Yamaha NS-630 (1973)
The Yamaha NS-630 is a 3-way, 3-speaker sealed (airtight) bookshelf system from 1973, sold at ¥27,000 per unit. It was the junior model in the NS-650 line. The two speakers differ only in the woofer, and the NS-630 uses a 20 cm cone unit (JA-2055) instead of the larger driver in its sibling. The NS-600 series was Yamaha's effort to return to the bookshelf type and deliver performance "not inferior to large systems" despite the compact cabinet.
The engineering is thorough for a small speaker. The JA-2055 woofer keeps its free-air resonance low (fo = 30 Hz, Qo = 0.30), so mounting it in the small sealed enclosure still gives an in-cabinet fo of 45 Hz. It has a large 52 mm voice coil with a 20 mm winding width for linear excursion, a 120 mm ferrite magnet, and a felt center cap that vents the gap to improve low-frequency response. The 12 cm cone midrange (JA-1201) has a free edge and an fo of 85 Hz, well below the 600 Hz crossover. The dome tweeter (JA-0508) uses a 30-micron duralumin diaphragm with edgewound aluminum ribbon wire connected directly, which eliminates the bobbin. The crossover network uses ferrite-core coils with resistance kept to 0.34 Ω (under 1/20 of the 8 Ω impedance), mounted at right angles to avoid mutual inductance. Continuously variable level controls for mid and high frequencies sit on the front baffle, which positions the mid and tweeter symmetrically to minimize diffraction effects. The enclosure is 18 mm plywood, fully sealed, with a removable back wall.
Specifications: 45 Hz–20 kHz playback, crossover at 600 Hz and 5 kHz (12 dB/oct.), 86 dB/W/m sensitivity (new JIS), 40 W maximum input, 8 Ω impedance, 280 × 500 × 256.5 mm (W×H×D), 11.5 kg.
Surviving documentation on the NS-630 is thin beyond the original Japanese catalog material. One Russian listing describes its sound as "rich and at the same time transparent," and a current market listing shows a pair offered at 36,000 rubles. No period reviews, production totals, or common-failure notes have surfaced. The later "NS-630 MKII" is a different speaker, a two-way bass-reflex design, and should not be confused with this model.
- 3-way, 3-speaker, airtight bookshelf system
- 20 cm cone woofer (JA-2055), 12 cm cone midrange (JA-1201), dome tweeter (JA-0508)
- 45 Hz–20 kHz; 8 Ω; 86 dB/W/m; 40 W max input
- ¥27,000 per unit (1973)
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