Sony APM-6 (1981–1986)
A high-end bookshelf monitor speaker from Sony’s Esprit line, engineered for precision audio reproduction with advanced APM driver technology.
Overview
The Sony APM-6, also known as the Sony Esprit APM-6 Monitor, is a bookshelf-type speaker system developed in the early 1980s. Built with advanced materials and proprietary driver designs, it was designed for accurate sound reproduction and was used in professional studio environments and high-end audio demonstrations. The system features a unique APM (Accurate Pistonic Motion) design in both woofer and tweeter, housed in a super-oval enclosure to minimize diffraction. It was launched two years after the APM-8 and earned recognition with 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, underscoring its significance within the company.
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 with a super-oval enclosure made of alternating layers of natural wood and particle board, designed to diffuse internal reflections and reduce diffraction. The woofer features a honeycomb-core aluminum-skin diaphragm driven at four points by four magnetic circuits and a voice coil, with a top pole to stabilize inductance and slits to suppress eddy currents. The tweeter uses a carbon fiber-skinned honeycomb-core diaphragm with four-point drive and a damper integrated into the magnetic circuit. The crossover network uses SBMC-encapsulated components with 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, marketed in Japan as a monitor speaker for its superior phase coherence and dispersion. It was used in Sony/Columbia studios and frequently demonstrated at audio shows. Despite a production run estimated at 500 pairs, very few remain today, making it rarer than the APM-8. It is considered by some to be the best-sounding model among the APM-8, APM-6, and APM-4/77, and is highly sought after by collectors.
Market
The APM-6 is extremely rare today, with few surviving units due to destructive restoration attempts. The fragile honeycomb woofer structure and carbon-fiber damping layers have been damaged by improper surround replacements using car rubber or ill-fitting materials. Original woofers are difficult 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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