Denon S-170mkII (c. 1975)
The Denon S-170mkII is a 2-way, 2-speaker, airtight (sealed) bookshelf speaker system from around 1975, originally priced at ¥39,500 per unit. Documentation on this model is thin. The most complete record comes from the Japanese Audio Database. What's recorded shows a carefully engineered speaker with some unusual material choices.
The woofer is the odd part. The 25 cm cone unit (model 25RW15) uses a "collagen cone" diaphragm - collagen fiber extracted from animal skin, chemically treated and fused with corn paper pulp. The intent was to keep the cone rigid while controlling internal loss, which suppresses the split-resonance region and high-frequency resonance. The surround is collagen fiber too. Denon claimed it minimized disturbance from inverse vibration between cone and edge, and lowered the lowest resonance frequency. The tweeter is a 4 cm dome type (40DT-01) with a flexible natural-fiber diaphragm, hand-coated several times, with glass-fiber sound absorption inside the dome.
The magnetic circuit uses a 120φ × 60φ × 17 barium ferrite magnet. The voice coil is steel-clad aluminum, for extended input tolerance and high-frequency behavior. The crossover is a 6 dB/octave network with an air-core coil and MF-type capacitor, chosen for low distortion at high input. The enclosure is a symmetrical design in 20 mm hard particle board with a full real-wood finish. Inside, three different densities of sound-absorbing material deal with standing waves.
Known specifications:
- Frequency response: 40 Hz – 20 kHz ± 5 dB
- Directional response: 45 Hz – 13 kHz ± 4 dB (at 30°)
- Maximum input: 60W (program source)
- Impedance: 8 Ω
- Sensitivity: 89 dB/W/m
- Crossover: 1.5 kHz
- Distortion: 1.5% or less (5W, 70 Hz or above)
- Dimensions: 320 × 597 × 291 mm (W×H×D)
- Weight: 16.5 kg
Used-market listings show pairs occasionally surfacing on Yahoo Auctions. One matched-serial pair bid at ¥3,000, another at ¥4,000, which suggests they're collectible but not expensive. No period reviews, production totals, or common failure information have surfaced in the research.
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