Sony apm-77 (1981-1985)
A high-end 3-way bookshelf speaker using planar drivers and Sony's APM technology, produced from 1981 to 1985.
Overview
The Sony APM-77 and its walnut-finish sibling, the APM-77W, are 3-way bass-reflex bookshelf loudspeakers developed by Sony as part of their Acoustic Pistonic Motion (APM) series. Produced from April 1981 to 1985, these speakers were positioned as an "affordable" option within the APM lineup, launched after the APM-8 but before the APM-6 and APM-4. The APM-77 features a unique planar driver array with advanced materials and construction techniques, delivering a balanced, precise sound with excellent dispersion. It was designed to be placed close to a wall, requiring only a 3–5 cm gap for optimal performance.
Specifications
| Product type | 3-way bass-reflex loudspeaker system, bookshelf type |
| Production years | April 1981 to 1985 |
| Original price | APM-77: ¥150,000; APM-77W: ¥160,000 |
| Frequency response | 28 Hz to 30 kHz (+4 / -8 dB ; DIN) |
| Sensitivity (SPL) | 90 dB /1W /1m |
| Impedance | 6 Ω |
| Peak power handling | 200W (DIN 45500) |
| Rated power handling | 100W (DIN 45500) |
| Crossover frequencies | 700 Hz, 4.5 kHz |
| Drivers | 1x 530 cm² planar bass (≈30 cm), 1x 27 cm² planar midrange (≈6 cm), 1x 7 cm² planar tweeter (≈3 cm dome) |
| Dimensions | 405 x 745 x 325 mm (W x H x D) |
| Weight | 32.0 kg |
| Internal volume | 66L |
| Finish options | APM-77: dark metallic/grey; APM-77W: walnut veneer with plywood grille frames |
| Features | Adjustable highs (0...-50 dB), adjustable mids (0...-50 dB), OFC wiring, separate crossover networks, bass-reflex port tuned below 25 Hz, glass wool + polymer fiber damping |
| Accessories | 3m speaker cord included; optional WS-500 stands (¥8500/pair), RK-10S cables (¥12,000) |
Design
The APM-77 uses Sony's proprietary APM (Acoustic Pistonic Motion) drivers with planar diaphragms. The woofer features a honeycomb sandwich structure (aluminum core and skins) driven at four points by four voice coils and magnetic circuits, with a center suspension to prevent rolling. The midrange and tweeter use aluminum honeycomb cores with carbon fiber skins, each driven by a single voice coil—optimized for low distortion and node-driven vibration control. Drivers are mounted in diecast aluminum chassis with aluminum honeycomb frames and damping sheets. The crossover networks are physically separated to reduce interference, and the enclosure uses high-density particle board with thin internal grooves to control vibration. The bass-reflex port is tuned below 25 Hz, and the design includes OFC wiring throughout, with 400µm OFC boards used in the tweeter and midrange filters.
Context
The APM-77 was introduced as a more accessible model in Sony's high-end APM speaker line, bridging the gap between the flagship APM-8 and later models like the APM-6 and APM-4. The APM-77W variant sold approximately 4,000 pairs. The APM drivers from this model were later reused in the ESPRIT APM-4, indicating shared engineering across product generations.
Market
A known issue with the APM-77 is degradation of the bass driver's foam surrounds, which Sony did not maintain as spare parts. Despite this, the speaker can continue functioning due to the four-piston drive and center suspension, though acoustic sealing is compromised when surrounds fail.
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