Denon SC-905 (circa 1985)
The Denon SC-905 is a three-way, three-speaker bass-reflex bookshelf system from the mid-1980s, introduced around 1985 at ¥49,800 per unit. It shows Denon experimenting with some interesting diaphragm materials.
The woofer is a 26 cm cone using what Denon called a "PCM diaphragm" - a polypropylene base mixed with carbon graphite and mica. Denon claimed it was roughly 2.5 times more rigid than a conventional woofer diaphragm and about 9 times stiffer than paper. The midrange is a 6 cm hard dome, and the tweeter is a 2.5 cm hard dome. Both use an α-boron diaphragm: a plasma-jet-fused boron compound and alumina layer on an aluminum base. Denon said it achieved about ten times the internal loss of a conventional metal diaphragm. The mid and tweeter were designed to radiate directly, with no diffuser in front of the diaphragm. The midrange also used a push-pull double suspension for improved linearity.
On paper, the SC-905 is rated at 6 Ω, with a frequency response of 35 Hz to 50 kHz, a maximum allowable input of 140W (program source), and a mean output sound pressure of 92 dB/W/m. Crossovers are at 800 Hz and 5 kHz, with continuously variable level controls for mid and high. The enclosure is rigid softwood particle board with a damping structure based on vibration analysis. The network uses a large audio-grade electrolytic capacitor. Each speaker measures 324 × 589 × 327 mm and weighs 17 kg.
The record on this model is thin beyond the specs. The detailed technical information comes from a single curated database entry, and no period reviews, owner commentary, or production end date have surfaced. What’s clear is that the SC-905 was a serious, material-obsessed design — the sort of speaker Denon was proud of in the mid-’80s, even if it hasn’t left much of a paper trail since. Occasional Yahoo Auctions listings in Japan have seen pairs sell for modest sums (a few thousand yen), suggesting they’re not particularly sought-after today, but they do turn up.
- Type: 3-way, 3-speaker, bass-reflex, bookshelf
- Drivers: 26 cm cone woofer, 6 cm α-boron dome mid, 2.5 cm α-boron dome tweeter
- Frequency response: 35 Hz – 50 kHz
- Impedance: 6 Ω
- Max input: 140W (program source)
- Sensitivity: 92 dB/W/m
- Crossovers: 800 Hz, 5 kHz
- Dimensions: 324 × 589 × 327 mm; 17 kg
- Price (1985, Japan): ¥49,800 each
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