Denon SC-907 (circa 1985)
The Denon SC-907 is a 3-way, 3-speaker bass-reflex bookshelf speaker that appears to date from around 1985, when it was priced at ¥65,000 per unit. Documentation is thin. Most of what survives comes from a single Japanese audio database entry. The engineering details that are recorded show Denon pushing its diaphragm materials hard in this period.
The woofer is a 32 cm cone using what Denon called a "PCM diaphragm" - a polypropylene base mixed with carbon graphite and mica. It was claimed to be roughly 2.5 times more rigid than a conventional woofer diaphragm and about 9 times more rigid than paper. The midrange is a 6 cm hard dome, and the tweeter is a 2.5 cm hard dome. Both use Denon's α-boron diaphragm, where boron compound and alumina particles are fused onto an aluminum base via plasma jet. Denon claimed this construction gave about 10 times the internal loss of conventional metal diaphragms. Both drivers were designed to radiate directly without a front diffuser, which the company said eliminated coloring up to the 50 kHz ceiling. The midrange also used a push-pull double suspension for improved linearity.
The crossover points are set at 800 Hz and 5 kHz, with continuously variable level controls for the mid and high ranges. The enclosure is built from rigid softwood particle board with a vibration-damping structure, and the network uses a large audio-grade electrolytic capacitor. Rated impedance is 6 Ω, maximum input is 150W (program source), and sensitivity is 92 dB/W/m. Frequency response is specified from 30 Hz to 50 kHz. The cabinet measures 370 × 680 × 327 mm (W×H×D) and weighs 23 kg.
A related variant, the SC-907V, appears in some listings with slightly different specifications. Treat it as a separate model. What little owner commentary exists comes mostly from Russian resale listings. It describes the sound as excellent and notes that the foam surrounds are prone to deterioration, a common issue for speakers of this era.
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