Denon SC-A7 (circa 1982)
The Denon SC-A7 is a big 3-way, 3-speaker bookshelf-type system from the early 1980s. It originally sold for ¥65,000 per unit. It was an early Denon design aimed at digital sources, and each cabinet is roughly 70 cm tall and weighs 23 kg. The woofer is 32 cm.
The drivers are the interesting part. The 32 cm woofer has a polypropylene polymer diaphragm, which Denon claimed transmitted sound about 2.5 times faster than paper. It also has concentric corrugation ribs for rigidity, large flat dampers, and aluminum die-cast frames. The 6 cm midrange and 2.5 cm tweeter both use Denon's "α-Boron" hard dome diaphragm. It is made by fusing boron compound and alumina particles onto aluminum alloy foil with plasma jet welding at over 10,000°C. Denon claimed it was roughly three times as rigid as titanium and had about ten times the internal loss of conventional metal diaphragms. The mid and high drivers use strontium ferrite magnets. The midrange also has a double suspension to prevent voice coil rolling.
The enclosure is bass-reflex with a 71L internal volume, built from rigid particle board. The phase inverter port is on the front. The mid and high ranges each have a continuously variable level control. Rated frequency response is 30 Hz to 50 kHz. Maximum allowable input is 140W (program source), impedance is 6 Ω, and average output sound pressure level is 92 dB/W/m. Crossover points are 800 Hz and 5 kHz.
Little is documented about the SC-A7's market history or reception. A Russian seller listing described the pair as sounding and looking excellent, and said the low-frequency drivers had new suspensions fitted, a common repair for speakers this age. The same listing called the Denon SC-903 a "younger model" relative to the SC-A5/A7 group. A current Moscow listing asks 140,000 ₽, and no production years have been confirmed. A related variant, the SC-A7L2, appears in Japanese listings, but how it relates to the SC-A7 is not documented.
Known specifications
- Type: 3-way, 3-speaker, bass-reflex, bookshelf
- Woofer: 32 cm cone, polypropylene polymer diaphragm
- Midrange: 6 cm hard dome, α-Boron diaphragm
- Tweeter: 2.5 cm hard dome, α-Boron diaphragm
- Frequency response: 30 Hz – 50 kHz
- Maximum input: 140W (program source)
- Impedance: 6 Ω
- Sensitivity: 92 dB/W/m
- Crossover frequencies: 800 Hz, 5 kHz
- Dimensions: 390 × 700 × 385 mm (W×H×D)
- Weight: approx. 23 kg
- Original price: ¥65,000 per unit (circa 1982)
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