Sony APM-33W (1982/1984)
A bookshelf speaker system from Sony using flat diaphragm drivers in a bass reflex enclosure.
Overview
The Sony APM-33W is a bookshelf type speaker system released in 1982/1984. It features a 2-way, 2-speaker configuration with a bass reflex design. The system uses Sony's original APM unit technology, incorporating flat diaphragms with a honeycomb sandwich structure for both the woofer and tweeter. This design aims to reduce resonance and deformation through high bending rigidity and simplified vibration patterns. The enclosure uses three types of sound-absorbing materials and vibration-damping grooves to improve acoustic performance.
Specifications
| Model Rating Method | 2-Way, 2-Speaker, Bass Reflex System, Bookshelf Type |
| Unit For low band | 324 cm^2 Plane type |
| Unit For high band | 16 cm^2 Plane type |
| Playback frequency band | 39 Hz to 20000 Hz |
| Output sound pressure level | 91dB/W/m |
| Impedance | 6 Ω |
| Instantaneous maximum input | 160W |
| Rated maximum input | 80W |
| Crossover frequency | 2.2kHz |
| Level control | + 0 to -50dB continuously variable |
| External dimensions | Width 315x Height 540x Depth 320 mm |
| Weight | 14.4kg |
Design
The APM-33W uses flat diaphragms with a honeycomb sandwich structure made of aluminum foil skins and a honeycomb core, achieving 500 to 1000 times the bending rigidity of conventional cones. The square-shaped diaphragms simplify vibration patterns, and specific driving points are selected at milestones of divided vibration modes to reduce distortion. The woofer uses four armatures connected directly to the voice coil at concentrated milestone points, while the tweeter shares the same diaphragm construction. The crossover uses oxygen-free copper wiring, parallel high-quality capacitors, and air-core coils to minimize loss. The enclosure's back plate is grooved to control vibrations, and three types of sound-absorbing materials are used inside.
Product Family
The APM-33W utilizes know-how accumulated through the development of the APM-6Monitor.
Market
A special stand, the WS-300, was sold separately for ¥6,000 per set of two, with dimensions of 295x140x290 mm and a weight of approximately 3.0 kg. One listing notes the speaker is offered "Untested / As Is," and another references "Sony APM-33W Speaker Service," suggesting service parts or documentation may be available.
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