Sony APM-6 (1981–1986)
A high-end bookshelf monitor speaker from Sony's Esprit line, built for accurate sound reproduction with APM driver technology.
Overview
The Sony APM-6, also known as the Sony Esprit APM-6 Monitor, is a bookshelf speaker system developed in the early 1980s. It uses advanced materials and proprietary driver designs. It was built for accurate sound reproduction and used in professional studios and high-end audio demonstrations. Both the woofer and the tweeter use the APM (Accurate Pistonic Motion) design, and the enclosure is a super-oval shape meant to minimize diffraction. It was launched two years after the APM-8. It won a Stereo Sound Best Product award and a Grand Prix from Japanese audio critics. Akio Morita was photographed with the APM-6 in Sony's anechoic chamber in 1982.
Specifications
| Rating Method | 2-Way, 2-Speaker, Bass Reflex System, Bookshelf Type |
| Unit For low band | 502 cm² Plane type |
| Unit For high band | 16 cm² Plane type |
| Playback frequency band | 20 Hz to 20000 Hz |
| Output sound pressure level | 88dB/W/m |
| Impedance | 8 Ω |
| Maximum instantaneous input level | 300W |
| Rated input level | 100W |
| Crossover frequency | 1200Hz |
| External dimensions | Width 545 x Height 820 x Depth 375 mm |
| Weight | 48kg |
Design
The APM-6 uses the APM (Accurate Pistonic Motion) system. The super-oval enclosure is made of alternating layers of natural wood and particle board, which diffuse internal reflections and reduce diffraction. The woofer has a honeycomb-core aluminum-skin diaphragm. Four magnetic circuits and a voice coil drive it at four points. A top pole stabilizes inductance, and slits suppress eddy currents. The tweeter has a carbon fiber-skinned honeycomb-core diaphragm with four-point drive and a damper built into the magnetic circuit. The crossover network uses SBMC-encapsulated components, oxygen-free copper wiring, air-core coils and isolated mounting to minimize interference. The two bass-reflex ports form an internal L-shaped labyrinth.
Context
The APM-6 was positioned as a more refined, two-way alternative to the larger APM-8. In Japan it was marketed as a monitor speaker for its superior phase coherence and dispersion. It was used in Sony/Columbia studios and often demonstrated at audio shows. Production is estimated at 500 pairs, and very few remain, which makes it rarer than the APM-8. Some consider it the best-sounding model among the APM-8, APM-6, and APM-4/77. Collectors seek it out.
Market
Few APM-6 units survive, mostly because of destructive restoration attempts. The honeycomb woofer structure is fragile, and so are the carbon-fiber damping layers. Both have been damaged by improper surround replacements made with car rubber or ill-fitting materials. Original woofers are hard to replace, and intact pairs are highly prized. The original price was ¥500,000 per unit, as recorded in a June 1981 sale.
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