000 tweeters and decades-old crossover components can require attention. Later SDA-1A, 1B and 1C versions incorporated various driver, tweeter and crossover changes, so it is important to identify the exact version before purchasing replacement parts.

For vintage-audio enthusiasts, however, a properly functioning and correctly positioned SDA-1 remains a fascinating loudspeaker. Its combination of deep bass, high efficiency, unusual imaging and innovative acoustic engineering makes it much more than simply another large speaker from the early 1980s. The SDA-1 is an important piece of Polk Audio history and one of the more adventurous loudspeaker designs of its era.

Product Specifications

• Type: 4-way Stereo Dimensional Array floorstanding loudspeaker
• Introduction: Early 1980s
• Enclosure: Passive-radiator design with separate vented mid/low-frequency sections
• Drivers: Multiple MW-series mid/low-frequency drivers
• Tweeters: 2 × SL1000 high-frequency drivers in the original SDA-1
• Passive radiator: 1 × D-1200-A, approximately 12 inches
• Frequency response: Approximately 20Hz–20kHz, depending on measurement
• Sensitivity: Approximately 95dB at 1 meter
• DC resistance: Approximately 5 ohms
• Crossover frequencies: Approximately 125Hz and 2.5kHz
• Crossover: Separate stereo and dimensional signal paths
• SDA connection: Dedicated inter-speaker SDA interconnect cable
• Cabinet dimensions: 43½” H × 16″ W × 12″ D
• Shipping weight: Approximately 85 lbs. per cabinet
• Cabinet orientation: Left/right mirror-imaged pair
• Special feature: Stereo Dimensional Array spatial-imaging system
• Original tweeter: SL1000 with Litz-wire voice coil