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 speaker released in 1982/1984. It's a 2-way, 2-speaker bass reflex design. Both the woofer and tweeter use Sony's original APM unit technology: a flat diaphragm with a honeycomb sandwich structure. The idea is to cut resonance and deformation with high bending rigidity and simpler vibration patterns. The enclosure uses three types of sound-absorbing materials and vibration-damping grooves.
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 diaphragms are flat, with aluminum foil skins over a honeycomb core. That gives 500 to 1000 times the bending rigidity of conventional cones. The diaphragms are square, which simplifies the vibration patterns, and the driving points are picked at milestones of the divided vibration modes to reduce distortion. The woofer has four armatures connected directly to the voice coil at those concentrated milestone points. 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 back plate of the enclosure is grooved to control vibrations, and three types of sound-absorbing materials go inside.
Product Family
The APM-33W uses know-how built up during development of the APM-6Monitor.
Market
A special stand, the WS-300, was sold separately for ¥6,000 per set of two. It measures 295x140x290 mm and weighs approximately 3.0 kg. One listing offers the speaker "Untested / As Is," and another references "Sony APM-33W Speaker Service," which suggests service parts or documentation may be available.
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